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S. Turbide,
L. Beaulieu,
P. Danielewicz,
V. E. Viola,
R. Roy,
K. Kwiatkowski,
W.-C. Hsi,
G. Wang,
T. Lefort, D. S. Bracken, [......],
R. Huang,
R. Korteling,
W. G. Lynch,
K. B. Morley,
E. Ramakrishnan,
L. P. Remsberg,
D. Rowland,
M. B. Tsang,
H. Xi,
S. J. Yennello
[show abstract]
[hide abstract]
ABSTRACT: Effects of in-medium cross sections and of optical potential on preequilibrium emission and on formation of a thermal source are investigated by comparing the results of transport simulations with experimental results from the p+197Au reaction at 6.2–14.6 GeV∕c. The employed transport model includes light-composite-particle production and allows for inclusion of in-medium particle-particle cross-section reduction and of momentum dependence in the particle optical potentials. Compared to the past, the model incorporates improved parametrizations of elementary high-energy processes. The simulations indicate that the majority of energy deposition occurs during the first 25 fm∕c of a reaction. This is followed by a preequilibrium emission and readjustment of system density and momentum distribution toward an equilibrated system. Within different variants of calculations, the best agreement with data, on the d∕p and t∕p yield ratios and on the residue mass and charge numbers, is obtained at the time of about 65 fm∕c from the start of a reaction, for simulations employing reduced in-medium cross sections and momentum-dependent optical potentials. By that time, the preequilibrium nucleon and cluster emission, as well as mean field readjustments, drive the system to a state of depleted average density, ρ∕ρ0∼1∕4–1∕3 for central collisions, and low-to-moderate excitation, i.e., the region of nuclear liquid-gas phase transition.
Phys. Rev. C. 07/2004; 70(1).
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[show abstract]
[hide abstract]
ABSTRACT: Multifragment breakup of natAg and 197Au nuclei bombarded by 1.8–4.8 GeV 3He ions has been studied with the Indiana Silicon Sphere 4π detector array. To investigate the properties of the emitting source as a function of excitation energy, a two-component moving-source analysis has been performed on the intermediate-mass-fragment spectra, gating on excitation energy. The results provide evidence for nuclear expansion∕dilution to a value of ρ∕ρ0≲1∕3 prior to breakup. For the most violent events, relatively low source velocities of v∕c~0.01 and slope temperatures of T∼15 MeV are obtained for the dominant thermal-like source. The dependence of isotope ratios on deposition energy and ejectile kinetic energy is examined for H and He isotopes, and the caloric curves for the 4.8 GeV data are presented.
Phys. Rev. C. 03/2004; 69(3).
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S. Turbide,
L. Beaulieu,
P. Danielewicz,
V.E. Viola,
R Roy,
K. Kwiatkowski,
W. C. Hsi,
G Wang,
T. Lefort, D.S. Bracken, [......],
R. Huang,
R. Korteling,
W. G. Lynch,
K.B. Morley,
E. Ramakrishnan,
L P Remsberg,
D. Rowland,
M. B. Tsang,
H. Xi,
S. J. Yennello
[show abstract]
[hide abstract]
ABSTRACT: Effects of in-medium cross-sections and of optical potential on pre-equilibrium emission and on formation of a thermal source are investigated by comparing the results of transport simulations with experimental results from the p+{197}Au reaction at 6.2-14.6 GeV/c. The employed transport model includes light composite-particle production and allows for inclusion of in-medium particle-particle cross-section reduction and of momentum dependence in the particle optical-potentials. Compared to the past, the model incorporates improved parameterizations of elementary high-energy processes. The simulations indicate that the majority of energy deposition occurs during the first ~25 fm/c of a reaction. This is followed by a pre-equilibrium emission and readjustment of system density and momentum distribution toward an equilibrated system. Good agreement with data, on the d/p and t/p yield ratios and on the residue mass and charge numbers, is obtained at the time of ~ 65 fm/c from the start of a reaction, provided reduced in-medium cross-sections and momentum-dependent optical potentials are employed in the simulations. By then, the pre-equilibrium nucleon and cluster emission, as well as mean-field readjustments, drive the system to a state of depleted average density, rho/rho_{0} ~ 1/4-1/3 for central collisions, and low-to-moderate excitation, i.e. the region of nuclear liquid-gas phase transition. Comment: 35 pages, 14 figures
02/2004;
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D. S. Bracken,
K. Kwiatkowski,
E. Renshaw Foxford†,
K. B. Morley,
V. E. Viola,
N. R. Yoder,
J. Brzychczyk,
E. C. Pollacco,
R. Legrain‡,
C. Volant,
R. G. Korteling
[show abstract]
[hide abstract]
ABSTRACT: Multifragment breakup of natAg and 197Au nuclei bombarded by 1.8–4.8 GeV 3He ions has been studied with the Indiana Silicon Sphere 4π detector array. To investigate the properties of the emitting source as a function of excitation energy, a two-component moving-source analysis has been performed on the intermediate-mass-fragment spectra, gating on excitation energy. The results provide evidence for nuclear expansion∕dilution to a value of ρ∕ρ0≲1∕3 prior to breakup. For the most violent events, relatively low source velocities of v∕c~0.01 and slope temperatures of T∼15 MeV are obtained for the dominant thermal-like source. The dependence of isotope ratios on deposition energy and ejectile kinetic energy is examined for H and He isotopes, and the caloric curves for the 4.8 GeV data are presented.
