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Disappearance of back-to-back high $p_T$ hadron correlations in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

C. Adler

TL;DR

The back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Abstract

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudo-rapidity range and full azimuth in Au+Au and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes already observed in elementary collisions. A strong back-to-back correlation exists for p+p and peripheral Au + Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Disappearance of back-to-back high $p_T$ hadron correlations in central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

TL;DR

The back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Abstract

Azimuthal correlations for large transverse momentum charged hadrons have been measured over a wide pseudo-rapidity range and full azimuth in Au+Au and p+p collisions at = 200 GeV. The small-angle correlations observed in p+p collisions and at all centralities of Au+Au collisions are characteristic of hard-scattering processes already observed in elementary collisions. A strong back-to-back correlation exists for p+p and peripheral Au + Au. In contrast, the back-to-back correlations are reduced considerably in the most central Au+Au collisions, indicating substantial interaction as the hard-scattered partons or their fragmentation products traverse the medium.

Paper Structure

This paper contains 3 equations, 3 figures, 1 table.

Figures (3)

  • Figure 1: Azimuthal distributions of same-sign and opposite-sign pairs for a) p+p, b) minimum bias Au+Au, and c) background-subtracted central Au+Au collisions. All correlation functions require a trigger particle with $4<p_T^{trig}<6$ GeV/c and associated particles with $2$ GeV/c $<p_T<p_T^{trig}$. The curves are one- or two- Gaussian fits.
  • Figure 2: Azimuthal distributions ($0<|\Delta \eta|<1.4$, $4<p_T^{trig}<6$ GeV/c) for Au+Au collisions (solid circles) compared to the expected distributions ${D^{\mathrm{model}}}$ from Equation \ref{['c2eqn']} (open circles). Also shown is the elliptic flow contribution for each centrality (solid curve).
  • Figure 3: Ratio of Au+Au and p+p (Equation \ref{['ratioeqn']}) for small-angle (squares, $|\Delta \phi|<0.75$ radians) and back-to-back (circles, $|\Delta \phi|>2.24$ radians) azimuthal regions versus number of participating nucleons for trigger particle intervals $4<p_T^{trig}<6$ GeV/c (solid) and $3<p_T^{trig}<4$ GeV/c (hollow). The horizontal bars indicate the dominant systematic error (highly correlated among points) due to the uncertainty in $v_2$.