Europhys. Lett.
Volume 74, Number 1, April 2006
Page(s) 29 - 35
Section Nuclear physics
Published online 08 March 2006
Europhys. Lett., 74 (1), pp. 29-35 (2006)
DOI: 10.1209/epl/i2005-10517-0

Rapidity equilibration and longitudinal expansion at RHIC

G. Wolschin

Institut für Theoretische Physik der Universität - Philosophenweg 16 D-69120 Heidelberg, Germany

received 10 December 2005; accepted in final form 14 February 2006
published online 8 March 2006

The evolution of net-proton rapidity spectra with $\sqrt{s_{NN}}$ in heavy relativistic systems is proposed as an indicator for local equilibration and longitudinal expansion. In a Relativistic Diffusion Model, bell-shaped distributions in central collisions at AGS energies and double-humped nonequilibrium spectra at SPS show pronounced longitudinal collective expansion when compared to the available data. The broad midrapidity valley recently discovered at RHIC in central Au + Au collisions at $\sqrt{s_{NN}}= 200\un{GeV}$ indicates rapid local equilibration which is most likely due to deconfinement, and fast longitudinal expansion of the locally equilibrated subsystem. A prediction is made for Au + Au at $\sqrt{s_{NN}}= 62.4\un{GeV}$.

25.75.-q - Relativistic heavy-ion collisions.
24.60.Ky - Fluctuation phenomena.
24.10.Jv - Relativistic models.

© EDP Sciences 2006