This project investigates the impact on B meson physics analysis of charged hadrons identification through precise time of flight measurements from fast scintillating crystals . It is set in the Compact Muon Solenoid (CMS) experiment framework, at the Large Hadron Collider (LHC). Precise time of flight measurement, with 30 ps resolution, will be provided by a new detector inserted in CMS for the High Luminosity LHC Program, the MIP Timing Detector (MTD).
The High Luminosity LHC program consists in an increase in instantaneous luminosity of collisions in LHC. This increase comes with a larger number of simultaneous interactions for each collision: hard interactions of interest for CMS happen in far fewer than the 1% of the total proton collisions, and are accompanied by a number of simultaneous interactions of ~30. At HL-LHC the number of simultaneous interaction will increase to 140-200.
The MTD detector will help in maintaining current CMS analysis performances in this new environment: charged particles time of flight information improves track to vertex assignment by separation of particles and vertexes in the time domain. The combination of the time-of-flight measurement from the MTD and momentum measurements from the tracker, provides a measurement the mass of charged particles. This sort of particle identification is unprecedented at CMS and is expected to have a large impact on heavy flavor physics. Searches for new physics are performed by studying the rates of B meson decays in semileptonic channels: the ratio of the branching fraction for a B to decay in leptons of different flavor and the same hadron are optimal probes for leptonic flavor violation studies.The signal is characterized by two leptons and an hadron, while the background is mostly formed by triplets misreconstructed due to uncorrect assignment of particles. Therefore the particle identification (PID) capabilities brought by the MTD is expected to significantly lower the backgrounds.
L¿identificazione di adroni carichi sulla base della misura della loro massa, o differenza in massa, è innovativa in CMS poiché l¿esperimento non possiede attualmente strumenti di distinzione di adroni. Sfrutta inoltre misure di tempo di volo di MTD che costituiscono per CMS un¿informazione inedita e non ridondante.
Il settore di fisica del mesone B in CMS, su cui si vuole valutare l¿impatto della PID,è inoltre uno dei settori in cui si rileva ad oggi una possibile anomalia del modello standard [1]. Per sviluppare gli studi nel settore della fisica del B, CMS ha raccolto nel 2018 un dataset dedicato, il B parking, che raccoglie eventi B-antiB tramitre un trigger tag and probe sui muoni, e che in un anno di presa dati ha raccolto 5 *10^9 eventi unbiased.
[1] LHCb Collaboration. Search for lepton-universality violation in B in K +ll decays. Phys. Rev. Lett.122,191801. 13 p, Mar. 2019, arXiv:1903.09252.