 You introduced me somehow, how does it yeah, yeah, we are live now. So hello everybody. Welcome to this new appointment with the Latin American women on physics today We have a very nice webinar because our speaker is good is Marco Dreos from University technical elite of Luban in Belgium. So Please for all the people that is following us remember to follow us in Twitter to comment your colleague mates or office mate in the university We are making all of these to make more accessible signs and physics or high-end physics atrophysics different topics that are hot topic now in in physics, so Don't forget to subscribe to our YouTube channel to our Twitter and Facebook and you can get all the news about what is happening with These webinar series. So today the speaker as I said before it's gonna be Marco Dreos from the university Take a to leak the Luvan in Belgium as I said before but he's Nowadays is a junior faculty in that university But before he have done many several postdocs one in in in Los Angeles in Switzerland in the University professional day, I don't know the FL of Luzan in Geneva, I mean in Switzerland, sorry And after that he did also postdoc in Hagen University in Germany and before that the last Post-op position before the one that he already have in junior faculty in in Belgium is in the Technician University of Munich in Germany. So He's gonna the talk of his webinar is very interesting because he gonna tell us about the the search of having neutrinos and Here we have Marco please Marco. How are you? Hey, thanks for this very nice introduction So I have to say this is the first time that I do something like this like this webinar talks I'm a little bit shy and Please don't hesitate to correct me if something goes wrong or to interrupt. Yeah, so I'm gonna share my screen from now on then Everything I hope everything works out Right Share All right, does it work now? Yeah, as soon as you put full screen. Yeah, perfect. You guys see the slides Yeah, all right, and you can hear me. So that sounds good so I'm going to talk about the search for having neutrinos and in fact When I say heavy neutrinos, I mean these particles that I'm going to talk about they're known under various different names They're also sometimes being referred to as right-handed, you know, still neutrinos or heavy neutroleptons or H&L So these terms are all closely related and I'm essentially going to use them more or less anonymously, so if I sometimes say having neutroleptons or still neutrinos Out of habit that piece that don't get confused. I mean Throughout this talk all these terms refer to precisely the same particle All right, so here's a little overview of what I'm going to talk about I'm gonna first try to motivate what is called the law scare seesaw mechanism and then a specific model on a specific implementation of this man Mechanism called me to number standard model. I'm going to talk about search with the LHG a little bit and then about searches at fixed target experiments and Finally about how how one can interpret the data if we actually find such a particle So let's start with the with the motivation So I was told that most of the people in the audience would be particle physicists So I assume that you have all heard of the seesaw mechanism before but let me briefly recap it anyway so the seesaw mechanism is a way to give mass to the neutrinos and It's based basically simply on the observation that all fermions and the standard model with the exception of neutrinos come In left and then right-handed corollity That's illustrated in this picture here on the left except the neutrinos they in the standard model They only exist with the left-handed corollity and the idea of the seesaw mechanism is very simple We just fill these these gaps here. We introduced right and neutrinos So these this picture looks more complete and at the Lagrangian level that looks like as what is shown above here Oh, that was too fast So to the standard model Lagrangian we add the right and neutrinos So we add a connect on then we couple the right and neutrino to the so there's the right and neutrino to the left Handed a left on doublets in the same way as the charged Charged left ones couple to the left left and right-handed parts couple to each other so L here is that left-handed left on doublet and the H is the Higgs field and This is the right and neutrino then you are an F is a matrix of you cover couplings But then there's something special about the right-handed neutrino because it is a gauge singlet It is allowed to have a myrana mass term. That's what's indicated here So down here you can in the second row you see this myrana mass term This is forbidden for a standard model fields because of gauge and variance, but the right and neutrino can have it And this introduces a new mass scale to the theory So the standard model has only one mass scale like the Higgs Higgs Veth Or maybe two if you introduce the slump mass and here we introduce one or several depending on the number of heavy neutrinos that we introduce new mass scales and With this mechanism we can potentially explain the neutrino masses But also maybe the barrier and the signature of the universe by that the genesis all these right-handed neutrinos could be dark matter candidates or they could explain different oscillation anomalies and Which of these problems we can address basically depends on the magnitude of this new mass scale that we add here um So Generally, it's assumed okay apart from myrana mass once electric symmetry is broken these interaction terms up here They turn into dirac mass terms because the Higgs is to be replaced by its expectation value Then we have a dirac mass term here And it's generally assumed that this myrana mass term here is much heavier than the dirac mass term In which case we are in the so-called seesaw limit and in this limit What you can see is described down here. Then there are two classes of mass eigenstates. So this So the new r and new l are the Are the chiral states and here on the left you can see down here. You can see the mass eigenstates little new and capital n So there are three three light mass eigenstates which are primarily at mixtures of oh, sorry that mixtures of the Yeah Of the left-handed s e to double it. So they're mixed with this PM and s nitrino mixing matrix here And have a smaller mixture of the right-handed singlet state And then there are these other states n which are almost entirely the right-handed singlet states But have a smaller mixture of the left-handed s e to doublet state And what happens is that these Small new these states here. They obtain a small mass of the order Well as described here where m is the marana mass and teta is a small mixing angle that is given by the ratio of the direct marana mass while the These heavy states here. They obtain a small interaction. So they In some sense, you could say the the previously masses left-handed Sino get a small mass and the previously absolutely interactionless right-handed retinos except for the u cover company obtained suppressed form of the weak interaction And this way we explained the light retino masses in the same time one predicts that there are these heavy states And then these heavy states Is what this talk is about and these heavy states because they are not entirely sterile anymore They have this that mixture here of the s u to doublet state They participate in the weak interaction, but with an amplitude that is suppressed by this mixing angle teta here All right, so as I said before it's the first time for me to do something like this Is it okay in terms of speed and understandability? Does it? Because I don't see any of you guys. Is it okay like this Roberto? Is that yeah? Yeah, it's perfect Yeah, okay, so let me continue. So thank thanks for the feedback. So, um So I said one introduces this new mass scale m the marana mask but As you can see from this formula here For the light retino masses here the mass scale is actually not fixed By the requirements. So here. This is the light retino mass matrix Which we know to some degree on the right hand side You see that this is combined by the combina is given by a combination of the hicks left new cover and the new mass scale And you see that retino station later can only Constrain this combination of mass and coupling. So therefore we cannot uniquely reconstruct the value of this marana mass scale by observing light retinos And in fact the the range of allowed values for this heavy man named marana mass scale is very big so in this The slide I try to summarize a little bit the uh the implication for Neutrino physics cosmology and high energy physics for different choices of these mass scales on the the axis here above You see the electron world kill electron and what mega electron was different possible choices And then you see the implications here for the different fields And you see the blue big blue bar explains says that Basically the seasonal mechanism works for almost any choice of the is marana mass scale. So And that's again because what I said before the light retino masses are given by the ratio of new cover squared and My rana mass so therefore I can always adjust Intense the new cover coupling constantly my rana my rana mass are both unknown. I can Pick any value of the my rana mass scale and then make This consistent with light neutrino properties by simply adjusting the u-cover coupling correspondingly So from purely neutrino physics viewpoint basically any choice is possible However, of course for cosmology and for experiment It does make a big difference whether these particles have a kev mass or gv mass or a gut scale mass You can see in particular if they're very light then they act as dark radiation and contribute to ineffective and cmb For intermediate ranges of kev. They can be the dark matter and for masses above a few tens of me v They can explain the bareness and trip the universe via leptogenesis And of course experimentally it also makes a gigantic difference what is the What is the mass of these particles when you want to look for them? And i'm the following i'm mostly gonna focus a bit of on masses between the pion mass and the