Decays Of Heavy Baryons Research Articles

Semileptonic Ωb→Ωcℓν¯ℓ transition in full QCD

We investigate the semileptonic decay of Ωb→Ωcℓν¯ℓ in three lepton channels. To this end, we use the QCD sum rule method in three point framework to calculate the form factors defining the matrix elements of these transitions. Having calculated the form factors as building blocks, we calculate the decay widths and branching fractions of the exclusive decays in all lepton channels and compare the results with other theoretical predictions. The obtained results for branching ratios and ratio of branching fractions at different leptonic channels may help experimental groups in their search for these weak decays. Comparison of the obtained results with possible future experimental data can be useful to check the order of consistency between the standard model theory predictions and data on the heavy baryon decays. Published by the American Physical Society 2024

Heavy baryon decays into light meson and dark baryon within LCSR

We studied the decays of Heavy baryon into a pseudoscalar meson and a dark baryon in the recently developed B-Mesogenesis scenario, where the two types of effective Lagrangians proposed by the scenario are both considered. The decay amplitudes of Λb0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda _b^0$$\\end{document} are calculated by light-cone sum rules using its light-cone distribution amplitudes. The decay amplitudes of Ξb0,±\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Xi _b^{0,\\pm }$$\\end{document} are related with those of Λb0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda _b^0$$\\end{document} through a flavor SU(3) analysis. The uncertainties of threshold parameter and the Borel parameter are both considered in the numerical calculation. The values of effective coupling constants in the B-Mesogenesis are taken as their upper limits that obtained from our previous study on the inclusive decay. The upper limits of the decay branching fractions are presented as functions of the dark baryon mass.

Charmonium decays of beauty baryons in the perturbative QCD approach

Motivated by recent advances in experimental measurements of heavy baryon decays, the charmonium decays of single b baryon are investigated systematically in the framework of perturbative QCD approach. We calculate the decay branching ratios and helicity amplitudes as well as many pertinent decay asymmetry parameters that characterize the angular decay distributions. In particular, we estimate the fragmentation fractions of b quark to b baryons based on the current world averages of the branching ratio multiplied by fragmentation fraction. Some of the featured results are compared with the predictions of other approaches and experimental data. We also evaluate the branching ratios and angular asymmetries of the Σb and Ξb′ decay modes, which have neither been measured experimentally nor calculated theoretically. Our results could be helpful for a future experimental search for them and provide deeper insights in the understanding of the dynamics of heavy-flavor weak decay processes. Published by the American Physical Society 2024

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.

A novel strategy for searching for CP violations in the baryon sector

Despite the large baryon-anti-baryon asymmetry in the observable Universe, the closely related phenomenon — the violation of the combined charge and parity symmetry (CPV) — has not been observed in the baryon sector in laboratories. In this paper, a new strategy for searching for CPV in heavy hadron multi-body decays is proposed, in which a set of novel observables measuring CPV in such decays — the partial wave CP asymmetries (PWCP As) — are introduced. This strategy is model-independent and applicable to multi-body decays of heavy hadrons with arbitrary spin configurations in both initial and final states, and with any number of particles in the final state. It is especially applicable for CPV investigations in multi-body decays of heavy baryons. As applications of this strategy, we suggest to measure the PWCP As in some decay channels of bottom baryons such as {Lambda}_b^0to p{pi}^{-}{pi}^{+}{pi}^{-} , Λb → pK−π+π−, {Lambda}_b^0to p{pi}^{-}{K}^{+}{K}^{-} , {Lambda}_b^0to Lambda {K}^{+}{pi}^{-} , and {Lambda}_b^0to p{pi}^{-}{K}_s .

Form-factor-independent test of lepton universality in semileptonic heavy meson and baryon decays

In the semileptonic decays of heavy mesons and baryons, the lepton-mass dependence factors out in the quadratic ${\mathrm{cos}}^{2}\ensuremath{\theta}$ coefficient of the differential $\mathrm{cos}\ensuremath{\theta}$ distribution. We call the corresponding normalized coefficient the convexity parameter. This observation opens the path to a test of lepton universality in semileptonic heavy meson and baryon decays that is independent of form-factor effects. By projecting out the quadratic rate coefficient, dividing out the lepton-mass-dependent factor, and restricting the phase space integration to the $\ensuremath{\tau}$ lepton phase space, one can define optimized partial rates which, in the Standard Model, are the same for all three $(e,\ensuremath{\mu},\ensuremath{\tau})$ modes in a given semileptonic decay process. We discuss how the identity is spoiled by new physics effects. We discuss semileptonic heavy meson decays such as ${\overline{B}}^{0}\ensuremath{\rightarrow}{D}^{(*)+}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and ${B}_{c}^{\ensuremath{-}}\ensuremath{\rightarrow}J/\ensuremath{\psi}({\ensuremath{\eta}}_{c}){\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ and semileptonic heavy baryon decays such as ${\mathrm{\ensuremath{\Lambda}}}_{b}\ensuremath{\rightarrow}{\mathrm{\ensuremath{\Lambda}}}_{c}{\ensuremath{\ell}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\ell}}$ for each $\ensuremath{\ell}=e$, $\ensuremath{\mu}$, $\ensuremath{\tau}$.

