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تسجيل مستخدم جديدMeasurement of the $CP$ asymmetry in $B^-to D_s^-D^0$ and $B^-to D^-D^0$ decays
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The $CP$ asymmetry in $B^-to D_s^-D^0$ and $B^-to D^-D^0$ decays is measured using LHCb data corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected in $pp$ collisions at centre-of-mass energies of 7 and 8 TeV. The results are $A^{CP}(B^-to D_s^-D^0)=(-0.4pm 0.5pm 0.5)%$ and $A^{CP}(B^-to D^-D^0)=( 2.3pm 2.7pm 0.4)%$, where the first uncertainties are statistical and the second systematic. This is the first measurement of $A^{CP}(B^-to D_s^-D^0)$ and the most precise determination of $A^{CP}(B^-to D^-D^0)$. Neither result shows evidence of $CP$ violation.
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We study the decays B- --> D*0 pi- and B- --> D*0 K-, where the D*0 decays into D0 pi0, with the D0 reconstructed in the CP-even (CP+) eigenstates K- K+ and pi- pi+ and in the (non-CP) channels K- pi+, K- pi+ pi+ pi-, and K- pi+ pi0. Using a sample o
f about 123 million BBbar pairs, we measure the ratios of decay rates R*(non-CP)=BR(B- --> D*0(non-CP) K-)/BR(B- --> D*0(non-CP) pi-) = 0.0813+-0.0040(stat)+0.0042-0.0031}(syst), and provide the first measurements of R*(CP+)= BR(B- --> D*0(CP+) K-)/BR(B- --> D*0(CP+) pi-) = 0.086+-0.021(stat)+-0. 007(syst), and of the CP asymmetry A*(CP+) = (BR(B- --> D*0(CP+) K-) - BR(B+ --> D*0(CP+) K+))/(BR(B- --> D*0(CP+) K-) + BR(B+ --> D*0(CP+) K+)) = -0.10+-0.23(stat)+0.03-0.04(syst).
We present a study of the decays B- --> D*0 pi- and B- --> D*0 K-, where the D*0 decays into D0 pi0, with the D0 reconstructed in the CP eigenstates K- K+ and pi- pi+ and in the (non-CP) channels K- pi+, K- pi+ pi+ pi-, and K- pi+ pi0. We use an unbi
nned maximum likelihood fit to measure the signal yields. Using a sample of about 123 million Y(4S) decays into B anti-B pairs, we measure the ratios of decay rates R*(CP+)=BR(B- --> D*0(CP+) K-)/BR(B- --> D*0(CP+) pi-) = 0.088+-0.021(stat)+0.007-0.005(syst), and provide the first measurements of R*(non-CP) = BR(B- --> D*0(non-CP) K-)/BR(B- --> D*0(non-CP) pi-) = 0.0805+-0.0040(stat)+0.0039-0.0032(syst), and of the CP asymmetry A*(CP+) = (BR(B- --> D*0(CP+) K-)-BR(B+ --> D*0(CP+) K+))/(BR(B- --> D*0(CP+) K-)+BR(B+ --> D*0(CP+) K+)) = -0.02+-0.24(stat)+-0.05(syst). These results are preliminary.
