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Tolos, L., Molina, R., Oset, E., & Ramos, A. (2010). (K)over-bar* mesons in dense matter. Phys. Rev. C, 82(4), 045210–12pp.
Abstract: We study the properties of (K) over bar* mesons in nuclear matter using a unitary approach in coupled channels within the framework of the local hidden gauge formalism and incorporating the (K) over bar pi decay channel in matter. The in-medium (K) over bar *N interaction accounts for Pauli blocking effects and incorporates the (K) over bar* self-energy in a self-consistent manner. We also obtain the (K) over bar* (off-shell) spectral function and analyze its behavior at finite density and momentum. At a normal nuclear matter density, the (K) over bar* meson feels a moderately attractive potential, while the (K) over bar* width becomes five times larger than in free space. We estimate the transparency ratio of the gamma A -> K+K*(-) A` reaction, which we propose as a feasible scenario at the present facilities to detect changes in the properties of the (K) over bar* meson in nuclear medium.
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Magas, V. K., Yamagata-Sekihara, J., Hirenzaki, S., Oset, E., & Ramos, A. (2010). Proton emission off nuclei induced by kaons in flight. Phys. Rev. C, 81(2), 024609–10pp.
Abstract: We study the (K-, p) reaction on nuclei with a 1 GeV/c momentum kaon beam, paying special attention to the region of emitted protons having kinetic energy above 600 MeV, which was used to claim a deeply attractive kaon nucleus optical potential. Our model describes the nuclear reaction in the framework of a local density approach and the calculations are performed following two different procedures: one is based on a many-body method using the Lindhard function and the other is based on a Monte Carlo simulation. The simulation method offers flexibility to account for processes other than kaon quasielastic scattering, such as K- absorption by one and two nucleons, producing hyperons, and allows consideration of final-state interactions of the K-, the p, and all other primary and secondary particles on their way out of the nucleus, as well as the weak decay of the produced hyperons into pi N. We find a limited sensitivity of the cross section to the strength of the kaon optical potential. We also show a serious drawback in the experimental setup-the requirement for having, together with the energetic proton, at least one charged particle detected in the decay counter surrounding the target-as we find that the shape of the original cross section is appreciably distorted, to the point of invalidating the claims made in the experimental paper on the strength of the kaon nucleus optical.
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Martinez Torres, A., & Oset, E. (2010). The gamma d -> K(+)K(-)np reaction and an alternative explanation for the “Theta(+)(1540) pentaquark” peak. Phys. Rev. C, 81(5), 055202–16pp.
Abstract: We present a calculation of the gamma d -> K(+)K(-)np reaction with the aim of seeing whether the experimental peak observed in the K(+)n invariant mass around 1526 MeV, from where evidence for the existence of the Theta(+) has been claimed, can be obtained without this resonance as a consequence of the particular dynamics of the process and the cuts applied in the experimental setup. We find that a combination of facts leads indeed to a peak around 1530 MeV for the invariant mass of K(+)n without the need to invoke any new resonance around this energy. This, together with statistical fluctuations that we prove to be large with the statistics of the experiment, is likely to produce the narrower peak observed there.
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Xie, J. J., Martinez Torres, A., & Oset, E. (2011). Faddeev fixed-center approximation to the N K K(bar) system and the signature of a N*(1920)(1/2+) state. Phys. Rev. C, 83(6), 065207–8pp.
Abstract: We perform a calculation for the three-body N (K) over barK scattering amplitude by using the fixed-center approximation to the Faddeev equations, taking the interaction between N and (K) over bar, N and K, and (K) over bar and K from the chiral unitary approach. The resonant structures show up in the modulus squared of the three-body scattering amplitude and suggest that a N (K) over barK hadron state can be formed. Our results are in agreement with others obtained in previous theoretical works, which claim a new N* resonance around 1920 MeV with spin-parity J(P) = 1/2(+). The existence of these previous works allows us to test the accuracy of the fixed center approximation in the present problem and sets the grounds for possible application in similar problems, as an explorative tool to determine bound or quasibound three-hadron systems.
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Bayar, M., Yamagata-Sekihara, J., & Oset, E. (2011). K-bar NN system with chiral dynamics. Phys. Rev. C, 84(1), 015209–9pp.
Abstract: We have performed a calculation of the scattering amplitude for the three-body system (K) over bar NN assuming (K) over bar scattering against a NN cluster using the fixed center approximation to the Faddeev equations. The (K) over bar N amplitudes, which we take from chiral unitary dynamics, govern the reaction and we find a (K) over bar NN amplitude that peaks around 40 MeV below the (K) over bar NN threshold, with a width in |T|(2) of the order of 50 MeV for spin 0 and has another peak around 27 MeV with similar width for spin 1. The results are in line with those obtained using different methods but implementing chiral dynamics. The simplicity of the approach allows one to see the important ingredients responsible for the results. In particular, we show the effects from the reduction of the size of the NN cluster due to the interaction with the (K) over bar and those from the explicit consideration of the pi Sigma N channel in the three-body equations.
