Azimuthal anisotropy of photon and charged parti cle emissionin 208Pb + 208Pb collisions at 158 $\ cdot A$ GeV/ c

The azimuthal distributions of photons and charged particles with respect to the event plane are investigated as a function of centrality in ²⁰⁸Pb + ²⁰⁸Pb collisions at 158 GeV/c in the WA98 experiment at the CERN SPS. The anisotropy of the azimuthal distributions is characterized using a Fourier analysis. For both the photon and charged particle distributions the first two Fourier coefficients are observed to decrease with increasing centrality. The observed anisotropies of the photon distributions compare well with the expectations from the charged particle measurements for all centralities.Received: 22 May 2004, Revised: 14 April 2005, Published online: 4 May 2005PACS: 25.75.Dw     

Coherent production ofρ − mesons in charged current antineutrino-neon interactions in BEBC

Coherent production ofρ ^? mesons in charged current antineutrino interactions on neon nuclei is studied in the BEBC bubble chamber exposed to the CERN SPS wide band beam. The cross section is measured to be (95±25)·10^?40 cm² per neon nucleus, averaged over the beam energy spectrum. The distributions of kinematical variables and the absolute value of the cross section are in agreement with theoretical predictions based on the CVC hypothesis and the vector meson dominance model.     

Observation of two-dimensional classical wave localization: third sound on superfluid 4He films on a disordered substrate

We present the results of measurements of the propagation of third sound waves on superfluid 4He adsorbed to two-dimensional ordered and disordered substrates. In the disordered case we compare the experimental results to theoretical predictions of classical wave localization in such systems and conclude that classical wave localization is present in our system.     

Study of the effect of initial conditions on the scaling properties of CaF2 thin films

The growth of thermally deposited CaF₂ films was studied using three different substrates for deposition: glass, gold and silicon. Each substrate was chosen because of its different topography and used to determine the effect of substrate roughness on the growth of CaF₂ films. After thermally depositing a range of CaF₂ film thicknesses on the substrates, the CaF₂ surfaces were imaged using atomic force microscopy. The images were then used to determine the characteristic exponents which described the surface. In each case the Hurst exponent, H was found to rapidly increase from the initial substrate condition to a constant value (H ≈ 0.85) with increasing CaF₂ film thickness. This rapid crossover is quite remarkable and occurs in films with nominal thicknesses less than ≈20 nm. These data indicate that the roughness of the substrate, or in other words the initial conditions, have little effect on the growth properties of CaF₂ films beyond the crossover at very small values of the film thickness. The scaling of the dynamic exponent, β, is also presented as are measurements of the CaF₂ film porosity.     

Transverse energy production in the target fragmentation region in16O-nucleus reactions at 60 and 200A GeV

Charged pion yields and transverse energies of baryons are measured for the reaction¹⁶O+Cu, Ag, Au at 60 and 200A GeV bombarding energy in the target fragmentation region employing the Plastic Ball detector. Only little dependence of the measured quantities on the bombarding energy is found. The data are compared with the multi-chain fragmentation model of Ranft. As a result it turns out that a leading order formation zone cascade is not sufficient to explain the baryon yield and the transverse energies of baryons in the target fragmentation region.     

A measurement of ∧ and Ξ<Superscript>−</Superscript> polarization in inclusive production by Σ<Superscript>−</Superscript> of 340 GeV/c in C and Cu targetsof 340 GeV/c in C and Cu targets

We have measured the polarization of ∧ and Ξ^? hyperons produced inclusively by a Σ^? beam of 340 GeV/c momentum in nuclear targets, using samples of 9.5 million ∧ decays and 880000 Ξ^? decays. The large statistics allowed a two-dimensional analysis as functions ofx _F andp _t . The polarization w.r.t. the production normal is mainly positive for ∧ and negative for Ξ^?. The positive sign of the ∧ polarization is opposite to predictions. Atp _t >1 Gev/c, the ∧ polarization decreases to zero or even negative values, in sharp contrast to the plateau abovep _t <1 GeV/c observed in inclusive ∧ production by protons. No such effect is observed for the Ξ^? polarization, and its sign is as expected.     

High transverse momentum prompt photon production by π− and π+ on protons at 280 GeV/c

The inclusive cross sections for prompt photon production by π^? and π⁺ on protons have been measured with a beam momentum of 280 GeV/c using a fine grained electromagnetic calorimeter and the CERN Omega spectrometer. The transverse momentum and Feynmanx _F ranges covered are 4.0<p _T <7.0GeV/c and ?0.45<x _F <0.55 respectively. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed.     

Oxygen-induced reactions at 60A GeV and 200A GeV studied by calorimetry

Results based on calorimetric measurements are presented from reactions of 60A GeV and 200A GeV¹⁶O projectiles with C, Cu, Ag, and Au nuclei. Minimum-bias cross sections are discussed. Energy spectra measured at zero degrees and transverse-energy distributions for the pseudorapidity range 2.4≦η≤5.5 are shown. An analysis of the average transverse energy in terms of the number of participating nucleons and the number of binary nucleon-nucleon collisions is presented. Estimates of nuclear stopping and of attained energy densities are made.