ATLAS experiment searches for ‘charming’ decay of the Higgs boson

Determine 1: Candidate occasion show of the ZH → μμ cc course of, the place a Z boson and a Higgs boson decay to 2 muons (purple tracks) and two charm-tagged jets (blue cones). Credit score: ATLAS Collaboration/CERN

Key to understanding the Higgs boson and its position within the Normal Mannequin 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). Though hints of second-generation lepton interactions have began to look, physicists have solely experimentally confirmed that the lots of the heaviest quarks originate from their interactions with the Higgs discipline. To this point, lighter quarks haven’t but been noticed interacting with the Higgs boson.

This week, physicists on the ATLAS Experiment at CERN launched a brand new direct seek for the decay of the Higgs boson to appeal quarks. Observing this decay would give physicists new perception into the Higgs boson’s relationship with the second technology of matter particles. Additional, measuring the energy (or “coupling”) of the Higgs boson’s interplay to the appeal quark might give physicists perception into new physics processes.

However recognizing this decay has confirmed fairly the problem. It accounts for simply 3% of Normal Mannequin Higgs boson decays and, extra importantly, its search is closely dominated by background processes. For his or her new end result, ATLAS researchers started by figuring out collision occasions with jets of particles originating from the hadronisation of appeal quarks. They used a brand new multivariate classification technique, which might tag hadrons with explicit 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.

ATLAS Experiment searches for "charming" decay of the Higgs boson
Determine 2: Distributions of the invariant mass of the 2 jets, after background subtraction and requiring one appeal tag (left) or two appeal tags (proper). Credit score: ATLAS Collaboration/CERN

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 Determine 2.

Researchers validated this evaluation technique by additionally learning occasions with two vector bosons that comprise the decay of a W boson to 1 appeal quark (VW(cq) or the decay of a Z boson to 2 appeal 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. Each measurements, utilizing appeal tagging, are in settlement with precision measurements at earlier experiments.

Physicists discovered no important signal of the decay of the Higgs boson to appeal quarks; the end result was used to set a restrict on the speed of the VH(cc) course of (on the 95% confidence degree) to be 26 occasions the speed predicted within the Normal Mannequin. This restrict additionally allowed ATLAS physicists to—for the primary time—give a significant interpretation of the Higgs–appeal coupling.

ATLAS’ new direct seek for Higgs-boson decays to appeal quarks constrains absolutely the worth of the modified coupling (on the 95% confidence degree) to be, at most, an element 8.5 from the worth predicted within the Normal Mannequin. After having noticed the coupling of the Higgs boson to the heaviest quarks, ATLAS physicists at the moment are increasing their exploration of the coupling of the Higgs boson to the lighter quarks.

ATLAS searches for pairs of Higgs bosons in a uncommon particle decay

Extra data:
Direct constraint on the Higgs-charm coupling utilizing Higgs boson decays to appeal quarks with the ATLAS detector (ATLAS-CONF-HIGG-2021-021): … ATLAS-CONF-2021-021/

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ATLAS Experiment

ATLAS experiment searches for ‘charming’ decay of the Higgs boson (2021, June 9)
retrieved 9 June 2021

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