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Wu, J. J., Molina, R., Oset, E., & Zou, B. S. (2011). Dynamically generated N* and Lambda* resonances in the hidden charm sector around 4.3 GeV. Phys. Rev. C, 84(1), 015202–15pp.
Abstract: The interactions of (D) over bar Sigma(c)-(D) over bar Lambda(c), (D) over bar*Sigma(c)-(D) over bar*Lambda(c), and related strangeness channels, are studied within the framework of the coupled-channel unitary approach with the local hidden gauge formalism. A series of meson-baryon dynamically generated relatively narrow N* and Lambda* resonances are predicted around 4.3 GeV in the hidden charm sector. We make estimates of production cross sections of these predicted resonances in (p) over barp collisions for the experiment of antiproton annihilation at Darmstadt (PANDA) at the forthcoming GSI Facility for Antiproton and Ion Research (FAIR) facility.
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Xie, J. J., Chen, H. X., & Oset, E. (2011). The pp -> p Lambda K(+) and pp -> p Sigma(0)K(+) reactions with chiral dynamics. Phys. Rev. C, 84(3), 034004–8pp.
Abstract: We report on a theoretical study of the pp -> p Lambda K(+) and pp -> p Sigma(0)K(+) reactions near threshold using a chiral dynamical approach. The production process is described by single-pion and single-kaon exchange. The final state interactions of nucleon-hyperon, K-hyperon, and K-nucleon systems are also taken into account. We show that our model leads to a fair description of the experimental data on the total cross section of the pp -> p Lambda K(+) and pp -> p Sigma(0)K(+) reactions. We find that the experimental observed strong suppression of Sigma(0) production compared to Lambda production at the same excess energy can be explained. However, ignorance of phases between some amplitudes does not allow one to properly account for the nucleon-hyperon final state interaction for the pp -> p Sigma(0)K(+) reaction. We also demonstrate that the invariant mass distribution and the Dalitz plot provide direct information about the Lambda and Sigma(0) production mechanisms and may be tested by experiments at COSY or HIRFL-CSR.
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Molina, R., Xiao, C. W., & Oset, E. (2012). J/psi reaction mechanisms and suppression in the nuclear medium. Phys. Rev. C, 86(1), 014604–9pp.
Abstract: Recent studies of the interaction of vector mesons with nuclei make possible and opportune the study of the interaction of the J/psi with nuclei and the investigation of the origin of the J/psi suppression in its propagation thorough a nuclear medium. We observe that the transition of J/psi N to VN with V being a light vector, rho, omega, phi, together with the inelastic channels, J/psi N -> (D) over bar Lambda(c) and J/psi N -> (D) over bar Sigma(c), leads to a particular shape of the inelastic cross section. Analogously, we consider the mechanisms where the exchanged D collides with a nucleon and gives pi Lambda(c) or pi Sigma(c). The cross section has a peak around root s = 4415 MeV, where the J/psi N couples to a resonance predicted recently. We study the transparency ratio for electron-induced J/psi production in nuclei at about 10 GeV and find that 30-35% of the J/psi produced in heavy nuclei are absorbed inside the nucleus. This ratio is in line with depletions of J/psi through matter observed in other reactions.
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Bayar, M., Xiao, C. W., Hyodo, T., Dote, A., Oka, M., & Oset, E. (2012). Energy and width of a narrow I=1/2 DNN quasibound state. Phys. Rev. C, 86(4), 044004–16pp.
Abstract: The energies and widths of DNN quasibound states with isospin I = 1/2 are evaluated in two methods, the fixed center approximation to the Faddeev equation and the variational method approach to the effective one-channel Hamiltonian. The DN interactions are constructed so they dynamically generate the Lambda(c)(2595) (I = 0, J(pi) = 1/2(-)) resonance state. We find that the system is bound by about 250 MeV from the DNN threshold, root s similar to 3500 MeV. Its width, including both the mesonic decay and the D absorption, is estimated to be about 20-40 MeV. The I = 0 DN pair in the DNN system is found to form a cluster that is similar to the Lambda(c)(2595).
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Martinez Torres, A., Bayar, M., Jido, D., & Oset, E. (2012). Strategy to find the two Lambda (1405) states from lattice QCD simulations. Phys. Rev. C, 86(5), 055201–13pp.
Abstract: Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the Lambda(1405). In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite-volume case, with sufficient precision to distinguish them. We find out that by using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two Lambda(1405) poles.
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