# Measurement of $CP$-violating and mixing-induced observables in $B_s^0 \to \phi\gamma$ decays

## TL;DR

This paper reports the first measurement of $CP$-violating and mixing-induced observables in $B_s^0 o \,phi\gamma$ decays using LHCb data, providing results consistent with Standard Model predictions.

## Contribution

It presents the first measurement of the $S$ and $C$ observables in radiative $B_s^0$ decays, using a time-dependent analysis of LHCb data at 7 and 8 TeV.

## Key findings

- Measured values of $S_{\phi\gamma}$, $C_{\phi\gamma}$, and $\mathcal{A}^{\Delta}_{\phi\gamma}$ with uncertainties.
- Results are consistent with Standard Model predictions.
- First such measurement in radiative $B_s^0$ decays.

## Abstract

A time-dependent analysis of the $B_s^0 \to \phi\gamma$ decay rate is performed to determine the $CP$-violating observables $S_{\phi\gamma}$ and $C_{\phi\gamma}$, and the mixing-induced observable $\mathcal{A}^{\Delta}_{\phi\gamma}$. The measurement is based on a sample of $pp$ collision data recorded with the LHCb detector, corresponding to an integrated luminosity of 3 fb$^{-1}$ at center-of-mass energies of 7 and 8 TeV. The measured values are \begin{align*} S_{\phi\gamma} &= 0.43 \pm 0.30 \pm 0.11, \\ C_{\phi\gamma} &= 0.11 \pm 0.29 \pm 0.11, \\ \mathcal{A}^{\Delta}_{\phi\gamma} &= -0.67 \, ^{+0.37}_{-0.41} \pm 0.17, \end{align*} where the first uncertainty is statistical and the second systematic. This is the first measurement of the observables $S$ and $C$ in radiative $B_s^0$ decays. The results are consistent with the Standard Model predictions.