Measurement of 𝐾−𝜋+ detection asymmetry with LHCb Run 3 data

This thesis presents the determination of the detection asymmetry 𝐴det (𝐾−𝜋+) for the 𝐾−𝜋+ pair using data collected by the LHCb experiment during the 2024 Run 3 at a centre-of-mass energy of 13.6 TeV. The analysis is based on the decay channels 𝐷+ → 𝐾−𝜋+𝜋+ and 𝐷+ → 𝐾0 𝑆 𝜋+. The signal is modelled by a Johnson 𝑆𝑈 distribution plus two Gaussian functions with a common mean, while the background is described by an exponential function. Raw asymmetries are extracted from simultaneous fits to the invariant mass distributions of 𝐷+ and 𝐷− candidates for each channel and magnet polarity. Subtracting the raw asymmetries of the two channels, the detection asymmetry 𝐴det (𝐾−𝜋+) is obtained: 𝐴det (𝐾−𝜋+) = (−0.95 ± 0.03) × 10−2. The measurement provides a crucial input for the determination of production asymmetries and for future studies of 𝐶𝑃 violation in the charm sector. It will be completed with a detailed study of systematic uncertainties within the Bologna LHCb group.