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Register a new user$Lambda_c to Lambda^*(1520)$ form factors from lattice QCD and improved analysis of the $Lambda_b to Lambda^*(1520)$ and $Lambda_b to Lambda_c^*(2595,2625)$ form factors
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We present the first lattice-QCD calculation of the form factors governing the charm-baryon semileptonic decays $Lambda_c to Lambda^*(1520)ell^+ u_ell$. As in our previous calculation of the $Lambda_b to Lambda^*(1520)$ form factors, we work in the $Lambda^*(1520)$ rest frame, but here we use four different heavy-baryon momenta instead of just two. Because of the lower mass of the $Lambda_c$, the moderately-sized momenta used here are sufficient to determine the form factors in the full kinematic range of the semileptonic decay. We also update the analysis of our lattice results for the $Lambda_b to Lambda^*(1520)$ and $Lambda_b to Lambda_c^*(2595,2625)$ form factors by imposing exact relations among the different form factors at zero recoil that follow from rotational symmetry. Imposing these relations ensures the correct behavior of the angular observables near the endpoint.
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We present the first lattice QCD determination of the $Lambda_b to Lambda^*(1520)$ vector, axial vector, and tensor form factors that are relevant for the rare decays $Lambda_b to Lambda^*(1520)ell^+ell^-$. The lattice calculation is performed in the $Lambda^*(1520)$ rest frame with nonzero $Lambda_b$ momenta, and is limited to the high-$q^2$ region. An interpolating field with covariant derivatives is used to obtain good overlap with the $Lambda^*(1520)$. The analysis treats the $Lambda^*(1520)$ as a stable particle, which is expected to be a reasonable approximation for this narrow resonance. A domain-wall action is used for the light and strange quarks, while the $b$ quark is implemented with an anisotropic clover action with coefficients tuned to produce the correct $B_s$ kinetic mass, rest mass, and hyperfine splitting. We use three different ensembles of lattice gauge-field configurations generated by the RBC and UKQCD collaborations, and perform extrapolations of the form factors to the continuum limit and physical pion mass. We give Standard-Model predictions for the $Lambda_b to Lambda^*(1520)ell^+ell^-$ differential branching fraction and angular observables in the high-$q^2$ region.
We present the first lattice-QCD determination of the form factors describing the semileptonic decays $Lambda_b to Lambda_c^*(2595)ell^-bar{ u}$ and $Lambda_b to Lambda_c^*(2625)ell^-bar{ u}$, where the $Lambda_c^*(2595)$ and $Lambda_c^*(2625)$ are the lightest charm baryons with $J^P=frac12^-$ and $J^P=frac32^-$, respectively. These decay modes provide new opportunities to test lepton flavor universality and also play an important role in global analyses of the strong interactions in $bto c$ semileptonic decays. We determine the full set of vector, axial vector, and tensor form factors for both decays, but only in a small kinematic region near the zero-recoil point. The lattice calculation uses three different ensembles of gauge-field configurations with $2+1$ flavors of domain-wall fermions, and we perform extrapolations of the form factors to the continuum limit and physical pion mass. We present Standard-Model predictions for the differential decay rates and angular observables. In the kinematic region considered, the differential decay rate for the $frac12^-$ final state is found to be approximately 2.5 times larger than the rate for the $frac32^-$ final state. We also test the compatibility of our form-factor results with zero-recoil sum rules.
The first lattice QCD calculation of the form factors governing $Lambda_c to Lambda ell^+ u_ell$ decays is reported. The calculation was performed with two different lattice spacings and includes one ensemble with a pion mass of 139(2) MeV. The resulting predictions for the $Lambda_c to Lambda e^+ u_e$ and $Lambda_c to Lambda mu^+ u_mu$ decay rates divided by $|V_{cs}|^2$ are $0.2007(71)(74):{rm ps}^{-1}$ and $0.1945(69)(72):{rm ps}^{-1}$, respectively, where the two uncertainties are statistical and systematic. Taking the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cs}|$ from a global fit and the $Lambda_c$ lifetime from experiments, this translates to branching fractions of $mathcal{B}(Lambda_ctoLambda e^+ u_e)=0.0380(19)_{rm LQCD::}(11)_{tau_{Lambda_c}}$ and $mathcal{B}(Lambda_ctoLambda mu^+ u_mu)=0.0369(19)_{rm LQCD::}(11)_{tau_{Lambda_c}}$. These results are consistent with, and two times more precise than, the measurements performed recently by the BESIII Collaboration. Using instead the measured branching fractions together with the lattice calculation to determine the CKM matrix element gives $|V_{cs}|= 0.949(24)_{rm LQCD::}(14)_{tau_{Lambda_c}}(49)_{mathcal{B}}$.
A lattice QCD determination of the $Lambda_c to N$ vector, axial vector, and tensor form factors is reported. The calculation was performed with $2+1$ flavors of domain wall fermions at lattice spacings of $aapprox 0.11:{rm fm},:0.085:{rm fm}$ and pion masses in the range $230:{rm MeV} lesssim m_pi lesssim 350$ MeV. The form factors are extrapolated to the continuum limit and the physical pion mass using modified $z$ expansions. The rates of the charged-current decays $Lambda_c to n, e^+ u_e$ and $Lambda_c to n, mu^+ u_mu$ are predicted to be $left( 0.405 pm 0.016_{,rm stat} pm 0.020_{,rm syst} right)|V_{cd}|^2 :{rm ps}^{-1}$ and $left( 0.396 pm 0.016_{,rm stat} pm 0.020_{,rm syst} right)|V_{cd}|^2 :{rm ps}^{-1}$, respectively. The phenomenology of the rare charm decay $Lambda_c to p, mu^+ mu^-$ is also studied. The differential branching fraction, the fraction of longitudinally polarized dimuons, and the forward-backward asymmetry are calculated in the Standard Model and in an illustrative new-physics scenario.
We present the prospects of an angular analysis of the $Lambda_b to Lambda(1520)ell^+ell^-$ decay. Using the expected yield in the current dataset collected at the LHCb experiment, as well as the foreseen ones after the LHCb upgrades, sensitivity studies are presented to determine the experimental precision on angular observables related to the lepton distribution and their potential to identify New Physics. The forward-backward lepton asymmetry at low dilepton invariant mass is particularly promising. NP scenarios favoured by the current anomalies in $bto sell^+ell^-$ decays can be distinguished from the SM case with the data collected between the Run 3 and the Upgrade 2 of the LHCb experiment.
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