In the mass of the w boson because that's where searches for these particles are most most efficient So we keep in mind the true important parameter the marana mass of these particles and this mixing angle that gives you there Interaction strength So this whole picture of masses and coupling was yes, I have this really I'd like to show this nice artistic illustration of this. So this is the This is here's the standard model which is what we know and then it's not clear whether the heavy neutrinos are very massive or if they are Not so massive but feebly coupled and depending on which in which direction it we have depending on whether they are heavy or Heavy and a bit stronger coupled or light and very feebly coupled We have to look for them either in high energy experiments or an intensity frontier experiments And that's what i'm going to talk about in the following this picture was taken from the cover picture of Next month's edition of the german physical societies journal, which is actually has a steel neutrinos as their cover story Which I think is very nice because it means that we are not the only one who are interested in this stuff Okay, so but now let's come let me come to the actual topic of my talk So I said this mass scale can have any value and typically people assume that the myrona mass is very large because Grain unification and things like that And now i'm trying to convince you that masses between the pion mass and the w-mass are well motivated So how does that fit into the picture? So in my opinion, there are two reasons why one could believe that a relatively low scale of the seesaw is Is interesting the first one is the hierarchy problem So we it's well known that The Higgs mass is not stabilized against radiative corrections. So if you introduce some very heavy degrees of freedom then these Then this would destabilize the the Higgs mass and that leads to the weak hierarchy problem However, if there are no heavy states, then there is also no weak hierarchy problem So if we somehow manage to address all the problems of particle physics and cosmology at low scales, then there's no hierarchy problem This is a motivation why physics might sit at low scales The other would be the second motivation has to do with the properties of the Higgs Particles which i've measured quite precisely now And one the picture that emerges is that okay first of all the properties of the Higgs are such that the Standard model electric vacuum is just at the verge of stability here. That's shown in the right plot where they have the Higgs mass and the top mass and you see that in the Green region the standard model vacuum is stable the red region. It's instable and we're just at the verge of stability What i find even more interesting is shown in the left plot here to see that the Higgs particles are Proper properties seem to be tuned just in a way that the standard model in principle could be a valid effective field theory All the way up to the Planck scale So if the properties of the Higgs particle were slightly different so its interactions thing would be a little seven the action would be a bit stronger or its mass would be a bit different then We would very easily either end up in an instable universe or End up with a standard model that becomes non-perturbative at scales below the Planck scale But for some reason the Higgs properties are precisely such that the standard model can be extrapolated to very high energies So maybe that tells us something So maybe that means that there is no intermediate energy scale between us and the Planck scale and then all the New physics problems should be addressed at the electric scale below All right So one very specific model that has been studied a lot in which i'm going to use as a benchmark model Throughout this talk is the neutrino minimal standard model And it's based on the idea that there are three right-handed neutrinos And two of them have the generate masses in the gev range And the third one has a kev mass and is a dark matter candidate Um, this model was invented by asaka and chaposhnikov From a phenomenological viewpoint It is basically it's effectively a theory with two right-handed neutrinos because the dark matter candidate practically decouples And it will not be seen in collider experiments So it can be seen as a effectively theory with two right-handed neutrinos from a collider viewpoint and uh But that doesn't matter so much because for most of the phenol aspects that i'm going to talk about in the following It doesn't really matter whether the right-handed neutrino that i'm talking about is part of this new MSM or not I'm just introducing that as a benchmark model All right, but uh This model okay now i said that there are two particles with masses in the gev range and one in the kev range And those two in the gev range should be master generated by the kev particle is almost decoupled to be a dark matter candidate That looks like a very specific spectrums You would think like why the hell should nature be like that that looks super artificial, right? But it's actually not as artificial as one might think because uh because of symmetry reasons So the standard model has a global b minus l symmetry but b is baron number and l is lepton number And if one assumes that the seesaw so the extension of the standard model respects a generalized version of this b minus l symmetry Then one actually expects precisely the kind of smart spectrum that i just described and that can be seen by uh writing the The mass term here and the u-cover company here in precisely the way how it is written now here And so i'm in a basis for the mirana masses diagonal And in the in this formula all the greek letters are parameters that go to zero in the limit where the symmetry is exact Where the lepton letters survive? So what are the telly so that tells you in the symmetric limit? Okay, first of all if you write things in this way There is only one dimensional parameter this average mass seesaw scale here in front And that we can place near the electric scale for the reasons that i already tried to convince you of on the previous slides And then there are only small parameters that go to zero in the symmetric limit And if you send those to zero what you find is that you have a pseudo dirac pair So the first Two of these particles become master generator You see these two mass eigenvalues become exactly the same limit mu equate zero and the couplings also become the same So these two guys form a dirac spinon Well, the third one becomes mass plus or very light and decoupled because they are only epsilon suppressed couplings here So that tells me that you get a the gen a pair of the generate states Which is precisely what you need for resonant leptogenesis and a lighter particle that is very feebly coupled Which is precisely what you need for dark matter. So this whole scenario can actually be justified by some symmetry in this Technically it's natural all right, so so much about the The motivation for the store business so now let's go to To the experimental searches and as I said before for most of these searches It doesn't really matter whether the right hand neutrino is part of this mu msm benchmark model or whether it's Embedded in some other model So the lhc has performed searches already for this of course So here you see the most updated limits that i'm aware of from cms where the the x axis here is the The mast of the heavy neutrino and the y axis is the square of the mixing angle with electrons and with muons These searches are based on this process here And one thing that you notice is that the bounds here the green line are the bounds. They are much stronger below the W mass when the mass is below the w most end when it's above And that's very easy to understand the reason is that then these particles as shown here can be produced in the Decay of real gauge bosons and that makes the production and colliders much more efficient Because of this in the following i'm going to focus on the mass range below the w mass Moreover i'm going to focus on a pure type one seesaw. So That is the right hand neutrino can only be produced via its mixing suppressed weak interactions Of course, there are many theories in which the right hand neutrino has additional interaction like left right symmetric theories and so on and then those the phenomenology is different and actually More encouraging because the additional interactions might be traditional production channels, but i'm going to talk so to say about the minimal most Difficult to test a seesaw model All right, so Once you have specified the model and here i've specified this minimal model But i introduced this new msn before one can see what existing constraints there are already And basically here we are looking at the mass claims banned by the mass and the mixing with neurons And all the gray areas actually already disfavored by the number of past constraints that are listed here There are conglado colada constraints fixed target experiment neutrino oscillation data and each one is so better decay Laptime universality things like muti igama ckm unit error team So they seek the unit the requirement to have unitary ckm matrix indirectly constraints the leptons because ckm elements are measured By processes that contain leptons and the interactions of leptons would be affected by the By the presence of these heavy neutrinos electric precision data and big bang nuclear synthesis So big bang nuclear synthesis just means that these particles have to decay on decay on time in the early universe that they don't disturb the formation of light elements in their So these bonds yeah This is grayer this this plot was produced for For for this paper here where you can find a detailed discussion of all these different plants And then there are of course collider searches There are different lines in this plot one from lhcb and then what some related to the lhc main detectors atlas and cms So I took the lines here from brian shuvis paper and from the anthosh fischer paper But here you see a number and bunch of other papers listed for people that did similar analysis And one thing that is kind of funny is That ah