Measurement of the relative width difference of the $B^0$-$\bar B^0$ system with the ATLAS detector

TL;DR

This paper reports the most precise measurement to date of the relative width difference in the $B^0$-$ar B^0$ system using ATLAS data, confirming Standard Model predictions.

Contribution

First measurement of $rac{ riangle ext{Width}}{ ext{Width}}$ of $B^0$-$ar B^0$ system with ATLAS, achieving highest precision and consistency with Standard Model.

Findings

$rac{ riangle ext{Width}}{ ext{Width}} = (-0.1 extpm 1.1 ext{(stat.)} extpm 0.9 ext{(syst.)}) imes 10^{-2}$

Result agrees with Standard Model and other experiments

Most precise single measurement of this quantity to date

Abstract

This paper presents the measurement of the relative width difference $\Delta \Gamma_d / \Gamma_d$ of the $B^0$-$\bar B^0$ system using the data collected by the ATLAS experiment at the LHC in $p p$ collisions at $\sqrt{s} = 7$ TeV and $\sqrt{s} = 8$ TeV and corresponding to an integrated luminosity of 25.2 fb$^{-1}$. The value of $\Delta \Gamma_d / \Gamma_d$ is obtained by comparing the decay-time distributions of $B^0 \to J/\psi K_S$ and $B^0 \to J/\psi K^{*0}(892)$ decays. The result is $\Delta \Gamma_d / \Gamma_d = (-0.1 \pm 1.1~\mbox{(stat.)} \pm 0.9~\mbox{(syst.)}) \times 10^{-2}$. Currently, this is the most precise single measurement of $\Delta \Gamma_d / \Gamma_d$. It agrees with the Standard Model prediction and the measurements by other experiments.