Géraldine Räuber ; Christoph Schwanda ; Gianluca Inguglia

2024
HEPHY Vienna

Abstract: This thesis presents a precise measurement of the CKM matrix element Vus using data collected at the Belle II experiment situated at the SuperKEKB electron- positron collider in Tsukuba, Japan. The measurement employs the ratio of branching fractions of tau lepton decays, denoted as RK/π, with both pion and kaon mesons in the final state, given by RK/π = B(τ− → K−ντ)/B(τ− → π−ντ). Selection criteria involve a tag side consisting of three charged particles, defining an overall 3×1- prong topology. The preliminary obtained result, RK/π = 0.06438 ± 0.00080, corre- sponds to a |Vus| value of 0.2229±0.0017, and takes into account only the main systematic uncertainty sources. Recognizing the systematic nature of this measurement, a dedicated study addressing leading systematic uncertainties is undertaken. Specifically, a performance assessment of pion identification corrections is conducted to enhance the reliability and precision of the measurement.

Note: Presented on 14 06 2024
Note: PhD