Entropy production in the Au+Au reaction between 150Aand 800AMeV

Systematics of stopping and flow in Au+ Au collisions

“…11) but with even larger slopes also for other light fragments. This intriguing phenomenon has already been reported for the lighter systems 40 Ar + 58 Ni, 58 Ni + 58 Ni, and 129 Xe + nat Sn, provided the '1-plane-per-particle' method was used for estimation of the reaction plane [21]. For these systems, a balance energy has been determined by associating it with the minima of the approximately parabolic excitation functions of the flow parameter which, in the cases of 40 Ar + 58 Ni and 58 Ni + 58 Ni, appeared at negative flow values.…”

“…At intermediate to low incident energies, especially for E/A < 100 MeV, the literature abounds with an impressive diversity in the choice of global observables that have been used in attempts to select either narrowly constrained impact parameters (keywords 'highly exclusive' or 'ultracentral') or events of special interest (keywords 'fully equilibrated', 'fully evaporated', 'signals of phase coexistence'). The observables vary from very simple ones like proton, neutron or total charged-particle multiplicity to more specific ones as, e.g., participant proton multiplicity (N p ) [53,54], total (E T ) [55,56] or light charged particle transverse kinetic energy (E 12 ⊥ ) [57], ratio of transverseto-longitudinal kinetic energy (Erat) [58,59], degree of isotropy of momenta (R) [60,61], transverse momentum directivity (D) [62][63][64][65], longitudinal kinetic-energy fraction (E e ) [66,67], linear momentum transfer [68], total kinetic-energy loss (T KEL) [69,70], average parallel velocity (V av ) [71], midrapidity charge (Z y ) [72], total charge of Z≥2 products (Z bound ) [73,74], longitudinal component of the quadrupole moment tensor (Q zz ) [75]. Even more complex observables are those obtained from sphericity [76,77], from the kinetic energy tensor [78,80] or momentum tensor [67,81,82], the thrust (T ) [67,83,84], the deflection angle of the projectile (Θ def l ) [85], the flow angle (Θ f low ) [3,86], the location in a 'Wilczyński plot' …”

Central collisions of Au on Au at 150, 250 and 400 A·MeV

“…Older exclusive information on heavy cluster formation from Bevalac times was limited to an experiment at 200 A MeV [15] concentrating on sideflow: a remarkable result of this study was the demonstrated higher sensitivity of the IMF's to flow, a fact that had been anticipated in the framework of hydrodynamical model calculations [16]. Since then, new information from central or semicentral collisions at energies beyond 100 A MeV has emerged from work done both at Berkeley and Darmstadt [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31].…”

“…Our collaboration, taking advantage of combined high multiplicity and low directivity event selection, first showed that the heavy clusters indeed were emitted from essentially one source located at midrapidity [17]. Soon after, we came to the conclusion, with use of statistical models, that the occurrence of so many IMF's had to be associated with a surprisingly low entropy [18,23]. The new radial flow phenomenon was then quantized [20] and a first attempt using the model of ref.…”

Shock compression and expansion in central collisions

“…Left panel shows entropy per nucleon as a function of reduced participant multiplicity, determined from 400 MeV/nucleon Au + Au wide-angle light-particle data of Ref 15. (stars) and from intermediate-mass fragment data of Ref 16. (cross).…”