Sorry, there's one thing that I didn't explain between these two blue lines here The baron asymmetry of the universe can be explained between these two blue lines that call leptogenesis In this minimum model So the in the entire white region we can explain the genome masses But between the two blue lines here this one and that one we can in addition also explain the baron asymmetry of the universe Sorry, I forgot to say that before All right, so let's come back to this lhc lines So we see that the lhcb line atlas those looks quite a lot more optimistic than atlas and cms line But I should warn you that these lines were done by different people under different assumptions And the lhcb line was done under somewhat more optimistic assumptions about the efficiency of the detectors So I think it's not really a fair comparison. What is being done here? Yeah, one clearly has to state the different assumptions And to understand this in a bit more detail We are currently doing our own analysis of this to compare the different lhc experiments in a sort of fair comparison that's work in progress So this is uh, this is displaced these searches based on displaced signatures So these heavy neutrinos are longer particles They can be quite long lived they can travel quite a Significant distance between the point when they're produced in a gauge boson decay and the point with a decay into standard model particles that are observable So one can look for these displaced decays in this case for muon tracks from the displaced vertex And uh, this is a these are preliminary results how sensitive the lhc could be in this master this mixing plane This is with 300 inverse femtobarms and interesting and for cms an interesting question to ask is how much could that improve with the high luminosity lhc And the answer is this Here these different lines that you see just correspond to different assumptions about the detector efficiency and and things like that so So there's like differences in the shape of this line depending on what you assume about these things And about the part of the detector volume that can efficiently be effectively be used For these searches and so on But you see what all these lines they have the same common overall shape and the shape can be understood quite easily So there's always a lower cut because the production cross section becomes too small So this u square here is the same as tether squared That is the square of the mixing angle on the y-axis So if the mixing angle is too small the production rate for these particles become Simply becomes too small and you don't make enough of them to be seen at the quality event rates go to zero So there's always a lower cut like this Then this upper right region here they decay promptly So they decay too quickly and one cannot really see the displacement And since this is a displaced vertex search, then you cannot remove the well You can't come to move the background that easily anymore from the signal And here down here, they're too long-lived So if these particles are too long-lived they're being produced But they basically fly out of the detector and they decay outside the cms detector And if the decay happens out at the cms detector, you can't see the displaced vertex and you can't see the particle So you can that's why all these shine lines always have this same overall shape Can understand the physics behind that All right, so let's put these uh these updated lh Expectations for the high luminosity lhc into this picture and you see Very nicely the sensitivity with the high luminosity lhc will become a lot better And we will be able to enter this cosmologically interesting region where we can explain the bearing as a mixture of the universe So one thing that I mentioned before let me go back here is that in this lower Lower left corner these particles are too long-lived. They don't decay inside the cms detector And people have thought a bit about ways how we could overcome this problem not only for heavy neutrinos But also for other longest particles and one way to overcome this problem is matthusa So matthusa is a proposed new detector for the lhc that stands on the surface. So Here this is the So this here this gray thing is the surface of the earth and underground sits the cms detector This is the beam line the beams collide here and then having a neutrino or another long-lived particle It's produced and flies out of the detector it flies flies flies It reaches the surface of the earth comes out and decays and if you build a huge detector volume on the surface of the earth Then like a huge building then you could observe this decay of these very long-lived particles That's the idea of matthus la. So there's a physics case paper and the letter of intent submitted And if Yeah, so okay, sorry. So what matthus la is is basically just a huge thing It's like 100 meter 100 or 200 meters long and maybe 20 meters tall it's surrounded by Cintillators and it has some trackers in the roof and it just looks for the decay nothing into something inside this volume and by observing this one can You can cover a bigger range of right and neutrino parameters Now you can see the plot becomes a lot more crowded because in the previous version of the plot are only short existing experiments But now I added all sorts of future proposals including matthus la. So matthus la is sitting here There are similar proposals to look for long-lived particles called code xp and phaser And there's another one called lx3 that I forgot to add here So there's several proposals matthus la is one of them and you can see with matthus la We one could explore the relatively low mass range here of a few gv while atlas and cms they operate more up here And typically colliders operate more up here and down here where we see matthus la Matthus la would compete not with colliders But with a fixed target experiment such as n a62 or a similar or the proposed chip experiment or A similar facility entity to kb So generically one can say that the mass is above The b meson mass they are more tested at colliders masses below the b meson mass are tested with fixed target experiments But matthus la is an exception from for this because it could make a collider sensitive at masses below the at low monsters Okay before later I will talk about fixed target experiments, but let me first finish the chapter about colliders So in this very messy crowded plot you don't only see the lhc lines that we talked about before You also see additional lines for future colliders So as always future colliders can do everything better because they have more energy more luminosity and that is more awesome So you see these lines for future colliders that could probe quite deeply into this so both the the chinese and the european Version of a new circular collider could probe deeply into this parameter space And even the isc could probe some part of the cosmologically relevant region Before moving on to the idea to look at for these protocols and fixed target experiments Let me propose one more idea that is a bit let's say unconventional that we had last year And that is one could also look for these particles in heavy ion collisions So here i've listed the pros and cons of this idea to look for Hidden part for long lift particles or heavy neutrinos and heavy iron runs So on the left we see the cons So obviously heavy ion collisions are known to have a high track multiplicity If you have ever seen a picture of a lead lead collision, you will see that there are a lot of tracks However, this is not such a big problem because the high luminosity lhc because of pile up will actually have a comparable track multiplicity as a high heavy ion collision so with a high luminosity lhc the uh The track multiplicity disadvantage of heavy ion collision as compared to proton collisions is actually not so big anymore Then of course the other disadvantage is the instantaneous luminosity during heavy ion collisions is lower This collision energy is slightly lower because they're neutrons in the nuclei And the schedule runs are shorter. I'm not going to talk about the last one because this is obviously a political not a science question But then there are also some pros first of all you need collision because each nucleus has a lot of nucleons in it So a nucleons if you collide to nuclear there's an a square enhancement due to the number of nucleus in each nuclear Nucleons in each nucleus and that to some degree Overcomes the low instantaneous luminosity Then there is no pile up and heavy ion collisions Which is an advantage for the background reduction and finally, uh Because of the low luminosity one can operate the main detectors with much lower triggers So let's see how that where that leads us So here's a table with a lot of numbers that we guide you through this table a little bit So each row in this table corresponds to a specific ion that one could potentially collide starting with hydrogen So that's standard proton collisions down to lead And then the most important columns in this table are the ones that I've marked here So the first the one marked in blue here gives you the cross section Including this a squared enhancement factor due to the number of nucleons in each nucleus You can see there lead greatly outperforms protons. So there's like a thousand versus 0.056 So here it looks like lead is actually much better from that viewpoint just because of the nuclear enhancement However, the instantaneous luminosity the next so the next two columns, which I have not marked named the instantaneous the starting luminosity and the This sort of beam lifetime and from these two quantities you can calculate What is in the green column namely the average instantaneous luminosity? There you see that it's the other way around so actually Even though the cross section is huge for that nuclei the the luminosity the average luminosity is actually much much lower so here Protons win and the last column basically summarizes all these information and tells you How many events roughly tells you how many events you would expect Normalize to what you get for protons. So this is for protons And you see let loses and the heavy other iron you