Identified charged particle spectra and yields in $\text{Au}+\text{Au}$ collisions at $\sqrt{{\mathit{s}}_{\mathit{N}\mathit{N}}}=200\text{GeV}$

The centrality dependence of transverse momentum distributions and yields for ${\pi }^{\pm },K^{\pm },p$, and $\overline{p}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$ at midrapidity are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider. We observe a clear particle mass dependence of the shapes of transverse momentum spectra in central collisions below $\sim 2\text{GeV}∕c$ in $p_T$. Both mean transverse momenta and particle yields per participant pair increase from peripheral to midcentral and saturate at the most central collisions for all particle species. We also measure particle ratios of ${\pi }^{-}∕{\pi }^{+}$, $K^{-}∕K^{+}$, $\overline{p}∕p$, $K∕\pi$, $p∕\pi$, and $\overline{p}∕\pi$ as a function of $p_T$ and collision centrality. The ratios of equal mass particle yields are independent of $p_T$ and centrality within the experimental uncertainties. In central collisions at intermediate transverse momenta $\sim 1.5–4.5\text{GeV}∕c$, proton and antiproton yields constitute a significant fraction of the charged hadron production and show a scaling behavior different from that of pions.

Figure 1

BBC vs ZDC analog response. The lines represent the centrality cut boundaries.

Figure 2

(Color online) Mass-squared vs momentum multiplied by charge distribution in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The lines indicate the PID cut boundaries for pions, kaons, and protons (antiprotons) from left to right, respectively.

Figure 3

Track reconstruction efficiency $\left({ϵ}_{\text{mult}}\right)$ as a function of centrality. The error bars on the plot represent the systematic errors.

Figure 4

The fractional contribution of protons $\left(\overline{p}\right)$ from $\Lambda \left(\overline{\Lambda }\right)$ decays in all measured protons $\left(\overline{p}\right)$, ${\delta }_{\text{feed}}\left(p_T\right)$, as a function of $p_T$. The solid (dashed) lines represent the systematic errors for protons $\left(\overline{p}\right)$. The error bars are statistical errors.

Figure 5

Transverse momentum distributions for pions, kaons, protons, and antiprotons in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The top two figures show $p_T$ spectra for the most central $0–5\%$ collisions. The bottom two are for the most peripheral $60–92\%$ collisions. The error bars are statistical only. The $\Lambda \left(\overline{\Lambda }\right)$ feed-down corrections for protons (antiprotons) have been applied.

Figure 6

Centrality dependence of the $p_T$ distribution for ${\pi }^{+}$ (left) and ${\pi }^{-}$ (right) in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The different symbols correspond to different centrality bins. The error bars are statistical only. For clarity, the data points are scaled vertically as quoted in the figure.

Figure 7

Centrality dependence of the $p_T$ distribution for $K^{+}$ (left) and $K^{-}$ (right) in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The different symbols correspond to different centrality bins. The error bars are statistical only. For clarity, the data points are scaled vertically as quoted in the figure.

Figure 8

Centrality dependence of the $p_T$ distribution for protons (left) and antiprotons (right) in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The different symbols correspond to different centrality bins. The error bars are statistical only. Feed-down corrections for $\Lambda \left(\overline{\Lambda }\right)$ decaying into proton $\left(\overline{p}\right)$ have been applied. For clarity, the data points are scaled vertically as quoted in the figure.

Figure 9

Transverse mass distributions for ${\pi }^{\pm },K^{\pm }$, protons, and antiprotons for central $0–5\%$ (top panels), midcentral $40–50\%$ (middle panels), and peripheral $60–92\%$ (bottom panels) in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The lines on each spectra are the fitted results using $m_T$ exponential function. The fit ranges are $0.2–1.0\text{GeV}∕c^2$ for pions and $0.1–1.0\text{GeV}∕c^2$ for kaons, protons, and antiprotons in $m_T–m_0$. The error bars are statistical errors only.

Figure 10

Mass and centrality dependence of inverse slope parameters $T$ in $m_T$ spectra for positive (left) and negative (right) particles in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The fit ranges are $0.2–1.0\text{GeV}∕c^2$ for pions and $0.1–1.0\text{GeV}∕c^2$ for kaons, protons, and antiprotons in $m_T–m_0$. The dotted lines represent a linear fit of the results from each centrality bin as a function of mass using Eq. (9).

Figure 11

Mean transverse momentum as a function of $N_{part}$ for pions, kaons, protons, and antiprotons in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The left (right) panel shows the $⟨p_T⟩$ for positive (negative) particles. The error bars are statistical errors. The systematic errors from cut conditions are shown as shaded boxes on the right for each particle species. The systematic errors from extrapolations, which are scaled by a factor of 2 for clarity, are shown in the bottom for protons and antiprotons (dashed-dot lines), kaons (dotted lines), and pions (dashed lines).

