What is the Higgs Boson?
The Higgs boson is an elementary particle that was potentially discovered on July 4th 2012. It was predicted by the Standard Model of Particle Physics, which consists of 17 particles, the Higgs being one of them, the others being the 6 quarks (up, down, charm, strange, top, bottom), 6 leptons (electron, muon, tau and their corresponding neutrinos), the photon, the gluon and the W and Z bosons. The quarks and leptons are part of a group of particles called fermions. These are the particles that make up the every day matter we see around us (protons and neutrons are made of up and down quarks, which when combined with electrons make atoms). The photon, gluon, W and Z and Higgs are all bosons. These are responsible for all the Universe's forces, except gravity, which as of yet hasn't been worked into the Standard Model. (There's always one that has to be difficult!!). Scientists believe that the Higgs boson is responsible for giving fermions mass.
How would a Higgs boson give fermions mass?
Higgs bosons obey the conservation of energy law, which states that no energy is created or destroyed, but is instead transferred. Firstly, the energy starts out in a gauge boson (photon, gluon, W or Z) that interacts with the Higgs field. This is energy in the form of kinetic energy, or movement. After the gauge boson interacts with the Higgs field, it slows down. The slowing reduces the amount of kinetic energy in the gauge boson. However, this energy cannot be destroyed, so it is instead transferred into mass-energy, which is normal mass that comes from energy. The mass created is what we call a Higgs boson. The amount of mass created comes from Einstein's famous equation E=mc2, which states that mass is equal to a large amount of energy (for example, 1 kilogram is equal to almost 90 petajoules- 90,000,000,000,000,000 J). Since the amount of mass-energy created by the Higgs field is equal to the amount of of kinetic energy that the gauge boson lost by being slowed, energy is conserved.
Independence Day discovery
On 4th July 2012, the two main experiments at the Large Hadron Collider (LHC), ATLAS (A Toroidal LHC Apparatus) and CMS (Compact Muon Solenoid) both independently reported the existence of a previously unknown particle with a mass of 125 GeV/c2, which is equivalent to about 133 proton masses, and is "consistent with the Higgs boson", and widely believed to be this long-elusive particle. Further work is needed to confirm if this is the case, but the scientific community widely accepts that the particle discovered is indeed the Higgs, as it bears many of the theoretically predicted properties of it.
So why has the Higgs been so elusive for the past 48 years?
The Higgs particle is a very massive particle, and like all large particles, decays almost instantly after its creation (under a septillionth of a second!), so only a very high-energy particle accelerator can observe and record it. Mathematical consistency of the Standard Model requires that anything capable of generating the masses of elementary particles become visible at energies above 1.4 TeV, therefore the LHC (designed to collide two 7 TeV proton beams, but currently running at 4 TeV each), was built to answer the question of whether the Higgs exists or not.
What if the particle discovered wasn't the Higgs?
Several Higgsless models of the Universe exist, where strongly interacting dynamics rather than an additional field produce the non-zero vacuum expectation value that breaks electroweak symmetry. Some of these mechanisms include:
- Technicolour- A class of models that attempts to mimic the dynamics of the strong force as a way of breaking electroweak symmetry.
- Extra-Dimensional Higgsless models- The role of the Higgs field is played by a fifth component of the gauge field.
- Abbott-Farhi Models- Composite W and Z vector bosons.
- Top Quark Condesate Theory- A fundamental scalar Higgs field is replaced by a composite field composed of the top quark and its antiquark.
- The Braid Model- A model of Standard Model particles by Sundance Bilson-Thompson, compatible with loop quantum gravity and similar theories.
