A first flavor-tagged measurement of the time-dependent $CP$-violating asymmetry in $B_s^0\to \varphi \varphi$ decays is presented. In this decay channel, the $CP$-violating weak phase arises due to $CP$ violation in the interference between $B_s^0\mathrm{\text{−}}{\overline{B}}_s^0$ mixing and the $b\to s\overline{s}s$ gluonic penguin decay amplitude. Using a sample of $pp$ collision data corresponding to an integrated luminosity of $1.0{\mathrm{fb}}^{-1}$ and collected at a center-of-mass energy of 7 TeV with the LHCb detector, 880 $B_s^0\to \varphi \varphi$ signal decays are obtained. The $CP$-violating phase is measured to be in the interval $[-2.46,-0.76]\mathrm{rad}$ at a 68% confidence level. The $p$ value of the standard model prediction is 16%.

• Received 28 March 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.241802

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© 2013 CERN, for the LHCb Collaboration