Diffractive two-meson electroproduction with a nucleon and deuteron target

Abstract

The diffractive electro-or photoproduction 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 us to easily access the chiral-odd transversity quark GPDs by selecting one of the produced vector mesons to be transversely polarized. Second, they are only sensitive to the so-called Efremov-Radyushkin-Brodsky-Lepage region where GPDs are not much constrained by forward quark distributions. Third, the skewness parameter ξ is not related to the Bjorken x Bj variable, but to the size of the rapidity gap. We analyze different channels (ρ 0 L ρ L=T , ρ 0 L ω L=T and ρ 0 L π 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 parametrizations 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.

Diffractive rho + lepton pair production at an electron-ion collider

“…In terms of non-perturbative inputs, the calculations show much greater sensitivity to the nucleon GPD input than to the ρ meson DA one. This GPD model sensitivity is due to the quite unique fact (see however [24][25][26] for a similar dependence) that the amplitude only depends on their behaviour in the ERBL region, which is quite unrestricted by current data analysis of the DVCS process. The cross section is dominated by the imaginary part of the Compton form factors and is maximized at small values of the hard scales Q 2 , Q 2 where higher order corrections to the formalism would be needed.…”

“…The fact that the cross section is rather small must be blamed on the presence of two hard scales (Q 2 and Q 2 ) which each play a crucial role in keeping a part of the process to be controlled by small-size hadronic configurations. This is to be contrasted with the diffractive process [24,26] eN → e ρπN with a large transverse momentum ρ meson, where this large transverse momentum was the single large scale controlling the perturbative treatment of both impact factors. The size of the diffractive ρ + lepton pair production cross section is more reminiscent of the deep electroproduction of a large invariant mass dilepton [27,28] or diphoton [29].…”

Accessing quark GPDs in diffractive events at an electron-ion collider

“…This process is sensitive to the chiral-odd nucleon GPDs. We compare different GPD and DA models, see [1] for details.…”

“…This process is sensitive to the chiral-even deuteron GPDs (ω L production, upper row) and chiral-odd deuteron GPDs (ω T production, lower row). We compare different GPD and DA models (see [1] for details).…”

Transversity GPDs of the proton from lattice QCD

“…Because they are chiral odd, they cannot be measured in DVCS, making them largely unexplored. However, they can be measured using DVMP, either through photon production of vector mesons [8], or from the diffractive production of two vector mesons [9,10]. Notably, chiral-odd GPDs are the leadingtwist contributions in γρ photoproduction [8,11] and simulations are presently being performed [12] in the kinematic range of the future Electron Ion Collider (EIC) to be build at Brookhaven National Laboratory in the U.S.…”