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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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Winney, D., Pilloni, A., Mathieu, V., Hiller Blin, A. N., Albaladejo, M., Smith, W. A., et al. (2022). XYZ spectroscopy at electron-hadron facilities. II. Semi-inclusive processes with pion exchange. Phys. Rev. D, 106(9), 094009–13pp.
Abstract: Semi-inclusive processes arc very promising to investigate XYZ hadrons at the next generation of electron-hadron facilities, because they generally boast higher cross sections. We extend our formalism of exclusive photoproduction to semi-inclusive final states. The inclusive production cross sections for charged axial-vector Z states from pion exchange are predicted. We isolate the contribution of Delta resonances at small missing mass. Production near threshold is shown to be enhanced roughly by a factor of two compared to the exclusive reaction. We benchmark the model with data of semi-inclusive b(1)(+/-) production.
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Hiller Blin, A. N., Ledwig, T., & Vicente Vacas, M. J. (2015). Chiral dynamics in the (gamma)over-right-arrowp -> p pi(0) reaction. Phys. Lett. B, 747, 217–222.
Abstract: We investigate the neutral pion photoproduction on the proton near threshold in covariant chiral perturbation theory with the explicit inclusion of A degrees of freedom. This channel is specially sensitive to chiral dynamics and the advent of very precise data from the Mainz microtron has shown the limits of the convergence of the chiral series for both the heavy baryon and the covariant approaches. We show that the inclusion of the Delta resonance substantially improves the convergence leading to a good agreement with data for a wider range of energies.
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Nys, J., Mathieu, V., Fernandez-Ramirez, C., Hiller Blin, A. N., Jackura, A., Mikhasenko, M., et al. (2017). Finite-energy sum rules in eta photoproduction off a nucleon. Phys. Rev. D, 95(3), 034014–20pp.
Abstract: The reaction gamma N -> eta N is studied in the high-energy regime (with photon lab energies E gamma(lab) > 4 GeV) using information from the resonance region through the use of finite-energy sum rules. We illustrate how analyticity allows one to map the t dependence of the unknown Regge residue functions. We provide predictions for the energy dependence of the beam asymmetry at high energies.
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Hiller Blin, A. N., Gutsche, T., Ledwig, T., & Lyubovitskij, V. E. (2015). Hyperon forward spin polarizability gamma(0) in baryon chiral perturbation theory. Phys. Rev. D, 92(9), 096004–9pp.
Abstract: We present the calculation of the hyperon forward spin polarizability gamma(0) using manifestly Lorentz-covariant baryon chiral perturbation theory including the intermediate contribution of the spin-3/2 states. As at the considered order the extraction of. 0 is a pure prediction of chiral perturbation theory, the obtained values are a good test for this theory. After including explicitly the decuplet states, our SU(2) results have a very good agreement with the experimental data and we extend our framework to SU(3) to give predictions for the hyperons'. 0 values. Prominent are the Sigma(-) and Xi(-) baryons as their photon transition to the decuplet is forbidden in SU(3) symmetry and therefore they are not sensitive to the explicit inclusion of the decuplet in the theory.
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Hiller Blin, A. N. (2017). Systematic study of octet-baryon electromagnetic form factors in covariant chiral perturbation theory. Phys. Rev. D, 96(9), 093008–19pp.
Abstract: We perform a complete and systematic calculation of the octet-baryon form factors within the fully covariant approach of SU(3) chiral perturbation theory at O(p(3)). We use the extended on-mass shell renormalization scheme and include explicitly the vector mesons and the spin-3/2 decuplet intermediate states. Comparing these predictions with data including magnetic moments, charges, and magnetic radii, we determine the unknown low-energy constants and give predictions for yet unmeasured observables, such as the magnetic moment of the Sigma(0) and the charge and magnetic radii of the hyperons.
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Hiller Blin, A. N., Ledwig, T., & Vicente Vacas, M. J. (2016). Delta(1232) resonance in the (gamma)over-right-arrowp -> p pi(0) reaction at threshold. Phys. Rev. D, 93(9), 094018–19pp.
Abstract: We calculate the neutral pion photoproduction on the proton near threshold in covariant baryon chiral perturbation theory, including the Delta(1232) resonance as an explicit degree of freedom, up to chiral order p(7/2) in the delta counting. We compare our results with recent low-energy data from the Mainz Microtron for angular distributions and photon asymmetries. The convergence of the chiral series of the covariant approach is found to improve substantially with the inclusion of the Delta(1232) resonance.
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Hiller Blin, A. N., Fernandez-Ramirez, C., Jackura, A., Mathieu, V., Mokeev, V. I., Pilloni, A., et al. (2016). Studying the P-c(4450) resonance in J/psi photoproduction off protons. Phys. Rev. D, 94(3), 034002–8pp.
Abstract: A resonancelike structure, the P-c(4450), has recently been observed in the J/psi p spectrum by the LHCb Collaboration. We discuss the feasibility of detecting this structure in J/psi photoproduction in the CLAS12 experiment at JLab. We present a first estimate of the upper limit for the branching ratio of the P-c (4450) to J/psi p. Our estimates, which take into account the experimental resolution effects, predict that it will be possible to observe a sizable cross section close to the J/psi production threshold and shed light on the P-c(4450) resonance in the future photoproduction measurements.
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Gutsche, T., Hiller Blin, A. N., Kovalenko, S., Kuleshov, S., Lyubovitskij, V. E., & Vicente Vacas, M. J. (2017). CP-violating decays of the pseudoscalars eta and eta' and their connection to the electric dipole moment of the neutron. Phys. Rev. D, 95(3), 036022–9pp.
Abstract: Using the present upper bound on the neutron electric dipole moment, we give an estimate for the upper limit of the CP-violating couplings of the eta(eta') to the nucleon. Using this result, we then derive constraints on the CP-violating eta(eta')pi pi couplings, which define the two-pion CP-violating decays of the eta and eta' mesons. Our results are relevant for the running and planned measurements of rare decays of the. eta and eta' mesons by the GlueX Collaboration at JLab and the LHCb Collaboration at CERN.
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Guerrero Navarro, G. H., Vicente Vacas, M. J., Hiller Blin, A. N., & Yao, D. L. (2019). Pion photoproduction off nucleons in covariant chiral perturbation theory. Phys. Rev. D, 100(9), 094021–18pp.
Abstract: Pion photoproduction off the nucleon close to threshold is studied in covariant baryon chiral perturbation theory at O(p(3)) in the extended-on-mass-shell scheme, with the explicit inclusion of the Delta(1232) resonance using the delta counting. The theory is compared to the available data of cross sections and polarization observables for all the charge channels. Most of the necessary low-energy constants arc well known from the analysis of other processes and the comparison with data constrains some of the still unknown ones. The Delta(1232) contribution is significant in improving the agreement with data, even at the low energies considered.
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