Probing the Initial State with Isolated-photon Production and Dijet Invariant Mass Distributions in Small Collision Systems with ALICE

Isolated photons and dijets measurements in small collision systems, i.e., pp and pA, probe the initial state of the collision, providing the opportunity to constrain PDFs, test pQCD predictions, and probe cold nuclear matter effects. In addition, dijet measurements are sensitive to interactions of partons with the medium produced in Pb–Pb collisions that induce modifications in jet properties. Therefore, measurements in small collision systems also offer a baseline for Pb–Pb collision measurements. In this article, we present the measurement of isolated photons and dijets in small collision systems, pp and p–Pb by ALICE. Isolated photons are measured in pp collisions at √ s = 8 and 13 TeV and in p–Pb collisions at √ sNN = 5.02 TeV, down to pT = 10 GeV/c, extending previous measurements at these centre-of-mass energies down to small x ∼ 10−3. The dijet invariant mass is measured in pp and p–Pb collisions at √ sNN = 5.02 TeV within the range from 80 to 150 GeV/c2, probing a region where medium effects are expected to be strong.