Physical Review C 01/2004; · 3.31 Impact Factor
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L Beaulieu,
T Lefort,
K Kwiatkowski,
R T de Souza,
W Hsi,
L Pienkowski,
B Back, D S Bracken,
H Breuer,
E Cornell, [......],
E Martin,
K B Morley,
E Ramakrishnan,
L P Remsberg,
D Rowland,
A Ruangma,
V E Viola,
G Wang,
E Winchester,
S J Yennello
[show abstract]
[hide abstract]
ABSTRACT: Excitation-energy-gated two-fragment correlation functions have been studied between E(*)/A = (2-9)A MeV for equilibriumlike sources formed in 8-10 GeV/c pi(-) and p+197Au reactions. Comparison with an N-body Coulomb-trajectory code shows an order of magnitude decrease in the fragment emission time in the interval E(*)/A = (2-5)A MeV, followed by a nearly constant breakup time at higher excitation energy. The decrease in emission time is strongly correlated with the onset of multifragmentation and thermally induced radial expansion, consistent with a transition from surface-dominated to bulk emission expected for spinodal decomposition.
Physical Review Letters 07/2000; 84(26 Pt 1):5971-4. · 7.37 Impact Factor
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L. Beaulieu,
K. Kwiatkowski,
W.-c. Hsi,
T. Lefort,
R. de Souza,
G. Wang, D.S. Bracken,
E. Cornell,
D.S. Ginger,
V.E. Viola, [......],
E. Martin,
E. Ramakrishnan,
D. Rowland,
A. Ruangma,
E. Winchester,
S.J. Yennello,
S. Gushue,
L.P. Remsberg,
H. Breuer,
B. Back
Physical Review Letters 01/2000; 84:5971. · 7.37 Impact Factor
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K. Kwiatkowski W.-c. Hsi,
G. Wang, D. S. Bracken,
E. Cornell,
D. S. Ginger,
R. G. Korteling,
K. B. Morley,
R. Huang,
W. G. Lynch,
M. B. Tsang,
H. Xi,
F. Gimeno-Nogues,
E. Ramakrishnan,
D. Rowland,
S. J. Yennello,
H. Breuer,
S. Gushue,
L. P. Remsberg,
A. Botvina,
W. A. Friedman
[show abstract]
[hide abstract]
ABSTRACT: Exclusive studies of angular distributions for intermediate-mass fragments (IMFs) produced in GeV hadron-induced reactions have been performed with the Indiana Silicon Sphere (ISiS) 4π detector array. Special emphasis has been given to understanding the origin of sideways peaking, which becomes prominent in the angular distributions for beam momenta above about 10 GeV/c. Both the magnitude of the effect and the peak angle increase as a function of fragment multiplicity and charge. When gated on IMF kinetic energy, the angular distributions evolve from forward-peaked to near isotropy as the fragment kinetic energy decreases. Fragment-fragment angular-correlation analyses show no obvious evidence for a dynamic mechanism that might signal shock wave effects or the breakup of exotic geometric shapes such as bubbles or toroids. Moving-source and intranuclear cascade simulations suggest that the observed sideways peaking is of kinematic origin, arising from significant transverse momentum imparted to the heavy recoil nucleus during the fast cascade stage of the collision. A two-step cascade and statistical multifragmentation calculation is consistent with this assumption.
