Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root s(NN)=5.02 TeV
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...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English English English |
| Published: |
Elsevier B.V.
2019
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| Subjects: | |
| Online Access: | http://irep.iium.edu.my/79918/ http://irep.iium.edu.my/79918/1/79918_Evidence%20for%20light-by-light%20scattering%20and%20searches_article.pdf http://irep.iium.edu.my/79918/2/79918_Evidence%20for%20light-by-light%20scattering%20and%20searches_scopus.pdf http://irep.iium.edu.my/79918/3/79918_Evidence%20for%20light-by-light%20scattering%20and%20searches_wos.pdf |
| Summary: | 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. |
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