just lose So then you might think okay, it's pointless. Obviously the lower luminosity is The benefit of the a square enhancement is not enough to compensate for the luminosity That's not so surprising because otherwise people would have been colliding heavy ions all the time to look for new products However, there are these other advantages that I mentioned one of them is that there's no pile up And no pilot means that there's no danger of misidentification of the primary vertex because all the tracks originate from the same femtometer size region where the nuclei so This is illustrated in this night in this little picture here where here you have the beam line and these red dots Indicate different collisions so that the pilot and he has a real primary vertex What you might think that the particles Here's a neutral the normative particle that decays there and then you can see you might misidentify the Reverse we haven't this worked out in detail yet, but we're working on it and the other advantage is that the that due to the low luminosity the The triggers of the main detectors can be run with much lower Yeah, which much lower cuts in particular in transverse momentum And that's quite interesting because for example having neutrinos can be produced in b meson decays Like that's where the line for matthewsla came from that I showed before And b mesons are produced in much larger numbers than w bosons at the lhc The problem is that Typically the having neutrinos that are produced in b meson decays They have a too small pt to be seen by the main detectors pt is like Like below the standard triggers and even below what future triggers assumed to be Um So we can see like 99 more than 90 percent of them have have pt below a 25 gv But during the heavy iron runs because of the lower luminosity one could lower the triggers and then look for these for this data for these And benefit from the fact that they are the production rate for b mesons is much larger than those for w bosons And of course whether or not that is efficient depends also on the luminosity and because the luminosities are different for different isotopes We have checked this for protons lead and for argon And we find here that uh, actually Even if you take this effect into account lead is still worse than proton So proton still beats lead proton collisions beat lead collisions However, argon collisions might be favorable and give a higher sensitivity than proton collisions that's shown in this in this so here red is lead and Violet is proton and blue is argon in terms of estimated sensitivity for assuming equal running time That's pretty cool. So now you might think why the hell should we think about argon because they don't collide argon with the lhc They collide lead, but that's actually not true because the heavy iron community is anyway thinking about using lighter isotopes such as the nova gases because it gives you longer beam lifetimes So so this could actually possibly be done in a parasitic mode top on top of normal heavy iron runs All right So that was it for the colliders Let's move on to the fixed target experiments apart from colliders one can also look for these things in fixed target experiments The ultimate fixed target experiment in the foreseeable future would of course be ship But ship is not yet approved and meanwhile we can already do or not be better Our experimented colleagues that are smart enough to operate these machines Can make searches for these particles at any 62. So any 62 is basically a little ship or The other way around any 62 people would say that ship is any 62 on steroids. So Depends on from which perspective you want to see it. So this is how any 62 looks like On the left corner here, you see this is a hall It's a experiment that is built in the turn north area and the primary purpose is to look for pion decays For k on decays into pions and neutrino and neutrino. That's a very rare decay in the standard model But that can also be used to search for any neutrinos Above here, you see my own view of the any 62 experiment experimentalists will probably disagree with this very simplified way of looking ahead But it's sufficient for the purpose now And a 62 can look for having neutrinos in two different modes So it can do that in the regular modes. So the way how the experiment is regularly operated is that So let me see a proton beam is sent on a target crashes into the target Then mesons are being produced from that a k on beam is extracted through a collimator The cairns fly fly fly fly fly they fly up to here There's a decay volume and in the decay volume the kons decay And they can amongst others decay into heavy neutrinos And because it's a two-body decay that so the k and with decay into heavy neutrino and a charged laptop Because it's a two-body decay if there's a heavy neutrino you would see a peak in the emission spectrum of the charge Laptom corresponding to the heavy neutrino mass And this kind of search have actually been done already. You can see that in this paper here such search has been done However, there's yet another way how one can operate the ny62 experiment And this other way is called the dump mode so I said before that ny62 can be used like a little ship Like when I say that I really refer to this dump mode here because in this mode here in the first mode in the k on Mode it is actually quite different from ship It's a k on experiment But in this sort of dump mode that is basically like ship and in the dump mode what you do is you don't Actually you remove the target and you basically smash the proton beam into the collimator The collimator acts as a beam dump and you produce all sorts of mesons in this dump For example, also heavier mesons than kons And these mesons fly a bit and then they decay they decay into heavy neutrinos is done in model particles The heavy neutrino can fly on on on on and then it might decay in the in this vacuum vessel here So in the vacuum vessel you see a decay nothing into something so sort of charge particles tracks appearing from nowhere And that's a signal to the need look for and that's exactly what the ship experiment would do So in that sense ny62 is a little ship This mode has the advantage that he can probe masses like heavy neutrino masses larger than the k on mass because in the first mode Obviously because the heavy neutrinos produced from a k on decay You can only look for heavy neutrinos with masses lighter than that the k on here. You can also go to larger masses So let's look at some results and forecasts. So in the k on mode, there are already some published results um, so on the left and the plot on the left we see the the constraint from ny62 in the Again here the x axis the mass and the y axis is the mixing angle compared to the past experiments And since the plot is a bit messy, let me point you this here This is the ny62 current ny62 limit and these all are others are Limits from other experiments, but ny62 is taking more data and sooner than expected to outperform all other experiments On the right you see the mass resolution of ny62 in different channels and that is actually very interesting You see these guys have an mev mass resolution. That's amazing It's in particular amazing because uh, they're right in between us if they really do leptogenesis A popular scenario how they could do this is resonant leptogenesis in which case you expect them to be master generator And if they're master generator, then a or quasi did you have to quasi to generate masses Then a good mass resolution is precisely what you need in order to distinguish the signal from the two Heavy neutrinos because they sit almost on the same mass shell So here the good mass resolution of ny62 is actually very important if you want to test leptogenesis So that's for the k on mode And then this is for the dump mode for the dump mode. There's no published data, but there are some Forecasts here. You see that in the on the left you see how the again the mass versus mixing plane How ny62 will improve the bounce on the mixing with neurons. You see this Improvement will be roughly half an order of magnitude But more spectacular when you when it comes to the mixing with tau You see that ny62 can improve the existing balance by several orders of magnitude So that's pretty cool. So yeah, here is the same thing shown Yes, ny62 9 the same thing shown together with all the other bounds that I discussed before Okay, so now I've talked a lot about how one could potentially discover heavy neutrinos Now one crucial question is let's assume we do find some heavy neutral particle at the lhc or in some other experiments How do we know that this particle is actually the right in which you know that we are looking for? That is, how do we know that this particle is responsible for the generation of Neutrino masses or maybe even for leptogenesis? Can we sort of study its properties in a way that we can test this hypothesis? And this is possible at least in this minimum model this new msm model that I introduced Before which is basically just the standard model extended by right-hand neutrinos and nothing else and Effectively, we're looking at the type 1c source of the standard model extended by two right-hand neutrinos In the new msm There's a third one that is a dark matter candidate But because this dark matter candidate has to be very feeble to be long-lived enough to be the dark matter Attractively decoupled from the system and it can be neglected for the In the content well when talking about collider experiments because it is not effectively produced addicted to colliders So for collider, we know we can talk about only two right-hand neutrinos And then to see what we know and what we don't know about these particles and what we might learn It's convenient to look at these So-called casas above our parameterization of the u-cover coupling So f is again the u-cover coupling matrix and it can be written in the following way As indicated down here and here i've indicated in green and red stuff that we know and stuff that we don't know about the u-cover coupling So first here we see the x-vef one over the x-vef we know the x-vef Second here is the pms matrix. So the