 The mass of the Higgs boson was an open question. In the early days, scientists started looking for a fairly light particle somewhere between the mass of an electron and a proton. But later it became clear it would actually have to have a mass that exceeded the proton mass by at least a factor of 100. Still they didn't quite know how heavy it was. Luckily the Higgs was also a very unique fundamental particle because it was predicted to have zero spin. No other fundamental particle has this property. So the search for the Higgs would aim to discover a new, heavy, uncharged particle with zero spin. This long experimental campaign actually spanned multiple decades and successfully more ambitious experimental setups. So for simplicity we're going to talk about the latest search for the Higgs which has led to its discovery. This discovery won Peter Higgs and Francois Engelbert the Nobel Prize in 2013 and it was made possible using the Large Hadron Collider otherwise known as LHC located at CERN in Europe. Before we talk more about the Higgs boson we're going to spend some time exploring the main tool we use to discover new particles. Particle accelerators like the LHC have been the key to most of our discoveries in particle physics since the 1950s. The LHC is currently the world's biggest particle accelerator made for smashing or colliding particles together at very high energies. The basic idea behind experiments using accelerators like LHC is this. If we can smash two very high energy particles together we might be able to produce new massive as yet undiscovered particles. This is because of Einstein's mass energy equivalence E equals mc squared. If there's a lot of energy available in a reaction then there's a chance that some of that energy can transform into new particles that have mass. We can then use complex detector systems to see how these new particles behave. This tells us a lot about their properties and helps us see if they fit into the standard model as we know it or if there's something new entirely. A good example of the production of new particles occurs in a phenomenon known as pair production. This is kind of like the inverse of electron-positron annihilation. In this case you have one gamma ray with an energy of greater than let's say 1022 kV. This gamma ray has the possibility of producing an electron-positron pair. Essentially the energy of the gamma ray or the photon is large enough to allow for some or all of that energy to be transformed into an electron-positron pair. The electron and positron as you call have a mass of a 511 kV. Pair production can also refer to the production of other particle antiparticle pairs in the same way. The Higgs boson search aimed to produce the Higgs boson via a similar reaction mechanism requiring much higher energies. In the next video we'll talk about the technology we use to achieve these high energies.