Nuclear modification factor of neutral pions in the forward and backward regions in $p$-Pb collisions

Abstract

The nuclear modification factor of neutral pions is measured in proton-lead collisions collected at a center-of-mass energy per nucleon of $8.16\mathrm{TeV}$ with the LHCb detector. The $\ddot{I}{€}^0$ production cross section is measured differentially in transverse momentum ($p_{\mathrm{T}}$) for $1.5<p_{\mathrm{T}}<10.0\mathrm{GeV}$ and in center-of-mass pseudorapidity ($\hat{I}{\cdot }_{c.m.}$) regions $2.5<\hat{I}{\cdot }_{c.m.}<3.5$ (forward) and $-4.0<\hat{I}{\cdot }_{c.m.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of $\ddot{I}{€}^0$ production, while the backward measurement shows the first evidence of $\ddot{I}{€}^0$ enhancement in proton-lead collisions at the LHC. Together, these measurements provide precise constraints on models of nuclear structure and particle production in high-energy nuclear collisions.

All figures and tables, along with any supplementary material and additional information, are available at https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2021-053.html (LHCb public pages)