Isotopic Flow in Xe+Sn Collisions

The high accuracy that can be achieved in the experimental determination of flow parameters from data collected with advanced 4π detection systems has recently been demonstrated in a combined analysis of INDRA and FOPI data [1]. Excitation functions for directed and elliptic flow in Au + Au reactions, measured at SIS by the two collaborations [2, 3], were found to agree within 5% to at most 10% in the overlap region 90 to 150 A MeV covered by the two data sets. Data with this level of precision can be useful for the investigation of presumably small isotopic effects related to the symmetry term in the nuclear equation of state, with the aim to reduce its present uncertainty at densities beyond the saturation density [4, 5]. Identifying the key observables sensitive to the neutron-proton asymmetry is a basic task here which may be achieved by studying collisions between partners with varying neutron-proton asymmetry.