SWITZERLAND: Scientists at CERN’s Large Hadron Collider (LHC) have achieved another breakthrough in particle physics as the ATLAS and CMS collaborations joined forces to provide the first evidence of the Higgs boson decaying into a Z boson and a photon.
This rare decay process could shed light on particles beyond the Standard Model and deepen our understanding of the nature of the Higgs boson.
The discovery of the Higgs boson in 2012 opened new avenues for research in particle physics. Since then, scientists have meticulously explored its properties and investigated its various decay processes.
At the recent Large Hadron Collider Physics conference, ATLAS and CMS presented their joint efforts to uncover the elusive decay of the Higgs boson into a Z boson and a photon.
The decay of the Higgs boson into a Z boson and a photon resembles a degeneration into two photons. However, these decays do not occur directly but involve an intermediate “loop” of “virtual” particles that researchers cannot observe directly.
These virtual particles could include yet undiscovered particles that interact with the Higgs boson, potentially challenging the predictions of the Standard Model.
According to the Standard Model, around 0.15% of Higgs bosons with a mass of approximately 125 billion electronvolts should decay into a Z boson and a photon.
However, theories extending beyond the Standard Model propose different decay rates. Scientists gain valuable insights into physics beyond the Standard Model and the characteristics of the Higgs boson itself by measuring the decay rate.
Previously, both ATLAS and CMS independently conducted extensive searches for the Higgs boson decay using data from proton-proton collisions at the LHC.
Employing similar strategies, they identified the Z boson through its decay into pairs of electrons or muons, heavier counterparts of electrons. The team found these Z boson decays in approximately 6.6% of the cases.
In their searches, ATLAS and CMS looked for collision events associated with the Higgs boson decay, represented by a narrow peak in the combined mass distribution of the decay products against a smooth background.
The collaborations categorized events based on the characteristics of the Higgs boson’s production processes and implemented advanced machine-learning techniques to distinguish between signal and background events.
In a new study, ATLAS and CMS combined their datasets from the second run of the LHC (2015-2018) to maximize the statistical precision of their search.
The collaboration resulted in the first evidence of the Higgs boson decaying into a Z boson and a photon, with a statistical significance of 3.4 standard deviations.
While the standard deviation falls short of the conventional requirement of 5 standard deviations for claiming an observation, the measured signal rate is 1.9 standard deviations above the Standard Model prediction.
Pamela Ferrari, an ATLAS physics coordinator, emphasized the significance of rare Higgs decays, stating that each particle has a unique relationship with the Higgs boson and searching for it is a high priority.
Florencia Canelli, a CMS physics coordinator, highlighted the potential implications of new particles on rare Higgs decay modes and expressed optimism about future advancements using the ongoing third run of the LHC and the forthcoming High-Luminosity LHC.
This collaborative effort by ATLAS and CMS brings us one step closer to unravelling the mysteries surrounding the Higgs boson and provides an insightful test of the Standard Model.
With further advancements and precision expected in future experiments, scientists anticipate probing even rarer Higgs decays, potentially uncovering new particles and revolutionizing our understanding of the universe’s fundamental building blocks.