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Aceti, F., Oset, E., & Roca, L. (2014). Composite nature of the Lambda (1520) resonance. Phys. Rev. C, 90(2), 025208–8pp.
Abstract: Recently, the Weinberg compositeness condition of a bound state was generalized to account for resonant states and higher partial waves. We apply this extension to the case of the Lambda (1520) resonance and quantify the weight of the meson-baryon components in contrast to other possible genuine building blocks. This resonance was theoretically obtained from a coupled channels analysis using the s-wave pi Sigma* and K Xi* and the d-wave (K) over bar N and pi Sigma channels, applying the techniques of the chiral unitary approach. We obtain the result that this resonance is essentially dynamically generated from these meson-baryon channels, leaving room for only 15% weight of other kinds of components in its wave function.
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Garzon, E. J., & Oset, E. (2015). Mixing of pseudoscalar-baryon and vector-baryon in the J(P)=1/2(-) sector and the N* (1535) and N* (1650) resonances. Phys. Rev. C, 91(2), 025201–7pp.
Abstract: We study the meson-baryon interaction with J(P) = 1/2 using the hidden-gauge Lagrangians and mixing pseudoscalar meson-baryon with the vector meson-baryon states in a coupled channels scheme with pi N, eta N, K Lambda, K Sigma, rho N, and pi Delta (d wave). We fit the subtraction constants of each channel to the S-11 partial wave amplitude of the pi N scattering data extracted from the partial wave analysis of the George Washington group. We find two poles that we associate to the N*(1535) and the N*(1650) resonances, with negative subtraction constants of natural size, and compare the results with empirical determinations of these pole positions. We calculate the branching ratios for the different channels of each resonance and we find a good agreement with the experimental data. The cross section for the pi(-)p -> eta n scattering is also evaluated and compared with experiment.
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Ren, X. L., Oset, E., Alvarez-Ruso, L., & Vicente Vacas, M. J. (2015). Antineutrino induced Lambda(1405) production off the proton. Phys. Rev. C, 91(4), 045201–11pp.
Abstract: We have studied the strangeness-changing antineutrino-induced reactions (v) over bar (l)p -> l(+)phi B, with phi B = K(-)p, (K) over bar (0)n, pi(0)Lambda, pi(0)Sigma(0), eta Lambda, eta Sigma(0), pi(+)Sigma(-), pi(-)Sigma(+), K+Xi(-), and K-0 Xi(0), using a chiral unitary approach. These ten coupled channels are allowed to interact strongly, using a kernel derived from the chiral Lagrangians. This interaction generates two Lambda(1405) poles, leading to a clear single peak in the pi Sigma invariant mass distributions. At backward scattering angles in the center-of-mass frame, (nu) over bar (mu)p -> mu(+)pi(0)Sigma(0) is dominated by the Lambda(1405) state at around 1420 MeV while the lighter state becomes relevant as the angle decreases, leading to an asymmetric line shape. In addition, there are substantial differences in the shape of pi Sigma invariant mass distributions for the three charge channels. If observed, these differences would provide valuable information on a claimed isospin I = 1, strangeness S = -1 baryonic state around 1400 MeV. Integrated cross sections have been obtained for the pi Sigma and (K) over barN channels and the impact of unitarization in the results has been investigated. The number of events with Lambda(1405) excitation in (nu) over bar μp collisions in the recent antineutrino run at the Main Injector Experiment for nu-A (MINER nu A) has also been obtained. We find that this reaction channel is relevant enough to be investigated experimentally and to be taken into account in the simulation models of future experiments with antineutrino beams.
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Miyahara, K., Hyodo, T., & Oset, E. (2015). Weak decay of Lambda(+)(c) for the study of Lambda(1405) and Lambda(1670). Phys. Rev. C, 92(5), 055204–8pp.
Abstract: We study the Lambda(c) decay process to pi(+) and the meson-baryon final state for the analysis of Lambda resonances. Considering the Cabibbo-Kobayashi-Maskawamatrix, color suppression, diquark correlation, and the kinematical condition, we show that the final meson-baryon state should be in a pure I = 0 combination, when the meson-baryon invariantmass is small. Because the I = 1 contamination usually makes it difficult to analyze Lambda resonances directly from experiments, the Lambda(c) decay is an ideal process to study Lambda resonances. Calculating the final-state interaction by chiral unitary approaches, we find that the pi Sigma invariant mass distributions have the same peak structure in the all charge combination of the pi Sigma states related to the higher pole of the two poles of the Lambda(1405). Furthermore, we obtain a clear Lambda(1670) peak structure in the (K) over bar N and eta Lambda spectra.
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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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Xie, J. J., Liang, W. H., & Oset, E. (2016). (K)over-bar-induced formation of the f(0)(980) and a(0)(980) resonances on proton targets. Phys. Rev. C, 93(3), 035206–8pp.
