Transverse-energy distributions at midrapidity in $p+p$, $d+\mathrm{Au}$, and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{\mathit{\text{NN}}}}=62.4$--200 GeV and implications for particle-production models

Transverse-energy distributions at midrapidity in $p + p$ , $d + Au$ , and $Au + Au$ collisions at $\sqrt{s_{NN}} = 62.4$ –200 GeV and implications for particle-production models

S. S. Adler et al. (PHENIX Collaboration)

Phys. Rev. C 89, 044905 – Published 9 April 2014

Abstract

Measurements of the midrapidity transverse-energy distribution, $d E_{T} / d η$ , are presented for $p + p$ , $d + Au$ , and $Au + Au$ collisions at $\sqrt{s_{NN}} = 200$ GeV and additionally for $Au + Au$ collisions at $\sqrt{s_{NN}} = 62.4$ and 130 GeV. The $d E_{T} / d η$ distributions are first compared with the number of nucleon participants $N_{part}$ , number of binary collisions $N_{coll}$ , and number of constituent-quark participants $N_{q p}$ calculated from a Glauber model based on the nuclear geometry. For $Au + Au$ , $〈 d E_{T} / d η 〉 / N_{part}$ increases with $N_{part}$ , while $〈 d E_{T} / d η 〉 / N_{q p}$ is approximately constant for all three energies. This indicates that the two-component ansatz, $d E_{T} / d η \propto (1 - x) N_{part} / 2 + x N_{coll}$ , which was used to represent $E_{T}$ distributions, is simply a proxy for $N_{q p}$ , and that the $N_{coll}$ term does not represent a hard-scattering component in $E_{T}$ distributions. The $d E_{T} / d η$ distributions of $Au + Au$ and $d + Au$ are then calculated from the measured $p + p$ $E_{T}$ distribution using two models that both reproduce the $Au + Au$ data. However, while the number-of-constituent-quark-participant model agrees well with the $d + Au$ data, the additive-quark model does not.