Weak decays of doubly heavy baryons: “decay constants”

Inspired by the recent observation of the Ξ_c~+_c~+)by the LHCb Collaboration, we explore the "decay constants" of doubly heavy baryons in the framework of QCD sum rules. With the Ξ_cc),Ξ_(bc),Ξ_(bb), and ?_(cc),?_(bc),?_(bb) baryons interpolated by three-quark operators, we calculate the correlation functions using the operator product expansion and include the contributions from operators up to dimension six. On the hadron side, we consider both contributions from the lowest-lying states with JP=1/2~+ and from negative parity baryons with JP=1/2~-. We find that the results are stable and the contaminations from negative parity baryons are not severe. These results are ingredients for the QCD study of weak decays and other properties of doubly-heavy baryons.     

Static properties and semileptonic transitions of lowest-lying double heavy baryons

The static properties and semileptonic decays of ground-state doubly heavy baryons are studied in the framework of a non-relativistic quark model. Using a phenomenological potential model, we calculate the ground-state masses and magnetic moments of doubly heavy Ω and Ξ baryons. In the heavy quark limit, we introduce a simple form of the universal Isgur-Wise function used as the transition form factor and then investigate the exclusive \begin{document}$ b \rightarrow c $\end{document} semileptonic decay widths and branching fractions for \begin{document}$ \dfrac{1}{2}\rightarrow \dfrac{1}{2} $\end{document} baryon transitions. Our obtained results are in agreement with other theoretical predictions.     

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D+→D0e+ν,DS+→D0e+ν,BS0→B+e-ν,DS+→D+e-e+ and BS0→B0e-e+ rare semileptonic decay processes,which are induced by decays of light quarks,the heavy quarks remain unchanged.The branching ratios of these decay processes are estimated in the heavy quark limit and with SU(3) flavor symmetry.We find that the decay rates are very tiny in the framework of the Standard Model.We also estimate the sensitivities of the measurements of these rare decays at the future experiments,such as BES-Ⅲ,super-B and LHC-b.Observations of these decays may shed some light on new physics beyond the standard model.     

Rare semileptonic decays of heavy mesons in the heavy quark limit

We study the branching ratios of D^＋ → D^0e^＋ν, Ds^＋ → D^0e^＋ν, Bs^0→B^＋e^-^-ν, Ds^＋→D^＋e^-e^＋ and Bs^0→B^0e^-e^＋ rare semileptonic decay processes, which are induced by decays of light quarks, the heavy quarks remain unchanged. The branching ratios of these decay processes are estimated in the heavy quark limit and with SU（3） flavor symmetry. We find that the decay rates are very tiny in the framework of the Standard Model. We also estimate the sensitivities of the measurements of these rare decays at the future experiments, such as BES-Ⅲ, super-B and LHC-b. Observations of these decays may shed some light on new physics beyond the standard model.     

Dipion decays of heavy baryons

Compared with the charmed baryons, the bottom baryons are not very well known, either experimentally or theoretically. In this paper, we investigate the dipion strong decays of the P-wave and D-wave excited bottom baryons in the framework of the QPC model. We also extend the same analysis to the charmed baryons.     

Isospin splittings of doubly heavy baryons

The SELEX Collaboration has reported a very large isospin splitting of doubly charmed baryons. We show that this effect would imply that the doubly charmed baryons are very compact. One intriguing possibility is that such baryons have a linear geometry Q–q–Q$Q\text{–}q\text{–}Q$ where the light quark q oscillates between the two heavy quarks Q  , analogous to a linear molecule such as carbon dioxide. However, using conventional arguments, the size of a heavy-light hadron is expected to be around 0.5 fm, much larger than the size needed to explain the observed large isospin splitting. Assuming the distance between two heavy quarks is much smaller than that between the light quark and a heavy one, the doubly heavy baryons are related to the heavy mesons via heavy quark–diquark symmetry. Based on this symmetry, we predict the isospin splittings for doubly heavy baryons including Ξ_cc${\Xi }_{cc}$, Ξ_bb${\Xi }_{bb}$ and Ξ_bc${\Xi }_{bc}$. The prediction for the Ξ_cc${\Xi }_{cc}$ is much smaller than the SELEX value. On the other hand, the Ξ_bb${\Xi }_{bb}$ baryons are predicted to have an isospin splitting as large as (6.3±1.7) MeV$(6.3\pm 1.7)\text{MeV}$. An experimental study of doubly bottomed baryons is therefore very important to better understand the structure of baryons with heavy quarks.     

