How large is the diffractive contribution to inclusive dijet photoproduction in ultraperipheral collisions at the LHC?

Vadim Guzey,Michael Klasen

doi:10.1103/physrevd.104.114013

Abstract

Using next-to-leading order (NLO) perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed $5-10$% in small-$x_A$ bins in the ATLAS kinematics at $\sqrt{s_{NN}}=5.02$ TeV. Its smallness is a result of the restricted kinematics ($p_{T1} > 20$ GeV and $x_A > 0.001$), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in diffraction. At the same time, using looser $p_T$ cuts, e.g., $p_{T1} > 10$ GeV and $p_{T i\neq 1} > 5-7$ GeV, we find that $(d\sigma_{\rm diff}/dx_A)/(d\sigma_{\rm inc}/dx_A)$ can reach $10-20$% at $x \approx 5 \times 10^{-4}$. Also, applying our framework to proton-proton UPCs at $\sqrt{s_{NN}}=13$ TeV, we find that the ratio of the diffractive and inclusive cross sections of dijet photoproduction $(d\sigma_{\rm diff}/dx_p)/(d\sigma_{\rm inc}/dx_p)$ is as large as $10-15$% for $x_p \sim 5 \times 10^{-4}$. An account of the contribution of Pomeron-Pomeron scattering, which is not included in our analysis, should make this ratio somewhat larger.

Highlights

Electroproduction and photoproduction of jets in electron-hadron scattering at high energies at Hadron-Electron Ring Accelerator (HERA) has proven to be a useful tool to study various aspects of the dynamics and structure of hadrons in quantum chromodynamics (QCD); for reviews, see Refs. [1,2,3]
Our study focuses on dijet photoproduction in protonproton and heavy-ion ultraperipheral collisions (UPCs) in the Large-Hadron Collider (LHC) kinematics, which in the latter case had been measured by the ATLAS collaboration [7,8]
Using the framework of next-to-leading order (NLO) perturbative QCD applied to inclusive [9,10] and diffractive [11] dijet photoproduction in UPCs at the LHC, we quantify the diffractive contribution to inclusive dijet photoproduction and find that it does not exceed 5–10% in small-xA bins for the kinematic

Summary

INTRODUCTION

Electroproduction and photoproduction of jets in electron-hadron scattering at high energies at Hadron-Electron Ring Accelerator (HERA) has proven to be a useful tool to study various aspects of the dynamics and structure of hadrons in quantum chromodynamics (QCD); for reviews, see Refs. [1,2,3]. Using the framework of next-to-leading order (NLO) perturbative QCD applied to inclusive [9,10] and diffractive [11] dijet photoproduction in UPCs at the LHC, we quantify the diffractive contribution to inclusive dijet photoproduction and find that it does not exceed 5–10% in small-xA bins for the kinematic. This estimate is relevant for obtaining complementary constraints on nuclear parton distribution functions (nPDFs) [12] using the LHC data on inclusive dijet photoproduction in heavy-ion UPCs in this kinematics and quantifies the correction factor to the inclusive data due to the experimentally excluded diffractive contribution; see the discussion in [5,13]. It can be used to stimulate studies of inclusive and diffractive dijet photoproduction in proton-proton and heavy-ion UPCs at future HL-LHC and HE-LHC [19,20]

CROSS SECTIONS OF INCLUSIVE AND DIFFRACTIVE DIJET PHOTOPRODUCTION IN

PREDICTIONS FOR DIJET PHOTOPRODUCTION IN HEAVY-ION AND

CONCLUSION