Speaker
Michael Tannenbaum
(Brookhaven National Laboratory (US))
Description
Measurements of mid-rapidity $dE_T/d\eta$ distributions in p+p, d+Au and Au+Au at $\sqrt{s_{NN}}=200$ GeV by PHENIX at RHIC are presented and analyzed in terms of the number of Constituent-Quark participants, $N_{\rm qp}$. This provides a physical way to introduce fluctuations in Glauber Model calculations of p+p collisions, since the spatial distribution of each of the three constituent quarks in a nucleon is generated according to the measured charge distribution of the proton. It had been noted previously that $dN_{\rm ch}/d\eta$ at mid-rapidity in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV as a function of centrality is not simply proportional to the number of nucleon participants, $N_{\rm part}$, (the Wounded Nucleon Model, WNM)
but is linearly proportional to the number of constituent-quark participants, $N_{\rm qp}$, (the NQP model).
For symmetric systems, the NQP model is identical to the Additive Quark Model (AQM)
used in the 1980's, to explain a similar disagreement of $dE_T/d\eta$ distributions with the Wounded Nucleon Model in $\alpha+\alpha$ relative to p+p collisions at $\sqrt{s_{NN}}=31$ GeV at the CERN-ISR. However, the AQM and NQP models differ for the case of asymmetric systems such as d+Au, where the AQM, which is a color-string model, is effectively proportional only to the number quark-participants in the projectile. The present d+Au data clearly reject the AQM model in favor of the NQP, which is also in excellent agreement with the Au+Au data. The NQP model also explains why the additional contribution proportional the number of binary-collisions, $N_{\rm coll}$, added to $N_{\rm part}$ to parametrize the centrality-dependence of A+A collisions works, but does not imply a hard-scattering component in $E_T$ distributions and thus is no longer in disagreement with lessons learned from measurements of $E_T$ distributions in p+p(${\bar{\rm p}}$) collisions at the CERN SpS, ISR and SpS-Collider.
| On behalf of collaboration: | PHENIX |
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Author
Michael Tannenbaum
(Brookhaven National Laboratory (US))