Figure 12

Mean transverse momentum versus particle mass for central $0–5\%$, midcentral $40–50\%$, and peripheral $60–92\%$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The left (right) panel shows the $⟨p_T⟩$ for positive (negative) particles. The error bars represent the total systematic errors. The statistical errors are negligible.

Figure 13

Particle yield per unit rapidity $\left(dN∕dy\right)$ per participant pair $\left(0.5N_{part}\right)$ as a function of $N_{part}$ for pions, kaons, protons, and antiprotons in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The left (right) panel shows the $dN∕dy$ for positive (negative) particles. The error bars represent the quadratic sum of statistical errors and systematic errors from cut conditions. The lines represent the effect of the systematic error on $N_{part}$ which affects all curves in the same way.

Figure 14

Particle ratios of (a) ${\pi }^{-}∕{\pi }^{+}$ for central $0–5\%$, (b) ${\pi }^{-}∕{\pi }^{+}$ for peripheral $60–92\%$, (c) $K^{-}∕K^{+}$ for central $0–5\%$, and (d) $K^{-}∕K^{+}$ for peripheral $60–92\%$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars indicate the statistical errors and shaded boxes around unity on each panel indicate the systematic errors.

Figure 15

Ratio of $\overline{p}∕p$ as a function of $p_T$ for central $0–5\%$ (left) and peripheral $60–92\%$ (right) in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars indicate the statistical errors and shaded boxes around unity on each panel indicate the systematic errors.

Figure 16

$\overline{p}∕p$ ratios as a function of $p_T$ for minimum bias events in $\text{Au}+\text{Au}$ at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars indicate the statistical errors and shaded box on the right indicates the systematic errors. Two theoretical calculations are shown: baryon junction model (solid line) and pQCD calculation (dashed line) taken from Ref. [46].

Figure 17

$K∕\pi$ ratios as a function of $p_T$ for central $0–5\%$ and peripheral $60–92\%$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The left is for $K^{+}∕{\pi }^{+}$ and the right is for $K^{-}∕{\pi }^{-}$. The error bars indicate the statistical errors.

Figure 18

Proton∕pion (top) and antiproton∕pion (bottom) ratios for central $0–10\%$, midcentral $20–30\%$, and peripheral $60–92\%$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. Open (filled) points are for charged (neutral) pions. The data at $\sqrt{s}=53\text{GeV}p+p$ collisions [47] are also shown. The solid line is the $\left(\overline{p}+p\right)∕\left({\pi }^{+}+{\pi }^{-}\right)$ ratio measured in gluon jets [48].

Figure 19

(Color online) Centrality dependence of particle ratios for ${\pi }^{-}∕{\pi }^{+},K^{-}∕K^{+}$, and $\overline{p}∕p$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars indicate the statistical errors. The shaded boxes on each data point are the systematic errors.

Figure 20

Comparison of PHENIX particle ratios with those of PHOBOS [44], BRAHMS [43], and STAR (preliminary) [51] results in $\text{Au}+\text{Au}$ central collisions at $\sqrt{s_{NN}}=200\text{GeV}$ at midrapidity. The thermal model prediction [10] for $200\text{GeV}\text{Au}+\text{Au}$ central collisions are also shown as dotted lines. The error bars on data indicate the systematic errors.

Figure 21

(Color online) Centrality dependence of particle ratios for (a) $K^{+}∕{\pi }^{+}$, (b) $K^{-}∕{\pi }^{-}$, (c) $p∕{\pi }^{+}$, and (d) $\overline{p}∕{\pi }^{-}$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars indicate the statistical errors. The shaded boxes on each data point are the systematic errors.

Figure 22

$p_T$ spectra scaled by the averaged number of binary collisions for averaged charged (a) pions, (b) kaons, and (c) $\left(p+\overline{p}\right)∕2$ in three different centrality bins: central $0–10\%$, midcentral $40–50\%$, and peripheral $60–92\%$ in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars are statistical only. Note the different horizontal and vertical scales on the three plots.

Figure 23

Central $\left(0–10\%\right)$ to peripheral $\left(60–92\%\right)$ ratios of binary-collision-scaled $p_T$ spectra, $R_{CP}$, as a function of $p_T$ for $\left(\overline{p}+p\right)∕2$, charged kaons, charged pions, and ${\pi }^0$ [14] in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The lines indicate the expectations of $N_{part}$ (dotted) and $N_{coll}$ (dashed) scaling, the shaded bars represent the systematic errors on these quantities.

Figure 24

(Color online) Centrality dependence of integrated $R_{CP}$ above $1.5\text{GeV}∕c$ normalized to the most peripheral $60–92\%$ value. The data show $R_{CP}$ for $\left(\overline{p}+p\right)∕2$, charged kaons, and charged pions in $\text{Au}+\text{Au}$ collisions at $\sqrt{s_{NN}}=200\text{GeV}$. The error bars are statistical only. The shaded boxes represent the systematic errors (see text for details).