Characterization of nuclear breakup as a function of hard-scattering kinematics using dijets measured by ATLAS in 𝑝+Pb collisions

This Letter analyzes the sensitivity of event geometry estimators to the initial-state kinematics of hard scattering in proton–lead collisions. This analysis uses dijets as a proxy for the parton–parton scattering configuration, correlating it with event geometry estimators, namely the energy deposited in the Zero-Degree Calorimeter and the transverse energy recorded in the Forward Calorimeter in the Pb-going direction. The analysis uses data recorded by the ATLAS detector at the Large Hadron Collider with a nucleon–nucleon center-of-mass energy of 8.16 TeV, corresponding to an integrated luminosity of 56 nb−1. The jets are measured within the pseudorapidity
interval −2.8 < 𝜂 < 4.5, where positive 𝜂 values correspond to the direction of the proton beam. Results are presented as a function of the Bjorken-𝑥 of the parton originating from the proton, 𝑥𝑝. Both event geometry estimators are found to be dependent on 𝑥𝑝, with the energy deposited in the Zero-Degree Calorimeter about six
times less sensitive to 𝑥𝑝 compared with the transverse energy deposited in the Forward Calorimeter.