High transverse momentum $\eta$ meson production in $p^+ p$, $d^+$ Au and Au+Au collisions at $S(NN) ^{(1/2)}$ = 200-GeV

The PHENIX collaboration
Phys.Rev.C 75 (2007) 024909, 2007.

Abstract (data abstract)
BNL-RHIC. Inclusive transverse momentum spectra of $\eta$ mesons in the range $p_T\approx$ 2-12 GeV/$c$ have been measured at mid-rapidity (|$\eta$| < 0.35) by the PHENIX experiment at RHIC in p+p, d+Au and Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV. The $\eta$ mesons are reconstructed through their $\eta\rightarrow\gamma\gamma$ channel for the three colliding systems as well as through the $\eta\rightarrow\pi^{0}\pi^{+}\pi^{-}$ decay mode in p+p and d+Au collisions. The nuclear modification factor in d+Au collisions, $R_{dAu}(p_T)\approx$ 1.0-1.1, suggests at most only modest $p_T$ broadening ("Cronin enhancement"). In central Au+Au reactions, the $\eta$ yields are significantly suppressed, with $R_{AuAu}(p_T)\approx$ 0.2. The ratio of $\eta$ to $\pi^{0}$ yields is approximately constant as a function of $p_T$ for the three colliding systems in agreement with the high-$p_T$ world average of $R_{\eta/\pi^{0}}\approx$ 0.5 in hadron-hadron, hadron-nucleus, and nucleus-nucleus collisions for a wide range of center-of-mass energies [$\sqrt{s_{NN}}\approx$ 3-1800 GeV] as well as, for high scaled momentum $x_p$, in $e^{+}e^{-}$ annihilations at $\sqrt{s}$ = 91.2 GeV. These results are consistent with a scenario where high-$p_T$ $\eta$ production in nuclear collisions at RHIC is largely unaffected by initial-state effects, but where light-quark mesons ($\pi^{0}$;$\eta$) are equally suppressed due to final-state interactions of the parent partons in the dense medium produced in Au+Au reactions.

  • Figure 12.1

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    Inelastic cross section measured in p+p at $\sqrt{s}$=200 GeV through $\eta \rightarrow \gamma \gamma$

  • Figure 12.2

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    Inelastic cross section measured in p+p at $\sqrt{s}$=200 GeV through $\eta \rightarrow \pi^{0} \pi^{+} \pi^{-}$

  • Figure 13.1

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    Inelastic cross section measured in d+Au at $\sqrt{s}$=200 GeV through $\eta \rightarrow \gamma \gamma$

  • Figure 13.2

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    Inelastic cross section measured in d+Au at $\sqrt{s}$=200 GeV through $\eta \rightarrow \pi^{0} \pi^{+} \pi^{-}$

  • Figure 14

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    Invariant yields measured in d+Au for different centrality classes

  • Figure 15

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    Invariant yields measured in Au+Au for different centrality classes

  • Figure 16

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    Nuclear modification factor $R_{dA}$ for $\eta$ measured in d+Au for different centrality classes

  • Figure 17

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    Nuclear modification factor $R_{AA}(p_T)$ for $\eta$ measured in Au+Au for different centrality classes

  • Figure 18

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    Ratio of $\eta$ and $\pi^{0}$ measured in p+p at $\sqrt{s}$=200 GeV

  • Figure 19

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    Ratio of $\eta$ and $\pi^{0}$ measured in d+Au for different centrality classes

  • Figure 20

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    Ratio of $\eta$ and $\pi^{0}$ measured in Au+Au for different centrality classes

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