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Penalva, N., Flynn, J. M., Hernandez, E., & Nieves, J. (2024). Study of new physics effects in (B)over-bars → Ds(*) τ-(ν)over-bar τ semileptonic decays using lattice QCD form factors and heavy quark effective theory. J. High Energy Phys., 01(1), 163–33pp.
Abstract: We benefit from the lattice QCD determination by the HPQCD of the Standard Model (SM) form factors for the (B) over bar (s) -> D-s [Phys. Rev. D101(2020) 074513] and the SM and tensor ones for the (B) over bar (s) -> D-s* (arXiv:2304.03137[hep-lat]) semileptonic decays, and the heavy quark effective theory (HQET) relations for the analogous B -> D-(*()) decays obtained by F.U. Bernlochner et al. in Phys. Rev. D95(2017) 115008, to extract the leading and sub-leading Isgur-Wise functions for the (B) over bar (s) -> D-s(()*()) decays. Further use of the HQET relations allows us to evaluate the corresponding scalar, pseudoscalar and tensor form factors needed for a phenomenological study of new physics (NP) effects on the (B) over bar (s) -> D-s(()*()) semileptonic decay. At present, the experimental values for the ratios R-D(*) = Gamma[ (B) over bar -> D-(*())(tau- (nu) over bar tau)]/Gamma[(B) over bar -> D-(*())e(-)(mu(-)) (nu) over bar (e(mu))]are the best signal in favor of lepton flavor universality violation (LFUV) seen in charged current (CC) b -> c decays. In this work we conduct a study of NP effects on the (B) over bar (s) -> D-s(()*()) tau(-)(tau) semileptonic decays by comparing tau spin, angular and spin-angular asymmetry distributions obtained within the SM and three different NP scenarios. As expected from SU(3) light-flavor symmetry, we get results close to the ones found in a similar analysis of the (B) over bar -> D-(*()) case. The measurement of the (B) over bar (s) -> D-s(()*())(l (nu) over bar tau) semileptonic decays, which is within reach of present experiments, could then be of relevance in helping to establish or rule out LFUV in CC b -> c transitions.
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Bourguille, B., Nieves, J., & Sanchez, F. (2021). Inclusive and exclusive neutrino-nucleus cross sections and the reconstruction of the interaction kinematics. J. High Energy Phys., 04(4), 004–42pp.
Abstract: We present a full kinematic analysis of neutrino-nucleus charged current quasielastic interactions based on the Local Fermi Gas model and the Random Phase Approximation. The model was implemented in the NEUT Monte Carlo framework, which allows us to investigate potentially measurable observables, including hadron distributions. We compare the predictions simultaneously to the most recent T2K and MINERvA charged current (CC) inclusive, CC0 pi and transverse kinematic-imbalance variable results. We pursuit a microscopic interpretation of the relevant reaction mechanisms, with the aim to achieving in neutrino oscillation experiments a correct reconstruction of the incoming neutrino kinematics, free of conceptual biasses. Such study is of the utmost importance for the ambitious experimental program which is underway to precisely determine neutrino properties, test the three-generation paradigm, establish the order of mass eigenstates and investigate leptonic CP violation.
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Penalva, N., Hernandez, E., & Nieves, J. (2022). Visible energy and angular distributions of the charged particle from the tau-decay in b -> C tau (mu(nu)over-bar(mu)nu(tau), pi nu(tau), rho nu(tau))(nu)over-bar(tau) reactions. J. High Energy Phys., 04(4), 026–25pp.
Abstract: We study the d(2)Gamma(d)/(d omega d cos theta(d) ), d Gamma(d)/d cos theta(d) and d Gamma(d)/dE(d) distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the tau-decay in b -> C tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau), reactions. These differential decay widths could be measured in the near future with certain precision. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the H-b -> H-c tau(nu) over bar (tau) parent decay and, from a dynamical point of view, they are richer than the commonly used one, d(2)Gamma(d)/(d omega dE(d)), since the latter only depends on the tau longitudinal polarization. We pay attention to the deviations with respect to the predictions of the standard model (SM) for these new observables, considering new physics (NP) operators constructed using both right- and left-handed neutrino fields, within an effective field-theory approach. We present results for Lambda(b) -> Lambda(c)tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau) and (B) over bar -> D-(*()) tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau) sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that d Gamma(d)/d cos theta(d) , which should be measured with sufficiently good statistics, becomes quite useful, especially in the tau -> pi nu(tau) mode. The study carried out in this work could be of special relevance due to the recent LHCb measurement of the lepton flavor universality ratio R Lambda(c) in agreement with the SM. The experiment identified the tau using its hadron decay into pi(-)pi(+)pi(-)nu(tau), and this result for R Lambda(c )which is in conflict with the phenomenology from the b-meson sector, needs confirmation from other tau reconstruction channels.
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Penalva, N., Hernandez, E., & Nieves, J. (2021). New physics and the tau polarization vector in b -> c tau barnutau decays. J. High Energy Phys., 06(6), 118–37pp.
