On the choice of colliding beams to study deformation effects in relativistic heavy ion collisions

It has been suggested that collisions between deformed shapes will lead to interesting effects on various observables such as K production and elliptic flow. Simple formulae can be written down which show how to choose the colliding beams which will maximise the effects of deformation.Comment: 2 pages, this version supersedes the previous on

Nuclear multifragmentation within the framework of different statistical ensembles

The sensitivity of the Statistical Multifragmentation Model to the underlying statistical assumptions is investigated. We concentrate on its micro-canonical, canonical, and isobaric formulations. As far as average values are concerned, our results reveal that all the ensembles make very similar predictions, as long as the relevant macroscopic variables (such as temperature, excitation energy and breakup volume) are the same in all statistical ensembles. It also turns out that the multiplicity dependence of the breakup volume in the micro-canonical version of the model mimics a system at (approximately) constant pressure, at least in the plateau region of the caloric curve. However, in contrast to average values, our results suggest that the distributions of physical observables are quite sensitive to the statistical assumptions. This finding may help deciding which hypothesis corresponds to the best picture for the freeze-out stageComment: 20 pages, 7 figure

A model for projectile fragmentation

A model for projectile fragmentation is developed whose origin can be traced back to the Bevalac era. The model positions itself between the phenomenological EPAX parametrization and transport models like "Heavy Ion Phase Space Exploration" (HIPSE) model and antisymmetrised molecular dynamics (AMD) model. A very simple impact parameter dependence of input temperature is incorporated in the model which helps to analyze the more peripheral collisions. The model is applied to calculate the charge, isotopic distributions, average number of intermediate mass fragments and the average size of largest cluster at different Z_{bound} of different projectile fragmentation reactions at different energies.Comment: Talk given by Gargi Chaudhuri at the 11th International Conference on Nucleus-Nucleus Collisions (NN2012), San Antonio, Texas, USA, May 27-June 1, 2012. 10 pages, 7 figure

Incorporating Radial Flow in the Lattice Gas Model for Nuclear Disassembly

We consider extensions of the lattice gas model to incorporate radial flow. Experimental data are used to set the magnitude of radial flow. This flow is then included in the Lattice Gas Model in a microcanonical formalism. For magnitudes of flow seen in experiments, the main effect of the flow on observables is a shift along the $E^*/A$ axis.Comment: Version accepted for publication in Phys. Rev. C, Rapid Communicatio

Upper Limit on the Cosmic Gamma-Ray Burst Rate from High Energy Diffuse Neutrino Background

We derive upper limits on the ratio $f_{GRB/CCSN}(z) \equiv R_{GRB}(z)/R_{CCSN}(z) \equiv f_{GRB/CCSN}(0)(1+z)^\alpha$, the ratio of the rate, $R_{GRB}$, of long-duration Gamma Ray Bursts (GRBs) to the rate, $R_{CCSN}$, of core-collapse supernovae (CCSNe) in the Universe ($z$ being the cosmological redshift and $\alpha\geq 0$), by using the upper limit on the diffuse TeV--PeV neutrino background given by the AMANDA-II experiment in the South Pole, under the assumption that GRBs are sources of TeV--PeV neutrinos produced from decay of charged pions produced in $p\gamma$ interaction of protons accelerated to ultrahigh energies at internal shocks within GRB jets. For the assumed ``concordance model'' of cosmic star formation rate, $R_{SF}$, with $R_{CCSN}(z) \propto R_{SF}(z)$, our conservative upper limits are $f_{GRB/CCSN}(0)\leq 5.0\times10^{-3}$ for $\alpha=0$, and $f_{GRB/CCSN}(0)\leq 1.1\times10^{-3}$ for $\alpha=2$, for example. These limits are already comparable to (and, for $\alpha\geq 1$ already more restrictive than) the current upper limit on this ratio inferred from other astronomical considerations, thus providing a useful independent probe of and constraint on the CCSN-GRB connection. Non-detection of a diffuse TeV--PeV neutrino background by the up-coming IceCube detector in the South pole after three years of operation, for example, will bring down the upper limit on $f_{GRB/CCSN}(0)$ to below few $\times10^{-5}$ level, while a detection will confirm the hypothesis of proton acceleration to ultrahigh energies in GRBs and will potentially also yield the true rate of occurrence of these events in the Universe.Comment: Two references added, an overall constant numerical factor corrected, Figures and relevant portions of abstract and main text slightly changed, main conclusions unchanged, 18 pages Latex with 4 Figures, version accepted for publication in PR

Distinguishing impurity concentrations in GaAs and AlGaAs, using very shallow undoped heterostructures

We demonstrate a method of making a very shallow, gateable, undoped 2-dimensional electron gas. We have developed a method of making very low resistivity contacts to these structures and systematically studied the evolution of the mobility as a function of the depth of the 2DEG (from 300nm to 30nm). We demonstrate a way of extracting quantitative information about the background impurity concentration in GaAs and AlGaAs, the interface roughness and the charge in the surface states from the data. This information is very useful from the perspective of molecular beam epitaxy (MBE) growth. It is difficult to fabricate such shallow high-mobility 2DEGs using modulation doping due to the need to have a large enough spacer layer to reduce scattering and switching noise from remote ionsied dopants.Comment: 4 pages, 5 eps figure

A study of the phase transition in the usual statistical model for nuclear multifragmentation

We use a simplified model which is based on the same physics as inherent in most statistical models for nuclear multifragmentation. The simplified model allows exact calculations for thermodynamic properties of systems of large number of particles. This enables us to study a phase transition in the model. A first order phase transition can be tracked down. There are significant differences between this phase transition and some other well-known cases

Nuclear Chemical and Mechanical Instability and the Liquid-Gas Phase Transition in Nuclei

The thermodynamic properties of nuclei are studied in a mean field model using a Skryme interaction. Properties of two component systems are investigated over the complete range of proton fraction from a system of pure neutrons to a system of only protons. Besides volume, symmetry, and Coulomb effects we also include momentum or velocity dependent forces. Applications of the results developed are then given which include nuclear mechanical and chemical instability and an associated liquid/gas phase transition in two component systems. The velocity dependence leads to further changes in the coexistence curve and nuclear mechanical and chemical instability curves.Comment: 21 pages, 9 figures, Results are changed due to error in progra

Possible effect of collective modes in zero magnetic field transport in an electron-hole bilayer

We report single layer resistivities of 2-dimensional electron and hole gases in an electron-hole bilayer with a 10nm barrier. In a regime where the interlayer interaction is stronger than the intralayer interaction, we find that an insulating state ($d\rho/dT < 0$) emerges at $T\sim1.5{\rm K}$ or lower, when both the layers are simultaneously present. This happens deep in the $"$metallic" regime, even in layers with $k_{F}l>500$, thus making conventional mechanisms of localisation due to disorder improbable. We suggest that this insulating state may be due to a charge density wave phase, as has been expected in electron-hole bilayers from the Singwi-Tosi-Land-Sj\"olander approximation based calculations of L. Liu {\it et al} [{\em Phys. Rev. B}, {\bf 53}, 7923 (1996)]. Our results are also in qualitative agreement with recent Path-Integral-Monte-Carlo simulations of a two component plasma in the low temperature regime [ P. Ludwig {\it et al}. {\em Contrib. Plasma Physics} {\bf 47}, No. 4-5, 335 (2007)]Comment: 5 pages + 3 EPS figures (replaced with published version