Measurement of the Centrality Dependence of the Dijet Yield in p + Pb Collisions at √_sNN = 8.16 TeV with the ATLAS Detector

ATLAS measured the centrality dependence of the dijet yield using 165  nb⁻¹ of 𝑝+Pb data collected at √_𝑠NN = 8.16  TeV in 2016. The event centrality, which reflects the 𝑝 +Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, 𝑅_CP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The 𝑅_CP shows a scaling with the Bjorken 𝑥 of the parton originating from the proton, 𝑥_𝑝, while no such trend is observed as a function of 𝑥_Pb. This analysis provides unique input to understanding the role of small proton spatial configurations in 𝑝 +Pb collisions by covering parton momentum fractions from the valence region down to 𝑥_𝑝 ∼10⁻³ and 𝑥_Pb ∼4 × 10⁻⁴.