000004516 001__ 4516
000004516 005__ 20240919092838.0
000004516 037__ $$aBELLE2-UTHESIS-2024-003
000004516 041__ $$aeng
000004516 100__ $$aLars von der Werth
000004516 245__ $$aStudy of sPlot Background Subtraction for Particle Identification Efficiency Determination at Belle II
000004516 260__ $$aGarching$$bMax Planck Institut for Physics$$c2024
000004516 300__ $$amult. p
000004516 500__ $$aPresented on 29 10 2024
000004516 502__ $$aBSc$$bMunich, Technical Universtiy of Munich$$c2024
000004516 520__ $$aParticle identification is a central experimental challenge in the precise measurement of Standard Model parameters and in the search for new physics beyond the standard model at the Belle II experiment. This also includes an accurate knowledge of the imperfections in particle identification efficiencies. This efficiency is typically determined from Monte Carlo simulations, but crosschecking and validating these simulations, requires to determine efficiencies directly from the real data.  In this thesis, we present the determination of muon identification efficiencies using J/Ψ → μ+μ− decays. To remove background events, that remain after event selection, we do a background subtraction using the sPlot method. In the existing implementation of the efficiency calculation, we observe in simulated J/Ψ → μ+μ− decays, that the efficiencies computed using background subtraction disagree with the Monte Carlo truth efficiencies in the momentum range below 1.5 GeV/c. The sPlot method can be impaired by correlations between the kinematic variables of the sample. Therefore, we investigate the effect of correlations to understand and mitigate a possible bias introduced by them to the determination of particle identification efficiencies.  We find out, that it is possible to improve the efficiency estimates by taking into account correlations between kinematic variables in the background subtraction. However, these improvements alone are not sufficient to reach agreement with the true efficiencies in the full momentum range. A possible explanation for the remaining discrepancies are observed imperfections of the parametrization of the probability density function used to model the invariant mass distribution of the two particle system, which is needed for the sPlot method.
000004516 700__ $$aStefan Wallner$$edir.
000004516 8560_ $$fge47yaj@mytum.de
000004516 8564_ $$uhttps://docs.belle2.org/record/4516/files/BELLE2-UTHESIS-2024-003.pdf
000004516 980__ $$aTHESIS