light new genome mixing matrix So inside this matrix, there are new genome mixing angles which have been measured But then there the dirac in my rana phase which have not yet been measured. So they are not yet known Then this here is the light new genome mass matrix in this parameterization appears it appears So the mass splitings between those guys have been measured, but the absolute mass scale has not been measured However in this minimal model because they are only two right and neutrinos The prediction is that the absolute mass scale is basically zero. So the light is the standard, but neutrinos should be zero So even though this quantity is in principle unknown. It's in this minimal model. It is it is fixed then in this Matrix r this sort of this is r is a complex rotation matrix that is parameterized by a single complex angle that For the complex mixing that are called omega and then on the right here. This is the mass matrix for the heavy neutrinos And they're two eigenvalues because they're two heavy neutrinos, but instead of considering those two eigenvalues One can also consider the average mass and the splitting between these two eigenvalues That is convenient because as I discussed before For leptogenesis and also for this b minus l symmetry reasons It is expected that these particles should be mass degenerates So they should have quasi degenerate masses and then it's more convenient to look at the average mass and the splitting than Both the mass of one and the other All right, so that leaves us with only six unknown parameters So the average mass and the mass splitting of the heavy neutrinos here And the real and imaginary part of this mixing angle omega and the r matrix And then the delta well the dirac in my rana phase The dirac in my rana phase and the light between the mixing matrix Note that in the model with two random neutrinos. There's only one my rana phase All right, but So let's see what of each of these particle parameters can be measured So the first two are masses masses of particles once we discover the particles we can measure their masses So at least these are in principle measurable Two of them are measurable So then the real part of this mixing angle and r it basically tells us if they're two random neutrinos n1 and n2 how strong the couplings of n1 are relative to the couplings of n2 So assuming that we discover both of them We can constrain this parameter because we can just measure the relative size of their cup The imaginary part of this angle gives us the overall coupling strength of this heavy neutrino So how strongly what's the overall normalization of their coupling strange also that we will know if these particles are discovered And then there are these phases So the dirac phase delta can be measured from a neutrino oscillation experiments will be measured for zero time as expected The my rana phase cannot be directly accessed However, the dirac and my rana phase together. They are not only responsible for cp violation, but they also Decide about how the flavor mixing pattern of the heavy neutrinos is So by measuring the heavy neutrino mixing to individual standard model Flavors electron blue and tau we can indirectly measure the my rana phase alpha. So then all of these parameters are in principle measurable But okay that I'm sorry about that But of course in practice if these particles are master-generate it might be difficult in practice to measure the mass splitting directly Moreover It might also if they are not distinguishable It might also be difficult to perform this measurement That gives us the real part of the angle this mixing angle to to compare the size of their couplings if we can't properly distinguish the resonances in the collider these two Quantities delta m and real part omega will most likely have huge error bars However, we could try to help out with other Observables it turns out that the neutrinos double beta decay can be sensitive to the real part of omega So what do you see those so several various people have studied the connection between hope Between these seven neutrinos the neutrinos neutrino list double beta decay And here's the list of references and here this in this figure You see the plot from this paper down here Where you see the the x-axis the mass of the lightest neutrino assuming normal mass ordering and the y-axis is this quantity m Better better that gives you the rate of neutrino list of a better decay And in the standard model you would only have this blue band which you might have seen in other plots before But you see if these have at the right hand neutrino all sorts of each point represents in the loud parameter choice you can See parameter choices all over the place. You can get a rate of neutrino list of a better decay That is quite different from that predicted by the standard scenario The color of these points simply indicates how much fine tuning you need to achieve this or that value And you can see that there's a chance to observe a non-standard value of neutrino list of a better decay And from that you could learn something about this real part of omega The other quantity that was hard to measure is this delta m the splitting between the two masses And to illustrate that uh here So in this plot what i'm showing you is for normal and inverted higher Okay, as I mentioned a leptogenesis is one reason to assume that these particles should have quasi degenerate masses because Then you can do resonant resonant version of leptogenesis um And then the question is how to generate do these particles have to be to do successful leptogenesis And the answer to this question Is uh in these two plots for normal inverted ordering For the x axis is the mass splitting of these you have in neutrinos and the y axis this u squared is the overall Strengths of the mixing angle summed over the standard model flavors So the red area here below is forbidden because they can't explain the The light neutrino masses and in the entire blue area in both of these plots you can do leptogenesis And as you can see from the scale of the x axis you actually do need quite small mass splittings for leptogenesis in this minimal model so It might be quite tricky to resolve that experiment to be even with n a62 However, that doesn't mean that there's no hope So on the right end of this plot the master generacy is not so big there you might actually be able to Criminate these two masses directly kinematically For smaller masses for smaller splittings. You probably can't dissolve the resonances at the collider However, one can do some indirect tests. For example, one might look for oscillations of these Of these right hand into into each other in the collider By looking by comparing the rates of lepton number violating decays and lepton number conserving decays of these particles So lepton l and v stands for lepton number violating lfv for lepton flavor violating And that can give you so that tells you the dirac-ness or mayaran-ness of these states So I don't have too much time to go into detail now But by looking at these observance one might be able to indirectly say something about these mass splitting that's been worked out by by many people Mentioned some of them listed down here some of them actually Well, I'm doing some of them might actually be online here because quite a few of them work in south america All right, so This is great because here we have a in principle So in principle, we can gain information about all these parameters from observation Which means that it's a fully testable theory in principle fully testable theory of new genome masses and barrier genesis so we can In principle constrain all parameters in the Lagrangian from different experiments And it's also a very nice example of how collider searches and new genome experiments can work together And even other intensity frontier experiments like new genus double battery cake can work together to explore something together So, um, I think I don't have too much time left, but in the last So how much time do I have left? Now you can still talk for another 10 minutes more or less Okay, then I rushed a little bit too much. Okay Okay, I mean no more. I mean, yeah Well, we cannot say this question just afterwards. So so so in the last few minutes it's probably going to be less than 10 I'd like to say Sorry, no, okay. That's fine So I claim that all these things can in principle be observed and constrained But of course so far we haven't discovered the right end in neutrino So so for example the masses here we don't know on the left But do we actually know something about the other parameters? What do we know already? and This is a little bit of nodding here Okay, good. Um, and what we already know can one way to classify this is before Are these triangle plots here? so before I said that Okay, let me go one step back So there these dirac and mayorana face here and they are they are responsible for the cp violation in the light between mixing matrix But I claim that they also tell us something about the flavor mixing pattern of the haven neutrinos So they're relative size of their coupling to emu tau and that we can actually observe Measure indirectly these phases by looking at this flavor mixing pattern and I'll explain a bit more detail what I mean by this So in these triangles we see basically how strongly a heavy neutrino would couple to electron mu on tau and flavors So basically there's a So the three sides of the triangle are e and mu and tau They're coupling to emu and tau but always normalized to their overall coupling So this ui and the Yeah, and the denominators for this thing here is the sum of their coupling to all three flavors So this is the electron coupling normalized to the total coupling of the heavy neutrino. So it's The fraction the fraction to which it mixes with electron as compared the fraction how it mixes with mu And you see that currently tuner oscillation data actually Constrains this quite a lot. So for normal hierarchy one is A Determine to sit in this red area for inverted hierarchy one must sit in this blue area here The different shades indicate one two and three sigma contours of light neutrino oscillation data And the