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http://bura.brunel.ac.uk/handle/2438/19200
Title: | Evidence for light-by-light scattering and searches for axion-like particles in ultraperipheral PbPb collisions at s<inf>NN</inf>=5.02TeV |
Authors: | Sirunyan, AM 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, VM 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, CE Zarucki, M Chekhovsky, V Mossolov, V Suarez Gonzalez, J De Wolf, EA 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, AK 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 |
Keywords: | Light-by-light;CMS;UPC;Photoproduction;PbPb |
Issue Date: | 1-Aug-2019 |
Publisher: | Elsevier |
Citation: | Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 2019, 797 |
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 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 Eγ T > 2 GeV, pseudorapidity |ηγ | < 2.4, diphoton invariant mass mγγ > 5 GeV, diphoton transverse momentum pγγ 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, 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 γγ → a → γγ process, in the mass range ma = 5–90 GeV. |
URI: | http://bura.brunel.ac.uk/handle/2438/19200 |
DOI: | http://dx.doi.org/10.1016/j.physletb.2019.134826 |
ISSN: | 0370-2693 http://dx.doi.org/10.1016/j.physletb.2019.134826 |
Appears in Collections: | Dept of Electronic and Electrical Engineering Research Papers |
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