Nonleptonic Weak Decays of Bottom Baryons

Cabibbo-allowed two-body hadronic weak decays of bottom baryons are analyzed. Contrary to the charmed baryon sector, many channels of bottom baryon decays proceed only through the external or internal W-emission diagrams. Moreover, W-exchange is likely to be suppressed in the bottom baryon sector. Consequently, the factorization approach suffices to describe most of the Cabibbo-allowed bottom baryon decays. We use the nonrelativistic quark model to evaluate heavy-to-heavy and heavy-to-light baryon form factors at zero recoil. When applied to the heavy quark limit, the quark model results do satisfy all the constraints imposed by heavy quark symmetry. The decay rates and up-down asymmetries for bottom baryons decaying into $(1/2)^++P(V)$ and $(3/2)^++P(V)$ are calculated. It is found that the up-down asymmetry is negative except for $\Omega_b \to (1/2)^++P(V)$ decay and for decay modes with $\psi'$ in the final state. The prediction $B(\Lambda_b \to J/\psi\Lambda)=1.6 \times 10^{-4}$ for $|V_{cb}|=0.038$ is consistent with the recent CDF measurement. We also present estimates for $\Omega_c \to (3/2)^++P(V)$ decays and compare with various model calculations.Comment: 24 pages, to appear in Phys. Rev. Uncertainties with form factor q^2 dependence are discusse

Effects of R-parity violation on CP asymmetries in Λb→pπ\Lambda_b \to p \pi decay

We have studied new CP violating effects in $\Lambda_b \to p \pi$ decay mode, that can arise in Minimal Supersymmetric Standard Model with R-parity violation. We have estimated how much R-parity violation modifies the Standard Model predictions for CP asymmetries within the present bounds. We found that in the R-parity violating model, the rate asymmetry ($a_{cp}$) is suppressed (about 10 times) and the asymmetry parameter $A(\alpha)$ is enhanced (approximately $10^2$ times) with respect to the SM predictions.Comment: Latex, 8 page

Weak Semileptonic Decays of Heavy Baryons Containing Two Heavy Quarks

In the heavy quark limit a heavy baryon which contains two heavy quarks is believed to be composed of a heavy diquark and a light quark. Based on this picture, we evaluate the weak semileptonic decay rates of such baryons. The transition form factors between two heavy baryons are associated with those between two heavy mesons by applying the superflavor symmetry. The effective vertices of the W-boson and two heavy diquarks are obtained in terms of the Bethe-Salpeter equation. Numerical predictions on these semileptonic decay widths are presented and they will be tested in the future experiments.Comment: 28 pages, Late

Heavy quark distribution functions in heavy baryons

Using the Bethe-Salpeter (BS) equations for heavy baryons ΛQ, ΣQ, ΞQ and ΩQ (Q=b or c), which were established in previous work, we calculate the heavy quark distribution functions in these baryons. The numerical results indicate that these distribution functions have an obvious peak at some fraction α0 of the baryon’s light-cone “plus” momentum component carried by the heavy quark, and that as mQ becomes heavier this peak becomes sharper and closer to 1. The dependence of the distribution functions on various input parameters in the BS model is also discussed. The results are seen to be qualitatively similar to an existing phenomenological model.X.-H. Guo, A. W. Thomas, and A. G. William

1/m_Q Corrections to the Bethe-Salpeter Equation for \Lambda_{Q} in the Diquark Picture

Corrections of order 1/m_Q (Q=b or c) to the Bethe-Salpeter (B-S) equation for \Lambda_Q are analyzed on the assumption that the heavy baryon \Lambda_Q is composed of a heavy quark and a scalar, light diquark. It is found that in addition to the one B-S scalar function in the limit m_Q -> \infty, two more scalar functions are needed at the order 1/m_Q. These can be related to the B-S scalar function in the leading order. The six form factors for the weak transition \Lambda_b -> \Lambda_c are expressed in terms of these wave functions and the results are consistent with heavy quark effective theory to order 1/m_Q. Assuming the kernel for the B-S equation in the limit m_Q -> \infty to consist of a scalar confinement term and a one-gluon-exchange term we obtain numerical solutions for the B-S wave functions, and hence for the $\Lambda_b \to \Lambda_c$ form factors to order 1/m_Q. Predictions are given for the differential and total decay widths for \Lambda_b -> \Lambda_c l \bar{\nu}, and also for the nonleptonic decay widths for \Lambda_b -> \Lambda_c plus a pseudoscalar or vector meson, with QCD corrections being also included.Comment: Latex, 24 pages, two figure

Direct CP Violation in \Lambda_b -> n (\Lambda)\pi^+\pi^- Decays via \rho-\omega Mixing

We study direct CP violation in the bottom baryon decays \Lambda_b -> f \rho^0 (\omega) -> f\pi^+\pi^- (f=n or \Lambda). It is found that in these decays via \rho-\omega mixing the CP violation could be very large when the invariant mass of the \pi^+\pi^- pair is in the vicinity of the \omega resonance. With a typical value N_c =2 in the factorization approach, the maximum CP-violating asymmetries are more than 50% and 68% for \Lambda_b -> n \pi^+\pi^- and \Lambda_b -> \Lambda \pi^+\pi^-, respectively. With the aid of heavy quark symmetry and phenomenological models for the hadronic wave functions of \Lambda_b, \Lambda and the neutron, we estimate the branching ratios of \Lambda_b -> n (\Lambda)\rho^0.Comment: 20 pages, 2 figires, Late