reason why there are like two dimensional areas in this triangle that are allowed is because we don't know delta and alpha So that's basically you can go around inside this allowed region by varying delta and alpha Vice versa that means that if I find the heavy neutrino and I fix it to some point in this triangle I can extract information about delta and alpha. So this is what I said before about measuring these phases From the flavor mixing pattern And we see in both cases that there's a hole inside this region And the hole in the middle of this region comes from the fact that there's already some knowledge about delta from From global fits to light neutrino oscillation data And basically by varying alpha the unknown phase one goes around this hole So if if delta would be measured exactly at infinite precision in a future experiment Then one would reduce this parameter space to some kind of ellipse that goes around this hole And by finding the right neutrino one could indirectly measure alpha All right, so yeah, that's what we know already one coin then one can improve this one can also put constraints from leptogenesis Which I don't have to try have time to talk about but let me just wrap this up by saying that In my opinion right-handed neutrinos are very interesting extension of the standard model Because they can explain various different problems. They can give neutrino masses They can explain barogenesis and they can maybe be dark matter candidates And this model model is very minimal. So if you just add right hand neutrinos, you don't actually have so many new parameters. So So in principle, this can be a fully tested the model of Barogenesis and neutrino masses and maybe even dark matter because at least in its minimal version the seesaw Model doesn't have that many free parameters And we could potentially measure all of them or constrain all of them from experiments Having said that of course all of this is based on the hope that the seesaw scale is below the tv scale Because of the seesaw scale is very high as it is in granny v type theories And we of course have no chance to discover the heavy neutrino However, if we are lucky and the masses below the tv scale or maybe even below the electric scale Then there are many different experiments that are looking for these particles and Could be that they are going to be discovered in the next few years. Okay. Thank you very much for your attention Okay, thank you very much marco. It was a very nice webinar in fact indeed very Completed about everything related with the heavy neutrinos. So let's start before before Everything. Thanks marco again. So Before to start with the question round We are going to start with just commenting to the people that is following this webinar series that you can subscribe to our YouTube channel as well as follow us in twitter and facebook So maybe we can start with question from the people that is present here in the in the hangout So for instance, please any anyone just unmute themselves and ask to marco If you have a question from Juan Carlos, okay, I have a question. Yeah Hi Hi I have a question related to the n a cc to experiment Okay What is the the process that makes this experiment sensitive to the mixing with the tau could you show me There's a whole range of processes because it depends what depends on the masses of these particles, but Um basically the Especially for the low masses, it's the production of time. So they can decay with associated with the I say the decay can occur together with the tau neutrino Okay So they can decay into via the the neutral current with the tau So there's a heavy neutral leptin that can decay into a tau that can basically go into a tau neutrino and And then you're via the neutral current interaction So that's why you can be sensitive to the tau mixing even for masses well below the tau mass Okay And what was the the mass range could you show me the slide again? Please just to check You mean you mean this so this is for this Yeah, okay, so up to one one gv Okay On the right hand side is actually the d meson mass. So basically My production channel here is in the decal d meson and these guys are heavier than the d meson Then they can only be produced in b meson decays and That is far less efficient at n a 62. So So basically the cutoff is given by the d meson threshold Okay, thank you So is there any any other question for marco? because Yeah, okay. I have a question Just take advantage that i'm the also the the host of the chairman of the webinar. So marco a question very kind of in this experiment like matusula and so on Do you expect also to to observe some signal related with strata neutrino for instance for sins is uh Let's say a surface the detector from Signature from cosmic rays itself Because i'm also in the case of ice cube. They also they have searches for strata neutrino But i don't know in the case of matusula if they or n a 62 or something like that, but To get extra observables, let's say So i think cosmic rays in the case of of uh Matusula They are more your enemy than your friend because they they produce of course a background of tracks in the detector So this is not so bad because the tracks obviously Most likely don't originate from their hc collision points that they can be reduced, but My understanding i mean i'm i'm not an experimentalist. So i'm i'm not I'm just a theorist. So but my understanding is that uh here for the sake of matusula Cosmic rays are more of a problem than a benefit because it's probably true that you might get some additional events due to collisions from cosmic rays, but I think in overall we better not to have them because Because they produce a background they produce a background for the experiment i mean as i said the Studies have shown that this background is not going to be a big problem it can be reduced by removing everything that uh, that doesn't come from the interaction point and so on but Still it could be better not to have them Yeah, so i would say it may be so to answer briefly so from my understanding it might be that you get a few extra events from that but i think the The disadvantage that cosmic rays bring with them is bigger than the advantage that they bring with them And it might i think these few extra events that you might get would probably in the data reduction for victim to those cuts That are meant to remove cosmic rays i suppose I don't know if anybody has thought about this to be honest I've never thought about this to be honest, but my so i'm just doing an educated guess and my my my guess would be that You will not Be able to make too much use of such events because basically you want to remove everything that looks cosmic ray like So that you can do a background free analysis of the lhc events But yeah, that's just my first guess. Does that answer your question? No, yeah, yeah, yeah, I mean any any any answer is good because to have an idea what is kind of happening there So another question just very fast because I guess there are people with more questions What is the status for instance because you were talking that this kind of detector are going to be kind of lhc based I mean Yeah in lhc are there similar experiment plan for the other type of accelerator like ioc or something like that or is Just it's much better to work with Adron Colliders more than lepton colliders something like that I think well in hard on colliders You get the biggest advantage. I would say I mean in principle you can do this also with fcce or so and I would say why not, you know I mean in in hard on colliders you get uh, I think okay I think the reason why one gets a bigger Effect in hard a bigger advantage in hard on colliders is because math was la has two advantages first of all That can look for long-lived things that because it's far away from the collision point So that means that you can look for long-lived things You lose part of this advantage because the detector doesn't have a four pi coverage So There's a there's a trade-off between having a smaller solid angle and then being further away and having a big detector So so that's the one side the other advantage that math was like gains you is that you basically remove all the Complicated stuff that happens in the main detector like all this qcd stuff other tracks You don't have them because basically the hundred meters of rock act as a very good filter for standard model backgrounds So the second advantage of math is that you remove standard model backgrounds And of course of those you have many more in hard on colliders than in lepton colliders So I would say out of the two advantages that things like math was law offer the second one Is a bigger advantage for hard on colliders because of this background Because you get a super efficient shielding due to the rocks. You see what I try to say Maybe maybe it's clear. Maybe it's not clear. I don't know. Is it clear what I try to say? Yeah, kind of yeah, I mean the rock is the the main filter for your signature and also the The the big numbers that uh outro collider can produce no you you have advantage of the statistic. Let's say Yeah, well, that's another collider would produce more Stry neutrinos in some sense because So there's of course a generic argument that the more luminosity you have the more the more you see right and So, yeah So for me, I mainly think about it for LHC But of course, there's nothing that prevents you from building such a thing at at the future left on a hard on collider I would say you gain more for hard on colliders, but I think it's still nice for lepton colliders as well yeah, so People from here from hangout they Do they have more questions and also for the people in youtube? I forgot to mention that you can ask question via the youtube chat So you can write it now while we are in this First round of of questions. I guess we have a question from holl jones. Yes. Yes. Thank you If so so so I was a bit surprised by by your statement that said that you it might be possible to measure the real part of omega because In principle you you get the typical ceso suppression and you need the imaginary part to to to give you the enhancement right so so so from what I've