Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at s<inf>NN</inf>=5.02TeV

Date Issued
10-10-2019
Author(s)
Sirunyan, A. M.
Tumasyan, A.
Adam, W.
Ambrogi, F.
Asilar, E.
Bergauer, T.
Brandstetter, J.
Dragicevic, M.
Erö, J.
Escalante Del Valle, A.
Flechl, M.
Frühwirth, R.
Ghete, V. M.
Hrubec, J.
Jeitler, M.
Krammer, N.
Krätschmer, I.
Liko, D.
Madlener, T.
Mikulec, I.
Rad, N.
Rohringer, H.
Schieck, J.
Schöfbeck, R.
Spanring, M.
Spitzbart, D.
Taurok, A.
Waltenberger, W.
Wittmann, J.
Wulz, C. E.
Zarucki, M.
Chekhovsky, V.
Mossolov, V.
Suarez Gonzalez, J.
De Wolf, E. A.
Di Croce, D.
Janssen, X.
Lauwers, J.
Pieters, M.
Van Haevermaet, H.
Van Mechelen, P.
Van Remortel, N.
Abu Zeid, S.
Blekman, F.
D'Hondt, J.
De Bruyn, I.
De Clercq, J.
Deroover, K.
Flouris, G.
Lontkovskyi, D.
Lowette, S.
Marchesini, I.
Moortgat, S.
Moreels, L.
Python, Q.
Skovpen, K.
Tavernier, S.
Van Doninck, W.
Van Mulders, P.
Van Parijs, I.
Beghin, D.
Bilin, B.
Brun, H.
Clerbaux, B.
De Lentdecker, G.
Delannoy, H.
Dorney, B.
Fasanella, G.
Favart, L.
Goldouzian, R.
Grebenyuk, A.
Kalsi, A. K.
Lenzi, T.
Luetic, J.
Postiau, N.
Starling, E.
Thomas, L.
Vander Velde, C.
Vanlaer, P.
Vannerom, D.
Wang, Q.
Cornelis, T.
Dobur, D.
Fagot, A.
Gul, M.
Khvastunov, I.
Poyraz, D.
Roskas, C.
Trocino, D.
Tytgat, M.
Verbeke, W.
Vermassen, B.
Vit, M.
Zaganidis, N.
Bakhshiansohi, H.
Bondu, O.
Brochet, S.
Bruno, G.
Caputo, C.
David, P.
DOI
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 5.02TeV 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 ETγ>2GeV, pseudorapidity |ηγ|<2.4, diphoton invariant mass mγγ>5GeV, diphoton transverse momentum pTγγ<1GeV, 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 (Figure presented.) process, in the mass range (Figure presented.).
Volume
797
Subjects