The Search Of W Boson Rare Decay Modes At LHCb

A search of W±→Ds±γ decay is presented with a data sample corresponding to pp collisions at a center of mass energy 13 TeV collected with LHCb detector.No evidence of the rare decay was found,and an upper limit on its branching fraction was measured at 95%confidence level.In the analysis,After event reconstruction and selection with DaVinic,we em-ploy a pre-selection that preserves a large fraction of signal events.Then,for the background estimation,we first fit the invariant mass of W candidates to get s-weight.with s-weight of cevent,we suppress combination background.In the end,the measurements of efficiency and systematic uncertainties are performed,followed with a calculation of upper limit of branching fraction.In the background study,we remove a large fraction of background events with offline events selection.In order to further suppress background,we fit the invariant mass distribution of Ds± to get weight for each event.Then,the weight are applied into W Boson candidates.The efficiency and systematic uncertainties are estimated using both data events and simulated events.The efficiency includes detector geometrical acceptance.reconstruction and events selection,trigger efficiency,the efficiency corrections for particle identi-fication and track reconstruction.For systematic uncertainties,we considered un-certainties from the integrated luminosity,branching ratio,efficiency and the mass fitting.Finally,there is no signal structure in our data,therefore,an upper limit is set to this rare decay mode using CLs method.