119531408
The thermodynamic model for nuclear multifragmentation
Abstract A great many observables seen in intermediate energy heavy ion collisions can be explained on the basis of statistical equilibrium. Calculations based on statistical equilibrium can be implemented in microcanonical ensemble (energy and number of particles in the system are kept fixed), canonical ensemble (temperature and number of particles are kept fixed) or grand canonical ensemble (fixed temperature and a variable number of particles but with an assigned average). This paper deals with calculations with canonical ensembles. A recursive relation developed recently allows calculations with arbitrary precision for many nuclear problems. Calculations are done to study the nature of phase transition in intermediate energy heavy ion collision, to study the caloric curves for nuclei and to explore the possibility of negative specific heat because of the finiteness of nuclear systems. The model can also be used for detailed calculations of other observables not connected with phase transitions, such as populations of selected isotopes in a heavy ion collision. The model also serves a pedagogical purpose. For the problems at hand, both the canonical and grand canonical solutions are obtainable with arbitrary accuracy hence we can compare the values of observables obtained from the canonical calculations with those from the grand canonical. Sometimes, very interesting discrepancies are found. To illustrate the predictive power of the model, calculated observables are compared with data from the central collisions of Sn isotopes.
119186084
Bimodality and Coulomb effects with a canonical thermodynamic model
Abstract The effect of the Coulomb interaction on the phase diagram of finite nuclei is studied within the Canonical Thermodynamic Model. If Coulomb effects are artificially switched off, this model shows a phenomenology consistent with the liquid–gas phase transition. The inclusion of Coulomb does not significantly affect the phase diagram but it drastically modifies the nature and order parameter of the transition. A clear understanding of the phenomenon can be achieved looking at the distribution of the largest fragment produced in each fragmentation event. Possible connections with experimental observations are outlined.
14927510
A Transport Model for Nuclear Reactions Induced by Radioactive Beams
Major ingredients of an isospin and momentum dependent transport model for nuclear reactions induced by radioactive beams are outlined. Within the IBUU04 version of this model we study several experimental probes of the equation of state of neutron‐rich matter, especially the density dependence of the nuclear symmetry energy. Comparing with the recent experimental data from NSCL/MSU on isospin diffusion, we found a nuclear symmetry energy of Esym(ρ) ≈ 31.6(ρ/ρ0)1.05 at subnormal densities. Predictions on several observables sensitive to the density dependence of the symmetry energy at supranormal densities accessible at GSI and the planned Rare Isotope Accelerator (RIA) are also made.
16308546
First Order Phase Transition in Intermediate-Energy Heavy Ion Collisions
We model the disassembly of an excited nuclear system formed as a result of a heavy ion collision. We find that, as the beam energy in central collisions in varied, the dissociating system crosses a liquid-gas coexistence curve, resulting in a first-order phase transition. Accessible experimental signatures are identified: a peak in specific heat, a power-law yield for composites, and a maximum in the second moment of the yield distribution.
2820708
Transverse momenta, nuclear equation of state, and momentum-dependent interactions in heavy-ion collisions.
We investigate the generation of transverse momentum in high-energy heavy-ion collisions and its relation to the nuclear equation of state. We find that streamer chamber data can be fitted by Boltzmann-Uehling-Uhlenbeck calculations with a momentum-dependent potential that closely models realistic nuclear matter interactions and yields an equation of state with {ital K}=215 MeV.
121836312
Excluded volume in nuclear fragmentation
122335370
Transverse energy distributions in participant number model for ultra-relativistic heavy-ion collisions
The transverse energy distribution in ultra-relativistic heavy-ion collisions has been obtained as a convolution over the number of projectile and target participants. The latter is computed using the geometrical overlap model as a function of impact parameter. The data from 10 A GeV to 200 A GeV heavy ion beams on various targets in different pseudo-rapidity domains have been successfully described.
119263848
Finite size scaling on the phase diagram of QCD
In the last few years there has been remarkable progress in the comparison of experimental data on the shape of event-by-event distributions of conserved quantities and lattice thermodynamic predictions based on the grand canonical ensemble. In this talk we discuss how the QCD crossover temperature and the freezeout curve are extracted from the analysis of fluctuations. We report that one can also go further and locate the QCD critical point at µ }~ 2Tc. We also list the systematics which must be brought under control in future.
119206892
Strange freezeout
We argue that known systematics of hadron cross sections may cause different particles to freeze out of the fireball produced in heavy-ion collisions at different times. We find that a simple model with two freezeout points is a better description of data than that with a single freezeout, while still remaining predictive. The resulting fits seem to present constraints on the late stage evolution of the fireball, including the tantalizing possibility that the QCD chiral transition influences the yields at √
14688147
Finding the critical end point of QCD: lattice and experiment
The current status of the search for the critical end point on the lattice and in experiments is discussed. A naive extrapolation is given of lattice results on the location of the critical end point to the continuum limit with the correct pion mass. An interpretation of current results on fluctuations is provided. A new method of analysis of experimental data is discussed, which provides a check on the removal of backgrounds, comparisons with QCD, and signals an approach to the critical end point.
122137195
Neutral charm production in 400 GeV proton-emulsion interactions
A search has been carried out for neutral charm production in 5,108 proton-emulsion interactions at 400 GeV/c. Nine charm candidates have been observed in our fiducial volume which extends from 100 μm-1,000 μm in the forward cone. One of these is a 4-prong and the others are 2-prong events with opening angle>10 mrad and momenta of both decay tracks>150 MeV/c. Search for associated charm decays was made in an extended fiducial volume around the primary stars of these nine candidates. This yielded two neutral 2-prong events, one associated with the 4-prong and the other with a 2-prong candidate. All unassociated candidates are consistent with being backgrounds due toKs, Λ decays, neutral interactions and γ conversions whereas the background to associated events is negligible. Based on the two associated decays the inclusive cross section forD0, −0 production is determined as 27±20 μb/nucleon. Detailed measurements on the 4-prong candidate lead to the identification of one decay track as an electron and another as a kaon. This is interpreted as a semi-leptonic, Cabbibo favouredD0/D−0 decay.