Measurement of the centrality dependence of the dijet yield in $p$+Pb collisions at $\sqrt{s_{{}_{\text{NN}}}}$ = 8.16 TeV with the ATLAS detector

Abstract

The measurement of hard scatterings in proton-nucleus collisions has resulted in a greater understanding of both the proton and nuclear structure. ATLAS measured the centrality dependence of the dijet yield using 165 nb${}^{-1}$ of $p$+Pb data collected at $\sqrt{s_{{}_{\text{NN}}}}$ = 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, $R_{\mathrm{CP}}$, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The $R_{\mathrm{CP}}$ 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 $x_{\mathrm{Pb}}$. 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 $x_p\sim 10^{-3}$ and $x_{\mathrm{Pb}}\sim 4\cdot 10^{-4}$.

30 pages, author list starting on page 13, 4 figures, 0 tables, published by PRL. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2023-05/

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• Correlations of event activity with hard and soft processes in $p$ + Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 200 GeV at STAR
• Selection bias effects on high-$p_{\mathrm{T}}$ yield and correlation measurements in Oxygen+Oxygen collisions