Backward K10 production in the reaction π−p→Λ0K+π− at 9 and 12 GeV/c

We have analysed about 85 000 fast Λ⁰ events, obtained in a fast proton triggered experiment performed at the CERN-Ω spectrometer at 9 and 12 GeV/c incident π^? beam. Nearly 2500 Λ⁰K⁺π^? events have been isolated. We find strong production of quasi-two-body processes $\text{Λ}{}^0\text{K}{}^{10}$ and $\text{∑}{}^{\mathrm{1?}}\text{K}{}^{\mathrm{+}}$ consistent with u-channel hyperon exchange. Results on Λ⁰ polarization, K¹⁰ decay parameters and differential cross sections are given for $\text{Λ}{}^0\text{K}{}^{10}\text{(892)}$ and $\text{Λ}{}^0\text{K}{}^{10}\text{(1430)}$ final states. A comparison is made with the associated backward $\text{Λ}{}^0\text{(1520)}\text{K}{}^{10}$ production seen in the four-prong reaction π^?p→pK^?K⁺π^? obtained in the same experiment.     

Photon channelling in foams

Experiments by Gittings, Bandyopadhyay and Durian (Europhys. Lett. 65, 414 (2004)) demonstrate that light possesses a higher probability to propagate in the liquid phase of a foam due to total reflection. The authors term this observation photon channelling which we investigate in this article theoretically. We first derive a central relation in the work of Gitting et al. without any free parameters. It links the photon's path-length fraction f in the liquid phase to the liquid fraction ɛ. We then construct two-dimensional Voronoi foams, replace the cell edges by channels to represent the liquid films and simulate photon paths according to the laws of ray optics using transmission and reflection coefficients from Fresnel's formulas. In an exact honeycomb foam, the photons show superdiffusive behavior. It becomes diffusive as soon as disorder is introduced into the foams. The dependence of the diffusion constant on channel width and refractive index is explained by a one-dimensional random-walk model. It contains a photon channelling state that is crucial for the understanding of the numerical results. At the end, we shortly comment on the observation that photon channelling only occurs in a finite range of ɛ.     

Freeze-out volume in multifragmentation --Dynamical simulations

Stochastic mean-field simulations for multifragmenting sources at the same excitation energy per nucleon have been performed. The freeze-out volume, a concept which needs to be precisely defined in this dynamical approach, was shown to increase as a function of three parameters: freeze-out instant, fragment multiplicity and system size.     

Fragment charge correlations and spinodal decomposition in finite nuclear systems

Enhanced production of events with almost equal-sized fragments is experimentally revealed by charge correlations in the multifragmentation of a finite nuclear system selected in ¹²⁹Xe central collisions on ^nat Sn. The evolution of their weight with the incident energy: 32, 39, 45, 50 AMeV, is measured. Dynamical stochastic mean-field simulations performed at 32 AMeV, in which spinodal instabilities are responsible for multifragmentation, exhibit a similar enhancement of this kind of events. The above experimental observation evidences the spinodal decomposition of hot finite nuclear matter as the origin of multifragmentation in the Fermi energy regime.Received: 22 November 2002, Revised: 22 April 2003, Published online: 30 September 2003PACS: 25.70.Pq Multifragment emission and correlations - 24.60.Ky Fluctuation phenomenaG. Tabacaru: Present address: Cyclotron Institute, Texas A&M University, College station, Texas 77845, USA.N. Le Neindre: Permanent address: Institut de Physique Nucléaire, IN2P3-CNRS, F-91406 Orsay cedex, France.     

Charge density: A probe for the nuclear interaction in microscopic transport models

The transport properties of the ³⁶Ar +⁵⁸Ni system at measured with the INDRA array, are studied within the BNV kinetic equation. A general protocol of comparison between the N-body experimental fragment information and the one-body distribution function is developed using global variables, with a special focus on charge density. This procedure avoids any definition of sources and any use of an afterburner in the simulation. We shall discuss the feasibility of such an approach and the distortions induced by the finite detection efficiency and the completeness requirements of the data selection. The sensitivity of the different global observables to the macroscopic parameters of the effective nuclear interaction will be studied in detail.Received: 21 January 2003, Published online: 5 August 2003PACS: 25.70.-z Low and intermediate energy heavy-ion reactions - 24.10.-i Nuclear reaction models and methodsN. Le Neindre: Permanent address: Institut de Physique Nuclaire, IN2P3-CNRS, F-91406 Orsay cedex, France.     

Crystallization of glasses in the germanium-tellurium-sulphur system

The glasses of the germanium-tellurium-sulphur ternary system were investigated in order to determine the formation and crystallization processes. Vitreous samples were prepared by quenching. The vitreous transition and crystallization temperatures, together with microhardnesses, were measured throughout the vitreous region. The latter was sub-divided into several zones, and the behaviour of the glasses in each of these zones was analyzed separately.     

Spontaneous symmetry-breaking in the 3-D wake of a long cylinder simulated by the lattice gas method and drag coefficient measurements

We present a direct numerical simulation by the lattice gas method of the three-dimensional non-stationary incompressible flow at a Reynolds number of 74, past a circular cylinder, with a uniform incident flow. We describe the three-dimensional structure and the time-evolution of the wake, which leads to an oblique vortex shedding situation.We also present early results on measurements of drag coefficients for spheres and cylinders at a Reynolds number of 20.     

Visualization of Intracellular CA2+ Dynamics with Simultaneous 2-Photon Excited Fluorescence and Third Harmonic Generation Microscope

We show that the simultaneous coupling of two laser scanning non-linear microscopies (2-photon excited fluorescence and third harmonic generation microscopy) give functional and morphological information for improving our understanding on intracellular calcium flows.     

Critical slowing down of fluctuations in p-terphenyl and p-quaterphenyl observed by proton spin-lattice relaxation

The temperature evolution of the proton spin-lattice relaxation time T₁ in p-terphenyl and in p-quaterphenyl around their order-disorder phase transition has been measured. In both cases pretransitional collective fluctuations destroy the high temperature Arrhenius behaviour of the relaxation rate corresponding to a single reorientational jump motion. The spin-lattice relaxation times present then a drastic decrease until the transition temperature (T₀ = 193 K in p-terphenyl, T₀ = 238 K in p-quaterphenyl). This decrease is associated to the critical slowing down of fluctuations. In the low temperature phase the ordering phenomena lead to a sharp drop of the spin-lattice relaxation rate.     

Fusion-fission of heavy systems

The influence of the entrance channel on fission processes was studied by forming the same composite system by two different target-projectile combinations (⁴⁰Ar+²⁰⁹Bi and⁵⁶Fe+¹⁸⁷Re, respectively). Compound nucleus fission and quasi fission were observed and the analysis was performed in the framework of the extra-extra-push model, which provides a qualitative interpretation of the results; limits for the extra-extra-push threshold are given, but problems with quantitative predictions for the extra-push are noted.