Relativistic corrections to decays of heavy baryons in the quark model

We investigate relativistic corrections of an order $1/{m}^{2}$, where $m$ is the constituent quark mass, to heavy baryon decays by emitting one pseudoscalar meson in the quark model. This work is motivated by shortcomings in the previous studies in the nonrelativistic quark model for decays of the Roper-like states, such as ${\mathrm{\ensuremath{\Lambda}}}_{c}(2765)$. We find that the relativistic corrections due to the internal motion of quarks are essential ingredients in improving their decay properties, such that the decay widths are significantly increased. In addition, such corrections can explain a phenomenological suppression of the quark axial-vector coupling constant ${g}_{A}^{q}$ for the ${\mathrm{\ensuremath{\Sigma}}}_{c}(2455)$ and ${\mathrm{\ensuremath{\Sigma}}}_{c}(2520)$ decays.

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.

Novel Ideas in Nonleptonic Decays of Double Heavy Baryons

The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology since they allow for studying the interplay of long and short distance dynamics of the Standard Model (SM). Furthermore, they allow one to search for New Physics effects beyond the SM. We review recent progress in experimental and theoretical studies of the nonleptonic decays of heavy baryons with a focus on double charm baryon states and their decays. In particular, we discuss new ideas proposed by the present authors to calculate the W-exchange matrix elements of the nonleptonic decays of double heavy baryons. An important ingredient in our approach is the compositeness condition of Salam and Weinberg, and an effective implementation of infrared confinement both of which allow one to describe the nonperturbative structure of baryons composed of light and heavy quarks. Furthermore, we discuss an ab initio calculational method for the treatment of the so-called W-exchange diagrams generated by W ± boson exchange between quarks. We found that the W ± -exchange contributions are not suppressed in comparison with the tree-level (factorizing) diagrams and must be taken into account in the evaluation of matrix elements. Moreover, there are decay processes such as the doubly Cabibbo-suppressed decay Ξ c + → p ϕ recently observed by the LHCb Collaboration, which is contributed to only by one single W-exchange diagram.

Heavy baryon decay widths in the large $$N_c$$ N c limit in chiral theory

We propose large N_c generalizations for the “diquark” representations of hbox {SU}(3)_mathrm{flav} relevant for positive parity heavy baryons, including putative exotic states. Next, within the framework of the Chiral Quark Soliton Model, we calculate heavy baryon masses and decay widths. We show that in the limit of N_c rightarrow infty all decay widths vanish, including the widths of exotica. This result is in fact more general than the model itself, as it relies only on the underlying symmetries: i.e. hbox {SU}(3)_mathrm{flav} and hedgehog symmetry. Furthermore, using explicit model formulae for the decay constants in the non-realtivistic limit, we show that there is a hierarchy of the decay couplings, which may explain observed pattern of experimental widths.

Weak decays of heavy baryons in the light-front approach**Supported by National Natural Science Foundation of China (11575110, 11655002, 11735010) and Natural Science Foundation of Shanghai (15DZ2272100)

In this work, we analyse semi-leptonic and non-leptonic weak decays of the heavy baryons: Λb, Ξb, Ωb and Λc, Ξc, Ωc. For non-leptonic decay modes, we study only the factorizable channels induced by the external W-emission. The two spectator quarks in the baryonic transitions are treated as a diquark and form factors are calculated in the light-front approach. Using the results for form factors, we also calculate some corresponding semi-leptonic and non-leptonic decay widths. We find that our results are comparable with the available experimental data and other theoretical predictions. Decay branching fractions for many channels are found to reach the level 10−3 ∼ 10−2, which is promising for discovery in future measurements at BESIII, LHCb and Belle II. The SU(3) symmetry in semi-leptonic decays is examined and sources of symmetry breaking are discussed.

