Large Hadron Collider: New physics in sight?

The magnet core of the Compact Muon Solenoid (CMS) which is one of the experiments at the Large Hadron Collider. Photo: AP   | Photo Credit: MARTIAL TREZZINI

In its second run, the Large Hadron Collider, among other things, will be looking for signs of physics beyond the standard model. In this search, of the experiments running in the LHC, the LHCb experiment could well be the first to detect such physics. In fact, according to an Indian group of theorists who analysed data from the previous run, at the LHCb experiment, such a sign may have been produced in the previous run itself.

There are several experiments running in the LHC which will collect data from the collisions of particles and several experimentalists and theorists waiting to analyse this data. Four of these are the ALICE (A large ion collider experiment), ATLAS (A toroidal LHC apparatus), CMS (Compact muon solenoid) and LHCb (Large hadron collider beauty) experiments.

Some of the most important questions that scientists are waiting to unravel from these experiments are signs of there being physics “beyond the standard model.”

Of these ATLAS and CMS look for evidence of supersymmetry, supersymmetric particles, dark matter and anything exotic and beyond the standard model.

The LHCb experiment in particular looks at rare decays of the elementary particles named B mesons with great precision. B mesons are a group of particles all of which contain the b quark, and, hence the name LHCb.

The experiment in particular studied the angular distribution of particles coming from the decay of B mesons into particles known as K* and a set of mu-leptons (heavier cousins of the well-known electron).

At the 50th Moriond Electroweak conference held at La Thuile, Italy, earlier this year, LHCb physicists revealed that such decays did indeed show a deviation from the standard model but that the statistical significance is not high enough to be counted as a discovery.

Rahul Sinha, professor at Institute of Mathematical Sciences, Chennai, and his group, have been working on this problem for many years.

Together with his student Rusa Mandal, he has developed a different way of analysing the decay which indicates a deviation from standard model at a higher significance (six sigma). This is high enough to say that proof of new physics has been discovered.

Standard Model

As is commonly known, the Standard Model is a theory that describes all known subatomic and subnuclear particles, and has been successful in describing electromagnetic, weak and strong forces.

With the discovery of the Higgs particle, all the particles described by this model have been discovered. However, physicists believe that this model is incomplete, and there exists physics beyond what is described by the standard model.

They believe that there could be new particles, which are “supersymmetric” partners of the known ones, whose existence would confirm the existence of a propertycalled supersymmetry, or SUSY for short.

For that matter, SUSY is a necessary ingredient of string theory, so the discovery of such particles would strengthen the position of string theory.

Another thing that the LHC will be looking for, which also implies physics beyond the standard model, is signs of existence of dark matter particles.

The LHC is the world’s largest and most powerful particle accelerator. In its first run, the LHC produced energies of the order of 7 TeV (teraelectronvolts) and in its present run, this has been increased to 13 TeV.

Inside this accelerator, two beams of particles travel at high speeds, close to that of light, and are made to collide with each other.

This is a task in itself, for the particles involved (protons, neutrons etc) are so small that it is like firing two needles at each other from a distance of ten kilometres, at such precision that they collide.

The particle collider recently started its second run after being upgraded, among other things, to higher energies. But from what Prof. Sinha’s paper, to be found at > on the arXiv, which is a repository of articles accessed by physicists across the world, suggests, it may have yielded a grand result in the first run itself. “While we await peer review of our work we are optimistic that LHC will reveal new particles in the present run,” he says.

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Printable version | Sep 19, 2021 3:18:21 AM |

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