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Register a new userMeasurement of the shape of the $Lambda_b^0toLambda_c^+ mu^- overline{ u}$ differential decay rate
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A measurement of the shape of the differential decay rate and the associated Isgur-Wise function for the decay $Lambda_b^0toLambda_c^+mu^-overline{ u}$ is reported, using data corresponding to $3 fb^{-1}$ collected with the LHCb detector in proton-proton collisions. The $Lambda_c^+mu^-overline{ u}$(+ anything) final states are reconstructed through the detection of a muon and a $Lambda_c^+$ baryon decaying into $pK^-pi^+$, and the decays $Lambda_b^0toLambda_c^+pi^+pi^-mu^-overline{ u}$ are used to determine contributions from $Lambda_b^0to Lambda_c^{star+}mu ^-bar{ u}$ decays. The measured dependence of the differential decay rate upon the squared four-momentum transfer between the heavy baryons, $q^2$, is compared with expectations from heavy-quark effective theory and from unquenched lattice QCD predictions.
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The shape of the $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ differential decay rate is obtained as a function of the hadron recoil using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb$^{-1}$ collected by the LHCb detector. The $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ decay is reconstructed through the decays $D_s^{*-}rightarrow D_s^{-}gamma$ and $D_s^{-}rightarrow K^-K^+pi^-$. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.
The differential branching fraction of the decay $Lambda_b^0rightarrowLambdamu^+mu^-$ is measured as a function of the square of the dimuon invariant mass, $q^2$. A yield of $78pm12$ $Lambda_b^0rightarrowLambdamu^+mu^-$ decays is observed using data, corresponding to an integrated luminosity of 1.0,fb$^{-1}$, collected by the LHCb experiment at a centre-of-mass energy of 7,TeV. A significant signal is found in the $q^2$ region above the square of the $J/psi$ mass, while at lower-$q^2$ values upper limits are set on the differential branching fraction. Integrating the differential branching fraction over $q^2$, while excluding the $J/psi$ and $psi(2S)$ regions, gives a branching fraction of $BF($Lambda_b^0rightarrowLambdamu^+mu^-$)=(0.96pm 0.16statpm 0.13systpm 0.21 (mathrm{norm}))times 10^{-6}$, where the uncertainties are statistical, systematic and due to the normalisation mode, $$Lambda_b^0rightarrow J/psiLambda$, respectively.
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.
The ratio of the Lambda b baryon lifetime to that of the B0 meson is measured using 1.0/fb of integrated luminosity in 7 TeV center-of-mass energy pp collisions at the LHC. The Lambda b baryon is observed for the first time in the decay mode Lambda b -> J/psi pK-, while the B0 meson decay used is the well known B0 -> J/psi pi+K- mode, where the pi+ K- mass is consistent with that of the K*0(892) meson. The ratio of lifetimes is measured to be 0.976 +/- 0.012 +/- 0.006, in agreement with theoretical expectations based on the heavy quark expansion. Using previous determinations of the B0 meson lifetime, the Lambda b lifetime is found to be 1.482 +/- 0.018 +/- 0.012 ps. In both cases the first uncertainty is statistical and the second systematic.
Experimental data on $ R(D^{(*)}) $, $ R(K^{(*)}) $ and $ R(J/psi) $, provided by different collaborations, show sizable deviations from the SM predictions. To describe these anomalies many new physics scenarios have been proposed. One of them is leptoquark model with introducing the vector and scalar leptoquarks coupling simultaneously to the quarks and leptons. To look for similar possible anomalies in baryonic sector, we investigate the effects of a vector leptoquark $U_3 (3,3, frac{2}{3})$ on various physical quantities related to the tree-level $ Lambda_b rightarrow Lambda_c ell ~ overline{ u}_ell$ decays ($ ell=mu, ~tau $), which proceed via $ b rightarrow c~ell ~ overline{ u}_ell$ transitions at quark level. We calculate the differential branching ratio, forward-backward asymmetry and longitudinal polarizations of lepton and $Lambda_{c}$ baryon at $ mu $ and $ tau $ lepton channels in leptoquark model and compare their behavior with respect to $ q^2 $ with the predictions of the standard model (SM). In the calculations we use the form factors calculated in full QCD as the main inputs and take into account all the errors coming from the form factors and model parameters. It is observed that ........
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