Measurement of Isolated Photon Production in Deep-Inelastic Scattering at HERA

TL;DR

This paper reports the measurement of isolated photon production in deep-inelastic scattering at HERA, comparing experimental results with theoretical predictions and highlighting discrepancies.

Contribution

First measurement of isolated photon production in deep-inelastic scattering at HERA with detailed comparison to theoretical models.

Findings

Measured cross sections for isolated photons in specified kinematic ranges.

Theoretical predictions significantly underestimate the measured cross sections.

Analysis includes events with varying jet multiplicities.

Abstract

The production of isolated photons in deep-inelastic scattering $ep\to e \gamma X$ is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared $4<Q^2<150 $~GeV$^2$ and a mass of the hadronic system $W_X>50$ GeV. The analysis is based on a total integrated luminosity of 227~pb$^{-1}$. The production cross section of isolatedphotons with a transverse energy in the range $3 < E_T^\gamma < 10$ GeV and pseudorapidity range $-1.2 < \eta^\gamma < 1.8$ is measured as a function of $E_T^\gamma$, $\eta^\gamma$ and $Q^2$. Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.