Extremely rare event observed at CERN, probability 1 in 100 million

At CERN in Geneva, the LHCb experiment has allowed the observation of an extremely rare event , the probability of which is equal to one in 100 million : it is the decay of a sigma-plus baryon , a subatomic particle that disintegrates producing a proton , an antimuon and a muon . The result, which confirms the correctness of the Standard Model , The research, published in the journal Physical Review Letters, features a significant contribution from the National Institute for Nuclear Physics. The research was led by Francesco Dettori, associate professor of Experimental Physics at the University of Cagliari and an associate at the INFN, and Francesca Dordei, a researcher at the INFN's Cagliari branch, in collaboration with the INFN's Perugia branch and the University of Santiago de Compostela. Baryons are the particles that make up the type of matter that makes up the visible universe . Studying their decay is crucial to verifying the accuracy of the predictions of the Standard Model , which describes the known particles and the forces that act between them, and the possible existence of clues to a ' new physics ' that goes beyond the Model . “The study of rare decays of particles we already know allows us to understand whether there are particles or interactions unknown to us , as the quantum effects due to the presence of the latter would modify the probability of these decays,” observes Dettori. The first evidence for the possible existence of sigma-plus baryon decay was collected by the HyperCP experiment at the FermiLab laboratory in Batavia, USA, about 20 years ago . The results at the time seemed to indicate that the process could involve phenomena not predicted by the Standard Model. This hypothesis has now been refuted by data recorded by the LHCb experiment between 2016 and 2018, obtained from the collision of protons in the Large Hadron Collider accelerator and processed using advanced machine learning techniques. “ This time too, the Standard Model prevailed ,” comments Dordei. "The data are still perfectly in line with its predictions, confirming its incredible robustness, despite having been developed decades ago. But precisely for this reason, we are motivated to push even further, searching for clues of new interactions in increasingly rare and elusive phenomena."