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Register a new userPrecision measurement of the ratio of the $Lambda^0_b$ to $overline{B}^0$ lifetimes
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The LHCb measurement of the lifetime ratio of the $Lambda^0_b$ to the $overline{B}^0$ meson is updated using data corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected using 7 and 8 TeV centre-of-mass energy $pp$ collisions at the LHC. The decay modes used are $overline{B}^0to J/psi p K^-$ and $overline{B}^0to J/psi pi^+ K^-$, where the $pi^+K^-$ mass is consistent with that of the $overline{K}^{*0}(892)$ meson. The lifetime ratio is determined with unprecedented precision to be $0.974pm0.006pm0.004$, where the first uncertainty is statistical and the second systematic. This result is in agreement with original theoretical predictions based on the heavy quark expansion. Using the current world average of the $overline{B}^0$ lifetime, the $Lambda^0_b$ lifetime is found to be $1.479 pm 0.009 pm 0.010$ ps.
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The branching fraction ratio $mathcal{R}(D^{*}) equiv mathcal{B}(overline{B}^0 to D^{*+}tau^{-}overline{ u}_{tau})/mathcal{B}(overline{B}^0 to D^{*+}mu^{-}overline{ u}_{mu})$ is measured using a sample of proton-proton collision data corresponding to 3.0invfb of integrated luminosity recorded by the LHCb experiment during 2011 and 2012. The tau lepton is identified in the decay mode $tau^{-} to mu^{-}overline{ u}_{mu} u_{tau}$. The semitauonic decay is sensitive to contributions from non-Standard-Model particles that preferentially couple to the third generation of fermions, in particular Higgs-like charged scalars. A multidimensional fit to kinematic distributions of the candidate $overline{B}^0$ decays gives $mathcal{R}(D^{*}) = 0.336 pm 0.027(stat) pm 0.030 (syst)$. This result, which is the first measurement of this quantity at a hadron collider, is $2.1$ standard deviations larger than the value expected from lepton universality in the Standard Model.
Using $pp$ collisions corresponding to 3$,text{fb}^{-1}$ integrated luminosity, recorded by the LHCb experiment at centre-of-mass energies of 7 and 8$,text{TeV}$, the ratio of branching fractions begin{align*} mathcal{B}(Lambda^0_b!topsi(2S) Lambda )/mathcal{B}(Lambda^0_b!to J/psi Lambda)= 0.513 pm 0.023, (text{stat}) pm 0.016 , (text{syst}) pm 0.011, (mathcal{B}) end{align*} is determined. The first uncertainty is statistical, the second is systematic and the third is due to the external branching fractions used.
The semileptonic $CP$ asymmetry in $B^0-overline{B}{}^0$ mixing, $a_{rm sl}^d$, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment. Semileptonic $B^0$ decays are reconstructed in the inclusive final states $D^-mu^+$ and $D^{*-}mu^+$, where the $D^-$ meson decays into the $K^+pi^-pi^-$ final state, and the $D^{*-}$ meson into the $overline{D}{}^0(rightarrow K^+pi^-)pi^-$ final state. The asymmetry between the numbers of $D^{(*)-}mu^+$ and $D^{(*)+}mu^-$ decays is measured as a function of the decay time of the $B^0$ mesons. The $CP$ asymmetry is measured to be $a_{rm sl}^d = (-0.02 pm 0.19 pm 0.30)%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{rm sl}^d$ to date and is consistent with the prediction from the Standard Model.
The $B^0$, $B^0_s$, $B^+$ and $Lambda^0_b$ hadron production asymmetries are measured using a data sample corresponding to an integrated luminosity of 3.0 fb$^{-1}$, collected by the LHCb experiment in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. The measurements are performed as a function of transverse momentum and rapidity of the $b$ hadrons within the LHCb detector acceptance. The overall production asymmetries, integrated over transverse momentum and rapidity, are also determined.
The $B^0 to K^{*0} overline{K}^{*0}$ and $B^0_s to K^{*0} overline{K}^{*0}$ decays are studied using proton-proton collision data corresponding to an integrated luminosity of 3fb$^{-1}$. An untagged and time-integrated amplitude analysis of $B^0_{(s)} to (K^+pi^-)(K^-pi^+) $ decays in two-body invariant mass regions of 150 MeV$/c^2$ around the $K^{*0}$ mass is performed. A stronger longitudinal polarisation fraction in the ${B^0 to K^{*0} overline{K}^{*0}}$ decay, ${f_L = 0.724 pm 0.051 ,({rm stat}) pm 0.016 ,({rm syst})}$, is observed as compared to ${f_L = 0.240 pm 0.031 ,({rm stat}) pm 0.025 ,({rm syst})}$ in the ${B^0_sto K^{*0} overline{K}^{*0}}$ decay. The ratio of branching fractions of the two decays is measured and used to determine $mathcal{B}(B^0 to K^{*0} overline{K}^{*0}) = (8.0 pm 0.9 ,({rm stat}) pm 0.4 ,({rm syst})) times 10^{-7}$.
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