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Alvarez-Ruso, L., Hayato, Y., & Nieves, J. (2014). Progress and open questions in the physics of neutrino cross sections at intermediate energies. New J. Phys., 16, 075015–62pp.
Abstract: New and more precise measurements of neutrino cross sections have renewed interest in a better understanding of electroweak interactions on nucleons and nuclei. This effort is crucial to achieving the precision goals of the neutrino oscillation program, making new discoveries, like the CP violation in the leptonic sector, possible. We review the recent progress in the physics of neutrino cross sections, putting emphasis on the open questions that arise in the comparison with new experimental data. Following an overview of recent neutrino experiments and future plans, we present some details about the theoretical development in the description of (anti) neutrino-induced quasielastic (QE) scattering and the role of multi-nucleon QE-like mechanisms. We cover not only pion production in nucleons and nuclei but also other inelastic channels including strangeness production and photon emission. Coherent reaction channels on nuclear targets are also discussed. Finally, we briefly describe some of the Monte Carlo event generators, which are at the core of all neutrino oscillation and cross-section measurements.
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Albertus, C., Hernandez, E., Hidalgo-Duque, C., & Nieves, J. (2014). (B)over-bar(s) -> K semileptonic decay from an Omnes improved constituent quark model. Phys. Lett. B, 738, 144–149.
Abstract: We study the f(+) form factor for the semileptonic (B) over bar (s) -> K+ l(-) (V) over bar (l) decay in a constituent quark model. The valence quark estimate is supplemented with the contribution from the (B) over bar* pole that dominates the high q(2) region. We use a multiply-subtracted Omnes dispersion relation to extend the quark model predictions from its region of applicability near q(max)(2) = (M-Bs – M-K)(2) similar to 23.75 GeV2 to all q(2) values accessible in the physical decay. To better constrain the dependence of f(+) on q(2), we fit the subtraction constants to a combined input from previous light cone sum rule by Duplancic and Melic (2008) [11] and the present quark model results. From this analysis, we obtain Gamma ( (B) over bar (s) -> K+ l(-) (V) over bar (l)) = (5.47(-0.46)(+0.54)) vertical bar Vub vertical bar(2) x 10(-9) MeV, which is about 10% and 20% higher than the predictions based on Lattice QCD and QCD light cone sum rules respectively. The former predictions, for both the form factor f(+) (q(2)) and the differential decay width, lie within the 1 sigma band of our estimated uncertainties for all q(2) values accessible in the physical decay, except for a quite small region very close to q(max)(2). Differences with the light cone sum results for the form factor f(+) are larger than 20% in the region above q(2) = 15 GeV2.
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Wang, E., Alvarez-Ruso, L., & Nieves, J. (2015). Single photon events from neutral current interactions at MiniBooNE. Phys. Lett. B, 740, 16–22.
Abstract: The MiniBooNE experiment has reported results from the analysis of v(e) and (v) over bar (e) appearance searches, which show an excess of signal-like events at low reconstructed neutrino energies, with respect to the expected background. A significant component of this background comes from photon emission induced by (anti) neutrino neutral current interactions with nucleons and nuclei. With an improved microscopic model for these reactions, we predict the number and distributions of photon events at the MiniBooNE detector. Our results are compared to the MiniBooNE in situ estimate and to other theoretical approaches. We find that, according to our model, neutral current photon emission from single-nucleon currents is insufficient to explain the events excess observed by MiniBooNE in both neutrino and antineutrino modes.
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Ledwig, T., Nieves, J., Pich, A., Ruiz Arriola, E., & Ruiz de Elvira, J. (2014). Large-N-c naturalness in coupled-channel meson-meson scattering. Phys. Rev. D, 90(11), 114020–17pp.
Abstract: The analysis of hadronic interactions with effective field theory techniques is complicated by the appearance of a large number of low-energy constants, which are usually fitted to data. On the other hand, the large-N-c limit helps to impose natural short-distance constraints on these low-energy constants, providing a parameter reduction. A Bayesian interpretation of the expected 1/N-c accuracy allows for an easy and efficient implementation of these constraints, using an augmented chi(2). We apply this approach to the analysis of meson-meson scattering, in conjunction with chiral perturbation theory to one loop and coupled-channel unitarity, and show that it helps to largely reduce the many existing ambiguities and simultaneously provide an acceptable description of the available phase shifts.
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Wang, E., Xie, J. J., & Nieves, J. (2014). Regge signatures from forward CLAS Lambda(1520) photoproduction data. Phys. Rev. C, 90(6), 065203–10pp.
Abstract: The γp→K+Λ(1520) reaction mechanism is investigated within a Regge--effective Lagrangian hybrid approach based on our previous study of this reaction [Physical Review C89, 015203 (2014)]. Near threshold and for large K+ angles, both the CLAS and LEPS data can be successfully described by considering the contributions from the contact, t-channel K¯ exchange, u-channel Λ(1115) hyperon pole, and the s-channel nucleon pole and N∗(2120) resonance contributions. However, for higher energies and forward K+ angles, systematic discrepancies with data appear, which hint the possible existence of sizable quark-gluon string mechanism effects. We show how the inclusion of a K¯ Regge--trajectory exchange in the t-channel leads to an efficient description of the Λ(1520) photoproduction channel over the whole energy and angular ranges accessible in the CLAS experiment.
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