54084723
Tracking the phase-transition energy in the disassembly of hot nuclei
In efforts to determine phase transitions in the disintegration of highly excited heavy nuclei, a popular practice is to parametrise the yields of isotopes as a function of temperature in the form $Y(z)=z^{-\tau}f(z^{\sigma}(T-T_0))$, where $Y(z)$'s are the measured yields and $\tau, \sigma$ and $T_0$ are fitted to the yields. Here $T_0$ would be interpreted as the phase transition temperature. For finite systems such as those obtained in nuclear collisions, this parametrisation is only approximate and hence allows for extraction of $T_0$ in more than one way. In this work we look in detail at how values of $T_0$ differ, depending on methods of extraction. It should be mentioned that for finite systems, this approximate parametrisation works not only at the critical point, but also for first order phase transitions (at least in some models). Thus the approximate fit is no guarantee that one is seeing a critical phenomenon. A different but more conventional search for the nuclear phase transition would look for a maximum in the specific heat as a function of temperature $T_2$. In this case $T_2$ is interpreted as the phase transition temperature. Ideally $T_0$ and $T_2$ would coincide. We invesigate this possibility, both in theory and from the ISiS data, performing both canonical ($T$) and microcanonical ($e=E^*/A$) calculations. Although more than one value of $T_0$ can be extracted from the approximate parmetrisation, the work here points to the best value from among the choices. Several interesting results, seen in theoretical calculations, are borne out in experiment.
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.
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.
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.
121836312
Excluded volume in nuclear fragmentation
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.
49270375
The correlation lengths and the order of the phase transition in three-dimensional Z 3 symmetric models
We present a high statistics Monte Carlo investigation of three-dimensional Z 3 symmetric models, which are related to SU(3) pure gauge theory at finite temperature. From the finite size scaling behaviour of bulk properties and the existence of metastable states, we conclude that these models exhibit a first-order phase transition. We have also performed detailed correlation length measurements in a cylindrical geometry with periodic boundary conditions as well as with a cold wall in the longitudinal direction. The correlation length, which appears to be independent of the boundary conditions, becomes very large near the critical point. Nonetheless, our data suggest that the correlation length developes a discontinuity at the critical point in the infinite volume limit.
14405851
Operator relations and chemical effects on chiral dynamics in QCD
We discuss effects of chemical potential on the dynamics of chiral transition by the Taylor expansion method in lattice QCD. Operators and their Taylor expansions which characterise the chiral dynamics are related through Maxwell’s relations and Chiral Ward identities. This reduces the computation to just measuring the renormalized expectation values of the chiral condensate and its Taylor coefficients. The various relations can then be used to extract information of the operators responsible for the characteristics of the chiral dynamics.
123618858
An experimental system for detection of high energy cosmic gamma ray bursts
Abstract While bursts of cosmic gamma rays of energies 0.1–10 MeV can be detected and studied only with satellite-borne detectors, bursts of gamma rays at GeV energies can be detected using sensitive ground-based detectors. An experimental system to detect these high energy gamma ray bursts is being operated at the mountain altitude laboratory at Ootacamund, India. The design features and the experimental details related to this system are described.
121871270
Sign-posting the phase diagram of quantum chromodynamics
The good agreement between lattice predictions and data for the shape of the distribution of event-by-event fluctuations of the baryon number is discussed. Such comparisons can give fine probes of thermalization, and can be used to provide a direct determination of the cross-over temperature Tc of QCD. The logic of these comparisons and the systematics involved are discussed. The same methods can be used to further explore the phase diagram.
123004962
Flavour degrees of freedom and the transition temperature in QCD
We study the finite temperature transition in QCD with four flavours of dynamical quarks. Our simulation is performed on an 8×16 3 lattice for quarks of mass ma=0.01. At the coupling β c =5.15, we find long-lived metastable states, as well as an abrupt change in the entropy density, suggesting a first order phase transition. Using presently available results from corresponding calculations of the hadron masses and the chiral condensate, this gives us a transition temperature T c ≅100 MeV, which is a factor two lower than the transition temperature found in quenched QCD.