Light meson nuclear modification factor in p-Pb collisions over an unprecedented $p_\mathrm{T}$ range with ALICE

TL;DR

This paper reports on measurements of light neutral meson production and nuclear modification factors in p-Pb collisions at the LHC, extending the $p_T$ range to unprecedented levels and comparing results with theoretical models.

Contribution

It provides the highest $p_T$ measurements of $ ext{pi}^0$ and $ ext{eta}$ mesons in p-Pb collisions, offering new insights into nuclear effects at high transverse momentum.

Findings

Suppression of mesons for $p_T<10$ GeV/$c$ consistent with CGC and cold nuclear matter models.

$ ext{pi}^0$ spectrum measured up to 200 GeV/$c$, the highest for identified particles.

$R_{pPb}$ approaches unity for $p_T>10$ GeV/$c$, aligning with theoretical predictions.

Abstract

Light neutral meson differential invariant cross section and nuclear modification factor measurements have been carried out with the ALICE detector at the CERN LHC in pp collisions at $\sqrt{s}=8$ TeV and p--Pb collisions at $\sqrt{s_\mathrm{NN}}=8.16$ TeV. The analysis combines results from several partially independent reconstruction techniques where the $\pi^0$ and $\eta$ meson decay photons were detected with the electromagnetic calorimeter, EMCal, the photon spectrometer, PHOS, or via reconstruction of $e^+e^-$ pairs from conversions in the ALICE detector material using the central tracking system. The neutral pion measurement reaching a $p_\mathrm{T}$ of 200 GeV/$c$ poses as the highest measured identified particle spectrum to date while the $\eta$ meson is measured to an unprecedented $p_\mathrm{T}$ of 50 GeV/$c$. The spectra are found to be generally overestimated by NLO pQCD calculations. The nuclear modification factors of both mesons exhibit a suppression for $p_\mathrm{T}<10$ GeV/$c$ which is stronger compared to previous measurements at $\sqrt{s_\mathrm{NN}}=5.02$ TeV and consistent with CGC and cold nuclear matter energy loss calculations. For $p_\mathrm{T}>10$ GeV/$c$, $R_\mathrm{pPb}$ is consistent with unity and theory predictions.