The role of secondary Reggeons in central meson production

We estimate the contribution of f2 trajectory exchange to the central η and η ′ production. It is shown that secondary Reggeons may give a large contribution to processes of double diffractive meson production at high energy. The Regge theory provides a natural and an economical description of hadron-hadron interactions at high energy and small momentum transfer [1]. In this approach the interaction between colliding particles is described by exchange of effective particles, i.e. Reggeons. At high energy, the pomeron with vacuum quantum numbers gives the dominant contribution to the hadron-hadron total cross sections. The Reggeons with different quantum numbers from vacuum ones can also contribute to the total cross sections and their contribution is vanishing at very high energy. An interest in double diffractive processes (DDP) is mediated by the idea that they can be a clean source of glueballs [2],[3]. Intensive studies of these processes were performed by WA102 collaboration at CERN recently. The mechanism of the central meson production in DDP at high energy is usually related to double pomeron exchange (DPE) [3],[4],[5]. This conclusion is based on the following observations: i) if the two pomeron fusion dominantly contributes to the central meson production, then one can explain rather weak energy dependence of the total production cross sections. ii) tand azimuthal dependencies of differential cross sections for the most mesons are consistent with two vector fusion mechanism and with additional assumption that the pomeron transforms as a vector current. iii) the quantum numbers of these effective vector exchanges, e.g. flavor, P and C parities, are the same as the pomeron quantum numbers. These arguments, however, fail if one looks into the details of the experimental data. For example, even in the simplest case of light pseudoscalar meson production, we find: i) the observed cross section of η production is larger than the cross section of η production [6], while the DPE mechanism predicts the opposite situation, i.e. ση << ση′ . This conclusion comes from consideration of the flavor singlet structure of the two pomeron fusion which leads to enhancement of flavor singlet meson production [8]. ii) the cross section of π meson production does not show any angular dependence in the range 0 < φ < 150 and shows a peak (possibly, a contribution from diffractive ∆ and nucleon resonance production [7]) at φ = 180, while the mechanism of two vector fusion predicts sinφ behavior with maximum at 90. Hence, the mechanism of π production is not consistent with two vector fusion at all. The main goal of this letter is to show an importance of secondary Reggeon exchanges in the central meson production. As an example, we will estimate the contribution of f2 exchange with P = C = +1 to the central production of η and η mesons for WA102 kinematics. Let us consider a two Reggeon fusion contribution to central η, η productions, as presented in Fig. (1), where the pomeron and f2 Reggeon are taken into consideration. The cross section of the meson production in the reaction p(p1) + p(p2) → p(p′1) + p(p′2) +M(pM ) (1) is given by the formula dσ = dPS 4 √