Sirunyan, AM;
Tumasyan, A;
Adam, W;
Ambrogi, F;
Bergauer, T;
Brandstetter, J;
Dragicevic, M;
... Woods, N; + view all
(2019)
Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root \sqrt{sNN} = 5.02 TeV.
Physics Letters B
, 797
, Article 134826. 10.1016/j.physletb.2019.134826.
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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 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 E^{γ}_{T} > 2 GeV, pseudorapidity |η^{γ}| < 2.4, diphoton invariant mass m^{γγ} > 5 GeV, diphoton transverse momentum p^{γγ}_{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, σ_{fid} (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 γγ → a → γγ process, in the mass range m_{a} = 5-90 GeV.
| Type: | Article |
|---|---|
| Title: | Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at root \sqrt{sNN} = 5.02 TeV |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1016/j.physletb.2019.134826 |
| Publisher version: | https://doi.org/10.1016/j.physletb.2019.134826 |
| Language: | English |
| Additional information: | © 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). |
| Keywords: | Light-by-light, CMS, UPC, Photoproduction, PbPb |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10089609 |
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