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Abstract: Evidence for the light-by-light scattering process, ????? , 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 ?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 ET? > 2 GeV , pseudorapidity |??| < 2.4 , diphoton invariant mass m?? > 5 GeV , diphoton transverse momentum pT?? < 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, ?fid(?????) = 120 ± 46 (stat) ± 28 (syst) ± 12 (theo )nb , is consistent with the standard model prediction. The m?? distribution is used to set new exclusion limits on the production of pseudoscalar axion-like particles, via the ?? ? a ? ?? process, in the mass range ma = 5-90 GeV.
Fuente: Physics Letters B, 797 134826 (2019)
Editorial: Elsevier
Fecha de publicación: 01/10/2019
Nº de páginas: 27
Tipo de publicación: Artículo de Revista
DOI: 10.1016/j.physletb.2019.134826
ISSN: 0370-2693,1873-2445
Url de la publicación: https://doi.org/10.1016/j.physletb.2019.134826
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SIRUNYAN, A. M.
JOSE IBAN CABRILLO BARTOLOME
ALICIA CALDERON TAZON
BARBARA CHAZIN QUERO
JORGE DUARTE CAMPDERROS
MARCOS FERNANDEZ GARCIA
PEDRO JOSE FERNANDEZ MANTECA
ANDREA GARCIA ALONSO
JUAN GARCIA FERRERO
GERVASIO GOMEZ GRAMUGLIO
MARIA AMPARO LOPEZ VIRTO
JESUS MARCO DE LUCAS
CELSO MARTINEZ RIVERO
PABLO MARTINEZ RUIZ DEL ARBOL
FRANCISCO MATORRAS WEINIG
JONATAN PIEDRA GOMEZ
CEDRIC GERALD PRIEELS
MARIA TERESA RODRIGO ANORO
ALBERTO RUIZ JIMENO
LUCA SCODELLARO
NICOLO TREVISANI
IVAN VILA ALVAREZ
ROCIO VILAR CORTABITARTE
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