Observation of forward neutron multiplicity dependence of dimuon acoplanarity in ultraperipheral Pb-Pb collisions at √sNN = 5.02 TeV
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Type :
Article
Publication Status :
Published
Access :
openAccess
https://creativecommons.org/licenses/by/4.0/
https://creativecommons.org/licenses/by/4.0/
Abstract
The first measurement of the dependence of γγ→μ+μ- production on the multiplicity of neutrons emitted very close to the beam direction in ultraperipheral heavy ion collisions is reported. Data for lead-lead interactions at sNN=5.02 TeV, with an integrated luminosity of approximately 1.5 nb-1, are collected using the CMS detector at the LHC. The azimuthal correlations between the two muons in the invariant mass region 8<mμμ[removed]8.3. The back-to-back correlation structure from leading-order photon-photon scattering is found to be significantly broader for events with a larger number of emitted neutrons from each nucleus, corresponding to interactions with a smaller impact parameter. This observation provides a data-driven demonstration that the average transverse momentum of photons emitted from relativistic heavy ions has an impact parameter dependence. These results provide new constraints on models of photon-induced interactions in ultraperipheral collisions. They also provide a baseline to search for possible final-state effects on lepton pairs caused by traversing a quark-gluon plasma produced in hadronic heavy ion collisions.
Source :
Physical Review Letters
Date :
2021-09-17
Volume :
127
Issue :
12
Publisher :
American Physical Society
URI
http://hdl.handle.net/10679/8201https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.122001
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