Search

The present study reveals interesting constraining effects of isospin filtering reactions on the low energy constants present in meson-baryon chiral effective Lagrangian, particularly, on the next-to-leading order constants. Our model has been developed within the framework of Unitarized Chiral Perturbation Theory and has been fitted to two-body scattering data in the sector of S = −1. In addition, the model was further elaborated by means of the inclusion of high-spin hyperonic resonances.

The hidden charm pentaquark state Pc(4450), observed recently by the LHCb collaboration in the Λb→J/ψK− p decay, may be of molecular nature, as advocated by some unitary approaches that also predict pentaquark partners in the strangeness S=−1 sector. In this work we argue that a hidden-charm strange pentaquark could also be seen in the decay of theΛb, but through the J/ψηΛ decay mode, by studying the invariant mass spectrum of J/ψΛ pairs. In our model we assume a standard weak decay topology, then incorporate the hadronization process and final state interaction effects, and we find that the J/ψηΛ final state is populated with the strength similar to that of the J/ψK− p. We have studied the dependence of our results on reasonable changes in the parameters of the models as well as on the unknown properties of the speculated hidden charm strange pentaquark. We have observed that, while there appear changes in the position of the peak and in the shapes of the distributions, a resonance signal in the J/ψΛ invariant mass spectrum is clearly seen in all the cases. This gives us confidence that such an experimental study could result into a successful proof of the existence of this new state.

This work contains a study of the meson-baryon interaction in the S = −1 sector by means of a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. In order to get more reliable values of the parameters which are present in the model, we performed several fits which take a large set of experimental scattering data in different two-body channels, threshold branching ratios, and the precise SIDDHARTA values of the energy shift and width of kaonic hidrogen into consideration. In previous studies, we had shown that the K− p → KΞ reactions are especially sensitive to the next to Weinberg-Tomozawa (WT) corrections in the hierarchy. In addition, we pointed out the need to employ processes which are described by pure isospin amplitudes as a tool to discern which models are more realistic among those which give small values for the χ2 in the fits. Following the former suggestion, we present results which include data from K− p → ηΛ, ηΣ reactions which have pure isospin I = 0 and I = 1 component respectively. Finally, to check the goodness of the new obtained parametrization of the model, we present a prediction for another process that filters the I = 1 isospin component: the pure I = 1 KL−p→K+Ξ0$K_L^ - p \to {K^ + }{\Xi ^0}$ reaction which could be measured at the proposed secondary K0L beam at Jlab.

We study the meson-baryon interaction in the strangeness S = −1 sector using a chiral unitary approach, paying particular attention to the K̄N → KΞ reaction, especially important for constraining the next-to-leading order chiral terms, and considering also the effect of high spin hyperonic resonances. We also present results for the production of Ξ hyperons in nuclei

Kaon pair production by 2.83 GeV protons has been investigated in two experiments using the ANKE magnetic spectrometer at COSY-Jülich: (1) Differential and total cross sections for the pp → ppK+ K− reaction are separated into kaon pairs arising from the decay of the ϕ-meson and the remainder. The measurements show that higher partial waves represent the majority of the pp → ppϕ cross section at an excess energy of 76 MeV. Taken together with existing low energy ANKE data, the energy dependence of the results seem to suggest some S-wave ϕp enhancement near threshold. The non-ϕ K+K− data can be described in terms of the combined effects of two-body final state interactions, using the same effective scattering parameters already determined from lower energy ANKE data. (2) The inclusive production of ϕ mesons on C, Cu, Ag, and Au targets has also been studied using the K+K− decay to detect the ϕ. The momentum dependence of the nuclear transparency ratio, the in-medium ϕ width, and the differential cross section for ϕ meson production at forward angles have been determined for these nuclei in the momentum range of 0.6 – 1.6 GeV/c. There are indications of a significant momentum dependence in the values extracted for the ϕ width, which on average exceed the free value by about an order of magnitude. The results are compared with data from other experiments at slightly higher momenta.