High transverse momentum triggered correlations over a large pseudorapidity acceptance in Au+Au collisions at sqrt(s_NN)=200 GeV

TL;DR

This paper reports on two-particle correlation measurements in Au+Au collisions at 200 GeV, revealing a broad away-side correlation and a long-range 'ridge' structure in pseudorapidity, indicating complex medium effects.

Contribution

It provides the first observation of a long-range pseudorapidity correlation ('ridge') in high transverse momentum triggered events in heavy-ion collisions.

Findings

Observation of away-side broadening in azimuthal correlations.

Detection of a long-range 'ridge' extending over |eltata| pprox 4.

Ridge yield decreases with collision centrality and is negligible in peripheral events.

Abstract

A measurement of two-particle correlations with a high transverse momentum trigger particle (p_T^{trig} > 2.5 GeV/c) is presented for Au+Au collisions at sqrt(s_NN) = 200 GeV over the uniquely broad longitudinal acceptance of the PHOBOS detector (-4 < \Delta\eta < 2). A broadening of the away-side azimuthal correlation compared to elementary collisions is observed at all \Delta\eta. As in p+p collisions, the near-side is characterized by a peak of correlated partners at small angle relative to the trigger particle. However, in central Au+Au collisions an additional correlation extended in \Delta\eta and known as the `ridge' is found to reach at least |\Delta\eta| \approx 4. The ridge yield is largely independent of \Delta\eta over the measured range, and it decreases towards more peripheral collisions. For the chosen p_T^{trig} cut, the ridge yield is consistent with zero for events with less than roughly 100 participating nucleons.