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Register a new userRevisiting $Lambda_{b}toLambda_{c}$ and $Sigma_{b}toSigma_{c}$ weak decays in the light-front quark model
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In this work, we study $Lambda_{b}toLambda_{c}$ and $Sigma_{b}toSigma_{c}$ weak decays in the light-front quark model. As is well known, the key point for such calculations is properly evaluating the hadronic transition matrix elements which are dominated by the non-perturbative QCD effect. In our calculation, we employ the light-front quark model and rather than the traditional diquark picture, we account the two spectator light quarks as individual ones. Namely during the transition, they retain their color indices, momenta and spin polarizations unchanged. Definitely, the subsystem composed of the two light quarks is still in a color-anti-triplet and possesses a definite spin, but we do not priori assume the two light quarks to be in a bound system-diquark. Our purpose is probing the diquark picture, via comparing the results with the available data, we test the validity and applicability of the diquark structure which turns a three-body problem into a two-body one, so greatly simplifies the calculation. It is indicated that the two approaches (diquark and a subsystem within which the two light quarks are free) lead to similar numerical results even though the model parameters in the two schemes might deviate slightly. Thus, the diquark approach seems sufficiently reasonable.
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The successful operation of LHC provides a great opportunity to study the processes where heavy baryons are involved. {In this work we mainly study} the weak transitions of $Sigma_bto Sigma_c$. Assuming the reasonable quark-diquark structure where the two light quarks constitute an axial vector, we calculate the widths of semi-leptonic decay $Sigma_{b}toSigma_c e u_e$ and non-leptonic decay modes $Sigma_{b}toSigma_c +M$ (light mesons) in terms of the light front quark model. We first construct the vertex function for the concerned baryons and then deduce the form factors which are related to two Isgur-Wise functions for the $Sigma_{b}toSigma_c$ transition under the heavy quark limit. Our numerical results indicate that $Gamma(Sigma_{b}toSigma_c e u_e)$ is about $1.38times10^{10}{rm s}^{-1}$ and $Gamma(Sigma_{b}toSigma_c +M)$ is slightly below $1times10^{10}{rm s}^{-1}$ which may be accessed at the LHCb detector. By the flavor SU(3) symmetry we estimate the rates of $Omega_btoOmega_c$. We suggest to measure weak decays of $Omega_btoOmega_c$, because $Omega_b$ does not decay via strong interaction, the advantage is obvious.
In this work, the full leading order results of the form factors for $Xi_{b}toXi_{c}$ and $Lambda_{b}toLambda_{c}$ are obtained in QCD sum rules. Contributions from up to dim-5 have been considered. For completeness, we also study the two-point correlation function to obtain the pole residues of $Xi_{Q}$ and $Lambda_{Q}$, and higher accuracy is achieved. For the three-point correlation function, since stable Borel regions can not be found, about $20%$ uncertainties are introduced for the form factors of $Xi_{b}toXi_{c}$ and $Lambda_{b}toLambda_{c}$. Our results for the form factors are consistent with those of the Lattice QCD within errors.
Without contamination from the final state interactions, the calculation of the branching ratios of semileptonic decays $Xi^{()}_{c}toXi+e^+ u_e$ may provide us more information about the inner structure of charmed baryons. Moreover, by studying those processes, one can better determine the form factors of $Xi_ctoXi$ which can be further applied to relevant estimates. In this work, we use the light-front quark model to carry out the computations where the three-body vertex functions for $Xi_c$ and $Xi$ are employed. To fit the new data of the Belle II, we re-adjust the model parameters and obtain $beta_{s[sq]}=1.07$ GeV which is 2.9 times larger than $beta_{sbar s}=0.366$ GeV. This value may imply that the $ss$ pair in $Xi$ constitutes a more compact subsystem. Furthermore, we also investigate the non-leptonic decays of $Xi^{()}_cto Xi$ which will be experimentally measured soon, so our model would be tested by consistency with the new data.
In this work we investigate the weak $Lambda_{b}toLambda_c$ semi-leptonic and non-leptonic decays. The light-front quark model and diquark picture for heavy baryons are adopted to evaluate the $Lambda_{b}toLambda_c$ transition form factors. In the heavy quark limit we study the Isgur-Wise function. By fitting the data of the semi-leptonic process we obtain the mass of the light scalar diquark as 817 MeV. The numerical predictions on the branching ratios of non-leptonic decay modes $Lambda_{b}toLambda_c M$ and various polarization asymmetries are made. A comparison with other approaches is discussed.
We calculate the decay width of h0 -> b bbar in the Minimal Supersymmetric Standard Model (MSSM) with quark flavour violation (QFV) at full one-loop level. We study the effect of scharm-stop mixing and sstrange-sbottom mixing taking into account the constraints from the B meson data. We discuss and compare in detail the decays h0 -> c cbar and h0 -> b bbar within the framework of the perturbative mass insertion technique using the Flavour Expansion Theorem. The deviation of both decay widths from the Standard Model values can be quite large. Whereas in h0 -> c cbar it is almost entirely due to the flavour violating part of the MSSM, in h0 -> b bbar it is mainly due to the flavour conserving part. Nevertheless, the QFV contribution to Gamma(h0 -> b bbar) due to scharm-stop mixing and chargino exchange can go up to about 8%.
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