Precision measurement of $CP$ violation in the penguin-mediated decay $B_s^0\to \varphi \varphi$

Abstract

A flavor-tagged time-dependent angular analysis of the decay $B_s^0\to \varphi \varphi$ is performed using $pp$ collision data collected by the LHCb experiment at $\sqrt{s}=13$ TeV, the center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 6 fb^{-1}. The $CP$-violating phase and direct $CP$-violation parameter are measured to be ${\varphi }_{s\bar{s}s}=-0.042\pm 0.075\pm 0.009$ rad and $|\lambda |=1.004\pm 0.030\pm 0.009$, respectively, assuming the same values for all polarization states of the $\varphi \varphi$ system. In these results, the first uncertainties are statistical and the second systematic. These parameters are also determined separately for each polarization state, showing no evidence for polarization dependence. The results are combined with previous LHCb measurements using $pp$ collisions at center-of-mass energies of 7 and 8 TeV, yielding ${\varphi }_{s\bar{s}s}=-0.074\pm 0.069$ rad and $|\lambda |=1.009\pm 0.030$. This is the most precise study of time-dependent $CP$ violation in a penguin-dominated $B$ meson decay. The results are consistent with $CP$ symmetry and with the Standard Model predictions.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-001.html (LHCb public pages)

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• Polarisation fractions in $B\to V_1{V}_2$: U-Spin constraints and new physics signatures
• Flavour Physics at LHCb -- 50 years of the KM paradigm