how does the nuclear matter „look like“?, how does it behave ? ...

1. Response of the Spectators to the Participants Blast as a Probe of the Momentum-Dependent Nuclear Mean FieldV. HENZLa, M. V. Ricciardia, T. Enqvista,[1], J. Pereirab, J. Benlliureb, M. Bernasc, E. Casarejosb,, A. Kelića, J. Taïebc,[2], K.-H. Schmidta,aGSI, Planckstr. 1, 64291, Darmstadt, Germany,bUniversity of Santiago de Compostela, 15706 Santiago de Compostela, Spain,cInstitut de Physique Nucléaire, 91406 Orsay Cedex, France[1] Present address: University of Jyväskylä, 40351 Jyväskylä, Finland, [2] Present address: CEA/Saclay DM2S/SERMA/LENR, 91191 Gif/Yvette CEDEX, France General motivation Experiment at the Fragment Separator Inverse kinematics: Fundamental questions: • how does the nuclear matter „look like“?, how does it behave ? ... Astrophysical interest: From ToF:  /∆ ≈ 400 • evolution of the early universe • supernovae explosions • formation and stability of neutron stars A/∆A ≈ 400 (36m) influenced by properties of the NM under extreme conditions (high T, P, ρ) Once mass and charge are identified (A, Z are integer numbers) the velocity is calculated from B => veryprecise determination! Properties of the NM:  /∆ = B/∆B≈ 2000 • static – (in)compressibility, phase transitions, excitation… • dynamic – viscosity, momentum dependence of the mean field… +unambiguous identification and precise longitudinal momenta + full acceptance of most of the fragments Present knowledge Recent analysis: (Danielewicz et al.) - Only one fragment in one reaction measured, no correlations, no multiplicity - Low acceptance for light and fission fragments(~10%) Possible values of the nuclear incompressibility constrained by the experiments. Velocity distributions of fragmentation residues 238U+Pb @ 1 AGeV 238U+Ti @ 1 AGeV T.Enqvist et al. NPA658(1999)47 M.V.Ricciardi et al.PRL 90(2003)212302 Science 298 (2002) 1592 Only the most extreme models of EoS could be excluded by the experiment Basic characteristics: Fact: Static properties are studied in dynamical processes !!! • width • position • shape • the interpretation is influenced by competing phenomena Problem: most of the experimental observables is not selective; !!! The results are very often ambiguous !!! Information on reaction mechanism !!! Tools to investigate the nuclear matter What can we learn from the spectator response? Theoretical calculations for 4 different EoS:(Shi, Danielewicz, Lacey) Experiment:(Enqvist and Ricciardi et al.)) (Fission events excluded !!!) BUU calculations : 124Sn +124Sn Tlab= 800 MeV/u b = 5 fm L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001) Standard tools: elliptic flow, sideward flow, transverse momentum, kaon production, … ! New ! ! New ! Spectator response: the spectator is not a passive witness, but rather a victim of violent participants ! Spectator response selectively reflects the MD properties of the nuclear MF !!! • Precise velocity measurement of projectile fragmentsprovides a novel access to investigate the MD of nuclear mean field • L. Shi, P. Danielewicz, R. Lacey, PRC 64 (2001) • M.V.Ricciardi et al.PRL 90(2003)212302 CHARMS (Collaboration for High-Accuracy Experiments on Nuclear Reaction Mechanisms with the FRS)