| Abstract: | Two-particle azimuthal ($Deltaphi$) and pseudorapidity ($Deltaeta$)
correlations using a trigger particle with large transverse momentum ($p_T$) in
$d$+Au, Cu+Cu and Au+Au collisions at $sqrt{s_{{NN}}}$ =xspace 62.4 GeV and
200~GeV from the STAR experiment at RHIC are presented. The
s correlation is
separated into a jet-like component, narrow in both $Deltaphi$ and
$Deltaeta$, and the ridge, narrow in $Deltaphi$ but broad in $Deltaeta$.
Both components are studied as a function of collision centrality, and the
jet-like correlation is studied as a function of the trigger and associated
$p_T$. The behavior of the jet-like component is remarkably consistent for
different collision systems, suggesting it is produced by fragmentation. The
width of the jet-like correlation is found to increase with the system size.
The ridge, previously observed in Au+Au collisions at $sqrt{s_{{NN}}}$ = 200
GeV, is also found in Cu+Cu collisions and in collisions at $sqrt{s_{{NN}}}$
=xspace 62.4 GeV, but is found to be substantially smaller at
$sqrt{s_{{NN}}}$ =xspace 62.4 GeV than at $sqrt{s_{{NN}}}$ = 200 GeV for the
same average number of participants ($ langle N_{mathrm{part}}
angle$).
Measurements of the ridge are compared to models. |
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