Y. Shao

Radial flow in Au + Au collisions at E = (0.25-1.15)A GeV

A systematic study of energy spectra for light particles emitted at midrapidity from Au+Au collisions at {ital E}= (0.25--1.15){ital A} GeV reveals a significant nonthermal component consistent with a collective radial flow. This component is evaluated as a function of bombarding energy and event centrality. Comparisons to quantum molecular dynamics and Boltzmann-Uehling-Uhlenbeck models are made for different equations of state.

Statistical signatures of critical behavior in small systems

The cluster distributions of three different systems are examined to search for signatures of a continuous phase transition. In a system known to possess such a phase transition, both sensitive and insensitive signatures are present; while in systems known not to possess such a phase transition, only insensitive signatures are present. It is shown that nuclear multifragmentation results in cluster distributions belonging to the former category, suggesting that the fragments are the result of a continuous phase transition.

Constructing the phase diagram of finite neutral nuclear matter

Author(s): Elliott, J.B.; Moretto, L.G.; Phair, L.; Wozniak, G.L.; Albergo, S.; Bieser, F.; Brady, F.P.; Caccia, Z.; Cebra, D.A.; Chacon, A.D.; Chance, J.L.; Choi, Y.; Costa, S.; Gilkes, M.L.; Hauger, J.A.; Hirsch, A.S.; Hjort, E.L.; Insolia, A.; Justice, M.; Keane, D.; Kintner, J.C.; Lindenstruth, V.; Lisa, M.A.; Matis, H.S.; McMahan, M.; McParland, C.; Muller, W.F.J.; Olson, D.L.; Partlan, M.D.; Porile, N.T.; Potenza, R.; Rai, G.; Rasmussen, J.; Ritter, H.G.; Romanski, J.; Romero, J.L.; Russo, G.V.; Sann, H.; Scharenberg, R.P.; Scott, A.; Shao, Y.; Srivastava, B.K.; Symons, T.J.M.; Tincknell, M.; Tuve, C.; Wang, S.; Warren, P.; Wieman, H.H.; Wienold, T.; Wolf, K.

Nuclear multifragmentation, percolation and the Fisher Droplet model: common features of reducibility and thermal scaling

It is shown that the Fisher droplet model, percolation, and nuclear multifragmentation share the common features of reducibility (stochasticity in multiplicity distributions) and thermal scaling (one-fragment production probabilities are Boltzmann factors). Barriers obtained, for cluster production on percolation lattices, from the Boltzmann factors show a power-law dependence on cluster size with an exponent of 0.42+/-0.02. The EOS Collaboration Au multifragmentation data yield barriers with a power-law exponent of 0.68+/-0.03. Values of the surface energy coefficient of a low density nuclear system are also extracted.

The search for the scaling function in the multifragmentation of gold nuclei

Abstract It is shown that thermodynamic scaling when applied to systems with few (∼150) constituents, in accordance with the theory of critical phenomena, is observed in nuclear multifragmentation. Yields of different nuclear fragments, obtained over a wide range of excitation energies, collapse with some scatter onto a universal curve. This curve is the nuclear scaling function, which is intimately related to the free energy of the system. The determination of the scaling function forms the basis for quantitatively predicting the critical behavior in nuclei.

Individual fragment yields and determination of the critical exponent σ

Abstract We have studied the yield of individual fragments formed in the projectile fragmentation of gold nuclei at 1 AGeV incident on a carbon target as a function of the total charge multiplicity. The yields of fragments of different nuclear charge peak at different multiplicities. We show that this behavior can be used to determine the critical exponent σ. We obtain σ = 0.68±0.05, consistent with the liquid-gas value.

Neutrons from multiplicity-selected La-La and Nb-Nb collisions at 400A MeV and La-La collisions at 250A MeV.

Triple-differential cross sections for neutrons from high-multiplicity La-La collisions at 250 and 400 MeV per nucleon and Nb-Nb collisions at 400 MeV per nucleon were measured at several polar angles as a function of the azimuthal angle with respect to the reaction plane of the collision. The reaction plane was determined by a transverse-velocity method with the capability of identifying charged-particles with Z=1, Z=2, and Z{gt}2. The flow of neutrons was extracted from the slope at mid-rapidity of the curve of the average in-plane momentum vs the center-of-mass rapidity. The {ital squeeze-out} of the participant neutrons was observed in a direction normal to the reaction plane in the normalized momentum coordinates in the center-of-mass system. Experimental results of the neutron squeeze-out were compared with BUU calculations. The polar-angle dependence of the maximum azimuthal anisotropy ratio r({theta}) was found to be insensitive to the mass of the colliding nuclei and the beam energy. Comparison of the observed polar-angle dependence of the maximum azimuthal anisotropy ratio r({theta}) with BUU calculations for {ital free} neutrons revealed that r({theta}) is insensitive also to the incompressibility modulus in the nuclear equation of state. {copyright} {ital 1999} {ital The American Physical Society}

Flow and multifragmentation in nuclear collisions at intermediate energies

Abstract Energy spectra of hydrogen and helium isotopes emitted in Au+Au collisions at 0.25, 0.40, 0.60, 0.80, 1.0, and 1.15 A GeV have been measured. A systematic study of the shapes of the spectra reveals a significant non-thermal component consistent with collective radial flow. The strength of this component is evaluated as a function of bombarding energy. Comparisons of the flow signal to predictions of QMD and BUU models are made. Using reverse kinematics, the breakup of gold nuclei has been studied in Au+C reactions at 1.0 A GeV. The moments of the resulting charged fragment distribution provide evidence that nuclear matter possesses a critical point observable in finite nuclei. Values for the critical exponents γ, β, and τ have been determined. These values are close to those for liquid-gas systems and different from those for 3D percolation.

Radial flow in Au + Au collisions at E = 0.25-A/GeV - 1.15-A/Gev

A systematic study of energy spectra for light particles emitted at midrapidity from Au+Au collisions at {ital E}= (0.25--1.15){ital A} GeV reveals a significant nonthermal component consistent with a collective radial flow. This component is evaluated as a function of bombarding energy and event centrality. Comparisons to quantum molecular dynamics and Boltzmann-Uehling-Uhlenbeck models are made for different equations of state.

A Detailed Comparison of Exclusive 1 GeV a Au on C Data with the Statistical Multifragmentation Model (SMM)

The mimimum requirement for a meaningful comparison of the 1 GeV Au on C data with the SMM1 predications is that the mass AR the charge Z R , and the excitation energy E x of the multifragmenting system be determined on an event by event basis. This can only be done if a full reconstruction of the collision is possible for each event. The EOS data2–4 provides a complete charge and momentum reconstruction for every event. Average fragment masses are determined. The basic remnant information A R (ZR, EX) is also used as input information for the SMM calculation. Thus a fragmentation event produced by SMM consists of M2s fragments with masses A F and charge Z F. A data fragmentation event consists of M2D fragments with mass A F and charge Z F . Since the remnant mass A R = A AU - M1 where M1 is the collisional particle multiplicity, it is convenient to introduce the total charged particle multiplicity M T for both the SMM predictions and the data. M T = M 2s + M1 for the SMM events and M T = M 2D + M1 for the Au on C events.