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Register a new userAb initio three-loop calculation of the W-exchange contribution to nonleptonic decays of double charm baryons
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We have made an ab initio three-loop quark model calculation of the $W$-exchange contribution to the nonleptonic two-body decays of the doubly charmed baryons $Xi_{cc}^{++}$ and $Omega_{cc}^{+}$. The $W$-exchange contributions appear in addition to the factorizable tree graph contributions and are not suppressed in general. We make use of the covariant confined quark model previously developed by us to calculate the tree graph as well as the $W$-exchange contribution. We calculate helicity amplitudes and quantitatively compare the tree graph and $W$-exchange contributions. Finally, we compare the calculated decay widths with those from other theoretical approaches when they are available.
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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 to study the interplay of long and short distance dynamics of the Standard Model (SM). Further, 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. Further we discuss an ab initio calculational method for the treatment of the so-called $W$-exchange diagrams generated by $W^{pm}$ boson exchange between quarks. We found that the $W^{pm}$-exchange contributions are not suppressed in comparison with the tree-level (factrorizing) 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 $Xi_c^+ to p phi$ recently observed by the LHCb Collaboration which is contributed to only by one single $W$-exchange diagram.
A global previous analysis of two-body nonleptonic decays of $D$ mesons has been extended to the decays involving light scalar mesons. The allowance for final state interaction also in nonresonant channels provides a fit of much improved quality and with less symmetry breaking in the axial charges. We give predictions for about 50 decay branching ratios yet to be measured. We also discuss long distance contributions to the difference $Delta Gamma$ between the $D_S$ and $D_L$ widths.
We calculate the radiative corrections to the nonleptonic inclusive B decay mode $brightarrow cbar u d$ taking into account the charm quark mass. Compared to the massless case, corrections resulting from a nonvanishing c quark mass increase the nonleptonic rate by (4--8)%, depending on the renormalization point. As a by--product of our calculation, we obtain an analytic expression for the radiative correction to the semileptonic decay $brightarrow utaubar u$ taking into account the $tau$ lepton mass, and estimate the c quark mass effects on the nonleptonic decay mode $brightarrow cbar c s$.
Exclusive nonleptonic decays of bottom and charm baryons are studied within a relativistic quark model. We include factorizing as well as nonfactorizing contributions to the decay amplitudes.
The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of $300$ kilo-electron volts, which is greater than $0$ by $5$ standard deviations. We also determine the splittings in the $Sigma$, $Xi$, $D$ and $Xi_{cc}$ isospin multiplets, exceeding in some cases the precision of experimental measurements.
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