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Register a new userSemileptonic $Lambda_c$ decay to $ u l^+$ and $Lambda(1405)$
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We study the semileptonic decay of $Lambda_c$ to $ u l^+$ and $Lambda(1405)$, where the $Lambda(1405)$ is seen in the invariant mass distribution of $pi Sigma$. We perform the hadronization of the quarks produced in the reaction in order to have a meson baryon pair in the final state and then let these hadron pairs undergo final state interaction from where the $Lambda(1405)$ is dynamically generated. The reaction is particularly suited to study this resonance because we show that it filters I=0. It is also free of tree level $pi Sigma$ production, which leads to a clean signal of the resonance with no background. This same feature has as a consequence that one populates the state of the $Lambda(1405)$ with higher mass around 1420 MeV, predicted by the chiral unitary approach. We make absolute predictions for the invariant mass distributions and find them within measurable range in present facilities. The implementation of this reaction would allow us to gain insight into the existence of the predicted two $Lambda(1405)$ states and their nature as molecular states.
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We evaluate the partial decay widths for the semileptonic $Lambda_b to bar u_l l Lambda_c(2595)$ and $Lambda_b to bar u_l l Lambda_c(2625)$ decays from the perspective that these two $Lambda^*_c$ resonances are dynamically generated from the $DN$ and $D^*N$ interaction with coupled channels. We find that the ratio of the rates obtained for these two reactions is compatible with present experimental data and is very sensitive to the $D^* N$ coupling, which becomes essential to obtain agreement with experiment. Together with the results obtained for the $Lambda_b to pi^- Lambda^*_c$ reactions, it gives strong support to the molecular picture of the two $Lambda^*_c$ resonances and the important role of the $D^*N$ component neglected in prior studies of the $Lambda_c(2595)$ from the molecular perspective.
We present our study on $B to pi l u$ semileptonic decay form factors with NRQCD action for heavy quark from a quenched lattice QCD simulation at $beta$=5.9 on a $16^3times 48$ lattice. We obtain form factors defined in the context of heavy quark effective theory by Burdman et al. and find that their $1/m_B$ correction is small. The limit of physical heavy and light quark masses can be performed without introducing any model function, and we obtain a prediction for the differential decay rate $dGamma/dq^2$. We also discuss the soft pion limit of the form factors.
We present a lattice QCD calculation of $Bto pi l u$ semileptonic decay form factors in the small pion recoil momentum region. The calculation is performed on a quenched $16^3 times 48$ lattice at $beta=5.9$ with the NRQCD action including the full 1/M terms. The form factors $f_1(vcdot k_{pi})$ and $f_2(vcdot k_{pi})$ defined in the heavy quark effective theory for which the heavy quark scaling is manifest are adpoted, and we find that the 1/M correction to the scaling is small for the $B$ meson. The dependence of form factors on the light quark mass and on the recoil energy is found to be mild, and we use a global fit of the form factors at various quark masses and recoil energies to obtain model independent results for the physical differential decay rate. We find that the $B^*$ pole contribution dominates the form factor $f^+(q^2)$ for small pion recoil energy, and obtain the differential decay rate integrated over the kinematic region $q^2 >$ 18 GeV$^2$ to be $|V_{ub}|^2 times (1.18 pm 0.37 pm 0.08 pm 0.31)$ psec$^{-1}$, where the first error is statistical, the second is that from perturbative calculation, and the third is the systematic error from finite lattice spacing and the chiral extrapolation. We also discuss the systematic errors in the soft pion limit for $f^0(q^2_{max})$ in the present simulation.
We calculate the $Lambda_b to Lambda_c^*(2595) l u$ and $Lambda_b to Lambda_c^*(2625) l u$ form factors and decay rates for all possible $b to c l bar u$ four-Fermi interactions in and beyond the Standard Model (SM), including nonzero charged lepton masses and terms up to order $mathcal{O}(alpha_s, 1/m_{c,b})$ in the heavy quark effective theory (HQET). We point out a subtlety involving the overcompleteness of the representation of the spin-parity $1/2^+ to 3/2^-$ antisymmetric tensor form factors, relevant also to other higher excited-state transitions, and present a general method for the counting of the physical form factors for any hadronic transition matrix element and their matching onto HQET. We perform a preliminary fit of a simple HQET-based parametrization of the $Lambda_b to Lambda_c^*$ form factors at $mathcal{O}(alpha_s, 1/m_{c,b})$ to an existing quark model, providing preliminary predictions for the lepton universality ratios $R(Lambda_c^*)$ beyond the SM. Finally, we examine the putative incompatibility of recent lattice QCD results with expectations from the heavy-quark expansion and available experimental data.
Inclusive semileptonic B_s^0 -> X^+ l^- u decays are studied for the first time using a 23.6 fb^{-1} data sample collected on the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. These decays are identified by the means of a lepton accompanied by a same-sign D_s^+ meson originating from the other B_s^0 in the event. The semileptonic branching fractions are measured in the electron and muon channels to be Bf(B_s^0 -> X^+ e^- u) = (10.9 pm 1.0 pm 0.9)% and Bf(B_s^0 -> X^+ mu^- u) = (9.2 pm 1.0 pm 0.8)%, respectively. Assuming an equal electron and muon production rate in B_s^0 decays, a combined fit yields an average leptonic branching fraction Bf(B_s^0 -> X^+ l^- u) = (10.2 pm 0.8 pm 0.9)%.
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