Studying beautiful flavour transitions
CMS and LHCb collaborations presented new findings on rare quark transformations at ICHEP, probing potential gaps in the Standard Model.
Researchers from the CMS and LHCb collaborations have unveiled their latest results on the rare decay process where a beauty quark transforms into a strange quark, a muon, and an antimuon. This transition, denoted as b→sμμ, is governed by the weak interaction and serves as a critical test of the Standard Model. Quantum effects from other particles can influence such transitions, and deviations from predictions may signal new physics beyond the current model.
The b→sμμ process is exceptionally rare, occurring in roughly one out of every ten million decays of beauty particles. Over the past decade, measurements have hinted that this transition may not align with Standard Model expectations. To investigate, CMS and LHCb analyzed six distinct decay types, measuring their branching fractions—the rates at which these decays occur—for the first time in a combined analysis.
CMS utilized data from the LHC’s third run, employing a new trigger system to achieve unprecedented statistical precision in measuring the branching fractions of these decays. The collaboration’s results showed small but consistent deviations across all six decay types when compared to Standard Model predictions. This consistency across multiple decay channels strengthens the case for further scrutiny of the process.
LHCb, using data from the first and second runs of the LHC, focused on one specific decay type: the transition of a neutral beauty meson to an excited kaon. The collaboration measured a property called P₅’, describing the angular distribution of decay products, and found a slight discrepancy with Standard Model predictions. The analysis was conducted without theoretical assumptions, and future work will incorporate data from the LHC’s third run to refine these measurements.