Transverse Energy ($E_T$) distributions at mid-rapidity in $p$$+$$p$, $d$$+$Au and Au$+$Au collisions at $\sqrt{s_{_{NN}}}$=200 GeV and implications for particle production models

Abstract

Measurements of the midrapidity transverse energy distribution $d{\rm E}_T/d\eta$ are presented for $p$$+$$p$, $d$$+$Au, and Au$+$Au Collisions at $\sqrt{s_{_{NN}}}$=62.4--200 GeV. The ${\rm E}_T$ distributions are compared with the number of participants, $N_{\rm part}$, the number of constituent-quark participants, $N_{qp}$, and the number of color-strings (Additive Quark Model-AQM) calculated from a Glauber model. For Au$+$Au, $\langle d{\rm E}_T/d\eta/(0.5 N_{\rm part})\rangle$ increases with $N_{\rm part}$, while $\langle d{\rm E}_T/d\eta/N_{qp}\rangle$ is approximately constant vs. centrality for $\sqrt{s_{_{NN}}} \geq 62.4$ GeV. This indicates that the two component ansatz, $d{\rm E}_T^{\rm AA}/d\eta=(d{\rm E}_T^{\rm pp}/d\eta)\ [(1-x)\, N_{\rm part}/2 + x\, N_{\rm coll}]$, which has been used to represent ${\rm E}_T$ distributions, is simply a proxy for $N_{qp}$, and that the $N_{\rm coll}$ term does not represent a hard-scattering component in ${\rm E}_T$ distributions. The $d{\rm E}_T/d\eta$ distributions of $d$$+$Au, and Au$+$Au are calculated from the measured $p$$+$$p$ ${\rm E}_T$ distribution using two models (AQM and $N_{qp}$) that both reproduce the Au$+$Au data. For the asymmetric $d$$+$Au system, the $N_{qp}$ model reproduces the data while the AQM does not.