Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at √&lt;em&gt;s&lt;/em&gt;&lt;sub&gt;NN&lt;/sub&gt; = 5.02TeV

Sirunyan, A.M.; Tumasyan, A.; Adam, W.; Ambrogi, F.; Asilar, E.; Bergauer, T.; Brandstetter, J.; Dragicevic, M.; Erö, J.; Escalante Del Valle, A.; Caminada, L.; Deiters, K.; Erdmann, W.; Horisberger, R.; Ingram, Q.; Kaestli, H.C.; Kotlinski, D.; Langenegger, U.; Rohe, T.; Wiederkehr, S.A.; Woods, N.

doi:10.1016/j.physletb.2019.134826

Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at √s_NN = 5.02TeV

Sirunyan AM, Tumasyan A, Adam W, Ambrogi F, Asilar E, Bergauer T, Brandstetter J, Dragicevic M, Erö J, Escalante Del Valle A, Caminada L, Deiters K, Erdmann W, Horisberger R, Ingram Q, Kaestli HC, Kotlinski D, Langenegger U, Rohe T, Wiederkehr SA, Woods N, et al.

Citation

Sirunyan, A. M., Tumasyan, A., Adam, W., Ambrogi, F., Asilar, E., Bergauer, T., … Woods, N. (2019). Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at √s_NN = 5.02TeV. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 797, 134826 (27 pp.). https://doi.org/10.1016/j.physletb.2019.134826

Persistent URL https://www.dora.lib4ri.ch/psi/islandora/object/psi:27869

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 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 E^γ_T >2GeV, 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 m^γγ 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 m_a= 5-90 GeV.