Key to understanding the Higgs boson and its function within the Standard Model is knowing the way it interacts with matter particles, i.e. quarks and leptons. There are three generations of matter particles, various in mass from the lightest (first technology) to the heaviest (third technology). Although hints of second-generation lepton interactions have began to seem, physicists have solely experimentally confirmed that the plenty of the heaviest quarks originate from their interactions with the Higgs subject. So far, lighter quarks haven’t but been noticed interacting with the Higgs boson.
This week, physicists on the ATLAS Experiment at CERN launched a new direct search for the decay of the Higgs boson to charm quarks. Observing this decay would give physicists new perception into the Higgs boson’s relationship with the second technology of matter particles. Further, measuring the power (or “coupling”) of the Higgs boson’s interplay to the charm quark may give physicists perception into new physics processes.
But recognizing this decay has confirmed fairly the problem. It accounts for simply 3% of Standard Model Higgs boson decays and, extra importantly, its search is closely dominated by background processes. For their new end result, ATLAS researchers started by figuring out collision occasions with jets of particles originating from the hadronisation of allure quarks. They used a brand new multivariate classification methodology, which might tag hadrons with specific properties, particularly their decay size from the LHC collision level. Then, to maximise their end result’s sensitivity to the sign, researchers categorized these occasions by these containing one or two charm-quark tags.
To additional suppress backgrounds from different physics processes, ATLAS physicists focused their search to Higgs bosons produced along with a vector boson (VH(cc)), the place the vector boson (W or Z) decays to 0, 1, or 2 electrons or muons. The di-charm invariant-mass distribution, after subtraction of the backgrounds, is proven in Figure 2.
Researchers validated this evaluation technique by additionally learning occasions with two vector bosons that comprise the decay of a W boson to at least one allure quark (VW(cq) or the decay of a Z boson to 2 allure quarks (VZ(cc)). The VW(cq) course of was measured with a sign significance of three.8 sigma, and the VZ(cc) course of with sign significance of two.6 sigma. Both measurements, utilizing allure tagging, are in settlement with precision measurements at earlier experiments.
Physicists discovered no vital signal of the decay of the Higgs boson to allure quarks; the end result was used to set a restrict on the speed of the VH(cc) course of (on the 95% confidence stage) to be 26 occasions the speed predicted within the Standard Model. This restrict additionally allowed ATLAS physicists to—for the primary time—give a significant interpretation of the Higgs–allure coupling.
ATLAS’ new direct seek for Higgs-boson decays to allure quarks constrains absolutely the worth of the modified coupling (on the 95% confidence stage) to be, at most, an element 8.5 from the worth predicted within the Standard Model. After having noticed the coupling of the Higgs boson to the heaviest quarks, ATLAS physicists are actually increasing their exploration of the coupling of the Higgs boson to the lighter quarks.
Direct constraint on the Higgs-charm coupling utilizing Higgs boson decays to allure quarks with the ATLAS detector (ATLAS-CONF-HIGG-2021-021): atlas.web.cern.ch/Atlas/GROUPS … ATLAS-CONF-2021-021/
ATLAS experiment searches for ‘charming’ decay of the Higgs boson (2021, June 9)
retrieved 9 June 2021
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