Journal Article

Precision measurement of the B 0 meson lifetime using B 0 → J /ψ K 0 decays with the ATLAS detector

Ferrari, Arnaud, Zwalinski, L., Mathisen, Thomas, Ellert, Mattias, Gonzalez Suarez, Rebeca, Dimitriadi, Christina, Ellajosyula, Venugopal, Aad, G., Mullier, Geoffrey A., Bergeås Kuutmann, Elin, Sunneborn Gudnadottir, Olga, Ekelöf, Tord, Brenner, Richard, Ripellino, Giulia

2025

Overview

A measurement of the B-0 meson lifetime using B-0 -> J/psi K*(0) decays in data from 13 TeV proton-proton collisions with an integrated luminosity of 140 fb(-1) recorded by the ATLAS detector at the LHC is presented. The measured effective lifetime is tau = 1.5053 +/- 0.0012 (stat.) +/- 0.0035 (syst.) ps. The average decay width extracted from the effective lifetime, using parameters from external sources, is Gamma(d) = 0.6639 +/- 0.0005 (stat.) +/- 0.0016 (syst.) +/- 0.0038 (ext.) ps(-1), where the uncertainties are statistical, systematic and from external sources. The earlier ATLAS measurement of Gamma(s) in the B-s(0) -> J/psi phi decay was used to derive a value for the ratio of the average decay widths Gamma(d) and Gamma(s) for B-0 and B-s(0) mesons respectively, of Gamma(d)/Gamma(s) = 0.9905 +/- 0.0022 (stat.)+/- 0.0036 (syst.)+/- 0.0057 (ext.). Themeasured lifetime, average decay width and decay width ratio are in agreement with theoretical predictions and with measurements by other experiments. This measurement provides the most precise result of the effective lifetime of the B-0 meson to date.