Amazing stuff! The scientists refer to their discovery as an "elusive dance". What were they smoking? Just kidding! 😊
"... For decades, physicists believed that the top quark, the heaviest known subatomic particle, was too short-lived to form a temporary pair with its antimatter partner. Unlike lighter quarks, which can combine to form protons, neutrons, or longer-lived quark–antiquark pairs, the top quark decays almost instantly. This made the idea of a top–antitop bound state – a fleeting association held together by the strong force – seem impossible. But now, the CMS collaboration at the Large Hadron Collider (LHC) has found the first evidence of such a state, which is dubbed toponium. ..."
"An unforeseen feature in proton-proton collisions previously observed by the CMS experiment at CERN’s Large Hadron Collider (LHC) has now been confirmed ... The result ... suggests that top quarks – the heaviest and shortest-lived of all the elementary particles – can momentarily pair up with their antimatter counterparts to produce a “quasi-bound-state” called toponium.
Further input based on complex theoretical calculations of the strong nuclear force -- called quantum chromodynamics (QCD) -- will enable physicists to understand the true nature of this elusive dance. ...
Basing itself on a simplified toponium production hypothesis, CMS measured the cross section for the top quark–antiquark excess to be 8.8 picobarns (pb) with an uncertainty of about 1.3 pb. This passed the “five sigma” level of certainty required to claim a discovery in particle physics and made it extremely unlikely that the excess over the background-only prediction is just a statistical fluctuation.
“The observation of a non-relativistic QCD effect that was thought to be too difficult to detect is a great triumph for the LHC experiment programme,” ..."
From the abstract:
"A search for resonances in top quark pair () production in final states with two charged leptons and multiple jets is presented, based on proton–proton collision data collected by the CMS experiment at the CERN LHC at , corresponding to 138 fb−1.
The analysis explores the invariant mass of the system and two angular observables that provide direct access to the correlation of top quark and antiquark spins.
A significant excess of events is observed near the kinematic threshold compared to the non-resonant production predicted by fixed-order perturbative quantum chromodynamics (pQCD).
The observed enhancement is consistent with the production of a color-singlet pseudoscalar () quasi-bound toponium state, as predicted by non-relativistic quantum chromodynamics. Using a simplified model for toponium, the cross section of the excess above the pQCD prediction is measured to be ."
Elusive romance of top-quark pairs observed at the LHC (original news release) "The CMS and ATLAS experiments at CERN’s Large Hadron Collider have observed an unforeseen feature in the behaviour of top quarks that suggests that these heaviest of all elementary particles form a fleeting union."
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