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Register a new userMeasurement of the CKM angle $gamma$ and $B^0_s$-$bar{B}^0_s$ mixing frequency with $B^0_s rightarrow D_s^mp h^pm pi^pm pi^mp$ decays
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The CKM angle $gamma$ is measured for the first time from mixing-induced $CP$ violation between $B^0_s rightarrow D_s^mp K^pm pi^pm pi^mp$ and $bar{B}^0_s rightarrow D_s^pm K^mp pi^mp pi^pm$ decays reconstructed in proton-proton collision data corresponding to an integrated luminosity of 9 ${rm fb}^{-1}$ recorded with the LHCb detector. A time-dependent amplitude analysis is performed to extract the $CP$-violating weak phase $gamma-2beta_s$ and, subsequently, $gamma$ by taking the $B^0_s$-$bar{B}^0_s$ mixing phase $beta_{s}$ as an external input. The measurement yields $gamma = (44 pm 12)^circ$ modulo $180^circ$, where statistical and systematic uncertainties are combined. An alternative model-independent measurement, integrating over the five-dimensional phase space of the decay, yields $gamma = (44^{,+,20}_{,-,13})^circ$ modulo $180^circ$. Moreover, the $B^0_s$-$bar{B}^0_s$ oscillation frequency is measured from the flavour-specific control channel $B^0_s rightarrow D_s^- pi^+ pi^+ pi^-$ to be $Delta m_s = (17.757 pm 0.007 ,({rm stat.}) pm 0.008 ,({rm syst.})) text{ps}^{-1}$, consistent with and more precise than the current world-average value.
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The B^0_s-bar{B}^0_s oscillation frequency Delta m_s is measured with 36 pb^{-1} of data collected in pp collisions at sqrt{s} = 7 TeV by the LHCb experiment at the Large Hadron Collider. A total of 1381 B^0_s -> D_s^- pi^+ and B^0_s -> D_s^- pi^+ pi^- pi^+ signal decays are reconstructed, with average decay time resolutions of 44 fs and 36 fs, respectively. An oscillation signal with a statistical significance of 4.6 sigma is observed. The measured oscillation frequency is Delta m_s = 17.63 pm 0.11 (stat) pm 0.02 (syst) ps^{-1}.
A search for the lepton-flavour violating decays $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb$^{-1}$ of $pp$ collisions at $sqrt{s} = 7$ TeV, collected by the LHCb experiment. The observed number of $B^0_s to e^{pm} mu^{mp}$ and $B^0 to e^{pm} mu^{mp}$ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be $BR(B^0_s to e^{pm} mu^{mp}) < 1.1 ,(1.4) times 10^{-8}$ and $BR (B^0 to e^{pm} mu^{mp}) < 2.8 ,(3.7) times 10^{-9}$ at 90% (95%) confidence level (C.L.). These limits are a factor of twenty lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, $M_{rm LQ} (B^0_s to e^{pm} mu^{mp}) > 107$ TeV/c$^2$ and $M_{rm LQ} (B^0 to e^{pm} mu^{mp}) > 126$ TeV/c$^2$ at 95% C.L., and are a factor of two higher than the previous bounds.
We report on measurements of the time-dependent CP violating observables in $B^0_srightarrow D^{mp}_s K^{pm}$ decays using a dataset corresponding to 1.0 fb$^{-1}$ of pp collisions recorded with the LHCb detector. We find the CP violating observables $C_f=0.53pm0.25pm0.04$, $A^{DeltaGamma}_f=0.37pm0.42pm0.20$, $A^{DeltaGamma}_{bar{f}}=0.20pm0.41pm0.20$, $S_f=-1.09pm0.33pm0.08$, $S_{bar{f}}=-0.36pm0.34pm0.08$, where the uncertainties are statistical and systematic, respectively. Using these observables together with a recent measurement of the $B^0_s$ mixing phase $-2beta_s$ leads to the first extraction of the CKM angle $gamma$ from $B^0_s rightarrow D^{mp}_s K^{pm}$ decays, finding $gamma$ = (115$_{-43}^{+28}$)$^circ$ modulo 180$^circ$ at 68% CL, where the error contains both statistical and systematic uncertainties.
The $B^0_s$ and $B^0$ mixing frequencies, $Delta m_s$ and $Delta m_d$, are measured using a data sample corresponding to an integrated luminosity of 1.0 fb^{-1} collected by the LHCb experiment in $pp$ collisions at a centre of mass energy of 7 TeV during 2011. Around 1.8x10^6 candidate events are selected of the type $B^0_{(s)} to D^-_{(s)} mu^+$ (+ anything), where about half are from peaking and combinatorial backgrounds. To determine the B decay times, a correction is required for the momentum carried by missing particles, which is performed using a simulation-based statistical method. Associated production of muons or mesons allows us to tag the initial-state flavour and so to resolve oscillations due to mixing. We obtain Delta m_s = (17.93 pm 0.22 (stat) pm 0.15 (syst)) ps^{-1}, Delta m_d = (0.503 pm 0.011 (stat) pm 0.013 (syst)) ps^{-1}. The hypothesis of no oscillations is rejected by the equivalent of 5.8 standard deviations for $B^0_s$ and 13.0 standard deviations for $B^0$. This is the first observation of $B^0_s$ mixing to be made using only semileptonic decays.
A model-dependent amplitude analysis of the decay $B^0rightarrow D(K^0_Spi^+pi^-) K^{*0}$ is performed using proton-proton collision data corresponding to an integrated luminosity of 3.0fb$^{-1}$, recorded at $sqrt{s}=7$ and $8 TeV$ by the LHCb experiment. The CP violation observables $x_{pm}$ and $y_{pm}$, sensitive to the CKM angle $gamma$, are measured to be begin{eqnarray*} x_- &=& -0.15 pm 0.14 pm 0.03 pm 0.01, y_- &=& 0.25 pm 0.15 pm 0.06 pm 0.01, x_+ &=& 0.05 pm 0.24 pm 0.04 pm 0.01, y_+ &=& -0.65^{+0.24}_{-0.23} pm 0.08 pm 0.01, end{eqnarray*} where the first uncertainties are statistical, the second systematic and the third arise from the uncertainty on the $Drightarrow K^0_S pi^+pi^-$ amplitude model. These are the most precise measurements of these observables. They correspond to $gamma=(80^{+21}_{-22})^{circ}$ and $r_{B^0}=0.39pm0.13$, where $r_{B^0}$ is the magnitude of the ratio of the suppressed and favoured $B^0rightarrow D K^+ pi^-$ decay amplitudes, in a $Kpi$ mass region of $pm50 MeV$ around the $K^*(892)^0$ mass and for an absolute value of the cosine of the $K^{*0}$ decay angle larger than $0.4$.
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