Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root s(NN)=5.02 TeV

Sirunyan, A. M. and Tumasyan, A. R. and Adam, Wolfgang and Ambrogi, Federico and Asilar, Ece and Md. Ali, Mohd. Adli (2019) Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root s(NN)=5.02 TeV. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 797. pp. 1-27. ISSN 0370-2693

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Abstract

Evidence for the light-by-light scattering process, γγ → γγ , in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02 TeV is reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390 μb−1 recorded by the CMS experiment at the LHC. Light-by-light scattering processes are selected in events with two photons exclusively produced, each with transverse energy Eγ T > 2 GeV, pseudorapidity |ηγ | < 2.4, diphoton invariant mass mγγ > 5 GeV, diphoton transverse momentum pγγ T < 1 GeV, and diphoton acoplanarity below 0.01. After all selection criteria are applied, 14 events are observed, compared to expectations of 9.0 ± 0.9 (theo) events for the signal and 4.0 ± 1.2 (stat) for the background processes. The excess observed in data relative to the background-only expectation corresponds to a significance of 3.7 standard deviations, and has properties consistent with those expected for the light-by-light scattering signal. The measured fiducial light-by-light scattering cross section, σfid(γγ → γγ ) = 120±46 (stat)±28 (syst)±12 (theo) nb, is consistent with the standard model prediction. The mγγ distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the γγ → a → γγ process, in the mass range ma = 5–90 GeV.

Item Type:	Article (Journal)
Additional Information:	7861/79918
Uncontrolled Keywords:	Light-by-light; CMS; UPC; Photoproduction; PbPb
Subjects:	Q Science > Q Science (General) Q Science > QC Physics
Kulliyyahs/Centres/Divisions/Institutes (Can select more than one option. Press CONTROL button):	Kulliyyah of Science Kulliyyah of Science > Department of Physics
Depositing User:	Dr Mohd Adli MD Ali
Date Deposited:	02 Jul 2020 08:38
Last Modified:	02 Jul 2020 08:38
URI:	http://irep.iium.edu.my/id/eprint/79918

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