# Measurement of CP violation in the $B_s^0\rightarrow\phi\phi$ decay and search for the $B^0\rightarrow \phi\phi$ decay

## TL;DR

This paper reports a detailed measurement of CP violation in $B_s^0
ightarrow\phi\phi$ decays using LHCb data, and sets a new upper limit on the rare decay $B^0
ightarrow\phi\phi$, providing insights into CP symmetry in b-quark transitions.

## Contribution

It presents the first comprehensive measurement of CP-violating phases in $B_s^0
ightarrow\phi\phi$ decays and sets a new upper limit on the $B^0
ightarrow\phi\phi$ decay branching fraction.

## Key findings

- CP-violating phase $\phi_s^{sar{s}s}$ measured as $-0.073 \, ext{rad}$ with uncertainties
- CP-violation parameter $|\lambda|$ close to 1, indicating no significant CP violation
- Upper limit on $ ext{Br}(B^0
ightarrow\phi\phi)$ set at $2.7 imes 10^{-8}$

## Abstract

A measurement of the time-dependent CP-violating asymmetry in $B_s^0\rightarrow\phi\phi$ decays is presented. Using a sample of proton-proton collision data corresponding to an integrated luminosity of $5.0$fb$^{-1}$ collected by the $\mbox{LHCb}$ experiment at centre-of-mass energies $\sqrt{s} = 7$ TeV in 2011, 8 TeV in 2012 and 13 TeV in 2015 and 2016, a signal yield of around 9000 $B_s^0\rightarrow\phi\phi$ decays is obtained. The CP-violating phase $\phi_s^{s\bar{s}s}$ is measured to be $-0.073 \pm 0.115$(stat)$\pm 0.027$(syst) rad, under the assumption it is independent on the helicity of the $\phi\phi$ decay. In addition, the CP-violating phases of the transverse polarisations under the assumption of CP conservation of the longitudinal phase are measured. The helicity-independent direct CP-violation parameter is also measured, and is found to be $|\lambda|=0.99 \pm 0.05 $(stat)$ \pm 0.01 $(syst). In addition, $T$-odd triple-product asymmetries are measured. The results obtained are consistent with the hypothesis of CP conservation in $b\rightarrow\bar{s}s\bar{s}$ transitions. Finally, a limit on the branching fraction of the $B^0\rightarrow \phi\phi$ decay is determined to be $\mathcal{B}(B^0\rightarrow \phi\phi)<2.7\times 10^{-8}$ at 90% confidence level.