University of Trieste
Trieste (Italy)
Study of the pi^0 reconstruction efficiency for the B^0->pi^0pi^0 decay at the Belle II experiment
2022
The aim of this Thesis is to study the efficiency of the reconstruction of the pi^0 meson in pi^0 -> gamma gamma decays at the Belle II experiment. Using D^0-meson decays reconstructed in data and simulation, I calculate a correction factor for an unbiased determination of the pi^0-reconstruction efficiency from simulation, and I investigate possible dependencies of this factor on the pi^0 kinematics and on the location of the photon clusters in the Belle II electromagnetic calorimeter. The pi^0-reconstruction efficiency is studied by comparing the measured signal yields of the decays D^{*+}-> D^0(-> K^-pi^+pi^0)pi^+_s and D^{*+}-> D^0(-> K^-pi^+)pi^+_s, reconstructed in the same data set. I use a sample which corresponds to an integrated luminosity of 190 fb^{-1} recorded by Belle II experiment in energy-asymmetric e^+e^- collisions delivered by the SuperKEKB collider at the center-of-mass energy of sqrt{s}=10.58 GeV. By comparing the signal-yield ratio in data and simulation, I obtain the correction factor which is determined for the photon- and pi^0-selection requirements used in the analysis of B^0->pi^0pi^0 decays. This factor is found to be 1.037+-0.007(stat)+-0.037(syst), where the first uncertainty is statistical and the second is systematic, and it is dominated by the uncertainty on the branching fractions of D^0 decays. The method detailed in this Thesis has been used to assess the systematic uncertainty due to the pi^0-reconstruction efficiency on the Belle II measurement of the B^0->pi^0pi^0 branching fraction, presented at the XLI International Conference of High Energy Physics held in July 2022 in Bologna.
technical-report