Speaker
Gary Westfall
(Michigan State University)
Description
The balance function, which measures the correlations between opposite sign charge pairs, is sensitive to the mechanisms of charge formation and the subsequent relative diffusion of the balancing charges. The study of the balance function can provide information about charge creation times as well as the subsequent collective behavior of particles. We present charge balance functions in terms of relative pseudorapidity ($\Delta \eta$) from Au+Au collisions at incident energies ranging from $\sqrt{s_{\rm NN}}$ = 7.7 to 200 GeV and compare these results with recent results for Pb+Pb collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV from the ALICE Collaboration [1]. We find that the charge balance function narrows as the collisions become more central and as the incident energy increases. This behavior is consistent with the concept of delayed hadronization of a deconfined quark-gluon plasma (QGP). We also present balance functions in terms of relative rapidity ($\Delta y$) for identified $\pi^{+}/\pi^{-}$ pairs, $K^{+}/K^{-}$ pairs, and $p/\bar{p}$ pairs from central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. We compare to a model [2] that relates these balance functions to the correlations of deconfined up, down, and strange quarks in the QGP that is created in central Au+Au collisions at $\sqrt{s_{\rm NN}}$ = 200 GeV. We find our results are consistent with two waves of quark creation in time, one early in the collision ($\sim 1$ fm/$c$) and a second occurring at hadronization ($\sim 5-10$ fm/$c$). We find that the densities of up, down, and strange quarks in the QGP extracted from the model comparison are consistent with current lattice gauge calculations.
[1] ALICE Collaboration, Phys. Lett. B **723**, 267 (2013).
[2] Scott Pratt, Phys. Rev. Lett. **108**, 212301 (2012), Scott Pratt, Phys. Rev. C **85**, 014904 (2012).
| On behalf of collaboration: | STAR |
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Author
Gary Westfall
(Michigan State University)