seen is that Once you make omega large, right? You I mean omega is is connected to a hyperbolic sine or a cosine, right? So for large for large omega, right? It's the same thing a hyperbolic sine or a cosine so so so what what what I found is that The real part ends up being like an overall phase right that okay might be might appear in uh in Neutrino lezabobita decay, right but from Neutrino lezabobita decay I think that that A mass difference is it's more important, right than the than the real part of omega Well, both of them enter so I think the real part I mean, I totally write that the real part of omega is the D parameter that most likely is going to suffer from the biggest trouble to be measured so So is true that if you want these came to which so let's put it like that is true that The imaginary part of omega leases to and leads to an enhancement of the signal But the this difference that you need to measure in order to extract real part that is not enhanced in the same way So in order to so you would have to measure a rather small effect on top of a big effect So that is very very so apart from the problem that it's challenging to So okay when it comes to the total mixing of these Of these particles um over flavors then indeed it is A very challenging measurement I would say right so so so in principle to to be able to do that you would have Let's say the you you would need to be able to measure delta m A very very precisely Such Delta m is very small than it be there will be extremely difficult if not impossible to measure the real part of omega Okay, great. That's what I think with present technology. I'm quite pessimistic actually about Measuring the real part of omega in any of the present searches But the reason why I emphasize this what I call maybe slightly over optimistically full testability is that to me It's a big difference if something is in principle measurable Or if it's absolutely impossible like if this you saw would be at the gut scale We can't see these particles and that's it But so here my take is that if if we discover these particles at any 62 or the LHC Then there will surely be funding for some more precise measurements Right, okay So I agree with you that with present technology or present experiment It would be very very challenging to expect this real part omega, but I would still like to emphasize that it is in principle possible Okay, great. Thank you Okay, so I guess we have more questions one from Hearing the question Q from Nicholas Rojas. Nicholas. Hello. Hello, Marco. Thanks for a nice talk I wanted to ask for the NA 62 experiment More or less in a similar way as the question that roberto did What are can you comment some in In in in some In one or two phrases. What are the backgrounds that are involved the the most both are in background backgrounds that you have on the experiment or and Uh, what are the regimes there in in which you are detecting? A neutrinos and heavy neutrinos if it is elastic scattering in elastic scattering. So can you Uh, so there are Sorry, no go on, please So the NA 62 can be run in these two different modes that are shown by this is the dump mode and this is this k on mode And in the k on so let me first talk about the k on mode. So the k on mode. You're basically Well, you first make k on that's what NA 62 is supposed to do and Typically NA 62 sorry typically NA 62 looks for very rare k on decays into pys and Neutrinos but of course, if there's a heavy neutrino, there would be also a very rare decay into K on decays into heavy neutrinos Instead so in each process, so let's say if kinematically process possible in each process where you usually would expect a normal neutrino You can Expect you also get a process where there's a heavy neutrino instead And then here you would not end in this k on mode You would not actually directly see the the heavy neutrino, but you would see its effect on the kinematics of the associated lepons So here the k of the here the k on Okay, let me try to hear the k on flies and then the fly on the k on decays inside the detector volume And then you don't see the heavy neutrino because it just basically flies away and escapes it's neutral You don't see it But it has an effect on the kinematics also to say on the emission spectrum of these charged lepons that are produced associated with it And that's how you see the heavy neutrino. So that's the process in the k on mode Okay, and then the mass range is obviously restricted to the mass by the k on mass because you need to be below the k on mass In order to make the heavy neutrino in a k on decay And then there's these other mode, which is yet still in a sort of more infant stage Where basically you and in this mode is basically like a ship So you make the heavy neutrino in whatever process here when the beam is dumped in the collimator and then the heavy neutrino decays into Charge particles So practically you can go to larger masses than decay on mass here but in reality the heaviest meson the you can only go up to the d meson mass because Okay, you could in principle also make heavier heavy neutrinos and be mesons But those guys would most likely have too much transfer momentum So they would not they would not hit the detector when they would sort of fly out here You see they would not not enough of them would decay into the detector And then here basically any decay channels of the heavy neutrino can be detected because they're always decaying to standard model particles So you can have charged and neutral current interactions and Laptonic and semi-laptonic decays you can look at all sorts of decay products here in the in the detector So here basically practically you are between the you can measure up to masses for sorry maybe Go up to the d meson mass Okay, is that does that answer your question or? Yes, yes, but In principle, you know specific No, no, no, no, no, I I wasn't thinking on any on anything specific But in principle you can detect other other scenarios in principle It's it's not only heavy neutrinos that you can detect on n a 62 But you can also detect that matter of course So so in that case probably you will you will have some Lows and lows of other byproducts of the decays and which well, okay You can always have many byproducts of many of your decays, but I wanted that you Comment to comment me on which could be those byproducts that can mess up your measurements You mean many have other standard. Are you mean? Okay. Do you mean non-standard model backgrounds like like dark matter or? standard model backgrounds well, okay I can reference my question into the non-standard model backgrounds that that is interesting as well Okay, I have not thought about that to be honest because okay So far nobody has seen any strength beyond the standard model So if we see anything everybody would be super excited, I guess And I mean if you see something of course the problem with this kind of I mean the The problem with this kind of things is that you only see the detail of this particle So it's a bit tricky to identify what exactly you saw That would be better for things like matthusla because in matthusla You can find the leptom from the primary and from the secondary vertex here from the production of the region and from the decay So you could in matthusla because you by okay The decay would be seen by matthusla and the production would be seen by cms So you could combine this data sets to sort of learn more about the particles that was flying around there in n a 62 you really only have the The information from these decay products under Okay, they're not made so for from standard model viewpoint We assume that it's a background free analysis simply because there is no standard model particle that could fly that far in decay But of course if you see something to be sure that you have to see in the right hand region Or not some other dark matter candidate You would have to look at many different channels and many different final states and yeah You see how they rather rather the branching ratios into different decay Yeah final states of this particle But yeah, I don't know. Yeah, I mean, I would be happy if anything is discovered if it's not the heavy new tune. It's also great Okay, thanks Okay, let's continue with the question So we have let's one question from the youtube chat that is basically they are asking if they from hit shield Let's say his name appear here is like if there is kind of a online resource to compare different adrenal Vertices interaction or multiple experiment observation kind of if there is kind of a website in which You can go to if you have doubts about this there are neutrinos having heavy neutrinos you go there and you can Make your exclusion plots and This kind I'm not aware of such a website. I mean there are several papers that summarize the the existing bounds I mean in the in the On the house called on the block I I provided some reference for reviews I mean some of them older some of the newer There are various different lines shown in this reviews and or some of them So, yeah, let's say that we can refer them to to go to the the blog post and check the reference there I would do so you can either check the references throughout this talk because I I posted some references for I mean, I'm not aware of any website where you can just look at the data, but So there's for example, there's this web. There's there's this there's this review here Oh, this tune at I'll review down here that contains some information and sorry there is I'm so that's down here this and Do you want to know for heavier masses? There's the ones That's this review by tie at I that's for heavier masses, but all of them are given on the on the On the on the this block page, so I would probably just say just browse through the reference on the block page. Okay Yeah, perfect. So now that we have still some very few questions to from the Hangout people here. So First is the Federico Please and me just have an answer All right. Hello, can you hear me? Hi Yes, I have two brief questions one is why did you consider only two neutrinos was it for minimality? Because I mean if you have three then I expect that maybe you cannot