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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Xie, J. J., Martinez Torres, A., Oset, E., & Gonzalez, P. (2011). Plausible explanation for the Delta(5/2)+(2000) puzzle. Phys. Rev. C, 83(5), 055204–11pp.
Abstract: From a Faddeev calculation for the pi-(Delta rho)(N5/2)-(1675) system we show the plausible existence of three dynamically generated I (J(P)) = 3/2(5/2(+)) baryon states below 2.3 GeV, whereas only two resonances, Delta(5/2)+ (1905)( ) and Delta(5/2)+(2000)(**), are cataloged in the Particle Data Book Review. Our results give theoretical support to data analyses extracting two distinctive resonances, Lambda(5/2)+(similar to 1740) and Lambda(5/2)+(similar to 2200), from which the mass of Delta(5/2)+ (2000) is estimated. We propose that these two resonances should be cataloged instead of Delta(5/2)+(2000). This proposal gets further support from the possible assignment of the other baryon states found in the approach in the I = 1/2, 3/2 with J(P) = 1/2(+), 3/2(+), 5/(2)+ sectors to known baryonic resonances. In particular, Delta(1/2)+(1750)(*) is naturally interpreted as a pi N-1/2-(1650) bound state.
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Alarcon, J. M., Martin Camalich, J., Oller, J. A., & Alvarez-Ruso, L. (2011). pi N scattering in relativistic baryon chiral perturbation theory reexamined. Phys. Rev. C, 83(5), 055205–14pp.
Abstract: We have analyzed pion-nucleon scattering using the manifestly relativistic covariant framework of infrared regularization up to O(q(3)) in the chiral expansion, where q is a generic small momentum. We describe the low-energy phase shifts with a similar quality as previously achieved with heavy baryon chiral perturbation theory, root s less than or similar to 1.14 GeV. New values are provided for the O(q(2)) and O(q(3)) low-energy constants, which are compared with previous determinations. This is also the case for the scattering lengths and volumes. Finally, we have unitarized the previous amplitudes and as a result the energy range where data are reproduced increases significantly.
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Xie, J. J., Oset, E., & Geng, L. S. (2016). Photoproduction of the f(2)'(1525), a(2)(1320), and K-2(*) (1430). Phys. Rev. C, 93(2), 025202–8pp.
Abstract: Assuming that the f(2)'(1525), a(2)(1320), and K-2(*) (1430) resonances are dynamically generated states from vector-meson-vector-meson interactions in the s-wave with spin S = 2, we study the gamma p -> f(2)'(1525)p, gamma p -> a(2)(0)(1320)p, and gamma p -> K-2(*)(1430)Lambda(Sigma) reactions. These reactions proceed in the following way: the incoming photon first mutates into a rho(0), omega, or phi meson via vector-meson dominance, which then interacts with the rho(0), omega, or K* emitted by the incoming proton to form the tensor mesons f(2)(')(1525), a(2)(1320), and K-2(*)(1430). The picture is simple and has no free parameters, as all the parameters of the mechanism have been fixed in previous studies. We predict the differential and total cross sections of these reactions. The results can be tested in future experiments and therefore offer new clues about the nature of these tensor states.
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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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Cabrera, D., Hiller Blin, A. N., Vicente Vacas, M. J., & Fernandez de Cordoba, P. (2017). phi meson transparency in nuclei from phi N resonant interactions. Phys. Rev. C, 96(3), 034618–6pp.
Abstract: We investigate the phi meson nuclear transparency using some recent theoretical developments on the phi in medium self-energy. The inclusion of direct resonant phi N scattering and the kaon decay mechanisms leads to a phi width much larger than in most previous theoretical approaches. The model has been confronted with photoproduction data from CLAS and LEPS and the recent proton induced phi production from COSY finding an overall good agreement. The results support the need of a quite large direct phi N-scattering contribution to the self-energy.
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Cabrera, D., Hiller Blin, A. N., & Vicente Vacas, M. J. (2017). phi meson self-energy in nuclear matter from phi N resonant interactions. Phys. Rev. C, 95(1), 015201–9pp.
