Identified Hadron Compositions in $p+p$ and $\mathrm{Au}+\mathrm{Au}$ Collisions at High Transverse Momenta at $\sqrt{s_{NN}}=200\mathrm{GeV}$

We report transverse momentum ($p_T\le 15\mathrm{GeV}/c$) spectra of ${\pi }^{\pm }$, $K^{\pm }$, $p$, $\overline{p}$, $K_S^0$, and ${\rho }^0$ at midrapidity in $p+p$ and $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{s_{NN}}=200\mathrm{GeV}$. Perturbative QCD calculations are consistent with ${\pi }^{\pm }$ spectra in $p+p$ collisions but do not reproduce $K$ and $p(\overline{p})$ spectra. The observed decreasing antiparticle-to-particle ratios with increasing $p_T$ provide experimental evidence for varying quark and gluon jet contributions to high-$p_T$ hadron yields. The relative hadron abundances in $\mathrm{Au}+\mathrm{Au}$ at $p_T\gtrsim 8\mathrm{GeV}/c$ are measured to be similar to the $p+p$ results, despite the expected Casimir effect for parton energy loss.

Figure 1

The invariant yields $d^{2}N/(2\pi p_{T}d{p}_{T}dy)$ of ${\pi }^{\pm }$, $K^{\pm }$, $K_S^0$, ${\rho }^0$, $p$, and $\overline{p}$ from nonsingly diffractive $p+p$ collisions (${\sigma }_{NSD}=30.0\pm 3.5\mathrm{mb}$ [5]), those of $K+p(\overline{p})$, $K_S^0$, and ${\rho }^0$ in central $\mathrm{Au}+\mathrm{Au}$ collisions, and NLO calculations with AKK [9] and DSS [10] FFs. The uncertainty of yields due to the scale dependence as evaluated in [10] is about a factor of 2. Bars and boxes (bands) represent statistical and systematic uncertainties, respectively.

Figure 2

Yield ratios ${\pi }^{-}/{\pi }^{+}$, $\overline{p}/p$, $K^{-}/K^{+}$, $p/{\pi }^{+}$, $\overline{p}/{\pi }^{-}$, and $(K^{\pm },K_S^0)/{\pi }^{\pm }$ versus $p_T$ in $p+p$ collisions, and nominal NLO calculations with AKK [9] and DSS [10] FFs without theoretical uncertainties. The open squares in panels (d) and (e) are the $p/{\pi }^{+}$ and $\overline{p}/{\pi }^{-}$ ratios in central $\mathrm{Au}+\mathrm{Au}$ collisions [14] with updated uncertainties at high $p_T$, and all other data points are from $p+p$ collisions. Bars and boxes (bands) represent statistical and systematic uncertainties, respectively.

Figure 3

(a) $R_{AA}$ of $K^{\pm }+p(\overline{p})$, $K_S^0$, ${\rho }^0$, and ${\pi }^{\pm }$ in central $\mathrm{Au}+\mathrm{Au}$ collisions as a function of $p_T$. The curves are the calculations for $K_S^0$ $R_{AA}$ with and without jet conversion in medium [15]. Bars and boxes (bands) represent statistical and systematic uncertainties, respectively. The height of the band at unity represents the normalization uncertainty. (b) The ratios of $R_{AA}[K^{\pm }+p(\overline{p}),{\rho }^0]$ to $R_{AA}({\pi }^{\pm })$ and $R_{AA}(K^{-}+\overline{p})$ to $R_{AA}(K^{+}+p)$. The boxes and shaded bands represent the systematic uncertainties for $R_{AA}({\rho }^0)/R_{AA}({\pi }^{\pm })$ and $R_{AA}[K^{\pm }+p(\overline{p})]/R_{AA}({\pi }^{\pm })$, respectively. The systematic uncertainties for $R_{AA}(K^{-}+\overline{p})/R_{AA}(K^{+}+p)$ are 2%–12% and left off for clarity.