Indications of Conical Emission of Charged Hadrons at the BNL Relativistic Heavy Ion Collider

Three-particle azimuthal correlation measurements with a high transverse momentum trigger particle are reported for $pp$, $d+\mathrm{Au}$, and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{\mathrm{NN}}}=200\mathrm{GeV}$ by the STAR experiment. Dijet structures are observed in $pp$, $d+\mathrm{Au}$ and peripheral $\mathrm{Au}+\mathrm{Au}$ collisions. An additional structure is observed in central $\mathrm{Au}+\mathrm{Au}$ data, signaling conical emission of correlated charged hadrons. The conical emission angle is found to be $\theta =1.37\pm 0.02(\mathrm{stat}{)}_{-0.07}^{+0.06}(\mathrm{syst})$, independent of $p_{\perp }$.

Figure 1

(a) Raw two-particle correlation signal $Y_2$ (red), background $a{B}_{\mathrm{inc}}{F}_2$ (solid histogram), and background systematic uncertainty from $a$ (dashed histograms). (b) Background-subtracted two-particle correlation ${\widehat{Y}}_2$ (red), and systematic uncertainties due to $a$ (dashed histograms) and flow (blue histograms). (c) Raw three-particle correlation $Y_3$. (d) $b{a}^2{Y}_2^{\mathrm{inc}}$. (e) Sum of trig-corr-bkgd and trigger flow. Data are from 12% central $\mathrm{Au}+\mathrm{Au}$ collisions. Statistical errors in (a),(b) are smaller than the point size.

Figure 2

Background-subtracted three-particle correlations, ${\widehat{Y}}_3$, for (a) $pp$, (b) $d+\mathrm{Au}$, (c) $80-50\%$ $\mathrm{Au}+\mathrm{Au}$, (d) $50-30\%$ $\mathrm{Au}+\mathrm{Au}$, (e) $30-10\%$ $\mathrm{Au}+\mathrm{Au}$, and (f) 12% central $\mathrm{Au}+\mathrm{Au}$. Statistical errors per bin are approximately $\pm 0.012$ in (a) and $\pm 0.006$ in (b), both at ($\pi$, $\pi$), and are $\pm 0.022$, $\pm 0.049$, $\pm 0.099$ and $\pm 0.077$ from (c) to (f), similar for all bins.

Figure 3

Projections of away-side three-particle correlations along the diagonal $\Sigma$ within $0<\Delta <0.35$ (squares) and along the off-diagonal $\Delta$ within $|\Sigma |<0.35$ (points) in (a) $d+\mathrm{Au}$ and (b) 12% central $\mathrm{Au}+\mathrm{Au}$ collisions. The shaded areas indicate systematic uncertainties on the off-diagonal projections. The histogram in (a) is the near-side off-diagonal projection. The histogram in (b) is the away-side off-diagonal projection of our result with $a=b=1$.

Figure 4

Three-particle correlation strength per ${\mathrm{rad}}^2$ versus $(N_{\mathrm{part}}/2{)}^{1/3}$, where $N_{\mathrm{part}}$ is the number of participants. Some of the data points have been displaced in $N_{\mathrm{part}}$ for clarity.