Mon·Aug 13, 2018Monday·August 13, 2018

1. 01*

   Evidence for light-by-light scattering in ultraperipheral PbPb collisions at $\sqrt{s_{NN}}$ = 5.02 TeV

   David d'Enterria (for the CMS Collaboration)🇨🇭

   Evidence for light-by-light (LbL) scattering, $\gamma \gamma \to \gamma \gamma$, in ultraperipheral PbPb collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV is reported. LbL scattering processes are selected in events with just two photons produced, with transverse energy $E_T^{\gamma }>2$ GeV, pseudorapidity $|{\eta }^{\gamma }|<2.4$; and diphoton invariant mass $m^{\gamma \gamma }>5$ GeV, transverse momentum $p_T^{\gamma \gamma }<1$ GeV, and acoplanarity $(1-\Delta {\varphi }^{\gamma \gamma }/\pi )<0.01$. After all selection criteria, 14 events are observed, compared to $11.1\pm 1.1$ (theo) and $3.8\pm 1.3$ (stat) events expected for signal and background processes respectively. The significance of the signal excess over the background-only hypothesis is $4.1\sigma$. The measured fiducial LbL scattering cross section, ${\sigma }_{fid}(\gamma \gamma \to \gamma \gamma )=122\pm 46$ (stat) $\pm 29$ (syst) $\pm 4$ (theo) nb is consistent with the standard model prediction.

   ↳ hep-exnucl-exNPA(2019)·14 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.