Backward timelike Compton scattering to decipher the photon content of the nucleon

Bernard Pire; Kirill M. Semenov-Tian-Shansky; Alisa A. Shaikhutdinova; Lech Szymanowski

doi:10.1140/epjc/s10052-022-10587-4

2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2022) 82: 656
https://doi.org/10.1140/epjc/s10052-022-10587-4

Regular Article - Theoretical Physics

Backward timelike Compton scattering to decipher the photon content of the nucleon

Bernard Pire¹, Kirill M. Semenov-Tian-Shansky²^,3^b, Alisa A. Shaikhutdinova²^,3 and Lech Szymanowski⁴

¹ CPHT, CNRS, École Polytechnique, I.P. Paris, 91128, Palaiseau, France
² National Research Centre Kurchatov Institute: Petersburg Nuclear Physics Institute, 188300, Gatchina, Russia
³ Higher School of Economics, National Research University, 194100, St. Petersburg, Russia
⁴ National Centre for Nuclear Research, NCBJ, 02-093, Warsaw, Poland

^b kirill.semenov@thd.pnpi.spb.ru

Received: 18 May 2022
Accepted: 4 July 2022
Published online: 30 July 2022

Abstract

The exclusive photoproduction off nucleon of a large invariant mass lepton pair in the backward region specified by the small Mandelstam variable $- u$ $$-u$$ is discussed in the framework of collinear QCD factorization. The amplitude is factorized in terms of photon-to-nucleon Transition Distribution Amplitudes (TDAs). These new non-perturbative objects, complementary to the “photon-inside-the-nucleon PDF”, lead to a tomographic picture of the nucleon’s photon content after Fourier transforming to the impact parameter space. This allows to address the question of where in the transverse plane the nucleon emits a photon. A simplistic model-estimate of photon-to-nucleon TDAs is used to estimate the magnitude of the corresponding cross sections. The background due to the electromagnetic Bethe–Heitler process is shown to be negligible in the kinematical regime of interest.

© The Author(s) 2022

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