Anomalous centrality evolution of two-particle angular correlations from Au-Au collisions at $\sqrt{s_{\rm NN}}$ = 62 and 200 GeV

The STAR collaboration
Phys.Rev.C 86 (2012) 064902, 2012.

Abstract (data abstract)
We present two-dimensional (2D) two-particle angular correlations on relative pseudorapidity $\eta$ and azimuth $\phi$ for charged particles from Au-Au collisions at $\sqrt{s_{\mathrm{NN}}}=62$ and $200 \mathrm{GeV}$ with transverse momentum $p_{t} \geq 0.15 \mathrm{GeV} / c,|\eta| \leq 1$ and $2 \pi$ azimuth. Observed correlations include $\mathrm{a}$ $\{$ same-side $\}$ (relative azimuth $<\pi / 2$ ) $2 \mathrm{D}$ peak, a closely-related away-side azimuth dipole, and an azimuth quadrupole conventionally associated with elliptic flow. The same-side 2 D peak and away-side dipole are explained by semihard parton scattering and fragmentation (minijets) in proton-proton and peripheral nucleus-nucleus collisions. Those structures follow N-N binary-collision scaling in Au-Au collisions until midcentrality where a transition to a qualitatively different centrality trend occurs within a small centrality interval. Above the transition point the number of same-side and away-side correlated pairs increases rapidly \{relative to $\}$ binary-collision scaling, the $\eta$ width of the same-side $2 \mathrm{D}$ peak also increases rapidly $(\eta$ elongation) and the $\phi$ width actually decreases significantly. Those centrality trends are more remarkable when contrasted with expectations of jet quenching in a dense medium. Observed centrality trends are compared to \{ Isc hijing\} predictions and to the expected trends for semihard parton scattering and fragmentation in a thermalized opaque medium. We are unable to reconcile a semihard parton scattering and fragmentation origin for the observed correlation structure and centrality trends with heavy ion collision scenarios which invoke rapid parton thermalization. On the other hand, if the collision system is effectively opaque to few-GeV partons the observations reported here would be inconsistent with a minijet picture.

  • Figure 1a

    Data from Fig. 1a

    10.17182/hepdata.101346.v1/t1

    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1b

    Data from Fig. 1b

    10.17182/hepdata.101346.v1/t2

    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1c

    Data from Fig. 1c

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    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1d

    Data from Fig. 1d

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    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1e

    Data from Fig. 1e

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    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1f

    Data from Fig. 1f

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    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1g

    Data from Fig. 1g

    10.17182/hepdata.101346.v1/t7

    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 1h

    Data from Fig. 1h

    10.17182/hepdata.101346.v1/t8

    FIG. 1. (Color online) Perspective views of $2 \mathrm{D}$ charge-independent angular correlations $\Delta \rho / \sqrt{\rho_{\mathrm{ref}}}$ on $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ for...

  • Figure 2a

    Data from Fig. 2a

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    FIG. 2. (Color online) Fit decomposition of the $46 \%-56 \%$ centrality data for 62 -GeV Au-Au collisions. The top...

  • Figure 3a

    Data from Fig. 3, top left panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 3b

    Data from Fig. 3, middle top panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 3c

    Data from Fig. 3, top left panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 3d

    Data from Fig. 3, bottom left panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 3e

    Data from Fig. 3, middle bottom panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 3f

    Data from Fig. 3, bottom right panel

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    FIG. 3. Fit parameters for $\left(\eta_{\Delta}, \phi_{\Delta}\right)$ correlation data from Au-Au collisions at $\sqrt{s_{N N}}=62$ (open symbols) and 200 GeV...

  • Figure 4a

    Data from Fig. 4a

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    FIG. 4. (Color online) (a) 2D data histogram from $0 \%-5 \%$ central 200 GeV Au-Au collisions $[(0,0)$ bin suppressed]....

  • Figure 9a

    Data from Fig. 9a

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    FIG. 9. (a) Amplitude of SS 2D peak (jet-correlated pairs per final-state hadron) for data (solid points), GLS extrapolation from...

  • Figure 9b

    Data from Fig. 9b

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    FIG. 9. (a) Amplitude of SS 2D peak (jet-correlated pairs per final-state hadron) for data (solid points), GLS extrapolation from...

  • Figure 9c

    Data from Fig. 9c

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    FIG. 9. (a) Amplitude of SS 2D peak (jet-correlated pairs per final-state hadron) for data (solid points), GLS extrapolation from...

  • Figure 9d

    Data from Fig. 9d

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    FIG. 9. (a) Amplitude of SS 2D peak (jet-correlated pairs per final-state hadron) for data (solid points), GLS extrapolation from...

  • Figure 11

    Data from Fig. 11, left panel

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    FIG. 11. (Color online) (Left) Uncorrected angular correlations from 62-GeV $37 \%-46 \%$ central Au-Au collisions showing pileup distortions, especially...

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