Thesis

Search for new physics via rare processes at the Large Hadron Collider

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Experimental Particle Physics

• Supervisor:

  Nuno Leonardo

• Co-Supervisor:

  Joao Varela

• Institution:

  Instituto Superior Técnico

• Host Institution:

  Laboratório de Instrumentação e Física Experimental de Partículas

• Abstract:

  Rare processes are a very promising means for detecting physics beyond the standard model (BSM). The subject of the thesis is the search and study of B meson rare decays. The project will be carried out in the framework of the CMS experiment at CERN’s LHC. The decays of neutral B mesons into muon pairs, sometimes dubbed golden rare decays, are particularly sensitive to new physics. They constitute flavor changing neutral currents (FCNC), being further disfavored by spin conservation. In this way, the decays are highly suppressed in the standard model and proceed only through higher-order (loop) diagrams, probing the underlying fundamental theory at the quantum level. Sizable enhancements of the decay rates are nevertheless predicted in the context of common classes of BSM scenarios, including supersymmetry (SUSY) and models with extended Higgs sectors. They constitute for this reason most promising probes for revealing the presence of new physics, and for characterizing it. Given their relevance, B→ μμ decays have been actively searched for over the past few decades, by various experiments at different accelerators. Sufficient experimental sensitivity is now attained for the first time at the LHC. The CMS experiment has unique capabilities to explore the dimuon signature and to carry out this important search. Analysis of the LHC Run I data has led CMS and LHCb to recently report independent evidence for the Bs rare decay [1]. The primary goal of the thesis project is to pursue and extend the search for the B→ μμ rare decays with CMS, exploring the LHC Run II dataset. Initially, the Bs signal will be established, and, as data accumulate, used in further sensitive measurements. Then, a dedicated search for the even rarer Bd decay will be designed and implemented. The proposal foresees the integration of the applicant in the CMS B Physics Group, which is currently co-led by LIP. The applicant will play a central role in this flagship LHC analysis. [1] PRL 111 (2013) 101804; PRL 111 (2013) 101805; CMS-PAS-BPH-13-007 (update to be published in Nature)