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

Abstract: 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 $<$ $\eta$ $<$ 4.5, where positive $\eta$ 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, $x_{p}$. Both event geometry estimators are found to be dependent on $x_{p}$, with the energy deposited in the Zero-Degree Calorimeter about six times less sensitive to $x_{p}$ compared with the transverse energy deposited in the Forward Calorimeter.