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 ${\pi }^0$ 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 (${\eta }_{c.m.}$) regions $2.5<{\eta }_{c.m.}<3.5$ (forward) and $-4.0<{\eta }_{c.m.}<-3.0$ (backward) defined relative to the proton beam direction. The forward measurement shows a sizable suppression of ${\pi }^0$ production, while the backward measurement shows the first evidence of ${\pi }^0$ 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.

arXiv commentAll 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)

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• Complete Next-to-Leading Order Calculation of Single Inclusive ${\pi }^0$ Production in Forward Proton-Nucleus Collisions
• Production of $\eta$ and ${\eta }^{\prime }$ mesons in $pp$ and $p$Pb collisions
• Physics with high-luminosity proton-nucleus collisions at the LHC
• Parton Fragmentation Functions