2018/10/31 by A.M. Sirunyan, CMS Collaboration, A. Tumasyan +98 · 214 citations
Physics and Astronomy · #Cosmology and Gravitation Theories #Dark Matter and Cosmic Phenomena #High-Energy Particle Collisions Research #Particle physics #Physics #hep-ex #nucl-ex
paper · pdf · doi:10.1016/j.physletb.2019.134826
published in Physics Letters B 797, 134826 (Elsevier BV) · Replaced with the published version. Added the journal reference. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/FSQ-16-012 (CMS Public Pages)
openalex created_date 2018/10/26 · openalex publication_date 2019/08/01 · arxiv created 2019/08/30 · arxiv updated 2019/09/02 · openalex updated_date 2026/08/06
Evidence for the light-by-light scattering process, γ γ → γ γ , 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 μ b − 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 T γ > 2 GeV , pseudorapidity | η γ | < 2.4 , diphoton invariant mass m γ γ > 5 GeV , diphoton transverse momentum p T γ γ < 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 ( γ γ → γ γ ) = 120 ± 46 (stat) ± 28 (syst) ± 12 (theo) nb , is consistent with the standard model prediction. The m γ γ distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the process, in the mass range .