Measurement of light-by-light scattering and the Breit-Wheeler process, and search for axion-like particles in ultraperipheral PbPb collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5.02 TeV

Abstract

Measurements of light-by-light scattering (LbL, $\gamma \gamma$ $\to$ $\gamma \gamma$) and the Breit-Wheeler process (BW, $\gamma \gamma$ $\to$ ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$) are reported in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV. The data sample, corresponding to an integrated luminosity of 1.7 nb${}^{-1}$, was collected by the CMS experiment at the CERN LHC in 2018. Events with an exclusively produced $\gamma \gamma$ or ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$ pair with invariant masses $m^{\gamma \gamma ,\mathrm{ee}}$ $>$ 5 GeV, along with other fiducial criteria, are selected. The measured BW fiducial production cross section, ${\sigma }_{\text{fid}}$($\gamma \gamma$ $\to$ ${\mathrm{e}}^{+}{\mathrm{e}}^{-}$) = 263.5 $\pm$ 1.8 (stat) $\pm$ 17.8 (syst) $\mu$b, as well as the differential distributions for various kinematic observables, are in agreement with leading-order quantum electrodynamics predictions complemented with final-state photon radiation. The measured differential BW cross sections allow discriminating between different theoretical descriptions of the photon flux of the lead ion. In the LbL final state, 26 exclusive diphoton candidate events are observed compared with 12.0 $\pm$ 2.9 expected for the background. Combined with previous results, the observed significance of the LbL signal with respect to the background-only hypothesis is above five standard deviations. The measured fiducial LbL scattering cross section, ${\sigma }_{\text{fid}}(\gamma \gamma$ $\to$ $\gamma \gamma )$ = 107 $\pm$ 24 (stat) $\pm$ 13 (syst) nb, is in agreement with next-to-leading-order predictions. Limits on the production of axion-like particles coupled to photons are set over the mass range 5-100 GeV, including the most stringent limits to date in the range of 5-10 GeV.

Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-21-015 (CMS Public Pages)

References in corpus (14)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• An Introduction to PYTHIA 8.2
• Description and performance of track and primary-vertex reconstruction with the CMS tracker
• The Physics of Ultraperipheral Collisions at the LHC
• Revised constraints and Belle II sensitivity for visible and invisible axion-like particles
• The CMS statistical analysis and combination tool: COMBINE
• gamma-UPC: Automated generation of exclusive photon-photon processes in ultraperipheral proton and nuclear collisions with varying form factors
• Overview of high-density QCD studies with the CMS experiment at the LHC
• Large Extra Dimension effects through Light-by-Light Scattering at the CERN LHC
• Status of Zero Degree Calorimeter for CMS Experiment
• Light-by-Light Scattering at Next-to-Leading Order in QCD and QED
• Two-loop massive QCD and QED helicity amplitudes for light-by-light scattering
• Dimuon and ditau production in photon-photon collisions at next-to-leading order in QED
• High-energy photon collisions at the LHC - dream or reality?

Cited by in corpus (1)

• Exclusive photon-fusion production of even-spin resonances and exotic QED atoms in high-energy hadron collisions