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Balance Functions from Au$+$Au, $d+$Au, and $p+p$ Collisions at $\sqrt{s_{NN}}$ = 200 GeV

The collaboration
Phys.Rev.C 82 (2010) 024905, 2010.

Abstract (data abstract)
Balance functions have been measured for charged particle pairs, identified charged pion pairs, and identified charged kaon pairs in Au+Au, d+Au, and p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV at the Relativistic Heavy Ion Collider using the STAR detector. These balance functions are presented in terms of relative pseudorapidity, $\Delta \eta$, relative rapidity, $\Delta y$, relative azimuthal angle, $\Delta \phi$, and invariant relative momentum, $q_{inv}$. In addition, balance functions are shown in terms of the three components of $q_{inv}$: $q_{long}$, $q_{out}$, and $q_{side}$. For charged particle pairs, the width of the balance function in terms of $\Delta \eta$ scales smoothly with the number of participating nucleons, while HIJING and UrQMD model calculations show no dependence on centrality or system size. For charged particle and charged pion pairs, the balance functions widths in terms of $\Delta \eta$ and $\Delta y$ are narrower in central Au+Au collisions than in peripheral collisions. The width for central collisions is consistent with thermal blast-wave models where the balancing charges are highly correlated in coordinate space at breakup. This strong correlation might be explained either by delayed hadronization or by limited diffusion during the reaction. Furthermore, the narrowing trend is consistent with the lower kinetic temperatures inherent to more central collisions. In contrast, the width of the balance function for charged kaon pairs in terms of $\Delta y$ shows little centrality dependence, which may signal a different production mechanism for kaons. The widths of the balance functions for charged pions and kaons in terms of $q_{inv}$ narrow in central collisions compared to peripheral collisions, which may be driven by the change in the kinetic temperature.

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Data from Figure 1

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The distribution of the reconstructed position of the event vertex along the beam direction for events from Au+Au collisions at...

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Data from Figure 2

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Calculated balance functions for all charged particles from central Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV using HIJING. The open...

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Data from Figure 3

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The balance function in terms of $\Delta \eta$ for all charged particle pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200...

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Data from Figure 4

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The balance function in terms of $\Delta y$ for identiﬁed charged pion pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200...

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Data from Figure 5

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The balance function in terms of $\Delta y$ for identiﬁed charged kaon pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200...

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Data from Figure 6

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The balance function for p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. The top panel shows the balance function for all...

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Data from Figure 6

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The balance function for p+p collisions at $\sqrt{s_{NN}}$ = 200 GeV. The top panel shows the balance function for all...

• #### Figure 7

Data from Figure 7

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The balance function in terms of $\Delta \eta$ for all charged particles from d+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV...

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Data from Figure 8

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The balance function in terms of $q_{inv}$ for charged pion pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in...

• #### Figure 9

Data from Figure 9

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The balance function in terms of $q_{inv}$ for charged-pion pairs in two centrality bins over the range 0 < $q_{inv}$...

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Data from Figure 10

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The balance function in terms of $q_{inv}$ for charged kaon pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in...

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Data from Figure 11

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The balance function in terms of $q_{inv}$ for charged pion pairs [part a)] and charged kaon pairs [part b)] from...

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Data from Figure 12

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The balance function in terms of $q_{long}$ for charged pion pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in...

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Data from Figure 13

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The balance function in terms of $q_{out}$ for charged pion pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV in...

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Data from Figure 14

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(Color online) The balance function in terms of $q_{side}$ for charged pion pairs from Au+Au collisions at $\sqrt{s_{NN}}$ = 200...

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Data from Figure 15

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(Color online) The balance function in terms of $\Delta\phi$ for all charged particles with 0.2< pt<2.0 GeV/c from Au+Au collisions...

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Data from Figure 16

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(Color online) The balance function in terms of $\Delta\phi$ for all charged particles with 1.0< pt<10.0 GeV/c from Au+Au collisions...

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Data from Figure 17 (Data $0-5\%$, HIJING Filtered)

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(Color online) The balance function in terms of $\Delta y$ for charged pions from central collisions of Au+Au at $\sqrt{s_{NN}}$...

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Data from Figure 17 (Blast Wave Model)

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(Color online) The balance function in terms of $\Delta y$ for charged pions from central collisions of Au+Au at $\sqrt{s_{NN}}$...

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Data from Figure 18 (Data $0-5\%$, HIJING Filtered)

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(Color online) The balance function in terms of $q_{inv}$ for charged pions from central collisions of Au+Au at $\sqrt{s_{NN}}$ =...

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Data from Figure 18 (Blast Wave Model)

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(Color online) The balance function in terms of $q_{inv}$ for charged pions from central collisions of Au+Au at $\sqrt{s_{NN}}$ =...

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Data from Figure 19 (AuAu, dAu)

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(Color online) The balance function width $<\Delta\eta>$ for all charged particles from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV compared...

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Data from Figure 19 (pp)

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(Color online) The balance function width $<\Delta\eta>$ for all charged particles from Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV compared...

• #### Figure 20

Data from Figure 20

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(Color online) The balance function widths for identified charged pions and charged kaons from Au+Au collisions at $\sqrt{s_{NN}}$ = 200...

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Data from Figure 21 (Pions)

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(Color online) The balance function width $\sigma$ extracted from $B(q_{inv})$ for identified charged pions and kaons from Au+Au collisions at...

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Data from Figure 21 (Kaons)

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(Color online) The balance function width $\sigma$ extracted from $B(q_{inv})$ for identified charged pions and kaons from Au+Au collisions at...

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Data from Figure 22

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(Color online) The widths for the balance functions for pions in terms of $q_{long}$, $q_{out}$, and $q_{side}$ compared with UrQMD...

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Data from Figure 23

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(Color online) The weighted average cosine of the relative azimuthal angle,$<\cos(\Delta\phi)$, extracted from $B(\Delta\phi)$ for all charged particles with \$0.2<...