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تسجيل مستخدم جديدMeasurements of CP violation in B mixing through $B to J/psi X$ decays at LHCb
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تأليف
Greig A. Cowan
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B mesons provide an ideal laboratory for measurements of CP violation and searches for CP violation beyond the Standard Model. Recent measurements of the mixing phases of the $B_s^0$ and $B^0$ mesons, $phi_s$ and $sin2beta$, using decays to $J/psi X$ final states are presented. In view of future improved measurements, a good understanding of pollution from sub-leading penguin topologies in these decays is needed. Those can be probed using suppressed decays like $B_s^0 to J/psi K_S^0$ and $B_s^0 to J/psi overline{K}^{*0}$. Recent results using these decay modes are presented.
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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 wi
th 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.
A study of B+ to J/psi pi+ and B+ to psi(2S) pi+ decays is performed with data corresponding to 0.37 fb-1 of proton-proton collisions at sqrt(s)=7 TeV. Their branching fractions are found to be B(B+ to J/psi pi+) = (3.88 +- 0.11 +- 0.15) x 10^{-5} an
d B(B+ to psi(2S) pi+) = (2.52 +- 0.26 +- 0.15) x 10^{-5}, where the first uncertainty is related to the statistical size of the sample and the second quantifies systematic effects. The measured CP asymmetries in these modes are ACP(J/psi pi) = 0.005 +- 0.027 +- 0.011 and ACP(psi(2S) pi) = 0.048 +- 0.090 +- 0.011 with no evidence of direct CP violation seen.
We report improved measurements of time-dependent CP violation parameters for B^0(bar{B}^0) -> psi(2S) K_S. This analysis is based on a data sample of 657x10^6 BBbar pairs collected at the Y(4S) resonance with the Belle detector at the KEKB energy-as
ymmetric e+e- collider. We fully reconstruct one neutral B meson in the psi(2S) K_S CP-eigenstate decay channel, and the flavor of the accompanying B meson is identified to be either B^0 or bar{B}^0 from its decay products. CP violation parameters are obtained from the asymmetries in the distributions of the proper-time intervals between the two B decays: S (psi(2S) K_S) = +0.72 +/- 0.09(stat) +/- 0.03(syst), A (psi(2S) K_S) = +0.04 +/- 0.07(stat) +/- 0.05(syst). These results are in agreement with results from measurements of B^0 -> J/psi K^0.
I report recent measurements in b-hadron decays reconstructed in the full data set of sqrt{s} = 1.96 TeV proton-antiproton collisions collected by the CDF experiment at the Tevatron. These include the final CDF results on: measurements of CP asymmetr
ies in two-body charmless decays of the Bd, Bs, and Lambda^0_b hadrons; bounds on the Bs mixing phase and on the decay width difference of Bs mass eigenstates; and updated measurements of branching ratios of Bs->Jpsi Phi and Bs->Ds(*)Ds(*) decays. All measurements are among the most precise from a single experiment and in agreement with the standard model predictions.
A measurement is presented of decay-time-dependent $CP$ violation in the decays $B^0rightarrow J/psi K^0_mathrm{S}$ and $B^0rightarrowpsi(2S) K^0_mathrm{S}$, where the $J/psi$ is reconstructed from two electrons and the $psi(2S)$ from two muons. The
analysis uses a sample of $pp$ collision data recorded with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of 3 $mathrm{fb}^{-1}$. The $CP$-violation observables are measured to be begin{equation*} begin{aligned} Cleft(B^0rightarrow J/psi K^0_mathrm{S}right)&=phantom{+},0.12,pm,0.07pm,0.02,, Sleft(B^0rightarrow J/psi K^0_mathrm{S}right)&=phantom{+},0.83,pm,0.08pm,0.01,, Cleft(B^0rightarrowpsi(2S) K^0_mathrm{S}right)&=-,0.05,pm,0.10pm,0.01,, Sleft(B^0rightarrowpsi(2S) K^0_mathrm{S}right)&=phantom{+},0.84,pm,0.10pm,0.01,, end{aligned} end{equation*} where $C$ describes $CP$ violation in the direct decay, and $S$ describes $CP$ violation in the interference between the amplitudes for the direct decay and for the decay after $B^0$-$overline{B}^0$ oscillation. The first uncertainties are statistical and the second are systematic. The two sets of results are compatible with the previous LHCb measurement using $B^0rightarrow J/psi K^0_mathrm{S}$ decays, where the $J/psi$ meson was reconstructed from two muons. The averages of all three sets of LHCb results are begin{equation*} begin{aligned} Cleft(B^0rightarrow[cbar{c}]K^0_mathrm{S}right)&=-0.017 pm 0.029,, Sleft(B^0rightarrow[cbar{c}]K^0_mathrm{S}right)&=phantom{+}0.760 pm 0.034,, end{aligned} end{equation*} under the assumption that higher-order contributions to the decay amplitudes are negligible. The uncertainties include statistical and systematic contributions.
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