The ATLAS experiment has confirmed that a trio of particles—a top-antitop quark pair and a W boson—occurs more frequently than expected in the wake of proton-proton collisions inside the Large Hadron Collider (LHC).
The process that creates these three particles post-impact is quite rare: Only one out of every 50,000 collisions at the LHC produces the trio, known as ttW. After popping into existence,and W bosons are short-lived and decay almost immediately, so the team identified ttW events based on the electrons and muons into which they decay.
The most recent measurement using the full dataset collected by ATLAS during Run 2 has led to a more precise measurement of ttW, finding the total production rate to be about 20 percent higher than theoretical predictions. Fresh results from the CMS experiment corroborate this excess. "This is something that hasn't been done before because it's very hard. But now, with our result, there's already theorists who are interested in putting in the effort," Bullard said."This measurement will be very useful to continue to better understand the Standard Model and maybe even identify some beyond-the-Standard-Model effects if we're lucky.
The other process ttW muddles is the production of four top quarks, an event that is 50 times rarer and which ATLAS and CMS recently observed for the first time. Further examination will allow physicists to probe new physics that might involve top quarks, the most massive particle in the Standard Model.
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