Is there a new heavy fundamental particle ?

Is there a new heavy fundamental particle ?

In most high energy physics experiments, two beams of protons are accelerated to a very high energy level and then, it is made to collide. This results in the creation of myriads of particles, mostly known but some hitherto unknown.

With each new accelerator, the energies are higher, making the possibility of detection of heavier particles significant. With their first run three years ago, the two experiments with the Large Hadron Collider (LHC) — ALICE and CMS — detected the famous Higgs Boson with mass of 125 GeV (Proton, has a mass of about 1 GeV).

These experiments had a proton beam energy of 8,000 GeV. They also gave copious information about the Top Quark, which has a mass of 175 GeV, which had been detected earlier.

After a break of about two years, the LHC experiments began again in June 2015 with beam protons having a much higher energy (13,000 GeV). Results that were revealed in December 2015 proved to be interesting. Both of them see the possibility of a very high mass particle with energy of about 750 GeV, making them the largest particles to be discovered.

The particle is detected by its decay into the two photons. While the signal levels of the discovery may not be very high, it is interesting to note that the signal was seen at the same energy. If the signal is real, it will be known in the next few months.

At present, the fundamental particles known are quarks, leptons and force carrier bosons. Atoms have a nucleus at the centre with electrons (a lepton) revolving round the centre at various distances.

Nucleus is made up of protons and neutrons which are made up of quarks. The number of quarks and leptons is six. However, since all these particles have anti-particles and quarks have colour, the total number of quarks and leptons is 48 .This makes up the Standard Model of Particle Physics.

The crowning glory of the model was the discovery of Higgs Boson which was the last missing puzzle piece. While the neutrino oscillation that was discovered recently has dented the model somewhat, the model, however, does not expect a new particle.

Endless possibilities
However, if the particle is real, it shows the lack of completeness of the standard model. New physics will have to be invoked to explain the particle. Therefore, the very possibility of a new particle has led the physics community to go in a frenzy. The number of papers about what the particle could be, has crossed 100.

There are many speculations about the new particle. It could be a partner of Higgs or a Graviton, the particle responsible for gravitational interactions, a Dark Matter particle or a super symmetry particle proposed by some theories which put fermions and bosons on the same footing. It should be noted that several cosmic ray experiments in the past have detected heavy mass particles. Due to the lack of control in those experiments there is no proper information about the cross section or the mass of those particles.

Therefore, it is not unlikely that heavy particles exist. As a researcher puts it, “If the 750 GeV bump is real, then the LHC has just made the most profound discovery in physics since the development of the Standard Model in the early 1970s.”

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