Albaladejo, M., & Nieves, J. (2022). Compositeness of S-wave weakly-bound states from next-to-leading order Weinberg's relations. Eur. Phys. J. C, 82(8), 724–12pp.
Abstract: We discuss a model-independent estimator of the likelihood of the compositeness of a shallow S-wave bound or virtual state. The approach is based on an extension of Weinberg's relations in Weinberg (Phys Rev 137:B672, 1965) and it relies only on the proximity of the energy of the state to the two-hadron threshold to which it significantly couples. The scheme only makes use of the experimental scattering length and the effective range low energy parameters, and it is shown to be fully consistent for predominantly molecular hadrons. As explicit applications, we analyse the case of the deuteron, the S-1(0) nucleon virtual state and the exotic D-so(*)(2317)(+/-) , and find strong support to the molecular interpretation in all cases. Results are less conclusive for the D* (s0)(2317)+/-, since the binding energy of this state would be significantly higher than that of the deuteron, and the approach employed here is at the limit of its applicability. We also qualitatively address the case of the recently discovered T + cc state, within the isospin limit to avoid the complexity of the very close thresholds (DD)-D-0*+ and D + D*(0), which could mask the ingredients of the approach proposed in this work.
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Abreu, L. M., Albaladejo, M., Feijoo, A., Oset, E., & Nieves, J. (2023). Shedding light on the X(3930) and X(3960) states with the B-> K- J/psi omega reaction. Eur. Phys. J. C, 83(4), 309–11pp.
Abstract: We have studied the contribution of the state X(3930), coming from the interaction of the D ($) over bar and D-s(+) D ($) over bar (s) channels, to the B- -> K- J/psi omega decay. The purpose of this work is to offer a complementary tool to see if the X(3930) state observed in the D+ D- channel is the same or not as the X(3960) resonance claimed by the LHCb Collaboration from a peak in the D-s(+) D s mass distribution around threshold. We present results for what we expect in the J/psi omega mass distribution in the B- -> K- J/psi omega decay and conclude that a clear signal should be seen around 3930 MeV. At the same time, finding no extra resonance signal at 3960 MeV would be a clear indication that there is not a new state at 3960 MeV, supporting the hypothesis that the near-threshold peaking structure peak in the D-s(+) D-s(-) mass distribution is only a manifestation of a resonance below threshold.
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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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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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Nieves, J., & Sobczyk, J. E. (2017). In medium dispersion relation effects in nuclear inclusive reactions at intermediate and low energies. Ann. Phys., 383, 455–496.
Abstract: In a well-established many-body framework, successful in modeling a great variety of nuclear processes, we analyze the role of the spectral functions (SFs) accounting for the modifications of the dispersion relation of nucleons embedded in a nuclear medium. We concentrate in processes mostly governed by one-body mechanisms, and study possible approximations to evaluate the particle hole propagator using SFs. We also investigate how to include together SFs and long-range RPA-correlation corrections in the evaluation of nuclear response functions, discussing the existing interplay between both type of nuclear effects. At low energy transfers (<= 50 MeV), we compare our predictions for inclusive muon and radiative pion captures in nuclei, and charge-current (CC) neutrino-nucleus cross sections with experimental results. We also present an analysis of intermediate energy quasi-elastic neutrino scattering for various targets and both neutrino and antineutrino CC driven processes. In all cases, we pay special attention to estimate the uncertainties affecting the theoretical predictions. In particular, we show that errors on the a,,sigma(mu)/sigma(e) ratio are much smaller than 5%, and also much smaller than the size of the SF+RPA nuclear corrections, which produce significant effects, not only in the individual cross sections, but also in their ratio for neutrino energies below 400 MeV. These latter nuclear corrections, beyond Pauli blocking, turn out to be thus essential to achieve a correct theoretical understanding of this ratio of cross sections of interest for appearance neutrino oscillation experiments. We also briefly compare our SF and RPA results to predictions obtained within other representative approaches.
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