Influence of aZ+(1540)resonance onK+Nscattering

Abstract

The impact of a (I = 0, J P = 1 2 + ) Z + (1540) resonance with a width of 5MeV or more on the K + N (I=0) elastic cross section and on the P 01 phase shift is examined within the KN meson-exchange model of the Jülich group. It is shown that the rather strong enhancement of the cross section caused by the presence of a Z + with the above properties is not compatible with the existing empirical information on KN scattering. Only a much narrower Z + state could be reconciled with the existing data -or, alternatively, the Z + state must lie at an energy much closer to the KN threshold.PACS NUMBERS: 13.75. Jz, 12.39.Pn, 14.20.Jn,12.40.-y KEYWORDS: Pentaquark, Strangeness, Meson-exchange Models 1 Recently the LEPS collaboration at Spring-8 presented evidence for the existence of a narrow baryon resonance with strangeness S = +1 [1]. In the following four other collaborations from different laboratories announced the observation of a similar structure in their experiments [2][3][4][5]. The observed structure was immediately brought into connection with an exotic pentaquark state called Z + whose existence had been proposed since long time in the context of different quark models 1 . Specifically, the resonance parameters with a peak position around 1540 MeV and a width around 20 MeV, extracted from these experiments, lie convincingly close to a theoretical prediction based on the chiral quark-soliton model of Diakonov et al. [6], who had proposed the existence of a Z + state with a mass around 1530 MeV and a width of around 15 MeV. Due to its quantum numbers, S = +1, I = 0, and J P = In the present note we use the Jülich meson-exchange model for the KN interaction to investigate the effect of including in the model a Z + -like resonance structure on the description of the experimental data. Within a realistic potential model the open parameters are fixed by a simultaneous fit to all KN partial waves and therefore the contributions to the P 01 channel (we use the standard spectral notation L I 2J ), which provide the background for the Z + (1540) resonance, are strongly constrained by the empirical information in the other partial waves and that means also from the other isospin channel. Furthermore, the use of a model allows one to produce a resonance structure from a bare pole interaction by dressing the bare baryon-meson vertex, with a width generated from self-energy loops, i.e. the non-pole and the pole part of the reaction amplitude can be treated consistently.A detailed description of the Jülich KN model can be found in Refs. [10,11]. The model was constructed along the lines of the (full) Bonn NN model [12] and its extension to the hyperon-nucleon (Y N) system [13]. Specifically, this means that one has used the same scheme (time-ordered perturbation theory), the same type of processes, and vertex parameters (coupling constants, cut-off masses of the vertex form-factors) fixed already by the study of these other reactions.1 We follow the historical nomenclature adopted in the particle data tables. More ...

Charmed meson rescattering in the reaction $$ \bar pd \uparrow \bar DDN $$

“…The main ingredients of the interaction are provided by vector meson (ρ, ω) exchange and higher-order box diagrams involvingD * N ,D∆, andD * ∆ intermediate states. The short range part is supplemented by additional contributions from genuine quark-gluon processes [47,48]. The reaction amplitude is obtained by solving a Lippmann-Schwinger type scattering equation for the interaction potential.…”

Analysis of Θproduction in K+- Xe collisions

“…The main ingredient of our calculation is an elementary KN scattering amplitude that is taken from the meson-exchange model developed by the Jülich group [3,4]. The role and significance of the Θ + (1540) for a quantitative description of the DIANA data is investigated by employing variants of the Jülich KN model where a Θ + resonance with different widths was included consistently [5,6]. Since the parity of the Θ + resonance is not yet known we consider here the cases of positive as well as negative parity.…”

Erratum: Study of the exoticΘ+with polarized photon beams [Phys. Rev. D69, 053009 (2004)]

“…Nevertheless, even smaller widths for the Θ + are claimed in the reports of Refs. [15,16,17,18]. Carlson et al [19] have shown the anti-decuplet10 with J P =…”