Thesis

Search for new physics via rare processes at the LHC

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• 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 of searching for physics beyond the standard model of particle physics. The proposed thesis project targets to explore heavy flavor rare decays in the unique datasets that are starting to be accumulated. Dileptonic decays of neutral B mesons, being highly suppressed and precisely predicted in the standard model (SM), provide a powerful, experimentally accessible signature that will be explored. During the first operation phase of the LHC (Run1), we have reached a flagship observation, after a 3-decade-long search across different accelerators and detectors: an initial Bs->mumu signal has been established for the first time, via the combined analysis of CMS and LHCb data. The work program builds up on the experience and success of these initial results, and will use the data being accumulated by CMS during the ongoing Run2 of the LHC. It starts by establishing the Bs->mumu signal in Run2 data, thereby delivering the first observation of this golden rare process by a single experiment, and by measuring sensitive observables, namely the effective lifetime. The B0->mumu signal is rarer, and hasn't been established in the Run1 data (despite tantalising hints, at the level of three standard deviations, indicating some tension with the SM predictions). An optimised search strategy, employing multivariate analyses techniques, for data selection and fitting, will be devised and applied to the full Run2 dataset to search for the B0 rare decay process. Remarks: - LIP has a leading involvement in this physics research area. The proposed supervisor of this thesis is the co-ordinator of the overall CMS-wide heavy flavour physics analysis group (PAG). - We are leading authors of the RunI1 flagship search, published in Nature 522 (2015) 68. This is considered to be a major LHC flagship discovery, following that of the Higgs boson. - Solid computing skills (C++) are a plus. Availability to travel to CERN for short periods is expected, in order to participate in data taking and in PAG meetings.