Abstract: For a general H-b -> Hc tau nu <overbar></mml:mover>tau decay we analyze the role of the tau polarization vector P μin the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes, in addition to the Standard Model (SM) contribution, vector, axial, scalar, pseudoscalar and tensor new physics (NP) terms which strength is governed by, complex in general, Wilson coefficients. We show that both in the laboratory frame, where the initial hadron is at rest, and in the center of mass of the two final leptons, a P -></mml:mover> component perpendicular to the plane defined by the three-momenta of the final hadron and the tau lepton is only possible for complex Wilson coefficients, being a clear signal for physics beyond the SM as well as time reversal (or CP-symmetry) violation. We make specific evaluations of the different polarization vector components for the Lambda (b) -> Lambda (c), <mml:mover accent=“true”>B<mml:mo stretchy=“true”><overbar></mml:mover>c -> eta (c), J/psi and <mml:mover accent=“true”>B<mml:mo stretchy=“true”><overbar></mml:mover> -> D-(*) semileptonic decays, and describe NP effects in the complete two-dimensional space associated with the independent kinematic variables on which the polarization vector depends. We find that the detailed study of P μhas great potential to discriminate between different NP scenarios for 0(-) -> 0(-) decays, but also for Lambda (b) -> Lambda (c) transitions. For this latter reaction, we pay special attention to corrections to the SM predictions derived from complex Wilson coefficients contributions.
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Penalva, N., Hernandez, E., & Nieves, J. (2021). The role of right-handed neutrinos in b -> c tau (pi nu(tau), rho nu(tau), mu(nu)over-bar(mu)nu(tau))(nu)over-bar(tau) from visible final-state kinematics. J. High Energy Phys., 10(10), 122–45pp.
Abstract: In the context of lepton flavor universality violation (LFUV) studies, we fully derive a general tensor formalism to investigate the role that left- and right-handed neutrino new-physics (NP) terms may have in b -> c tau(nu) over bar (tau) transitions. We present, for several extensions of the Standard Model (SM), numerical results for the Lambda(b) -> Lambda(c)tau(nu) over bar (tau) semileptonic decay, which is expected to be measured with precision at the LHCb. This reaction can be a new source of experimental information that can help to confirm, or maybe rule out, LFUV presently seen in (B) over bar meson decays. The present study analyzes observables that can help in distinguishing between different NP scenarios that otherwise provide very similar results for the branching ratios, which are our currently best hints for LFUV. Since the tau lepton is very short-lived, we consider three subsequent tau-decay modes, two hadronic pi nu(tau) and rho nu(tau) and one leptonic mu(nu) over bar (mu)nu(tau), which have been previously studied for (B) over bar -> D(*) decays. Within the tensor formalism that we have developed in previous works, we re-obtain the expressions for the differential decay width written in terms of visible (experimentally accessible) variables of the massive particle created in the tau decay. There are seven different tau angular and spin asymmetries that are defined in this way and that can be extracted from experiment. Those asymmetries provide observables that can help in constraining possible SM extensions.
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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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Oset, E. et al, Albaladejo, M., Nieves, J., Fernandez-Soler, P., & Sun, Z. F. (2016). Weak decays of heavy hadrons into dynamically generated resonances. Int. J. Mod. Phys. E, 25(1), 1630001–105pp.
Abstract: In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.
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Albaladejo, M., Guo, F. K., Hanhart, C., Meissner, U. G., Nieves, J., Nogga, A., et al. (2017). Note on X(3872) production at hadron colliders and its molecular structure. Chin. Phys. C, 41(12), 121001–3pp.
Abstract: The production of the X (3872) as a hadronic molecule in hadron colliders is clarified. We show that the conclusion of Bignamini et al., Phys. Rev. Lett. 103 (2009) 162001, that the production of the X(3872) at high pT implies a non-molecular structure, does not hold. In particular, using the well understood properties of the deuteron wave function as an example, we identify the relevant scales in the production process.
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Guo, F. K., Meissner, U. G., Nieves, J., & Yang, Z. (2016). Remarks on the P-c structures and triangle singularities. Eur. Phys. J. A, 52(10), 318–6pp.
Abstract: It was proposed that the narrow P-c(4450) structure observed by the LHCb Collaboration in the reaction Lambda(b) -> J/psi pK might be due to a triangle singularity around the chi(c1)-proton threshold at 4.45 GeV. We discuss the occurrence of a similar triangle singularity in the J/psi p invariant mass distribution for the decay Lambda(b) -> J/psi p pi, which could explain the bump around 4.45 GeV in the data. More precise measurements of this process would provide valuable information towards an understanding of the P-c structures.
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Albertus, C., Hernandez, E., & Nieves, J. (2014). Exclusive c -> s, d Semileptonic Decays of Spin-1/2 and Spin-3/2 cb Baryons. Few-Body Syst., 55(8-10), 767–771.
Abstract: We present results for exclusive semileptonic decay widths of ground state spin-1/2 and spin-3/2 cb baryons corresponding to a c -> s, d transition at the quark level. The relevance of hyperfine mixing in spin-1/2 cb baryons is shown. Our form factors are compatible with heavy quark spin symmetry constraints obtained in the infinite heavy quark mass limit.
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