Ground-state triply and doubly heavy baryons in a relativistic three-quark model

Mass spectra of the ground-state baryons consisting of three or two heavy (b or c  ) and one light (u,d,s)$(u,d,s)$ quarks are calculated in the framework of the relativistic quark model and the hyperspherical expansion. The predictions of masses of the triply and doubly heavy baryons are obtained by employing the perturbation theory for the spin-independent and spin-dependent parts of the three-quark Hamiltonian.     

Non-leptonic weak decays of charmed baryons

It is shown that the ΔC _h=ΔS decays of a baryon sextuplet, triplet and singlet of SU (3), into meson and baryon, can provide simple tests of the iscspin and SU (3) transformation properties of the ΔC _h=ΔS non-leptonic interaction in the Glashow Iliopoulos-Maiani scheme.     

Triply heavy baryons in the constituent quark model

The constituent quark model is used to compute the ground and excited state masses of QQQ baryons containing either c or b quarks.The quark model parameters previously used to describe the properties of charmonium and bottomonium states were used in this analysis.The non-relativistic three-body bound state problem is solved by means of the Gaussian expansion method which provides sufficient accuracy and simplifies the subsequent evaluation of the matrix elements.Several low-lying states with quantum numbers J^P=1/2^±,3/2^±,5/2^±and 7/2^+are reported.We compare the results with those obtained by the other theoretical formalisms.There is a general agreement for the mass of the ground state in each sector of triply heavy baryons.However,the situation is more puzzling for the excited states,and appropriate comments about the most relevant features of our comparison are given.     

Weak radiative decays of baryons

Using recent experimental baryon weak radiative decay data for the fiveB→B′γ decays, we employ the pole model self-consistently to extract the reduced matrix elements 〈B′|H _w|B〉. The resulting pattern is compatible with weak pion decaysB→B′π and also with the quark model.     

Weak decays of charmed baryons

We use the quark model framework to calculate the weak decays of the lowest lying charmed baryons into ground state baryons and mesons. We present detailed results on the predicted flavour and multipole composition of the final state configurations which can be tested in the near future. For the decays 1/2⁺→1/2⁺+0^? we also give symmetry and current algebra estimates which we compare with the quark model results. Semileptonic branching ratios in charmed baryon decays are calculated to be of the order of ～5%. The total lifetime of charmed baryons is predicted to be ～7 10^?14 s which is 5–10 times smaller than the free quark model estimate.     

Static properties and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model

We evaluate static properties and semileptonic decays for the ground state of doubly heavy Ξ, Ξ', Ξ ^* and Ω, Ω', Ω ^* baryons. Working in the framework of a nonrelativistic quark model, we solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one-gluon exchange. Our results for static properties (masses, charge radii and magnetic moments) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy Ξ, Ξ'(J = 1/2) and Ω, Ω'(J = 1/2) baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark-diquark approximation. An erratum to this article is available at .     

Weak decays of doubly heavy baryons: SU(3) analysis

Motivated by the recent LHCb observation of doubly charmed baryon \(\Xi _{cc}^{++}\) in the \(\Lambda _c^+ K^-\pi ^+\pi ^+\) final state, we analyze the weak decays of doubly heavy baryons \(\Xi _{cc}\), \(\Omega _{cc}\), \(\Xi _{bc}\), \(\Omega _{bc}\), \(\Xi _{bb}\) and \(\Omega _{bb}\) under the flavor SU(3) symmetry. The decay amplitudes for various semileptonic and nonleptonic decays are parametrized in terms of a few SU(3) irreducible amplitudes. We find a number of relations or sum rules between decay widths and CP asymmetries, which can be examined in future measurements at experimental facilities like LHC, Belle II and CEPC. Moreover, once a few decay branching fractions have been measured in the future, some of these relations may provide hints for exploration of new decay modes.     

Strong decays of newly observed heavy flavor hadrons

In this talk, we briefly review the experimental status of newly observed charmed hadrons during the past years. Then we introduce the theoretical progresses on these charmed hadrons, especially our studies on the strong decays of new charmed hadrous during the past one year.     

Radiative decays of heavy baryons with heavy quark symmetry

The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.     

Weak decays of heavy mesons in the instantaneous Bethe Salpeter approach

In the framework of the instantaneous Bethe Salpeter equation we investigate weak decays ofB andD mesons. Mesons are described asq $\bar q$ states interacting via a mixture of a scalar and a vector confining kernel and a one gluon exchange. The model parameters are fixed by a fit to the meson mass spectrum including also the light mesons. We calculate form factors and compare our results to the pole dominance hypothesis. From a fit to ARGUS and CLEO data onB→D ^*?v semileptonic decay we extract the Cabbibo Kobayashi Maskawa matrix element to beV _cb =(0.032 ± 0.003)(1.49ps/τ _b )^1/2 The Isgur Wise function is calculated utilizing the heavy quark mass limit. Finally, we give some results on nonleptonic decays.