Search for new physics via rare processes at the LHC
IDPASC Portugal - PHD Programme 2015
2015 / 2016
Experimental Particle Physics
Instituto Superior Técnico
Laboratório de Instrumentação e Física Experimental de Partículas
The study of rare physics processes is a promising means for finding evidence of physics beyond the standard model (BSM). The subject of this project is the search and study of B meson decays to muon pairs, dubbed “golden” rare decays. While highly suppressed in the SM, sizable enhancements of the decay rates are predicted in the context of common classes of BSM scenarios, such as supersymmetry. They constitute for this reason most promising probes for revealing the presence and characterizing new physics. The B →μμ rare decays have been searched for over three decades, by many experiments at different accelerators. Sufficient experimental sensitivity however has only been reached with the LHC. Recently, the Bs rare decay into a muon pair was observed for the first time via a combined analysis of the CMS and LHCb datasets (see Nature article: arXiv:1411.4413), forming one of the flagship discoveries of LHC Run 1. The project consists of studying the Bs and Bd rare decays using the LHC Run 2 data to be shortly collected by CMS. The goal is to establish the Bs signal with the larger CMS dataset, and search for the rarer Bd decay. The Run 1 data hinted for an excess relative to the SM in the Bd search. A multivariate optimization of the analysis for the Bd search will be pursued. The measurement of the Bs effective lifetime, that provides additional sensitivity to new physics, will be also performed.