Erratum: Hard photoproduction of a diphoton with a large invariant mass [Phys. Rev. D 96 , 074008 (2017)]

Abstract

We correct the expression for the γN → γγN 0 amplitude in the generalized Bjorken regime, where the diphoton is nearly forward and its invariant mass is the hard scale enabling to factorize the scattering amplitude in terms of generalized parton distributions. This amplitude has a very peculiar and interesting analytic structure, while the cross section estimates are only slightly changed.

Exclusive production of a large mass photon pair

“…In the quasi-real photoproduction limit, we recover the results of our previous work [3] : the C-odd (valence) GPDs are accessed in a peculiar way, since the QCD amplitude is proportional to these GPDs taken at their border values x = ±ξ. By scrutinizing the Q 2 dependence of the single Bethe-Heitler and the QCD amplitudes, we can quantify what we mean by "quasi-real", which turns out to depend very much on the overall energy domain.…”

“…In a previous work [3,4], we studied the exclusive photoproduction of two photons on an unpolarized proton or neutron target γ(q, ) + N (P 1 , s 1 ) → γ(k 1 , 1 ) + γ(k 2 , 2 ) + N (P 2 , s 2 ) ,…”

Deeply virtual meson production on neutrons

“…In what follows we will consider only the case of unpolarized beams (r L = 0) and targets, since the corresponding asymmetries might be observed only if the target is polarized, and in the case of neutrons inside a nucleus this presents a difficult technical problem [58][59][60][61] and requires modeling of nuclear interactions [62]. In this limit, the cross-sections dσ L T (7) and dσ T T (8) vanish.…”

“…Today, this structure is parametrized in terms of the so-called generalized parton distributions (GPDs) which can be studied in Bjorken kinematics in a wide class of processes [1,2]. While the number of processes which can be used for studies of GPDs is rather large [3][4][5][6][7][8][9][10][11], the precision analyses are currently performed with deeply virtual Compton scattering (DVCS) [12][13][14][15][16][17][18][19] and deeply virtual production of light mesons (DVMP) , with most of the existing studies focusing on proton (liquid hydrogen) targets or production off protons inside nuclei. There are fewer studies of exclusive processes on neutrons [44][45][46][47][48], which might be partially due to the technical difficulties with accessing them experimentally, or perhaps the belief that they probe "the same" GPDs as in case of protons.…”

Diffractive two-meson electroproduction with a nucleon and deuteron target

“…This property is also present in the diffractive DVCS reaction [21]. 3 This property is also present in the diphoton electroproduction case [22,23]. the various nonperturbative inputs needed to perform the cross section estimates, namely the distribution amplitudes (DAs) of the produced mesons and the generalized parton distributions (GPDs) of the nucleon and deuteron, the latter calculated in a convolution model.…”