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Sobczyk, J. E., Nieves, J., & Sanchez, F. (2020). Exclusive-final-state hadron observables from neutrino-nucleus multinucleon knockout. Phys. Rev. C, 102(2), 024601–16pp.
Abstract: We present results of an updated calculation of the two particle two hole (2p2h) contribution to the neutrino-induced charge-current cross section. We provide also some exclusive observables, interesting from the point of view of experimental studies, e.g., distributions of momenta of the outgoing nucleons and of available energy, which we compare with the results obtained within the NEUT generator. We also compute, and separate from the total, the contributions of 3p3h mechanisms. Finally, we discuss the differences between the present results and previous implementations of the model in MC event generators, done at the level of inclusive cross sections, which might significantly influence the experimental analyses, particularly in the cases where the hadronic observables are considered.
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Sobczyk, J. E., Rocco, N., Lovato, A., & Nieves, J. (2018). Scaling within the spectral function approach. Phys. Rev. C, 97(3), 035506–15pp.
Abstract: Scaling features of the nuclear electromagnetic response functions unveil aspects of nuclear dynamics that are crucial for interpreting neutrino-and electron-scattering data. In the large momentum-transfer regime, the nucleon-density response function defines a universal scaling function, which is independent of the nature of the probe. In this work, we analyze the nucleon-density response function of C-12, neglecting collective excitations. We employ particle and hole spectral functions obtained within two distinct many-body methods, both widely used to describe electroweak reactions in nuclei. We show that the two approaches provide compatible nucleon-density scaling functions that for large momentum transfers satisfy first-kind scaling. Both methods yield scaling functions characterized by an asymmetric shape, although less pronounced than that of experimental scaling functions. This asymmetry, only mildly affected by final state interactions, is mostly due to nucleon-nucleon correlations, encoded in the continuum component of the hole spectral function.
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Sobczyk, J. E., Rocco, N., Lovato, A., & Nieves, J. (2019). Weak production of strange and charmed ground-state baryons in nuclei. Phys. Rev. C, 99(6), 065503–16pp.
Abstract: We present results for the quasielastic weak production of Delta and Sigma hyperons induced by (nu) over bar. scattering off nuclei in the kinematical region of interest for accelerator neutrino experiments. We employ realistic hole spectral functions and we describe the propagation of the hyperons in the nuclear medium by means of a Monte Carlo cascade. The latter strongly modifies the kinematics and the relative production rates of the hyperons, leading to a nonvanishing Sigma(+) cross section, to a sizable enhancement of the Lambda production and to a drastic reduction of the Sigma(0) and Sigma(-) distributions. We also compute the quasielastic weak Lambda(c) production cross section, paying special attention to estimate the uncertainties induced by the model dependence of the vacuum n -> Lambda(c) weak matrix element. In this regard, the recent BESIII measurements of the branching ratios of Lambda(c) -> Lambda l(+)nu(l) (l = e, mu) are used to benchmark the available theoretical predictions.
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Sobczyk, J. E., Rocco, N., & Nieves, J. (2019). Polarization of tau in quasielastic (anti)neutrino scattering: The role of spectral functions. Phys. Rev. C, 100(3), 035501–14pp.
Abstract: We present a study of the tau polarization in charged-current quasielastic (anti)neutrino-nucleus scattering. The spectral function formalism is used to compute the differential cross section and the polarization components for several kinematical setups, relevant for neutrino-oscillation experiments. The effects of the nuclear corrections in these observables are investigated by comparing the results obtained using two different realistic spectral functions, with those deduced from the relativistic global Fermi gas model, where only statistical correlations are accounted for. We show that the spectral functions, although they play an important role when predicting the differential cross sections, produce much less visible effects on the polarization components of the outgoing tau.
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Tolos, L., Cabrera, D., Garcia-Recio, C., Molina, R., Nieves, J., Oset, E., et al. (2013). Strangeness and charm in nuclear matter. Nucl. Phys. A, 914, 461–471.