Phys. Rev. C. 08/1999; 60(3).
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L. Beaulieu,
K. Kwiatkowski,
W. C. Hsi,
T. Lefort,
L. Pienkowski,
R. G. Korteling,
G Wang,
B. Back, D.S. Bracken,
H. Breuer, [......],
K.B. Morley,
E. Ramakrishnan,
L P Remsberg,
D. Rowland,
A. Ruangma,
M. B. Tsang,
V.E. Viola,
E. Winchester,
H. Xi,
S. J. Yennello
[show abstract]
[hide abstract]
ABSTRACT: Excitation-energy distributions have been derived from measurements of 5.0-14.6 GeV/c antiproton, proton and pion reactions with $^{197}$Au target nuclei, using the ISiS 4$\pi$ detector array. The maximum probability for producing high excitation-energy events is found for the antiproton beam relative to other hadrons, $^3$He and $\bar{p}$ beams from LEAR. For protons and pions, the excitation-energy distributions are nearly independent of hadron type and beam momentum above about 8 GeV/c. The excitation energy enhancement for $\bar{p}$ beams and the saturation effect are qualitatively consistent with intranuclear cascade code predictions. For all systems studied, maximum cluster sizes are observed for residues with E*/A $\sim$ 6 MeV. Comment: 14 pages including 5 figures and 1 table. Accepted in Physics Letter B. also available at http://nuchem.iucf.indiana.edu/
06/1999;
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G. Wang,
K. Kwiatkowski, D. S. Bracken,
E. Renshaw Foxford,
K. B. Morley W.-c. Hsi,
C. Volant,
R. Legrain,
E. C. Pollacco,
R. G. Korteling,
W. A. Friedman,
A. Botvina,
J. Brzychczyk,
H. Breuer
[show abstract]
[hide abstract]
ABSTRACT: To investigate the source size and time dependence of multifragmentation reactions, small- and large-angle relative velocity correlations between coincident complex fragments have been measured for the 1.8–4.8 GeV 3He+natAg, 197Au systems. The results support an evolutionary scenario for the fragment emission process in which lighter IMFs (Z≲6) are emitted from a hot, more dense source prior to breakup of an expanded residue. For the most highly excited residues, for which there is a significant yield of fragments with very soft energy spectra (E/A<~3 MeV), comparisons with an N-body simulation suggest a breakup time of τ∼50 fm/c for the expanded residue. Comparison of these data with both the evolutionary expanding emitting source model and the Copenhagen statistical multifragmentation model shows good agreement for heavier IMF’s formed in the final breakup stage, but only the evolutionary model is successful in accounting for the lighter IMFs.
Phys. Rev. C. 06/1999; 60(1).
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J. Brzychczyk,
E. C. Pollacco,
C. Volant,
D. Lacroix,
R. Legrain,
K. Kwiatkowski, D. S. Bracken,
K. B. Morley,
E. Renshaw Foxford,
V. E. Viola,
N. R. Yoder,
J. Cugnon,
R. G. Korteling,
H. Breuer
[show abstract]
[hide abstract]
ABSTRACT: The charge-moment technique has been used to study the fragment charge distribution for the 3He(4.8 GeV)+197Au reaction. A large variety of fragment charges characterized by a relative variance ∼2.3, is observed for excitation energies around 5.5 MeV/nucleon. Similar signals related to a phase transition are predicted by the percolation model and the statistical multifragmentation model. Effects of detector acceptance and contribution from fission are discussed.
Physical Review C 01/1998; · 3.31 Impact Factor
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K. Kwiatkowski,
W.-c. Hsi,
G. Wang,
T. Lefort, D.S. Bracken,
E. Cornell,
E. Renshaw Foxford,
D.S. Ginger,
V.E. Viola,
N.R. Yoder, [......],
M.B. Tsang,
H. Xi,
H. Breuer,
K.B. Morley,
S. Gushue,
L.P. Remsberg,
L. Pienkowski,
J. Brzychezyk,
A. Botvina,
W.A. Friedman
[show abstract]
[hide abstract]
ABSTRACT: Multifragmentation studies with GeV light-ion beams indicate that for the most violent collisions, complex fragments are emitted during expansion of the hot source, followed by near simultaneous breakup of the system near ρ/ρ0 ∼ 1/3. The results are compared with hybrid INC/EES and INC/SMM models. Preliminary data for the 8 GeV/c π− and preactions on 197Au show enhanced deposition energy for the antiproton beam.
