Abstract
This paper describes a measurement of light-by-light scattering based on Pb+Pb collision data recorded by the ATLAS experiment during Run 2 of the LHC. The study uses 2.2 nb−1 of integrated luminosity collected in 2015 and 2018 at sqrt{s_{mathrm{NN}}} = 5.02 TeV. Light-by-light scattering candidates are selected in events with two photons produced exclusively, each with transverse energy {E}_{mathrm{T}}^{gamma } > 2.5 GeV, pseudorapidity |ηγ| < 2.37, diphoton invariant mass mγγ> 5 GeV, and with small diphoton transverse momentum and diphoton acoplanarity. The integrated and differential fiducial cross sections are measured and compared with theoretical predictions. The diphoton invariant mass distribution is used to set limits on the production of axion-like particles. This result provides the most stringent limits to date on axion-like particle production for masses in the range 6–100 GeV. Cross sections above 2 to 70 nb are excluded at the 95% CL in that mass interval.
Highlights
Background estimation6.1 Dielectron final states The γγ → e+e− process has a relatively high cross section and can be a source of fake diphoton events
This paper describes a measurement of light-by-light scattering based on
Small systematic differences between the central values of the exclusive dielectron data and the Monte Carlo (MC) prediction are seen in the tail of the dielectron pT distribution, likely due to a missing contribution from the QED final-state radiation which is not simulated by the MC generator
Summary
The ATLAS detector [29] at the LHC covers nearly the entire solid angle around the collision point. It consists of an inner tracking detector surrounded by a thin supercon-. The high-granularity silicon pixel detector (Pixel) covers the collision region It provides four measurements per track, with the first hit being in the insertable Blayer (IBL) [30, 31], which was installed at a mean distance of 3.3 cm from the beam pipe before the start of Run 2. The ATLAS trigger system [33] consists of a Level-1 trigger implemented using a combination of dedicated electronics and programmable logic, and a software-based highlevel trigger (HLT)
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