# Measurement of the CP-violating phase $\phi_s$ in the decay $\B^0_s ->\J/psi \phi$

Abstract : We present a measurement of the time-dependent CP-violating asymmetry in B_s -> J/psi phi decays, using data collected with the LHCb detector at the LHC. The decay time distribution of B_s -> J/psi phi is characterized by the decay widths Gamma_H and Gamma_L of the heavy and light mass eigenstates of the B_s-B_s-bar system and by a CP-violating phase phi_s. In a sample of about 8500 B_s -> J/psi phi events isolated from 0.37 fb^-1 of pp collisions at sqrt(s)=7 TeV we measure phi_s = 0.15 +/- 0.18 (stat) +/- 0.06 (syst) rad. We also find an average B_s decay width Gamma_s == (Gamma_L + Gamma_H)/2 = 0.657 +/- 0.009 (stat) +/- 0.008 (syst) ps^-1 and a decay width difference Delta Gamma_s == Gamma_L - Gamma_H} = 0.123 +/- 0.029 (stat) +/- 0.011 (syst) ps^-1. Our measurement is insensitive to the transformation (phi_s,DeltaGamma_s --> pi - phi_s, - Delta Gamma_s.
Document type :
Journal articles

http://hal.in2p3.fr/in2p3-00653545
Contributor : Claudine Bombar <>
Submitted on : Monday, December 19, 2011 - 4:39:07 PM
Last modification on : Friday, November 20, 2020 - 3:30:13 PM

### Citation

R. Aaij, C. Abellan Beteta, B. Adeva, M. Adinolfi, C. Adrover, et al.. Measurement of the CP-violating phase $\phi_s$ in the decay $\B^0_s ->\J/psi \phi$. Physical Review Letters, American Physical Society, 2012, 108, pp.101803. ⟨10.1103/PhysRevLett.108.101803⟩. ⟨in2p3-00653545⟩

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