Abstract
The diffractive electro- or photo-production of two mesons separated by a large rapidity gap gives access to generalized parton distributions (GPDs) in a very specific way. First, these reactions allow to easily access the chiral-odd transversity quark GPDs by selecting one of the produced vector meson to be transversely polarized. Second, they are only sensitive to the so-called ERBL region where GPDs are not much constrained by forward quark distributions. Third, the skewness parameter $\xi$ is not related to the Bjorken $x_\text{Bj}$ variable, but to the size of the rapidity gap. We analyze different channels ($\rho_L^0\,\rho_{L/T}, \rho^0_L\,\omega_{L/T}$ and $\rho^0_L\,\pi$ production) on nucleon and deuteron targets. The analysis is performed in the kinematical domain where a large momentum transfer from the photon to the diffractively produced vector meson introduces a hard scale (the virtuality of the exchanged hard Pomeron). This enables the description of the hadronic part of the process in the framework of collinear factorization of GPDs. We show that the unpolarized cross sections depend very much on the parameterizations of both chiral-even and chiral-odd quark distributions of the nucleon, as well as on the shape of the meson distribution amplitudes. The rates are shown to be in the range of the capacities of a future electron-ion collider.
Highlights
Diffractive events are known to constitute a large part of the cross section in high-energy scattering
We show that the unpolarized cross sections depend very much on the parametrizations of both chiral-even and chiral-odd quark distributions of the nucleon, as well as on the shape of the meson distribution amplitudes
Provided on the one hand that a hard scale allows the use of perturbative quantum chromodynamics (QCD), and on the other hand that the kinematical regimes are in the so-called generalized Bjorken region [1], the impact factors can be calculated in the collinear factorization framework, with a perturbatively calculable coefficient function convoluted with
Summary
Diffractive events are known to constitute a large part of the cross section in high-energy scattering. Distribution amplitudes (DAs) and generalized parton distributions (GPDs) encoding their long distance parts This hybrid factorization picture has been shown to be valid, at least to the leading order, in the pioneering study [2] where the exclusive process, e þ N → e0 þ ρ0L þ ρþ þ N0; ð1Þ has been studied in the kinematical regime where the two ρ mesons are separated by a large rapidity gap and the hard scale is the virtuality of the hard Pomeron; see Fig. 1. Let us summarize the characteristic features of these reactions in the chosen kinematical domain and in the leading order approximation used to calculate their amplitudes [2,3]: (1) The cross sections are independent of the γðÃÞN or γðÃÞD squared invariant mass s, and their rates are quite large in the high energy domain. Ð12Þ which shows that at large energy, our process probes large values of ξ, for instance, ξ ≈ 0.5 (0.33) when s1 1⁄4 2s=3 (s1 1⁄4 s=2)
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