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Register a new userMeasurement of the $B_c^+$ meson lifetime using $B_c^+ to J!/!psimu^+ u_{mu} X$ decays
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The lifetime of the $B_c^+$ meson is measured using semileptonic decays having a $J!/!psi$ meson and a muon in the final state. The data, corresponding to an integrated luminosity of $2mathrm{~fb^{-1}}$, are collected by the LHCb detector in $pp$ collisions at a centre-of-mass energy of $8,mathrm{TeV}$. The measured lifetime is $$tau = 509 pm 8 pm 12 mathrm{~fs},$$ where the first uncertainty is statistical and the second is systematic.
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The difference in total widths between the $B_c^+$ and $B^+$ mesons is measured using 3.0fb$^{-1}$ of data collected by the LHCb experiment in 7 and 8 TeV centre-of-mass energy proton-proton collisions at the LHC. Through the study of the time evolution of $B_c^+ rightarrow J/psi pi^+$ and $B^+rightarrow J/psi K^+$ decays, the width difference is measured to be $$ DeltaGamma equiv Gamma_{B_c^+} - Gamma_{B^+} = 4.46 pm 0.14 pm 0.07mm^{-1}c,$$ where the first uncertainty is statistical and the second systematic. The known lifetime of the $B^+$ meson is used to convert this to a precise measurement of the $B_c^+$ lifetime, $$tau_{B_c^+} = 513.4 pm 11.0 pm 5.7fs,$$ where the first uncertainty is statistical and the second systematic.
A measurement is reported of the ratio of branching fractions $mathcal{R}(J/psi)=mathcal{B}(B_c^+,to,J/psitau^+ u_tau)/mathcal{B}(B_c^+,to,J/psi mu^+ u_mu)$, where the $tau^+$ lepton is identified in the decay mode $tau^+,to,mu^+ u_muoverline{ u}_tau$. This analysis uses a sample of proton-proton collision data corresponding to 3.0$mathrm{,fb}^{-1}$ of integrated luminosity recorded with the LHCb experiment at center-of-mass energies $7,mathrm{TeV}$ and $8,mathrm{TeV}$. A signal is found for the decay $B_c^+,to,J/psi tau^+ u_tau$ at a significance of 3 standard deviations, corrected for systematic uncertainty, and the ratio of the branching fractions is measured to be $mathcal{R}(J/psi) = 0.71 pm 0.17 mathrm{,(stat)} pm 0.18mathrm{,(syst)}$. This result lies within 2 standard deviations above the range of existing predictions in the Standard Model.
The first measurement that relates semileptonic and hadronic decay rates of the $B_c^+$ meson is performed using proton-proton collision data corresponding to 1.0 fb$^{-1}$ of integrated luminosity collected with the LHCb detector. The measured value of the ratio of branching fractions, ${cal B}(B_c^+ to J/psi pi^+)/{cal B}(B_c^+to J/psimu^+ u_mu)=0.0469 pm 0.0028 (stat.) pm 0.0046 (syst.)$, is at the lower end of available theoretical predictions.
Recent studies of properties and decays of the $B_c^+$ meson by the LHC experiments are presented. Mass and lifetime measurements are discussed and some of the many new observed decays are reported.
In this paper, we calculate the $B_cto J/psi$ helicity form factors (HFFs) up to twist-4 accuracy by using the light-cone sum rules approach. After extrapolating those HFFs to the physically allowable $q^2$ region, we investigate the $B^+_c$-meson two-body decays and semi-leptonic decays $B_c^+ to J/psi+(P, V, ell^+ u_ell)$, where $P$ and $V$ stand for a light pseudo-scalar meson and a vector meson, respectively. The branching fractions can be derived by using the CKM matrix element and the $B_c$ lifetime from the Particle Data Group, and we obtain ${cal B}(B_c^+ to J/psi pi^+)=(0.132^{+0.002}_{-0.002})%$, ${cal B}(B_c^+ to J/psi K^+)=(0.010^{+0.000}_{-0.000})%$, ${cal B}(B_c^+ to J/psi rho^+) =(0.755^{+0.030}_{-0.034})%$, ${cal B}(B_c^+ to J/psi K^{ast +})=(0.043^{+0.001}_{-0.001})%$, ${cal B}(B_c^+ to J/psi mu^+ u_mu)=(2.808^{+0.547}_{-0.704})%$ and ${cal B}(B_c^+ to J/psi tau^+ u_tau)=(0.563^{+0.137}_{-0.178})%$. We then obtain ${cal R}_{pi^+/mu^+ u_mu} = 0.047^{+ 0.009}_{-0.012}$ and ${cal R}_{K^+ / pi^+} = 0.075^{+0.005}_{-0.005}$, which agree with the LHCb measured value within $1sigma$-error. We also obtain ${cal R}_{J/psi}=0.200^{+ 0.062}_{-0.081}$, which like other theoretical predictions, are consistent with the LHCb measured value within $2sigma$-error.
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