Neutral Pion Production in Au+Au Collisions at s(NN)**(1/2) = 200-GeV

The collaboration
Phys.Rev.C 80 (2009) 044905, 2009.

Abstract
The results of mid-rapidity ($0 < y < 0.8$) neutral pion spectra over an extended transverse momentum range ($1 < p_T < 12$ GeV/$c$) in $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions, measured by the STAR experiment, are presented. The neutral pions are reconstructed from photons measured either by the STAR Barrel Electro-Magnetic Calorimeter (BEMC) or by the Time Projection Chamber (TPC) via tracking of conversion electron-positron pairs. Our measurements are compared to previously published $\pi^{\pm}$ and $\pi^0$ results. The nuclear modification factors $R_{\mathrm{CP}}$ and $R_{\mathrm{AA}}$ of $\pi^0$ are also presented as a function of $p_T$ . In the most central Au+Au collisions, the binary collision scaled $\pi^0$ yield at high $p_T$ is suppressed by a factor of about 5 compared to the expectation from the yield of p+p collisions. Such a large suppression is in agreement with previous observations for light quark mesons and is consistent with the scenario that partons suffer considerable energy loss in the dense medium formed in central nucleus-nucleus collisions at RHIC.

• #### Figure 1 a, b

Data from Figure 1, panels a and b (low $p_{T}$)

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The diphoton invariant mass distributions using the EMC-TPC method in 0-20% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 1 c, d

Data from Figure 1, panels c and d (high $p_{T}$

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The diphoton invariant mass distributions using the EMC-TPC method in 0-20% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 2

Data from Figure 2

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The diphoton invariant mass distributions using the EMC-EMC method in 0-20% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (exp, EMC-TPC, MB)

Experimental data from Figure 3 with EMC-TPC method in minimum-bias (MB) events

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (exp, EMC-TPC, HT)

Experimental data from Figure 3 with EMC-TPC method in the events with high-tower (HT) trigger

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (exp, EMC-EMC, HT)

Simulated data from Figure 3 with EMC-EMC method in the events with high-tower (HT) trigger

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (sim, EMC-TPC, MB)

Simulated data from Figure 3 with EMC-TPC method in minimum-bias (MB) events

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (sim, EMC-TPC, HT)

Simulated data from Figure 3 with EMC-TPC method in the events with high-tower (HT) trigger

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 3 (sim, EMC-EMC, HT)

Simulated data from Figure 3 with EMC-EMC method in the events with high-tower (HT) trigger

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The $\pi^0$ invariant mass peak positions and widths as a function of $p_{T}$ in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 4 (left)

Data from Figure 4, left panel

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Photon conversion point radius distribution from real data and MC simulation in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 4 (right)

Data from Figure 4, right panel

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Conversion probability correction factor for $\pi^0$ as a function of $p_{T}$

• #### Figure 5 (exp, EMC-TPC, MB)

Experimental data from Figure 3 with EMC-TPC method in minimum-bias (MB) events

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The overall detection efficiency of $\pi^0$ from embedding studt in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 5 (exp, EMC-TPC, HT)

Experimental data from Figure 3 with EMC-TPC method in the events with high-tower (HT) trigger

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The overall detection efficiency of $\pi^0$ from embedding studt in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 5 (exp, EMC-EMC, HT)

Simulated data from Figure 3 with EMC-EMC method in the events with high-tower (HT) trigger

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The overall detection efficiency of $\pi^0$ from embedding studt in 0-80% Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 6 (EMC-TPC, MB)

Data from Figure 6 with EMC-TPC method in minimum-bias (MB) events

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Invariant yield of STAR $\pi^0$ as a function of $p_{T}$ at midrapidity for different collision centrality bins in Au+Au collisions...

• #### Figure 6 (EMC-TPC, HT)

Data from Figure 6 with EMC-TPC method in the events with high-tower (HT) trigger

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Invariant yield of STAR $\pi^0$ as a function of $p_{T}$ at midrapidity for different collision centrality bins in Au+Au collisions...

• #### Figure 6 (EMC-EMC, HT)

Data from Figure 6 with EMC-EMC method in the events with high-tower (HT) trigger

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Invariant yield of STAR $\pi^0$ as a function of $p_{T}$ at midrapidity for different collision centrality bins in Au+Au collisions...

• #### Figure 7

Data from Figure 7

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The ratios of STAR $\pi^0$ spectra over $\pi^{\pm}$ from STAR and $\pi^0$ from PHENIX for different collision centrality bins in...

• #### Figure 8

Data from Figure 8

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The nuclear modification factor $R_{CP}$ as a functon of $p_{T}$ of STAR $\pi^0$ in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.

• #### Figure 9

Data from Figure 9

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The nuclear modification factor $R_{AA}$ as a functon of $p_{T}$ of STAR $\pi^0$ in Au+Au collisions at $\sqrt{s_{NN}}=200$ GeV.