Evidence from $d+\mathrm{A}\mathrm{u}$ Measurements for Final-State Suppression of High-$p_T$ Hadrons in $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ Collisions at RHIC

We report measurements of single-particle inclusive spectra and two-particle azimuthal distributions of charged hadrons at high transverse momentum (high $p_T$) in minimum bias and central $d+\mathrm{A}\mathrm{u}$ collisions at $\sqrt{s_{NN}}=200\mathrm{G}\mathrm{e}\mathrm{V}$. The inclusive yield is enhanced in $d+\mathrm{A}\mathrm{u}$ collisions relative to binary-scaled $p+p$ collisions, while the two-particle azimuthal distributions are very similar to those observed in $p+p$ collisions. These results demonstrate that the strong suppression of the inclusive yield and back-to-back correlations at high $p_T$ previously observed in central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions are due to final-state interactions with the dense medium generated in such collisions.

Figure 1

Uncorrected charged particle multiplicity distributions measured in $-3.8<\eta <-2.8$ (Au direction) for $d+\mathrm{A}\mathrm{u}$ collisions. Points are for minimum bias (triangles) and peripheral (circles, ZDC-$d$ single neutron) collisions. Both are normalized to the total number of $d+\mathrm{A}\mathrm{u}$ collisions. Histograms are Glauber model calculations.

Figure 2

Inclusive $p_T$ distributions for minimum bias and central $d+\mathrm{A}\mathrm{u}$ collisions, and non-singly diffractive $p+p$ collisions [5]. Hash marks at the top indicate bin boundaries for $p_T>3.8\mathrm{G}\mathrm{e}\mathrm{V}/c$.

Figure 3

$R_{AB}(p_T)$ from Eq. (1) for minimum bias and central $d+\mathrm{A}\mathrm{u}$ collisions, and central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions [5]. The minimum bias $d+\mathrm{A}\mathrm{u}$ data are displaced $100\mathrm{M}\mathrm{e}\mathrm{V}/c$ to the right for clarity. The bands show the normalization uncertainties, which are highly correlated point-to-point and between the two $d+\mathrm{A}\mathrm{u}$ distributions.

Figure 4

(a) Efficiency corrected two-particle azimuthal distributions for minimum bias and central $d+\mathrm{A}\mathrm{u}$ collisions, and for $p+p$ collisions [6]. Curves are fits using Eq. (3), with parameters given in Table 1. (b) Comparison of two-particle azimuthal distributions for central $d+\mathrm{A}\mathrm{u}$ collisions to those seen in $p+p$ and central $\mathrm{A}\mathrm{u}+\mathrm{A}\mathrm{u}$ collisions [6]. The respective pedestals have been subtracted.