Beam-energy and system-size dependence of the space-time extent of the pion emission source produced in heavy ion collisions

Abstract

Two-pion interferometry measurements are used to extract the Gaussian radii $R_{\mathrm{out}}$, $R_{\mathrm{side}}$, and $R_{\mathrm{long}}$, of the pion emission sources produced in Cu$+$Cu and Au$+$Au collisions at several beam collision energies $\sqrt{s_{{}_{NN}}}$ at PHENIX. The extracted radii, which are compared to recent STAR and ALICE data, show characteristic scaling patterns as a function of the initial transverse size $\bar{R}$ of the collision systems and the transverse mass $m_T$ of the emitted pion pairs, consistent with hydrodynamiclike expansion. Specific combinations of the three-dimensional radii that are sensitive to the medium expansion velocity and lifetime, and the pion emission time duration show nonmonotonic $\sqrt{s_{{}_{NN}}}$ dependencies. The nonmonotonic behaviors exhibited by these quantities point to a softening of the equation of state that may coincide with the critical end point in the phase diagram for nuclear matter.

622 authors, 8 pages, 5 figures, data from 2005, 2007, and 2010. Submitted to Phys. Rev. Lett. Plain text data tables for the points plotted in figures for this and previous PHENIX publications are (or will be) publicly available at http://www.phenix.bnl.gov/papers.html

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