Observation of Forward Neutron Multiplicity Dependence of Dimuon Acoplanarity in Ultraperipheral Pb-Pb Collisions at √{sN N }=5.02 TeV
Abstract
The first measurement of the dependence of γ γ →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 √{sN N }=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 <mμ μ<60 GeV are extracted for events including 0, 1, or at least 2 neutrons detected in the forward pseudorapidity range |η | >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.
- Publication:
-
Physical Review Letters
- Pub Date:
- September 2021
- DOI:
- 10.1103/PhysRevLett.127.122001
- arXiv:
- arXiv:2011.05239
- Bibcode:
- 2021PhRvL.127l2001S
- Keywords:
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- High Energy Physics - Experiment;
- Nuclear Experiment
- E-Print:
- Replaced with the published version. Added the journal reference and the DOI. All the figures and tables can be found at http://cms-results.web.cern.ch/cms-results/public-results/publications/HIN-19-014 (CMS Public Pages)