7/13/2023 0 Comments Accelerator particles![]() "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." But now, with our result, there's already theorists who are interested in putting in the effort," Bullard said. ![]() "This is something that hasn't been done before because it's very hard. Theorists make predictions from the Standard Model through piecewise approximations of increasing difficulty, and subtle effects that have not yet been incorporated into these approximations may be able to explain the discrepancy.Įither way, theorists must now try to figure out the truth by taking these yet-to-be-calculated subtle effects into account as they approximate ttW. It's possible that new physics beyond the Standard Model is responsible.Īlternatively, it's possible that the models used today lack necessary elements to correctly predict ttW production. "It's still unclear what exactly could be causing this discrepancy, but these results really do seem to indicate that there's something going on that we're not taking into account," Bullard said. Fresh results from the CMS experiment corroborate this excess. 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. Subsequent measurements using a subset of data collected during Run 2 (2015-2018) suggested that ttW was cropping up more than predicted by the Standard Model of particle physics, which physicists use to describe the behavior of subatomic particles. "The only measurements of ttW production come from the LHC-it is the first collider that can produce these types of events at a large enough rate to be measured," said Brendon Bullard, research associate at SLAC National Accelerator Laboratory and leader of this data analysis.ĪTLAS first observed the ttW process in 2015 using data collected during the LHC's Run 1, which took place between 20. The results will help researchers better test theories of elementary particle physics as well as help experimentalists studying other particle physics processes. Members of the ATLAS group at the Department of Energy's SLAC National Accelerator Laboratory have spent the last three years completing a complex analysis to measure the process, including developing novel methods to estimate and remove background and detector effects to maximize the accuracy and detail of the analysis of the measurement. After popping into existence, top quarks 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 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.
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