Speaker
Description
We present a first measurement of two-particle angular correlations for charged hadrons emitted from photon-proton, $\gamma p$, interactions over a wide range of pseudorapidity and full azimuth. The $\gamma p$ events were produced within ultra-peripheral pPb collisions at $\sqrt{s_{NN}}$ = 8.16 TeV and were selected by requiring a large rapidity gap in the lead-going direction and no neutron emission from the lead nucleus. The results are compared to a sample of minimum-bias pPb events with same multiplicity. The observed azimuthal correlations at large relative pseudorapidity are used to extract the first, second and third-order two-particle anisotropy harmonics, V1D, V2D, and V3D as a function of track multiplicity and transverse momentum pT. For both the photon-p and minimum-bias pPb samples V1D is negative, V2D is positive and V3D is negative but consistent with zero. The single particle second-order harmonic, v2 (pT) is larger for photon-p events than for minimum-bias pPb collisions of the same multiplicity.
