# Measurement of the $t\bar{t}\gamma$ production cross section in proton-proton collisions at $\sqrt{s} = 8$ TeV with the ATLAS detector

## TL;DR

This paper reports a measurement of the top-quark pair production with an associated photon at 8 TeV using ATLAS data, finding results consistent with theoretical predictions and providing differential cross sections.

## Contribution

First measurement of $t\bar{t}\gamma$ production cross section at 8 TeV with detailed differential analysis using ATLAS data.

## Key findings

- Measured cross section: 139 ± 7 (stat) ± 17 (syst) fb.
- Results agree with NLO theoretical prediction of 151 ± 24 fb.
- Provided differential cross sections as functions of photon transverse momentum and pseudorapidity.

## Abstract

The cross section of a top-quark pair produced in association with a photon is measured in proton-proton collisions at a centre-of-mass energy of $\sqrt{s} = 8$ TeV with $20.2$ fb$^{-1}$ of data collected by the ATLAS detector at the Large Hadron Collider in 2012. The measurement is performed by selecting events that contain a photon with transverse momentum $p_\mathrm{T} > 15$ GeV, an isolated lepton with large transverse momentum, large missing transverse momentum, and at least four jets, where at least one is identified as originating from a $b$-quark. The production cross section is measured in a fiducial region close to the selection requirements. It is found to be $139 \pm 7 (\mathrm{stat.}) \pm 17 (\mathrm{syst.})$ fb, in good agreement with the theoretical prediction at next-to-leading order of $151 \pm 24$ fb. In addition, differential cross sections in the fiducial region are measured as a function of the transverse momentum and pseudorapidity of the photon.