Determine so like say the angle omega or so because you have more parameters Yes Okay, was it then for minimality and and second about the The case where you have is I let you answer sorry No worries. I mean for two reasons. I mean first of all It's kind of an Occam's razor razor approach. You say, okay, how much do we need? We don't know what that's absolute in genome mass scale And if the absolute in genome mass scale the standard model is Zero if the light is done up on each of us masters, then you only need to write and each you know to explain If you know say later So to write and each you know is basically the minimal model that you can use So it's minimal. It has small number of parameters. It's testable. So that's sort of Minimality the other thing is that what I I before I showed this this new msm Like what I'm what is now in the slides? So there are three right hand each, you know, but one of them becomes the dark matter candidate So if you have such a model like such a structure as it's shown on the slide here right now where they're three right hand each, you know, but one of them But there's a b minus l symmetry then Okay, you can either argue from a phenol viewpoint I say I want one of them to be the dark matter candidate and it decouples Or I can argue from model building viewpoint and say I want the b minus l symmetry So that I can get large mixing angles for the pseudo direct pair But then also the third one should be coupled in the symmetric limit So either way one of the stereo neutrinos is likely to Like either from the phenol or from the dark matter viewpoint One could argue that one of them is likely to have very feeble interactions Then one can look on an effective theory that describes the other two And that's what is the case in this new msm model. So there in the new msm model. There's a sort of Deeper reason why the two right hand neutrino picture is correct But if you don't like the new msm if you want to forget about the new msm Then one could argue just what you said It's just minimality and testability, but I totally agree if you have three right hand neutrinos The model becomes much bigger the parameter space becomes much bigger Um It becomes less testable in the sense that you can't extract all parameters. However Sorry, let me fast forward to the leptogenesis plot You saw before in these plots the region where the progenesis work is always very restricted Right there were these two leptogenesis lines if you have three right hand neutrinos basically Well now you can see the mass of mixing and all these blue dots give you points where the leptogenesis works So if you have three right hand neutrinos leptogenesis actually works with much bigger mixing angles So it's a trade-off if you have three right hand neutrinos, it's much more difficult Probably even impossible to reconstruct all model parameters from observation on the other hand the chances for discovery of a cosmologically motivated model with leptogenesis might be much better because the The leptogenesis possible with much larger mixing angles, which gives you much larger rates at colliders. So that's Yeah, that's what I was shown in this plot Okay, great and and just regarding leptogenesis. I mean you need a small mass difference so at some point You will have like radiative corrections which mess up with this mass difference or can you comment on that Yes, there are two answers to this. So first of all, uh, you need the small mass splitting only when there are two right hand neutrinos When there are three right hand neutrinos as for this plot here, you don't necessarily need the mass fittings to be small so the The requirement to have quasi degenerate masses for leptogenesis is something that is specifically true only for the minimal extensions with two right hand neutrinos With 300 right hand neutrinos you can do leptogenesis without the master generacy If you want very large mixing angles up here at the Atlas and CMS range Then you then you need the master genesis again, but somewhere here in the middle of the parameter space You can do it without master genesis. So The master genesis actually not absolutely needed. So that's the first answer So the second answer is about radiative corrections. So If there is such a master generacy then, uh, I think it is well motivated to have such a master generacy Only in the okay, it's sorry for rushing but I have to go to the very end of the talk again Only in this symmetric limit that I already mentioned here this b minus l symmetric limit And in the symmetric limit, uh, the master generacy can be explained by the symmetry So all these parameters the Greek letters would go to zero in the symmetric limit And that tells you that in the symmetric limit You don't only get a master generacy, but you also see that there's a specific structure in the u-cover and this is specific structure in the u-covers Tends to tell you that So to say Radiative corrections are not arbitrary if that makes any sense. So do you Okay, so they are protected basically Yes, not 100% okay Yeah, I I would have to look at the formula again to be 100 percent sure what exactly is the correction But I think they are to some to be protected due to the symmetry I don't want to make a too strong statement right now because I forgot the exact formula, but uh Yes, but they're they're not arbitrary. Let's put it like that. I think they are actually protected Okay, we have one more two more questions and then I guess it's time to To finish this. Yeah, Juan Carlos, please ask a question Yeah, I have a question. I think I already answered the question to myself, but again to related to the n a n a 62 experiment You show this Sorry Can you go to this is life or when you showed that the dam mode, please This one. Yes. So you are not detecting the the The lepton, I mean the the standard model part of the decay from the mesons, right from the Yeah, I think nobody this one's here. Yes. Yeah, you can't you can't not an n a 62 That's one of the advantages of matthewsla that in matthewsla you could see this part of the process with cms But not an n a 62 And can you in principle have tau leptons for instance there as well? Yeah, I mean if you have a b meson then you can certainly make a tau lepton Yeah, I suppose that you also took into account that contribution because in principle the tau can decay into heavy nutrients as well Or maybe it's it's negligible Yes, that was uh, I I think that was not the dominant channel, but I think it's in the code Yeah, yeah, okay. Thank you Okay, so on the last question because we yeah, we are Over time from joel Thank you Okay, so so I'm asking this only because I've seen that you've had you have hundred of backup slides So This is off topic, right? So so what about the situation of of uh of dark matter? um Is uh, I I understand that the new star Observations really constrain it, but I don't know if there's There any news or So I there you have I have this plot here and it doesn't have the newest new star in it because there was a new star paper quite recently Um, I have to say I'm not an expert on the analysis of these x-ray data So with the previous new star Publication, there were some doubts by my collaborators who work on this about how robust their bounds are The newest ones. I have not talked to sort of let's say my expert collaborators yet. So What is true is that if you take the new star bound series the most the latest Publication, then they would cut away a fair bit of so in this drop Oh, sorry in this plot x axis is again the massive y axis the mixing and then The blue dot here is this claim 3.5 kv Emission three line and the Around it. There's a range of allowed parameters and yet to the left you're ruled out by by liman alpha and below the blue Like it's here to the left. This is ruled out by liman alpha and below the green line Is ruled out by uh, well you by bbn. So basically you're constrained to this In the minimal model where in the new msm model you're constrained to this Triangle here and the new star observations indeed seem to rule out some part of this triangle However, there's also a remaining part of the triangle. So parameter space is reduced but not zero and also keep in mind that this lower bound here from From bbn It is it only applies in this minimal model where the heavy neutrinos are produced via msw like resonance from weak interactions If the heavy neutrinos produced if the sterile neutrino dark matters produced Let's say in the decay of some heavier particles in the early universe then these green line down here is basically Disappears and also these Structure formation bounds here on the left become much weaker So I would say that sterile neutrino dark matter within the framework of the minimal neutrino Minimal standard model is A bit under pressure even though they're still by the parameter space while sterile neutrino dark matter in general has A lot more air to breathe, but even the new msm there's still quite quite some parameter space left. So it's not impossible. Okay Super super. Thank you very much Okay, so I think that is all for today Again, marco was very nice women and also you did a lot A lot of working here with answering all the questions that we have there were many many many So first of all, thank you to you So all of them perfectly I feel like there's a problem, but yeah If somebody has a more Want to follow up please feel free to email me Yeah, we are gonna put your this information also in the blog post also your slides if you send it there Okay, anyway, so for the people that is following us Thank you for watching this webinar series to support in us and please Don't forget to subscribe or to talk to your colleagues mates at the university in the office or whatever That you can come here to to know what is happening in in in physics and research in different topics related with Partial physics astrophysics. So for all the rest, thank you also for being here for the Attendance to this hangout session and see you next time. We are going to restart with the webinars again in in march We are going to have a little bit of holidays. Let's say and in march we start again So see you soon around here in judo. Bye Bye