Marian Smoluchowski
Institute of Physics

Supervisor: dr Eryk Czerwiński

Defence year: 2023

The main goal of these studies is to determine a correction factor for the efficiency of selection obtained using KSKL -> pi+pi-pi0pi0 Monte Carlo events using experimentally collected data in the function of time difference Deltat between decays of kaons. It constitutes a continuation of an analysis for Re(epsilon'/epsilon) and Im(epsilon'/epsilon) parameters, which began in [1]. Measurement principle is based on the selection of background channels having common properties with KSKL -> pi+pi-pi0pi0. The chosen decays were KSKL -> pi+/-l-/+nipi0pi0, KSKL -> pi+pi-3pi0 and KSKL -> pi+pi-pi+pi- corresponding to signal-like parts K -> pi0pi0, K -> pi+pi-, respectively. The first step was to perform a selection under the hypothesis of each tagging decay (K -> pi+/-l-/+nipi0pi0, KL -> 3pi0 and KS -> pi+pi-) and reach the highest possible purity. Then, the number of tagging events was weighted with a branching ratio for each signal-like part to obtain so-called expected distributions of the time difference. The additional selection under the hypothesis of K -> pi0pi0 or K -> pi+pi- was imposed on the events after tagging to mimic the selection performed for KSKL -> pi+pi-pi0pi0 using MC. Importantly, independence between charged and neutral parts of decay had to be conserved, so the method of trilateration was adapted to reconstruct a neutral vertex. Finally, having determined the expected and selected distributions of Deltat, a correction factor can be calculated via the division of efficiency obtained from data by the efficiency from MC. The result is not a uniform distribution, so there exists a specific factor for each bin of the Deltat histogram. Final uncertainties were determined using a standard propagation of a measurement error. A measured correction will be used in the further studies over CP symmetry breaking in the entangled kaons? systems.