Yao, D. L., Alvarez-Ruso, L., & Vicente Vacas, M. J. (2017). Extraction of nucleon axial charge and radius from lattice QCD results using baryon chiral perturbation theory. Phys. Rev. D, 96(11), 116022–11pp.
Abstract: We calculate the nucleon axial form factor up to the leading one-loop order in a covariant chiral effective field theory with the Delta(1232) resonance as an explicit degree of freedom. We fit the axial form factor to the latest lattice QCD data and pin down the relevant low-energy constants. The lattice QCD data, for various pion masses below 400 MeV, can be well described up to a momentum transfer of similar to 0.6 GeV. The Delta(1232) loops contribute significantly to this agreement. Furthermore, we extract the axial charge and radius based on the fitted values of the low-energy constants. The results are g(A) = 1.237(74) and < r(A)(2)> = 0.263(38) fm(2). The obtained coupling g(A) is consistent with the experimental value if the uncertainty is taken into account. The axial radius is below but in agreement with the recent extraction from neutrino quasielastic scattering data on deuterium, which has large error bars. Up to our current working accuracy, r(A) is predicted only at leading order, i.e., the one-loop level. A more precise determination might need terms of O(p(5)).
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Yao, D. L. (2018). Masses and sigma terms of doubly charmed baryons up to O(p(4)) in manifestly Lorentz-invariant baryon chiral perturbation theory. Phys. Rev. D, 97(3), 034012–12pp.
Abstract: We calculate the masses and sigma terms of the doubly charmed baryons up to next-to-next-to-next-toleading order [i.e., O(p(4))] in a covariant baryon chiral perturbation theory by using the extended-on-mass-shell renormalization scheme. Their expressions both in infinite and finite volumes are provided for chiral extrapolation in lattice QCD. As a first application, our chiral results of the masses are confronted with the existing lattice QCD data in the presence of finite-volume corrections. Up to O(p(3)), all relevant low-energy constants can be well determined. As a consequence, we obtain the physical values for the masses of Xi(cc) and Omega(cc) baryons by extrapolating to the physical limit. Our determination of the Xi(cc) mass is consistent with the recent experimental value by LHCb Collaboration, however, larger than the one by SELEX Collaboration. In addition, we predict the pion-baryon and strangeness-baryon sigma terms, as well as the mass splitting between the Xi(cc) and Omega(cc) states. Their quark mass dependences are also discussed. The numerical procedure can be applied to the chiral results of O(p(4)) order, where more unknown constants are involved, when more data are available for unphysical pion masses.
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Dai, L. Y., Kang, X. W., Meissner, U. G., Song, X. Y., & Yao, D. L. (2018). Amplitude analysis of the anomalous decay eta ' -> pi(+) pi(-) gamma. Phys. Rev. D, 97(3), 036012–12pp.
Abstract: In this paper we perform an amplitude analysis of eta ' -> pi(+)pi(-)gamma and confront it with the latest BESIII data. Based on the final-state interaction theorem, we represent the amplitude in terms of an Omnes function multiplied by a form factor that corresponds to the contributions from left-hand cuts and right-hand cuts in the inelastic channels. We also take into account the isospin violation effect induced by rho-omega mixing. Our results show that the anomaly contribution is mandatory in order to explain the data. Its contribution to the decay width of Gamma(eta ' -> pi pi gamma) is larger than that induced by isospin violation. Finally we extract the pole positions of the rho and omega as well as their corresponding residues.
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Yao, D. L., Alvarez-Ruso, L., Hiller Blin, A. N., & Vicente Vacas, M. J. (2018). Weak pion production off the nucleon in covariant chiral perturbation theory. Phys. Rev. D, 98(7), 076004–25pp.
Abstract: Weak pion production off the nucleon at low energies has been systematically investigated in manifestly relativistic baryon chiral perturbation theory with explicit inclusion of the Delta(1232) resonance. Most of the involved low-energy constants have been previously determined in other processes such as pion-nucleon elastic scattering and electromagnetic pion production off the nucleon. For numerical estimates, the few remaining constants are set to be of natural size. As a result, the total cross sections for single pion production on neutrons and protons, induced either by neutrino or antineutrino, are predicted. Our results are consistent with the scarce existing experimental data except in the nu(mu)n -> mu(-)n pi(+) channel, where higher-order contributions might still be significant. The Delta resonance mechanisms lead to sizeable contributions in all channels, especially in nu(mu)p -> mu(-) p pi(+), even though the considered energies are close to the production threshold. The present study provides a well-founded low-energy benchmark for phenomenological models aimed at the description of weak pion production processes in the broad kinematic range of interest for current and future neutrino-oscillation experiments.
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Du, M. L., Albaladejo, M., Fernandez-Soler, P., Guo, F. K., Hanhart, C., Meissner, U. G., et al. (2018). Towards a new paradigm for heavy-light meson spectroscopy. Phys. Rev. D, 98(9), 094018–8pp.
Abstract: Since 2003 many new hadrons, including the lowest-lying positive-parity charm-strange mesons D*(s0) (2317) and D-s1 (2460), have been observed that do not conform with quark-model expectations. It was recently demonstrated that various puzzles in the charm-meson spectrum find a natural resolution if the SU(3) multiplets for the lightest scalar and axial-vector states, among them the D*(s0) (2317) and the D-s1 (2460), owe their existence to the nonperturbative dynamics of Goldstone-boson scattering off D-(s) and D*((s)) mesons. Most importantly the ordering of the lightest strange and nonstrange scalars becomes natural. We demonstrate for the first time that this mechanism is strongly supported by the recent high quality data on the B- -> D+ pi(-)pi(-) provided by the LHCb experiment. This implies that the lowest quark-model positive-parity charm mesons, together with their bottom counterparts, if realized in nature, do not form the ground-state multiplet. This is similar to the pattern that has been established for the scalar mesons made from light up, down, and strange quarks, where the lowest multiplet is considered to be made of states not described by the quark model. In a broader view, the hadron spectrum must be viewed as more than a collection of quark-model states.
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