Abstract: We perform a calculation of the cross section for nine reactions induced by (K) over bar scattering on protons. The reactions studied are K- p -> Lambda pi(+)pi(-), K- p -> Sigma(0)pi(+)pi(-), K- p -> Lambda pi(0)eta, K- p -> Sigma(0)pi(0)eta, K- p -> Sigma(+)pi(-)eta, (K) over bar (0) p -> Lambda pi(+)eta, (K) over bar (0) p -> Sigma(0)pi(+)eta, (K) over bar (0) p -> Sigma(+)pi(+)pi(-), and (K) over bar (0) p -> Sigma+pi(0)eta. We find that in the reactions producing pi(+)pi(-), a clear peak for the f(0)(980) resonance is found, while no trace of f(0)(500) appears. Similarly, in the cases of p. production, a strong peak is found for the a(0)(980) resonance, with the characteristic strong cusp shape. Cross sections and invariant mass distributions are evaluated which should serve, by comparing them with future data, to test the dynamics of the chiral unitary approach used for the evaluations and the nature of these resonances.
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Chen, H. X., Geng, L. S., Liang, W. H., Oset, E., Wang, E., & Xie, J. J. (2016). Looking for a hidden-charm pentaquark state with strangeness S =-1 from Xi(-)(b) decay into J/Psi K- Lambda. Phys. Rev. C, 93(6), 065203–9pp.
Abstract: Assuming that the recently observed hidden-charm pentaquark state, P-c(4450), is of molecular nature as predicted in the unitary approach, we propose to study the decay of Xi(-)(b) -> J/psi K-Lambda to search for the strangeness counterpart of the P-c(4450). There are three ingredients in the decay mechanism: the weak decay mechanism, the hadronization mechanism, and the final state interactions in the meson-baryon system of strangeness S = -2 and isospin I = 1/2 and of the J/psi Lambda. All these have been tested extensively. As a result, we provide a genuine prediction of the invariant mass distributions where a strangeness hidden-charm pentaquark state, the counterpart of the P-c(4450), can be clearly seen. The decay rate is estimated to be of similarmagnitude as the Lambda(0)(b) -> J/psi K(-)p measured by the LHCb Collaboration.
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Wang, E., Xie, J. J., Liang, W. H., Guo, F. K., & Oset, E. (2017). Role of a triangle singularity in the gamma p -> K+Lambda (1405) reaction. Phys. Rev. C, 95(1), 015205–9pp.
Abstract: We show the effects of a triangle singularity mechanism for the gamma p -> K+Lambda(1405) reaction. The mechanism has a N-* resonance around 2030 MeV, which decays into K*Sigma. The K-* decays to K+ pi, and the pi Sigma merge to form the Lambda (1405). This mechanism produces a peak around root s = 2110 MeV, and has its largest contribution around cos theta= 0. The addition of this mechanism to other conventional ones leads to a good reproduction of d sigma/dcos theta and the integrated cross section around this energy, providing a solution to a problem encountered in previous theoretical models.
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Xie, J. J., Liang, W. H., Oset, E., Moskal, P., Skurzok, M., & Wilkin, C. (2017). Determination of the eta He-3 threshold structure from the low energy pd -> eta He-3 reaction. Phys. Rev. C, 95(1), 015202–9pp.
Abstract: We analyze the data on cross sections and asymmetries for the pd -> eta He-3 reaction close to threshold and look for bound states of the eta He-3 system. Rather than parameterizing the scattering matrix, as is usually done, we develop a framework in which the eta He-3 optical potential is the key ingredient, and its strength, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the eta He-3 loop function incorporates the range of the interaction given by the empirical He-3 density. We find a local Breit-Wigner form of the eta He-3 amplitude T below threshold with a clear peak in vertical bar T vertical bar(2), which corresponds to an eta He-3 binding of about 0.3 MeV and a width of about 3 MeV. By fitting the potential we can also evaluate the eta He-3 scattering length, including its sign, thus resolving the ambiguity in the former analyses.
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Miyahara, K., Hyodo, T., Oka, M., Nieves, J., & Oset, E. (2017). Theoretical study of the Xi(1620) and Xi(1690) resonances in Xi(c)-> pi(+) MB decays. Phys. Rev. C, 95(3), 035212–12pp.
Abstract: Nonleptonic weak decays of Xi(c) into pi(+) and a meson (M)-baryon (B) final state, MB, are analyzed from the viewpoint of probing S = -2 baryon resonances, i.e., Xi(1620) and Xi(1690), of which spin-parity and other properties are not well known. We argue that the weak decay of Xi(c) is dominated by a single quark-line diagram, preferred by the Cabibbo-Kobayashi-Maskawa coefficient, color recombination factor, the diquark correlation, and the kinematical condition. The decay process has an advantage of being free from meson resonances in the p+ M invariantmass distribution. The invariant mass distribution of the meson-baryon final state is calculated with three different chiral unitary approaches, assuming that the Xi(1620) and Xi(1690) resonances have J(P) = 1/2(-). It is found that a clear peak for the Xi(1690) is seen in the pi Xi and K Lambda spectra. We also suggest that the ratios of the pi Xi, K Lambda, and K Sigma final states are useful to distinguish whether the peak is originated from the Xi(1690) resonance or it is a K Sigma threshold effect.
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