Discovery potentials of doubly charmed baryons**Supported by National Natural Science Foundation of China (11505083, 11505098, 11647310, 11575110, 11375208, 11521505, 11621131001, 11235005, 11447032, U1732101) and Natural Science Foundation of Shanghai (15DZ2272100)

The existence of doubly heavy flavor baryons has not been well established experimentally so far. In this Letter we systematically investigate the weak decays of the doubly charmed baryons, and , which should be helpful for experimental searches for these particles. The long-distance contributions are first studied in the doubly heavy baryon decays, and found to be significantly enhanced. Comparing all the processes, and are the most favorable decay modes for experiments to search for doubly heavy baryons.

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.

Heavy-flavor-conserving hadronic weak decays of heavy baryons

More than two decades ago, we studied heavy-flavor-conserving weak decays of heavy baryons within the framework that incorporates both heavy-quark and chiral symmetries. In view of the first observation of $\Xi_b^-\to\Lambda_b^0\pi^-$ by LHCb recently, we have reexamined these decays and presented updated predictions. The predicted rates for $\Xi_b^-\to\Lambda_b^0\pi^-$ in the MIT bag and diquark models are consistent with experiment. The major theoretical uncertainty stems from the evaluation of baryon matrix elements. The branching fraction of $\Xi_c\to\Lambda_c\pi$ is predicted to be of order $10^{-4}$. It is suppressed relative to $Br(\Xi_b\to\Lambda_b\pi)$ owing to the shorter lifetime of $\Xi_c$ relative to $\Xi_b$ and the destructive nonspectator $W$-exchange contribution. The kinematically accessible weak decays of the sextet heavy baryon $\Omega_Q$ are $\Omega_Q\to\Xi_Q\pi$. Due to the absence of the $B_6-B_{\bar 3}$ transition in the heavy quark limit and the $B_6-B_6$ transition in the model calculations, $\Omega_Q\to\Xi_Q\pi$ vanish in the heavy quark limit.

Decay rates and branching ratios of $\Xi_{b}\rightarrow\Xi_{c}$ and $\Lambda_{b}\rightarrow\Lambda_{c}$ modes

Decay widths and branching ratios of $\Xi$ and $\Lambda$ heavy baryon decays are analyzed within the Isgur-Wise formalism with a potential combination containing Hulthen and linear terms. The problem is considered in the hyperspherical approach and the corresponding results are motivating.

Possible large CP violation in three-body decays of heavy baryon

We propose a new mechanism which can introduce large CP asymmetries in the phase spaces of three-body decays of heavy baryons. In this mechanism, a large CP asymmetry is induced by the interference of two intermediate resonances, which subsequently decay into two different combinations of final particles. We apply this mechanism to the decay channel Λb0→pπ0π−, and find that the differential CP asymmetry can reach as large as 50%, while the regional CP asymmetry can reach as large as 16% in the interference region of the phase space.

Electromagnetic decays of the charmed and bottom baryons in chiral perturbation theory

We have investigated the electromagnetic decays of the antitriplet and sextet charmed baryon systems with $J^P= \frac{1}{2}^+, \frac{3}{2}^+$ in the framework of the heavy baryon chiral perturbation theory. We first construct the chiral Lagrangians at $O(p^2)$ and $O(p^3)$. Then we calculate the electromagnetic (EM) decay amplitudes of the charmed baryon systems up to $O(p^3)$. With the help of the quark model, we estimate the low energy constants. The numerical results of the EM decay widths show good convergence of the chiral expansion. We notice that the two neutral EM decay processes $\Xi_c'^0\rightarrow\gamma+\Xi_c^0$ and ${\Xi_c^*}'^0\rightarrow\gamma+\Xi_c^0$ are strongly suppressed by the SU(3) U-spin flavor symmetry. With the same formalism, we also estimate the EM decay widths of the bottomed baryons. The EM decay widths of the heavy baryons may be measured at facilities such as LHCb and JPARC. The explicit chiral structures of the heavy baryon decay amplitudes derived in this work may be useful to the possible chiral extrapolations of the future lattice simulations of these EM decay amplitudes.

Production of triply heavy baryons at LHC

Triply heavy baryons are very interesting hadrons to be explored for they provide particular information about strong interactions, hadron structures, and weak decays of heavy baryons. We calculate the hadronic production cross sections of the Ω ccc and the Ω ccb , which are dominated by the gg fusion subprocesses containing 4362 and 1454 Feynman diagrams, respectively. A method for generating and calculating tree level Feynman diagrams automatically is developed to deal with complicated processes containing so many diagrams. Our results show that 104 − 105 events of triply heavy baryons can be accumulated for 10 fb −1 integrated luminosity at LHC. Signatures of the triply heavy baryons are pointed out, with emphasis on the decay modes Ω ccc → Ω sss + 3π + and Ω ccb → Ω sss + 3π + + π −. We conclude that it is quite promising to discover them at LHC.