J. A. Hauger

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.

The energy dependence of flow in Ni induced collisions from 400A to 1970A MeV

We study the energy dependence of collective (hydrodynamic-like) nuclear matter flow in (400{endash}1970){ital A} MeV Ni+Au and (1000{endash}1970){ital A} MeV Ni+Cu reactions. The flow increases with energy, appears to reach a maximum, and then to decrease at higher energies. A way of comparing the energy dependence of flow values for different projectile-target mass combinations is introduced, which demonstrates a more-or-less common scaling behavior among flow values from different systems. {copyright} {ital 1997} {ital The American Physical Society}

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.

A time-of-flight detector based on silicon avalanche diodes

Abstract We have investigated reach-through silicon avalanche diodes (AVDs) as time of flight detectors for nuclear and particle physics experiments. The signal is initiated by a minimum ionizing charged particle passing directly through the AVD. We have studied the effect of pulse amplitude and noise characteristics on timing using β − particles. The time resolution of four AVDs has been measured with a range of standard deviations, σ = 65–87 ps. This time resolution is comparable to the best available with the conventional alternative, a plastic scintillator and photomultiplier tube. Further optimization of the AVD results appears possible.

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.

Λ hyperons in 2 a GeV Ni + Cu collisions

A sample of �s produced in 2 AGeV 58 Ni + nat Cu collisions has been obtained with the EOS Time Projection Chamber at the Bevalac. Low background in the invariant mass distribution allows for the unambiguous demonstration ofdirected flow. ThemT spectrum at mid-rapidity has the characteristic shoulder-arm shape of particles undergoing radial transverse expansion. A linear dependence ofmul- tiplicity on impact parameter is observed, from which a total � + � 0 production cross section of 112 ± 24 mb is deduced. Detailed comparisons with the ARC and RVUU models are made.

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.