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Register a new userMeasurement of CP violation in Bs --> J/psi phi decay
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Michal Kreps
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We briefly discuss measurements of CP violation in Bs --> J/psi phi decay. Both the phenomenology of Bs mixing and the importance of the measurement to searches for new physics, as well as technical details and issues with the analysis are included. While current results are consistent with the standard model, even large contributions from new physics cannot be excluded.
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Study of CP violation in the decay channel Bs->J/psi phi is essential to exploring and constraining physics beyond the Standard Model in the quark flavour sector. The experimental progress in this area of activity at the LHC and Tevatron is discussed.
Measurement of the mixing-induced CP-violating phase phi_s in Bs decays is of prime importance in probing new physics. Here 7421 +/- 105 signal events from the dominantly CP-odd final state J/psi pi+ pi- are selected in 1/fb of pp collision data collected at sqrt{s} = 7 TeV with the LHCb detector. A time-dependent fit to the data yields a value of phi_s=-0.019^{+0.173+0.004}_{-0.174-0.003} rad, consistent with the Standard Model expectation. No evidence of direct CP violation is found.
The CP asymmetry predicted by the Standard Model in the decay modes Bs;d -> J/psi eta and Bs -> J/psi phi is very small, and the observation of a sizeable e ect would be a clear indication of new physics beyond the Standard Model. Contrary to the final state J/psi phi, the former final state is a CP eigenstate, and therefore complex angular distribution analyses are not necessary for the asymmetry measurement. In this paper, the approaches for the study of these two decay channels are presented.
Measurements are presented of the $CP$ violation observables $S$ and $C$ in the decays of $B^0$ and $overline{B}{}^0$ mesons to the $J/psi K^0_S$ final state. The data sample corresponds to an integrated luminosity of $3.0,text{fb}^{-1}$ collected with the LHCb experiment in proton-proton collisions at center-of-mass energies of $7$ and $8,text{TeV}$. The analysis of the time evolution of $41500$ $B^0$ and $overline{B}{}^0$ decays yields $S = 0.731 pm 0.035 , text{(stat)} pm 0.020 ,text{(syst)}$ and $C = -0.038 pm 0.032 , text{(stat)} pm 0.005,text{(syst)}$. In the Standard Model, $S$ equals $sin(2beta)$ to a good level of precision. The values are consistent with the current world averages and with the Standard Model expectations.
The CP-violating weak phase $phi_mathrm{s}$ and the decay width difference $DeltaGamma_{mathrm{s}}$ of $mathrm{B}^{0}_{mathrm{s}}$ mesons are measured by the CMS experiment at the LHC using a data sample of $mathrm{B}^{0}_{mathrm{s}} ! to mathrm{J} / psi,phi$ decays. The analysed dataset corresponds to an integrated luminosity of about $20~mathrm{fb}^{-1}$ collected in $pp$ collisions at a centre-of-mass energy $sqrt{s} = 8~mathrm{TeV}$. A total of $49,000$ reconstructed $mathrm{B}^{0}_{mathrm{s}}$ decays are used to extract the values $phi_mathrm{s}$ and $DeltaGamma_mathrm{s}$ by performing a time-dependent and flavour-tagged angular analysis of the $mu^+mu^-mathrm{K}^+mathrm{K}^-$ final state.The weak phase is measured to be $phi_mathrm{s} = -0.03 pm 0.11~mathrm{(stat.)} pm 0.03~mathrm{(syst.)}~mathrm{rad}$, and the decay width difference between the $mathrm{B}^{0}_{mathrm{s}}$ mass eigenstates is $DeltaGamma_mathrm{s} = 0.096 pm 0.014~mathrm{(stat.)} pm 0.007~mathrm{(syst.)}~mathrm{ps}^{-1}$.
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