Abstract: The first measurements of the Fourier coefficients of the azimuthal distributions of charged hadrons emitted from photon-proton (?p) interactions are presented. The data are extracted from 68.8 nb?1 of ultra-peripheral proton-lead (pPb) collisions at using the CMS detector. The high energy lead ions produce a flux of photons that can interact with the oncoming proton. This ?p system provides a set of unique initial conditions with multiplicity lower than in photon-lead collisions but comparable to recent electron-positron and electron-proton data. The coefficients are presented in ranges of event multiplicity and transverse momentum () and are compared to corresponding hadronic minimum bias pPb results. For a given multiplicity range, the mean
of charged particles is smaller in ?p than in pPb collisions. For both the ?p and pPb samples, is negative,
is positive, and consistent with 0. For each multiplicity and range, is larger for ?p events. The ?p data are consistent with model predictions that have no collective effects.
