Heavy Quark Spin-flavor Symmetry Research Articles

Magnetic moments of the spin−1/2 singly charmed baryons in covariant baryon chiral perturbation theory

Recent experimental advances have reignited theoretical interests in heavy-flavor hadrons. In this work, we study the magnetic moments of the spin-1/2 singly charmed baryons up to the next-to-leading order in covariant baryon chiral perturbation theory with the extended-on-mass-shell renormalization scheme. The pertinent low energy constants $g_{1-4}$ are fixed with the help of the quark model and the heavy quark spin flavor symmetry, while the remaining $d_2$, $d_3$, $d_5$ and $d_6$ are determined by fitting to the lattice QCD pion-mass dependent data. We study the magnetic moments as a function of $m_\pi^2$ and compare our results with those obtained in the heavy baryon chiral perturbation theory. We find that the loop corrections induced by the anti-triplet states are dominated by the baryon pole diagram. In addition, we predict the magnetic moments of the spin-1/2 singly charmed baryons and compare them with those of other approaches.

Analysis of Λc(2595) , Λc(2625) , Λb(5912) , Λb(5920) based on a chiral partner structure

We construct an effective hadronic model including $\Lambda_c(2595)$, $\Lambda_c(2625)$, $\Lambda_b(5912)$ and $\Lambda_b(5920)$ regarding them as chiral partners to $\Sigma_c(2455)$, $\Sigma_c(2520)$, $\Sigma_b$ and $\Sigma_b^\ast$, respectively, with respecting the chiral symmetry and heavy-quark spin-flavor symmetry. We determine the model parameters from the experimental data for relevant masses and decay widths of $\Sigma_c^{(\ast)}$ and $\Lambda_c(2595)$. Then, we study the decay widths of $\Lambda_c(2625)$, $\Lambda_b(5912)$ and $\Lambda_b(5920)$. We find that, although the decay of $\Lambda_c(2595)$ is dominated by the resonant contribution through $\Sigma_c(2455)$, non-resonant contributions are important for $\Lambda_c(2625)$, $\Lambda_b(5912)$ and $\Lambda_b(5920)$, which reflects the chiral partner structure. We also study the radiative decays of the baryons, and show that each of their widths is determined from the radiative decay width of their chiral partners.

Chiral partner structure of doubly heavy baryons with heavy quark spin-flavor symmetry

The spectrum of the doubly heavy baryons (DHBs) is estimated with respect to the new observation from the LHCb collaboration (Aaij et al (LHCb Collaboration) 2017 Phys. Rev. Lett. 119 112001) by using the chiral partner structure and heavy quark spin-flavor symmetry. The effects of heavy quark flavor symmetry breaking and light quark flavor symmetry are considered. The mass splitting of DHBs with the same spin but opposite parity arises from the generalized Goldberger–Treiman relation. The intermultiplet one-pion transition and intramultiplet radiative transitions are also be estimated.

Lowest-lying even-parity {bar{B}}_s mesons: heavy-quark spin-flavor symmetry, chiral dynamics, and constituent quark-model bare masses

The discovery of the D^*_{s0}(2317) and D_{s1}(2460) resonances in the charmed-strange meson spectra revealed that formerly successful constituent quark models lose predictability in the vicinity of two-meson thresholds. The emergence of non-negligible effects due to meson loops requires an explicit evaluation of the interplay between Q{bar{q}} and (Q{bar{q}})(q{bar{q}}) Fock components. In contrast to the c{bar{s}} sector, there is no experimental evidence of J^P=0^+,1^+ bottom–strange states yet. Motivated by recent lattice studies, in this work the heavy-quark partners of the D_{s0}^*(2317) and D_{s1}(2460) states are analyzed within a heavy meson chiral unitary scheme. As a novelty, the coupling between the constituent quark-model P-wave {bar{B}}_s scalar and axial mesons and the {bar{B}}^{(*)}K channels is incorporated employing an effective interaction, consistent with heavy-quark spin symmetry, constrained by the lattice energy levels.

Formula omitted] breaking corrections to the D, [formula omitted], B, and [formula omitted] decay constants

We report on a first next-to-next-to-leading order calculation of the decay constants of the D (D⁎) and B (B⁎) mesons using a covariant formulation of chiral perturbation theory. It is shown that, using the state-of-the-art lattice QCD results on fDs/fD as input, one can predict quantitatively the ratios of fDs⁎/fD⁎, fBs/fB, and fBs⁎/fB⁎ taking into account heavy-quark spin-flavor symmetry breaking effects on the relevant low-energy constants. The predicted relations between these ratios, fDs⁎/fD⁎<fDs/fD and fBs/fB>fDs/fD, and their light-quark mass dependence should be testable in future lattice QCD simulations, providing a stringent test of our understanding of heavy quark spin-flavor symmetry, chiral symmetry and their breaking patterns.

Radiative transitions in heavy mesons in a relativistic quark model

The radiative decays of ${D}^{*},$ ${B}^{*},$ and other excited heavy mesons are analyzed in a relativistic quark model for the light degrees of freedom and in the limit of heavy quark spin-flavor symmetry. The analysis of strong decays carried out in the corresponding chiral quark model is used to calculate the strong decays and determine the branching ratios of the radiative ${D}^{*}$ decays. Consistency with the observed branching ratios requires the inclusion of the heavy quark component of the electromagnetic current and the introduction of an anomalous magnetic moment for the light quark. It is observed that not only $D,$ but also B meson transitions within a heavy quark spin multiplet are affected by the presence of the heavy quark current.

HEAVY QUARK EFFECTIVE THEORY ON THE LIGHT FRONT

The light front heavy quark effective theory is derived to all orders in 1/mQ. In the limit mQ→∞, the theory exhibits the familiar heavy quark spin-flavor symmetry. This new formalism permits a straightforward canonical quantization to all orders in 1/mQ; moreover, higher order terms have rather simple operator structures. The light front heavy quark effective theory can serve as a useful framework for the study of nonperturbative QCD dynamics of heavy hadron bound states.

Light quark spin-flavor symmetry for baryons containing a heavy quark in large N QCD

The couplings and interactions of baryons containing a heavy quark are related by light quark spin-flavor symmetry in the large N limit. The single pion coupling constant which determines all heavy quark baryon-pion couplings is equal to the pion coupling constant for light quark baryons. Light quark symmetry relations amongst the baryon couplings are violated at order 1 N 2 . Heavy quark spin-flavor symmetry is used in conjunction with large N light quark spin-flavor symmetry to determine the couplings of the degenerate doublets of heavy quark baryons.

Light quark dependence of the Isgur-Wise function

Heavy quark spin flavor symmetry allows the form factors for B→ D and B→D ∗ semileptonic decay to be written in terms of a single universal function, the Isgur-Wise function. In the SU(3) v limit, the Isgur-Wise function is independent of light quark flavor. Leading SU(3) v violating corrections to the ratio of Isgur-Wise functions for B S versus B decay are computed in chiral perturbation theory. The correction is velocity dependent, but vanishes at zero recoil as required by heavy quark symmetry.