Abstract: The phi-meson properties in cold nuclear matter are investigated by implementing resonant phi N interactions as described in effective approaches including the unitarization of scattering amplitudes. Several N*-like states are dynamically generated in these models around 2 GeV, in the vicinity of the phi N threshold. We find that both these states and the non-resonant part of the amplitude contribute sizably to the phi collisional self-energy at finite nuclear density. These contributions are of a similar strength as the widely studied medium effects from the KK cloud. Depending on model details (position of the resonances and strength of the coupling to phi N) we report a phi broadening up to about 40-50 MeV, to be added to the phi -> KK in-medium decay width, and an attractive optical potential at threshold up to about 35 MeV at normal matter density. The phi spectral function develops a double peak structure as a consequence of the mixing of resonance-hole modes with the phi quasiparticle peak. The former results point in the direction of making up for missing absorption as reported in phi nuclear production experiments.
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Pavon Valderrama, M. (2011). Perturbative renormalizability of chiral two-pion exchange in nucleon-nucleon scattering: P and D waves. Phys. Rev. C, 84(6), 064002–23pp.
Abstract: We study the perturbative renormalizability of chiral two-pion exchange in nucleon-nucleon scattering for p and d waves within the effective field theory approach. The one-pion exchange potential is fully iterated at the leading order in the expansion, a choice generating a consistent and well-defined power counting that we explore in detail. The results show that perturbative chiral two-pion exchange reproduces the data up to a center-of-mass momentum of k(cm) similar to 300 MeV at next-to-next-to-leading order and that the effective field theory expansion converges up to k(cm) similar to 350 MeV.
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Pavon Valderrama, M. (2011). Perturbative renormalizability of chiral two-pion exchange in nucleon-nucleon scattering. Phys. Rev. C, 83(2), 024003–11pp.
Abstract: We study the perturbative renormalizability of chiral two-pion exchange for singlet and triplet channels within effective field theory, provided that the one-pion exchange piece of the interaction has been fully iterated. We determine the number of counterterms/subtractions needed to obtain finite results when the cutoff is removed, resulting in three counterterms for the singlet channel and six for the triplet. The results show that perturbative chiral two-pion exchange reproduce the data up to a center-of-mass momentum of k similar to 200-300 MeV in the singlet channel and k similar to 300-400 MeV in the triplet.
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Escrig, S. et al, & Morales, A. I. (2021). Persistence of the Z=28 shell gap in A=75 isobars: Identification of a possible (1/2(-)) μs isomer in Co-75 and beta decay to Ni-75. Phys. Rev. C, 103(6), 064328–12pp.
Abstract: Background: The evolution of shell structure around doubly magic exotic nuclei is of great interest in nuclear physics and astrophysics. In the 'southwest' region of Ni-78, the development of deformation might trigger a major shift in our understanding of explosive nucleosynthesis. To this end, new spectroscopic information on key close-lying nuclei is very valuable. Purpose: We intend to measure the isomeric and beta decay of Co-75, with one-proton and two-neutron holes relative to Ni-78, to access new nuclear structure information in Co-75 and its beta-decay daughters Ni-75 and Ni-74. Methods: The nucleus Co-75 is produced in relativistic in-flight fission reactions of U-238 at the Radioactive Ion Beam Factory in the RIKEN Nishina Center. Its isomeric and f decay are studied exploiting the BigRIPS and EURICA setups. Results: We obtain partial beta-decay spectra for Ni-75 and Ni-74, and report a new isomeric transition in Co-75. The energy [E-gamma = 1914(2) keV] and half-life [t(1/2) = 13(6) μs] of the delayed gamma ray lend support for the existence of aJ(pi) = (1/2(-)) isomeric state at 1914(2) keV. A comparison with PFSDG-U shell-model calculations provides a good account for the observed states in Ni-75, but the first calculated 1/2(-) level in Co-75, a prolate K = 1/2 state, is predicted about 1 MeV below the observed (1/2(-)) level. Conclusions: The spherical-like structure of the lowest-lying excited states in Ni-75 is proved. In the case of Co-75, the results suggest that the dominance of the spherical configurations over the deformed ones might be stronger than expected below Ni-78. Further experimental efforts to discern the nature of the J(pi) = (1/2(-)) isomer are necessary.
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