On a possible manifestation of f1 trajectory in J/ψ photoproduction

Abstract

We analyze a possible manifestation of f 1 -trajectory in elastic J/ψ photoproduction at high energy and large momentum transfer. Inspite of the small contribution of f 1 -trajectory in total cross sections, it becomes significant in various spin observables. In particular, we show that the crucial test for f 1 -exchange can be made by measuring the single beam-and double parity-and beam-target asymmetries at large momentum transfers, where a strong deviation from the exchange of conventional Pomerons is expected. This effect is caused by the interference of natural (Pomeron) and unnatural (f 1 ) parity exchange parts of amplitude in the region where their contributions become comparable to each other and might be interesting to observe in forthcoming experiments, if feasible.PACS numbers: 13.85.Dz 12.40. Nn, 13.85.Lg Typeset using REVT E X * Email address: roy@radix.h.kobe-u.ac.jp † Email address: morii@kobe-u.ac.jp ‡ Email address: atitov@thsun1.jinr.ruHadronic diffraction has regained popularity in the recent years due to many new interesting experiments at HERA and TEVATRON. One of them is the vector meson photoproduction at HERA. This channel is exciting because here one can study any of the known vector mesons from the lightest ρ to heavier J/ψ and Υ and hope to see the transition from the "soft" to the "hard" regime. The most popular models for description of the diffractive processes at high energy are based on the Regge theory [1] where the corresponding multiparticle exchanges with definite quantum numbers are expressed by the effective exchange of one Regge pole whose propagator is given by (s/s 0 ) α(t) . The Regge trajectory α(t) has a simple linear form α(t) = α(0) + α ′ t and the main contribution to the elastic forward photoproduction of light vector mesons comes from the Pomeron (so-called "soft" Pomeron) trajectory with intercept 1.08 and slope of 0.25 GeV −2 [2]. This leads to rather weak energy dependence of the cross section gradually becoming almost constant at very high energies. However, the Pomeron, though amply used to successfully analyze the high energy total hadron cross sections, still remains mysterious in its partonic content, hence its manifestation in QCD also remains unknown.Recent studies of elastic vector meson photoproduction data shows that the J/ψ crosssection shows a steep rise with the energy W [3]. This behavior is quite different from that of other light vector mesons like ρ, ω and φ which are characterized by a weak dependence of their cross section on energy [σ ∝ W 0.22 ], while for J/ψ it is parameterized as W 0.8 . This new phenomenon drew a lot of attention in this field leading to several models being proposed to explain the data [4][5][6][7]. However, this subject still remains controversial. Donnachie and Landshoff [4] claimed that perturbative QCD does not work in this energy region and suggested the use of a small admixture of the second "hard" Reggeon exchange whose trajectory is given by α h (t) = 1.418 + 0.1 t. The conventional mesonic trajector...