Seminars

Two CERN experiments show signs of a rare Higgs boson process

They were announced in early August virtually at the world’s largest particle physics conference, ICHEP, but today they were presented in person at the headquarters of the European Laboratory for Particle Physics (CERN), near the Swiss city of Geneva. These are the new results recorded by the ATLAS and CMS detectors of the Large Hadron Collider (LHC), which show how the Higgs boson disintegrates into two muons, particles similar to electrons but heavier. The phenomenon is extremely rare. According to the results presented on Tuesday, only one in every 5,000 Higgs bosons produced in the world’s largest particle accelerator, the LHC, decays into a pair of muons.

The muon is one of the elementary particles of the so-called ‘second generation’ of the standard model, a theory that describes the elements that make up everything we see in the universe and their interactions, and now it is the first time that higgs have been observed interacting with particles of this ‘second generation’. In the model, elementary particles are grouped into three generations according to their mass. All matter we see is made up of three first-generation particles: up and down quarks (which form protons and neutrons in atomic nuclei) and electrons, which belong to a type of particle called leptons. The two remaining generations are made up of heavier ‘relatives’ of quarks and leptons. One of them is the muon, about 200 times heavier than the electron.

The origin of these differences in the mass of elementary particles is unknown, but the study of the Higgs boson, discovered by the ATLAS and CMS experiments in 2012, is essential to shed light on this fact. Both experiments had already observed the disintegration of the Higgs boson into very heavy particles such as the W and Z bosons, responsible for the weak interaction (responsible for radioactive processes), the bottom and top quarks and the tau leptons. Although now it is the first time that the interaction of the Higgs with a second generation particle has been observed, the results are not statistically conclusive. The results of the so-called Run 3, the third period of operation of the LHC that begins in 2021, will be able to confirm this mode of disintegration.

For now, the results obtained fit the predictions of the standard model. The data that will be obtained in Run 3 (2021-2024) and in the High Luminosity LHC, an important improvement of the accelerator and its experiments that will work from 2027, will allow reaching the necessary statistical significance (5 sigma) to confirm this decay behavior of the Higgs boson into a pair of muons.

According to the scientists, the precision study of these processes will allow exploring the limits of the standard model itself and searching for new physics beyond known theories.

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