Hard photoproduction of a diphoton with a large invariant mass

Abstract

The electromagnetic probe has proven to be a very efficient way to access the $3-$dimensional structure of the nucleon, particularly thanks to the exclusive Compton processes. We explore the hard photoproduction of a large invariant mass diphoton in the kinematical 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. We calculate unpolarized cross sections and the angular asymmetry triggered by a linearly polarized photon beam.Comment: 8 pages, 9 figures. Version 2, as to be published in Phys Rev D96, contains minor improvements including a brief comparison of different GPD models and a brief discussion of the very high energy behavior of the cross sectio

Probing axial quark generalized parton distributions through exclusive photoproduction of a γπ± pair with a large invariant mass

“…[7,8] at high energy, and a similar strategy has also been advocated in ref. [9][10][11][12]. 2 The absence of any pinch singularity has been proven for cases which involves at least one photon [14].…”

NLO collinear factorization of large mass diphoton photoproduction amplitude

“…After a first rich crop of experimental data [1], it becomes clear [2] that trustable information on the quark and gluon 3−dimensional content of hadrons needs to gather experimental data from a set of reactions not restricted to the simplest ones (spacelike, timelike or double DVCS on the one hand, exclusive meson electroproduction on the other hand). After a Born order study [3,4] which demonstrated its phenomenological interest, we thus studied, at next to leading order (NLO) in the QCD coupling constant α s , the photoproduction of a large mass diphoton on a nucleon target…”

“…We use dimensional regularization as the main tool of our proof. Let us first outline the results of the LO study for photoproduction [3] and electroproduction [4]. Due to charge parity constraint, the contributing GPDs at any order in α s are the chargeodd quark GPDs (which are not accessed by DVCS) and there is no gluon GPD contribution.…”

Exclusive production of a large mass photon pair

“…The exclusive photoproduction of two photons on a unpolarized proton or neutron target γ(q, ε) + N(p 1 , s 1 ) → γ(k 1 , ε 1 ) + γ(k 2 , ε 2 ) + N (p 2 , s 2 ) , (1.1) in the kinematical regime of large invariant diphoton mass M γγ of the final photon pair and small momentum transfer t = (p 2 − p 1 ) 2 between the initial and the final nucleons, has a number of interesting features [1]. First, it is a purely electromagnetic process at Born order -as are deep inelastic scattering (DIS), deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) -and, although there is no deep understanding of this fact, this property is usually accompanied by early scaling.…”