Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at √ s NN = 5.02 TeV
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1-s2.0-S0370269319305404-main.pdf
Description
Published version
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1.31 MB
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Adobe PDF
Checksum (MD5)
780296228c7b4a2cbf8d4239960bd8c8
Author(s)
CMS Collaboration
Date Issued
August 2019
Journal
Physics Letters B
Publisher
Elsevier BV
Citation
CMS Collaboration (Sirunyan, A.M. et al). "Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at √ s NN = 5.02 TeV." Physics Letters B 797 (October 2019): 134826 © 2019 The Author(s)
Version
Final published version
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 5.02TeV is reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390μb−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 ETγ>2GeV, pseudorapidity |ηγ|<2.4, diphoton invariant mass mγγ>5GeV, diphoton transverse momentum pTγγ<1GeV, 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 (Figure presented.) process, in the mass range (Figure presented.).
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Department of Nuclear Science and Engineering
Massachusetts Institute of Technology. Laboratory for Nuclear Science
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Creative Commons Attribution 4.0 International license
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DOI of Published Version
https://doi.org/10.1016/J.PHYSLETB.2019.134826
