Physicists from the ATLAS and CMS collaborations at CERN’s Large Hadron Collider (LHC) have independently conducted extensive searches for the rare Higgs boson decay into a Z boson and a photon.
The Standard Model predicts that, if the Higgs boson has a mass of around 125 billion electronvolts (GeV), approximately 0.15% of Higgs bosons will decay into a Z boson and a photon. But some theories that extend the Standard Model predict a different decay rate.
Measuring the decay rate therefore provides valuable insights into both physics beyond the Standard Model and the nature of the Higgs boson.
Previously, using data from proton-proton collisions at the LHC, ATLAS and CMS independently conducted extensive searches for the decay of the Higgs boson into a Z boson and a photon.
Both searches used similar strategies, identifying the Z boson through its decays into pairs of electrons or muons — heavier versions of electrons. These Z boson decays occur in about 6.6% of the cases.
In these searches, collision events associated with this Higgs boson decay would be identified as a narrow peak, over a smooth background of events, in the distribution of the combined mass of the decay products.
To enhance the sensitivity to the decay, ATLAS and CMS exploited the most frequent modes in which the Higgs boson is produced and categorized events based on the characteristics of these production processes.
They also used advanced machine-learning techniques to further distinguish between signal and background events.
“The discovery of the Higgs boson in 2012 by the ATLAS and CMS collaborations has been followed by a detailed program of measurements that have confirmed its couplings and other properties are consistent with those predicted in the Standard Model,” they said.
“However, there are several Higgs boson decay channels, including H → Zγ, that have small predicted branching fractions and have not yet been observed.”
“These channels also provide probes for…
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