"One of the questions that scientists have not yet found an answer to is the reason for the disappearance of antimatter in the universe. The theory describing particles and their interactions (Standard Model) predicts that the decay processes of particles and antiparticles are not perfectly specular, known as CP violation. Such violation predicted by the model is not sufficient to justify such an asymmetry, so it is necessary to measure it in experiments at particle accelerators. "CP violation is proportional to the area of a triangle whose sides and angles depend on the fundamental quantities of flavor physics. The angle GAMMA is of particular interest," explains Anna Lupato, a researcher at the University of Padua, "since it is measurable through particle decays for which anomalous behaviors, indicative of new physics, are not expected or are very small. The measurement of this angle through the decays of neutral B mesons is particularly intriguing because it allows a clear comparison with theoretical results." The LHCb collaboration, with the fundamental contribution of the Padua group, has recently measured the angle GAMMA with a sample of Bs→DsK decays collected during LHC accelerator collisions between 2015 and 2018 (5 fb-1). “This is a complicated analysis”, says Alessandro Bertolin (researcher at INFN Padua), “as it requires a time-dependent fit to extract CP-violating observables expressed as amplitudes of the four different decay paths that arise from Bs and anti Bs decaying into the final states Ds∓K±. “ The neutral mesons, as a function of time, can appear as either particles or antiparticles due to a quantum effect. Consequently, the variation in the number of events involving a specific neutral meson over time exhibits an oscillatory pattern, as depicted in the figure. The obtained value of GAMMA = (74 ± 11) degrees is compatible with theoretical predictions and is the most precise value ever obtained through neutral mesons. This measurement was first presented at the 12th International CKM Workshop last September and is currently featured tin the latest issue of the CERN COURIER (Jan/Feb '23).
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