The reaction pp→ppη and the eta–nucleon and nucleon–nucleon interactions

Abstract

The π, η and ρ exchange contributions to the cross-section for the reaction pp → ppη near threshold are calculated, with a phenomenological description of the intermediate S11 (N(1535)) resonance for all exchange mechanisms. The final state interaction in the pp system is described by realistic nucleon-nucleon interaction models. The sensitivity of the results to the phenomenological models for the η-nucleon transition amplitude and the nucleon-nucleon interaction is explored. The η exchange mechanism is found to play a dominant role. The off-shell behavior of the ηN → ηN amplitude within the η−exchange amplitude leads to a result significantly different from that obtained with the constant scattering length approximation. The twonucleon amplitudes that are associated with the short range components of the nucleon-nucleon interaction contribute significantly to the cross section.

η meson production inNNcollisions

“…This is rather different from the findings of Ref. [16]; there, instead of the resonance current, the shorter range part of the nucleonic current gives a large contribution to the pp → ppη cross section. It will be interesting to know whether their model can also give a good description of pn → pnη data, as achieved here(lower panel of Fig.3).…”

“…The MNN * vertex, where the exchanged meson is also off-shell, is multiplied by an extra form factor F M (q 2 ) in order to account for the off-shellness of this meson (see Eqs. (16,20)). The corresponding full form factor is, therefore, given by the product…”

“…In contrast to the findings of Refs. [12][13][14][15], Peña et al [16] have found that the dominant contribution arises, not from the S 11 (1535) resonance current, but from the shorter range part of the nucleonic currents. In this work, we shall report on another possible scenario for exciting the S 11 (1535) resonance that reproduces both the pp → ppη and pn → pnη reactions and discuss the possibility of disentangling these reaction mechanisms.…”

“…The differential cross section data for the pp → ppη reaction [9] are also available. Consequently, there have been a large number of theoretical investigations on these reactions [10][11][12][13][14][15][16].…”

Final state interactions in theηdsystem

“…It is believed to be dominated by an intermediate ρ meson exchange, although other mesons may also contribute [5], [40], [41], [42], [43]. In particular the recent calculation, [44], stresses the role of η meson exchange. All models assume three stages for this process, namely, NN → NN(1535) → NNη, where the intermediate stage is dominated by the N(1535) resonance.…”