Evidence For Light-By-Light Scattering And Searches For Axion-Like Particles İn Ultraperipheral Pbpb Collisions At ?Snn=5.02 TeV
Yükleniyor...
Tarih
2019
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
The CMS Collaboration
Erişim Hakkı
Özet
Evidence for the light-by-light scattering process, ?????, in ultraperipheral PbPb collisions at a centre-of-mass energy per nucleon pair of 5.02TeVis reported. The analysis is conducted using a data sample corresponding to an integrated luminosity of 390?b?1recorded 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>2GeV, pseudorapidity |??| <2.4, diphoton invariant mass m??>5GeV, diphoton transverse momentum p??T<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, ?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=5–90GeV.
Açıklama
Anahtar Kelimeler
Light-by-light, CMS, UPC, Photoproduction, PbPb
Kaynak
WoS Q Değeri
Q1
Scopus Q Değeri
Q1
Cilt
Sayı
Künye
Physics Letters B 797(2019)134826