Abstract: The properties of strange (K, (K) over bar and (K) over bar*) and open-charm (D, (D) over bar and D*) mesons in dense matter are studied using a unitary approach in coupled channels for meson-baryon scattering. In the strangeness sector, the interaction with nucleons always comes through vector-meson exchange, which is evaluated by chiral and hidden gauge Lagrangians. For the interaction of charmed mesons with nucleons we extend the SU(3) Weinberg-Tomozawa Lagrangian to incorporate spin-flavor symmetry and implement a suitable flavor symmetry breaking. The in-medium solution for the scattering amplitude accounts for Pauli blocking effects and meson self-energies. On one hand, we obtain the K, (K) over bar and (K) over bar* spectral functions in the nuclear medium and study their behaviour at finite density, temperature and momentum. We also make an estimate of the transparency ratio of the gamma A -> K+ K*(-) A' reaction, which we propose as a tool to detect in-medium modifications of the (K) over bar* meson. On the other hand, in the charm sector, several resonances with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with 1/2(+) and 3/2(+) baryons. The properties of these states in matter are analyzed and their influence on the open-charm meson spectral functions is studied. We finally discuss the possible formation of D-mesic nuclei at FAIR energies.
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Vidaña, I., Feijoo, A., Albaladejo, M., Nieves, J., & Oset, E. (2023). Femtoscopic correlation function for the Tcc(3875)+ state. Phys. Lett. B, 846, 138201–9pp.
Abstract: We have conducted a study of the femtoscopic correlation functions for the D0D*+ and D+D*0 channels that build the Tcc state. We develop a formalism that allows us to factorize the scattering amplitudes outside the integrals in the formulas, and the integrals involve the range of the strong interaction explicitly. For a source of size of 1 fm, we find values for the correlation functions of the D0D*+ and D+D*0 channels at the origin around 30 and 2.5, respectively, and we see these observables converging to unity already for relative momenta of the order of 200 MeV. We conduct tests to see the relevance of the different contributions to the correlation function and find that it mostly provides information on the scattering length, but should the correlation functions be measured with the precision of the latest experiments, the effective range of the D0D*+ could also be obtained.
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Wang, E., Alvarez-Ruso, L., Hayato, Y., Mahn, K., & Nieves, J. (2015). Photon emission in neutral current interactions at the T2K experiment. Phys. Rev. D, 92(5), 053005–8pp.
Abstract: We have applied a microscopic model for single photon emission in neutral current interactions on nucleons and nuclei to determine the number and distributions of such events at the Super-Kamiokande detector, for the flux and beam exposure of the T2K experiment in neutrino mode. These reactions represent an effectively irreducible background in electron-(anti) neutrino appearance measurements aimed at a precise measurement of mixing angle theta(13) and the CP violating phase. We have obtained a total number of photon events that is twice as large as the one from the NEUT event generator (version 5.1.4.2) used in the analysis of T2K data. Detailed comparisons of energy and angular distributions for the nu μand (nu) over bar μfluxes have also been performed.
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Wang, E., Alvarez-Ruso, L., & Nieves, J. (2014). Photon emission in neutral-current interactions at intermediate energies. Phys. Rev. C, 89(1), 015503–21pp.
Abstract: Neutral-current photon emission reactions with nucleons and nuclei are studied. These processes are important backgrounds for nu(mu) -> nu(e) ((nu) over bar (mu) -> (nu) over bar (e)) appearance oscillation experiments where electromagnetic showers instigated by electrons (positrons) and photons are not distinguishable. At intermediate energies, these reactions are dominated by the weak excitation of the Delta(1232) resonance and its subsequent decay into N gamma. There are also nonresonant contributions that, close to threshold, are fully determined by the effective chiral Lagrangian of strong interactions. In addition, we have also included mechanisms mediated by nucleon excitations (N*) from the second resonance region above the Delta(1232). From these states, the contribution of the D-13 N*(1520) turns out to be sizable for (anti) neutrino energies above 1.5 GeV. We have extended the model to nuclear targets taking into account Pauli blocking, Fermi motion, and the in-medium Delta resonance broadening. We present our predictions for both the incoherent and coherent channels, showing the relevance of the nuclear corrections. We also discuss the target mass dependence of the cross sections. This study is important to reduce systematic effects in neutrino oscillation experiments.
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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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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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