Speaker
Description
LFU studies has been on the forefront of HEP physics analyses in the recent years, due to the reported tension with SM predictions in LHCb measurements for R(µ/e) ratios. Some of the reported tension has been resolved, but a potential discrepancies could still be found in the R(τ/e) and R(τ/µ) ratios. To investigate these decay ratios, ttbar events have been chosen as a source of leptons for this analysis, as they provide a straight forward way to acquire unbiased set of events (t->W->τ/µ/e). To measure these ratios, there is need to identify the τ lepton, which is an unstable particle. This is done by searching for leptons that decay from τ particle in (τ->e) and (τ->µ) decay channels, where the resulting electrons and muons usually end up with lower pT and higher transverse displacement their counterparts from direct W boson decay. To distinguish these leptons coming from W(promt) and τ (non-promt), a 2D fit is performed in bins of pT and dxy. To increase the event statistics available, there is a need to use the low-pT leptons (<15 GeV), as significant part of electrons and muons coming from τ decay are in this pT region. There are many difficulties when working with low-pT leptons and one of them is the scale factor calculations, which are plagued by limited signal event statistics and high background contamination. To improve the existing scale factors and their uncertainties, a revised approach of using J/Ψ decays from various datasets is used with the goal of reducing the overall uncertainties in scale factor measurements.
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