Observation of forward neutron multiplicity dependence of dimuon acoplanarity in ultraperipheral Pb-Pb collisions at sqrt(s[NN]) = 5.02 TeVстатья
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Дата последнего поиска статьи во внешних источниках: 29 сентября 2021 г.
Аннотация: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, were collected using the CMS detector at the LHC. The azimuthal correlations between the two muons in the invariant mass region 8 <mμμ< 60 GeV are extracted for events including zero, one, or at least two 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.