The ATLAS and CMS collaborations have both presented the observation of a very rare process today at the Moriard conference: the production of four top quarks simultaneously. They were noticed utilizing information from impacts during Run 2 of the Enormous Hadron Collider (LHC).
The observations of ATLAS’ observation with 6.1 sigma, higher than the expected significance of 4.3 sigma, and CMS’ observation with 5.5 sigma, higher than the expected 4.9 sigma, qualify as the first observations of this process because they meet the criteria for statistical significance of five sigma.
The top quark has the strongest ties to the Higgs boson because it is the heaviest particle in the Standard Model. Because of this, top quarks are ideal for searching for evidence of physics outside of the Standard Model.
A top quark can be made in a variety of ways. They are usually seen as pairs of quarks and antiquarks, but they can also be seen by themselves from time to time. Four top quarks—two top quark–antiquark pairs—can be produced simultaneously, according to the Standard Model.
Four-top-quark production is elusive because the predicted rate of production is 70 thousand times lower than that of top quark–antiquark pairs. Proof for this peculiarity has recently been found by Map Book in 2020 and 2021 and by CMS in 2022. However, there had never been an observation up until this point.
Four-top-quark production is not only uncommon but also notoriously difficult to detect. The “signature” of an event is what physicists look for when looking for it: the characteristics of a decay’s final particles. These point to the brief occurrences that they are looking for. W bosons and bottom quarks are produced when every top quark breaks down.
The W boson can then decay into either a quark–antiquark pair or a charged lepton and a neutrino. This means that four-top-quark events can have a wide range of signatures, ranging from zero to four charged leptons and up to 12 quark-generated jets. This makes it hard to find the four-top quark production signature.
The algorithms that select the four top-quark candidate events were developed by both CMS and ATLAS using cutting-edge machine learning methods to assist in the search for these events. The analyses distinguish the events with four top quarks from the background caused by other Standard Model processes with higher production rates by utilizing the stunning four top quark signature, which includes multiple electrons, muons, and (bottom quark-tagged) jets. Both CMS and ATLAS looked for event signatures with at least two leptons in them.
An exciting new step in the process of learning more about this fascinating particle is the first direct observation of four-top-quark production. The two tests anticipate proceeding to concentrate on this peculiarity during LHC Run 3.
More information: Moriond conference
ATLAS physics briefing
CMS physics briefing
