Near-side azimuthal and pseudorapidity correlations using neutral strange baryons and mesons in $d+\mathrm{Au}$, Cu + Cu, and Au + Au collisions at $\sqrt{s_{NN}}=200$ GeV

We present measurements of the near side of triggered di-hadron correlations using neutral strange baryons $(\mathrm{\Lambda },\overline{\mathrm{\Lambda }})$ and mesons $\left(K_S^0\right)$ at intermediate transverse momentum $(3 < p_T <6 \mathrm{GeV}/c)$ to look for possible flavor and baryon-meson dependence. This study is performed in $d+\mathrm{Au}$, Cu+Cu, and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV measured by the STAR experiment at RHIC. The near-side di-hadron correlation contains two structures, a peak which is narrow in azimuth and pseudorapidity consistent with correlations from jet fragmentation, and a correlation in azimuth which is broad in pseudorapidity. The particle composition of the jet-like correlation is determined using identified associated particles. The dependence of the conditional yield of the jet-like correlation on the trigger particle momentum, associated particle momentum, and centrality for correlations with unidentified trigger particles are presented. The neutral strange particle composition in jet-like correlations with unidentified charged particle triggers is not well described by PYTHIA. However, the yield of unidentified particles in jet-like correlations with neutral strange particle triggers is described reasonably well by the same model.

Figure 1

Corrected 2D $K_S^0$-h correlation function for $3 < p_T^{\mathrm{trigger}} <$ 6 GeV/$c$ and $1.5$ GeV/$c < p_T^{\mathrm{associated}} < p_T^{\mathrm{trigger}}$ for 0%–20% Cu+Cu. The data have been reflected about $\mathrm{\Delta }\eta =0$ and $\mathrm{\Delta }\varphi =0$.

Figure 2

Corrected correlation functions $\frac{d{N}_J}{d\mathrm{\Delta }\eta }$ in $|\mathrm{\Delta }\varphi |<$ 0.78 for $3 < p_T^{\mathrm{trigger}} <$ 6 GeV/$c$ and $1.5$ GeV/$c < p_T^{\mathrm{associated}} < p_T^{\mathrm{trigger}}$ for (a) $\mathrm{\Lambda }$-h and (b) $K_S^0$-h for minimum bias $d$+Au, 0%–20% Cu+Cu, and 40%–80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV after background subtraction. The data have been reflected about $\mathrm{\Delta }\eta =0$.

Figure 3

$\mathrm{\Lambda }/K_S^0$ ratio measured in the jet-like correlation in 0%–60% Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV for $3 < p_T^{\mathrm{trigger}} <$ 6 GeV/$c$ and $2.0 <p_T^{\mathrm{associated}}<$ 3.0 GeV/$c$ along with this ratio obtained from inclusive $p_T$ spectra in $p$+$p$ collisions. Data are compared to calculations from PYTHIA [33] using the Perugia 2011 tunes [51] and Tune A [52].

Figure 4

The jet-like yield in $|\mathrm{\Delta }\eta |<0.78$ as a function of $p_T^{\mathrm{trigger}}$ for $K_S^0$-h and $\mathrm{\Lambda }$-h correlations for $1.5$ GeV/$c < p_T^{\mathrm{associated}} < p_T^{\mathrm{trigger}}$ in (a) minimum bias $d$+Au and 40%–80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV and (b) 0%–60% Cu+Cu and 0%–12% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. For comparison h-h correlations [9] from 40%–80% Au+Au collisions are shown as a band where the width represents the uncertainty. Peripheral Au+Au points have been shifted in $p_T^{\mathrm{trigger}}$ for visibility. The systematic uncertainty from the uncertainty on the associated particle's reconstruction efficiency (5%) and background level extraction (2%) are not shown.

Figure 5

Centrality dependence of the jet-like yield of $K_S^0$-h and $\mathrm{\Lambda }$-h correlations for $3 < p_T^{\mathrm{trigger}} <$ 6 GeV/$c$ and $1.5$ GeV/$c < p_T^{\mathrm{associated}} < p_T^{\mathrm{trigger}}$ in $d$+Au, Cu+Cu, and Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV. The data are compared to PYTHIA [33] calculations using the Perugia 2011 tune [51]. The systematic uncertainty from the uncertainty on the associated particle's reconstruction efficiency (5%) and background level extraction (2%) are not shown.

Figure 6

The jet-like yield as a function of $p_T^{\mathrm{associated}}$ for $K_S^0$-h and $\mathrm{\Lambda }$-h correlations for $3 < p_T^{\mathrm{trigger}} <$ 6 GeV/$c$ in $d$+Au and 0%–60% Cu+Cu collisions at $\sqrt{s_{NN}}=200$ GeV. The data are compared to the jet-like yield from h-h correlations [9] from 40%–80% Au+Au collisions shown as a line. Data are binned in $1.0 <p_T^{\mathrm{associated}}<$ 1.5 GeV/$c,1.5 <p_T^{\mathrm{associated}}<$ 2.0 GeV/$c$, and $2.0 <p_T^{\mathrm{associated}}<$ 3.0 GeV/$c$ and are plotted at the mean of the bin. The systematic uncertainty from the uncertainty on the associated particle's reconstruction efficiency (5%) and background level extraction (2%) are not shown.