Nuclear Physics A. 654(1):786.
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E. Renshaw Foxford,
K. Kwiatkowski, D. S. Bracken,
K. B. Morley,
V. E. Viola,
N. R. Yoder,
C. Volant,
E. C. Pollacco,
R. Legrain,
R. G. Korteling,
W. A. Friedman,
J. Brzychczyk,
H. Breuer
[show abstract]
[hide abstract]
ABSTRACT: Multifragmentation of natAg and 197Au nuclei induced by 1.8–4.8 GeV 3He ions has been studied with the Indiana Silicon Sphere 4π detector array. Rapidity, moving source, and sphericity-coplanarity analyses are consistent with near-simultaneous emission from a source in approximate kinetic equilibrium. For the most dissipative collisions, the spectral peaks are broadened and shifted to very low energies, indicative of emission from an extended nuclear system with ρ/ρ0∼1/3. Predictions of an intranuclear cascade/expanding, emitting source model compare well with experimental multiplicity distributions and the evolution of fragment spectral shapes. © 1996 The American Physical Society.
Phys. Rev. C. 54(2).
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L. Beaulieu,
T. Lefort,
K. Kwiatkowski,
W.-c. Hsi,
G. Wang, D. S. Bracken,
E. Cornell,
D. S. Ginger,
K. B. Morley,
R. Laforest F. Gimeno-Nogues, [......],
R. G. Korteling,
L. Pienkowski,
H. Breuer,
B. Back,
S. Gushue,
L. P. Remsberg,
M. J. Huang,
W. G. Lynch,
M. B. Tsang,
H. Xi
[show abstract]
[hide abstract]
ABSTRACT: The relation between excitation energy and reaction observables has been examined for (6.0–14.6)-GeV/c protons, (5.0–9.2)-GeV π-, and 8.0-GeV/c antiprotons incident on a 197Au target. Relative to proton and π- beams, 8.0-GeV/c antiprotons are found to be the most effective projectile for depositing high excitation energies in the targetlike residue. For protons and π- the excitation-energy distributions are nearly identical and appear to be independent of beam momentum above 6–8GeV/c. It is found that total measured charge, total thermal energy, and total charged-particle multiplicity scale most directly with excitation energy, whereas IMF multiplicity and total transverse energy exhibit large fluctuations. Correlations of the observed fragment multiplicity, charge, and kinetic-energy distributions with excitation energy indicate a transition in the reaction observables near E*/A≈4–6MeV. These experimental signals are consistent with a multifragmentation mechanism that becomes the dominant deexcitation mode above in the range E*/A∼4–6MeV.
Phys. Rev. C. 64(6).
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E.C. Pollacco,
J. Brzychczyk,
C. Volant,
R. Legrain,
R.G. Korteling, D.S. Bracken,
K. Kwiatkowski,
K.B. Morley,
E. Renshaw Foxford,
V.E. Viola,
N.R. Yoder,
H. Breuer,
J. Cugnon
[show abstract]
[hide abstract]
ABSTRACT: In the reaction (1.8 GeV) + , events are observed with a heavy fragment (HF), A≥10, in coincidence with charged particles detected over 70% of 4π solid angle. Calorimetric measurements show high thermal excitation energies of the target primary fragment: 6–8 MeV per nucleon for HF mass ≳45. For these excitation energies, the probability for having an evaporative residue is shown to be unexpectedly high when compared with current multifragmentation models. This result is interpreted as linked to the use of light ion projectiles at relatively low incident energy.
Physics Letters B.
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K. Kwiatkowski,
K.B. Morley,
E. Renshaw Foxford, D.S. Bracken,
V.E. Viola,
N.R. Yoder,
C. Volant,
E.C. Pollacco,
R. Legrain,
R. G. Korteling,
J. Brzychczyk,
H. Breuer,
W. A. Friedman
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K. Kwiatkowski, D.S. Bracken,
J. Brzychczyk,
D. Cook,
J. Dorsett,
T. Hamilton,
K. Komisarcik,
N. Madden,
K. McDonald,
K.B. Morley,
J. Ottarson,
C Powell,
E. Renshaw,
N.R. Yoder,
V.E. Viola
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