Four top quarks were observed using data from collisions during the second run of the Bolshoi
ATLAS is one of the four mainexperiments at the LHC at the European Organization for Nuclear Research CERN, Geneva. The experiment is carried out on a detector of the same name, designed to study proton-proton collisions. CMS (Compact Muon Solenoid) is one of two large universal particle detectors at the Large Hadron Collider (LHC) at CERN.
The top quark is the heaviest particle in the Standard Model, and therefore the particle with the strongest connections to the Higgs boson. This makes it ideal for learning new physics.
There are many ways to gettop quark. Most often they are observed in pairs of quarks and antiquarks, and sometimes on their own. According to the theory of the Standard Model, four top quarks, consisting of two top-quark-antiquark pairs, can appear simultaneously.
However, scientists predict that the speedformation will be 70 thousand times lower than that of top-quark-antiquark pairs. Therefore, physicists consider the appearance of four top quarks a real breakthrough. Evidence of this phenomenon was previously recorded by ATLAS in 2020 and 2021 and CMS in 2022 . However, there have been no observations to date.
Display of four top quark production events from ATLAS (left) and CMS (right). Image: CERN
It is known that the birth of four top quarksis rare. Each of them decays into a W boson and a down quark. The W boson can then decay into either a charged lepton and a neutrino, or a quark-antiquark pair. This means that the signature of events with four top quarks can vary greatly. This makes searching difficult.
ATLAS and CMS used new methodsmachine learning to create algorithms that select candidate events with four top quarks. Both ATLAS and CMS looked for signatures of events containing two or more leptons. The first direct observation of the formation of four top quarks is a new step in the study of this particle. Both experiments will continue to operate during the third launch at the LHC.
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