# Measurement of the $CP$-violating phase $\phi_s$ from $B_{s}^{0}\to J/\psi\pi^+\pi^-$ decays in 13 TeV $pp$ collisions

## TL;DR

This paper measures the $CP$-violating phase $\,phi_s$ in $B_s^0$ decays using 13 TeV collision data, providing results consistent with the Standard Model and combining with previous measurements for improved precision.

## Contribution

First measurement of $\,phi_s$ from $B_s^0 o J/ar{ ext{psi}} ext{pi}^+ ext{pi}^-$ decays at 13 TeV, with combined analysis enhancing the precision of $CP$ violation parameters.

## Key findings

- Measured $\,phi_s = -0.057 \, rad$ with uncertainties.
- Determined decay-width difference as $-0.050 \, ps^{-1}$.
- Combined results yield $\,phi_s = 0.002 \, rad$ with improved accuracy.

## Abstract

Decays of $B_{s}^{0}$ and $\overline{B}{}_{s}^{0}$ mesons into $J/\psi\pi^+\pi^-$ final states are studied in a data sample corresponding to 1.9 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in 13 TeV $pp$ collisions. A time-dependent amplitude analysis is used to determine the final-state resonance contributions, the $CP$-violating phase $\phi_s=-0.057\pm 0.060\pm 0.011$ rad, the decay-width difference between the heavier mass $B_{s}^{0}$ eigenstate and the $B^{0}$ meson of $-0.050\pm 0.004\pm 0.004$ ps$^{-1}$, and the $CP$-violating parameter $|\lambda|=1.01_{-0.06}^{+0.08}\pm0.03$, where the first uncertainty is statistical and the second systematic. These results are combined with previous LHCb measurements in the same decay channel using 7 TeV and 8 TeV $pp$ collisions obtaining $\phi_s =0.002\pm0.044\pm0.012$ rad, and $|\lambda| =0.949\pm0.036\pm0.019$.