Semileptonic Decays Of Heavy Baryons Research Articles

Sterile neutrinos in Λb0→(Λc+,p+)ℓ1−ℓ2−ℓ3+ν decays

We study lepton number violating and lepton number conserving semi-leptonic decays of heavy baryons $\Lambda_b^0$ to three charged leptons and a neutrino. The decays occur through two intermediate quasi-degenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, \emph{i.e.,} branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements $|V_{eN}|$ and $|V_{\mu N}|$, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)\mu\mu e\nu$ with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of $\Lambda_b^0\to (\Lambda_c,p)ee\mu\nu$ is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.

Semileptonic Decays of Heavy Baryons

Semileptonic decays of heavy baryons are studied within the relativistic quark model based on the quasi-potential approach and quantum chromodynamics. Form factors parametrizing the matrix elements of weak transitions are calculated in the entire available kinematic interval with consistent consideration of relativistic effects. The results on the probabilities of semileptonic decays and other observable quantities are in good agreement with the available experimental data.

Semileptonic Decays of Heavy Baryons in the Relativistic Quark Model

Semileptonic and rare semileptonic decays of heavy baryons are studied in the framework of the relativistic quark model based on the quark-diquark picture, quasipotential approach, and quantum chromodynamics (QCD). The form factors parametrizing the matrix elements of the weak transitions are calculated in the whole accessible kinematical range with the comprehensive account of the relativistic effects. The obtained results for the branching ratios and other observables agree well with the available experimental data.

A new angle on an old problem: helicity approach to neutron beta decay in the Standard Model

We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron beta decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays B_1 rightarrow B_2 + W_mathrm{off-shell} and W_{mathrm{off-shell}} rightarrow ell + nu _ell whereas neutron beta decays are analyzed as true three-body decays n rightarrow p + e^- +{bar{nu }}_e. Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron beta decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the q^2 averages of the observables up to NLO and NNLO in the recoil parameter delta =(M_n-M_p)/(M_n+M_p)= 0.689cdot 10^{-3}. Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.

Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.

Semileptonic decays of heavy baryons in the relativistic quark model

Semileptonic decays of heavy baryons consisting of one heavy (Q=b,c) and two light (q=u,d,s) quarks are considered in the heavy-quark--light-diquark approximation. The relativistic quasipotential equation is used for obtaining masses and wave functions of both diquarks and baryons within the constituent quark model. The weak transition matrix elements are expressed through the overlap integrals of the baryon wave functions. The Isgur-Wise functions are determined in the whole accessible kinematic range. The exclusive semileptonic decay rates and different asymmetries are calculated with applying the heavy quark 1/m_Q expansion. The evaluated Lambda_b -> Lambda_c l nu decay rate agrees with its experimental value.

The bound state corrections to the semileptonic decays of the heavy baryons

We present an investigation of the lepton energy distributions in the inclusive semileptonic weak decays of heavy baryons performed within a relativistic quark model formulated on the light front (LF). Using the heavy-quark LF distribution functions related to the equal time momentum wave functions taken from the Kalman-Tran-D'Souza model we compute the electron energy spectra and the total semileptonic widths of the Λ Q and Ξ Q ( Q = c, b) baryons and confront the results with existing data.

Strong and radiative decays of heavy flavored baryons

We analyze strong one-pion and radiative one-photon decays of heavy flavored baryons within a relativistic three-quark model. Employing the same parameters as were used for the description of the semileptonic decays of heavy baryons, we calculate the couplings of one-pion and one-photon transitions of both ground and excited heavy baryon states. We predict the decay rates for all relevant decay modes and compare them with experimental data when available and with the results of other model calculations.

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 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 future experiments.

Second-order power corrections in the heavy-quark effective theory. II. Baryon form factors.

The analysis of $1/m_Q^2$ corrections of the previous paper is extended to the semileptonic decays of heavy baryons. We focus on the simplest case, the ground state $\Lambda_Q$ baryons, in which the light degrees of freedom are in a state of zero total angular momentum. The formalism, while identical in spirit, is considerably less cumbersome than for heavy mesons. The general results are applied to the semileptonic decay $\Lambda_b\to\Lambda_c\,\ell\,\nu$. An estimate of the leading power corrections to the decay rate at zero recoil, which are of order $1/m_Q^2$, is presented. It is pointed out that a measurement of certain asymmetry parameters would provide a direct measurement of $1/m_Q^2$ corrections. Finally, it is shown how the analysis could be extended to include excited heavy baryons such as the $\Sigma_Q$ and the $\Sigma_Q^*$.

Semileptonic decays of heavy Λ's into excited baryons

We use the heavy quark effective theory to investigate the form factors that describe the semileptonic decays Λ b → Λ c ∗ and Λ c + → Λ ∗, both to leading order and to order 1/ m c in the effective lagrangian. In leading order, we find that a single form factor is needed in the former case, and that two are needed for each heavy → light transition. We also investigate these transitions to order 1/ m c in the heavy quark lagrangian, and find that the results to this order are also quite simple, although the number of form factors needed increases. We briefly discuss the relationship between our form factors and the recently developed Bjorken-Dunietz-Taron sum rules for inclusive semileptonic decays of heavy baryons.