Eur. Phys. J. A (2014) 50: 38
https://doi.org/10.1140/epja/i2014-14038-5

Regular Article - Experimental Physics

Flow probe of symmetry energy in relativistic heavy-ion reactions

¹ INFN, Sezione di Catania, I-95123, Catania, Italy
² IFIN-HH, Reactorului 30, 077125, Măgurele-Bucharest, Romania
³ GSI Helmholtzzentrum für Schwerionenforschung GmbH, D-64291, Darmstadt, Germany
⁴ STFC Daresbury Laboratory, WA4 4AD, Warrington, UK
⁵ School of Science, Huzhou Teachers College, 313000, Huzhou, P.R. China
⁶ IFJ-PAN, Pl-31342, Kraków, Poland

^* e-mail: w.trautmann@gsi.de

Received: 23 July 2013
Revised: 24 September 2013
Accepted: 8 October 2013
Published online: 26 February 2014

Abstract

Flow observables in heavy-ion reactions at incident energies up to about 1GeV per nucleon have been shown to be very useful for investigating the reaction dynamics and for determining the parameters of reaction models based on transport theory. In particular, the elliptic flow in collisions of neutron-rich heavy-ion systems emerges as an observable sensitive to the strength of the symmetry energy at supra-saturation densities. The comparison of ratios or differences of neutron and proton flows or neutron and hydrogen flows with predictions of transport models favors an approximately linear density dependence, consistent with ab initio nuclear-matter theories. Extensive parameter searches have shown that the model dependence is comparable to the uncertainties of existing experimental data. Comprehensive new flow data of high accuracy, partly also through providing stronger constraints on model parameters, can thus be expected to improve our knowledge of the equation of state of asymmetric nuclear matter.