The $CP$ violation observables $S$ and $C$ in the decay channel $B^0 !rightarrow D^+ D^-$ are determined from a sample of proton-proton collisions at center-of-mass energies of 7 and 8 TeV, collected by the LHCb experiment and corresponding to an int
egrated luminosity of 3 fb$^{-1}$. The observable $S$ describes $CP$ violation in the interference between mixing and the decay amplitude, and $C$ parametrizes direct $CP$ violation in the decay. The following values are obtained from a flavor-tagged, decay-time-dependent analysis: begin{align*} S &= -0.54 , ^{+0.17}_{-0.16} , text{(stat)} pm 0.05 , text{(syst)},, ewline C &= phantom{-}0.26 , ^{+0.18}_{-0.17} , text{(stat)} pm 0.02 , text{(syst)},. end{align*} These values provide evidence for $CP$ violation at a significance level of 4.0 standard deviations. The phase shift due to higher-order Standard Model corrections is constrained to a small value of begin{align*} Deltaphi = -0.16,^{+0.19}_{-0.21},text{rad},. end{align*}
The first full angular analysis of the $B^0 to D^{*-} D_s^{*+}$ decay is performed using 6 fb$^{-1}$ of $pp$ collision data collected with the LHCb experiment at a centre-of-mass energy of 13 TeV. The $D_s^{*+} to D_s^+ gamma$ and $D^{*-} to bar{D}^0
pi^-$ vector meson decays are used with the subsequent $D_s^+ to K^+ K^- pi^+$ and $bar{D}^0 to K^+ pi^-$ decays. All helicity amplitudes and phases are measured, and the longitudinal polarisation fraction is determined to be $f_{rm L} = 0.578 pm 0.010 pm 0.011$ with world-best precision, where the first uncertainty is statistical and the second is systematic. The pattern of helicity amplitude magnitudes is found to align with expectations from quark-helicity conservation in $B$ decays. The ratio of branching fractions $[mathcal{B}(B^0 to D^{*-} D_s^{*+}) times mathcal{B}(D_s^{*+} to D_s^+ gamma)]/mathcal{B}(B^0 to D^{*-} D_s^+)$ is measured to be $2.045 pm 0.022 pm 0.071$ with world-best precision. In addition, the first observation of the Cabibbo-suppressed $B_s^0 to D^{*-} D_s^+$ decay is made with a significance of seven standard deviations. The branching fraction ratio $mathcal{B}(B_s^0 to D^{*-} D_s^+)/mathcal{B}(B^0 to D^{*-} D_s^+)$ is measured to be $0.049 pm 0.006 pm 0.003 pm 0.002$, where the third uncertainty is due to limited knowledge of the ratio of fragmentation fractions.
First observations and measurements of the branching fractions of the $bar{B}_s^0to D^+D^-$, $bar{B}_s^0to D_s^+D^-$ and $bar{B}_s^0to D^0bar{D}^0$ decays are presented using 1.0 fb$^{-1}$ of data collected by the LHCb experiment. These branching fra
ctions are normalized to those of $bar{B}^0to D^+D^-$, $B^0to D_s^+D^-$ and $B^-to D^0D_s^-$, respectively. An excess of events consistent with the decay $bar{B}^0to D^0bar{D}^0$ is also seen, and its branching fraction is measured relative to that of $B^-to D^0D_s^-$. Improved measurements of the branching fractions ${cal{B}}(bar{B}_s^0to D_s^+D_s^-)$ and ${cal{B}}(B^-to D^0D_s^-)$ are reported, each relative to ${cal{B}}(B^0to D_s^+D^-)$. The ratios of branching fractions are {-0.2in} {center} {align*} {{cal{B}}(bar{B}_s^0to D^+D^-)over {cal{B}}(bar{B}^0to D^+D^-)} &= 1.08pm 0.20pm0.10, {{cal{B}}(bar{B}_s^0to D_s^+D^-)over {cal{B}}(B^0to D_s^+D^-)} &= 0.050pm 0.008pm0.004, {{cal{B}}(bar{B}_s^0to D^0bar{D}^0)over {cal{B}}(B^-to D^0D_s^-)} &= 0.019pm 0.003pm0.003, {{cal{B}}(bar{B}^0to D^0bar{D}^0)over {cal{B}}(B^-to D^0D_s^-)} &= 0.0014pm 0.0006pm0.0002,{{cal{B}}(bar{B}_s^0to D_s^+D_s^-)over {cal{B}}(B^0to D_s^+D^-)} &= 0.56pm 0.03pm0.04, {{cal{B}}(B^-to D^0D_s^-)over {cal{B}}(B^0to D_s^+D^-)} &= 1.22pm 0.02pm0.07, {align*} {center} oindent where the uncertainties are statistical and systematic, respectively.
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