Energy losses of muons, pions, protons, and deuterons channeled in Si

The energy loss of positive muons, pions, protons, and deuterons channeled in Si crystals has been investigated by computer simulation. The model considers the individual trajectories of particles inside the target and calculates the electronic energy loss for each particle history. The results show important differences in the energy loss distributions, stopping powers, and straggling values for low and intermediate energies, as a consequence of channeling effects.     

Channeling of protons,pions and deuterons in the GeV region

Strong directional effects have been observed when 1.15 and 1.35 GeV/c protons, π⁺ and π^?, and deuterons penetrate through germanium crystals. Transmission, wide-angle scattering, and an attempt to do blocking distributions are obtained from experiments using position-sensitive drift chambers. Corresponding measurements of energy loss in germanium crystals are also presented. These experimental results are compared to theory for energy loss, and satisfactory agreement is obtained.     

Volume emission of pions in relativistic heavy-ion collisions

We consider the possibility of volume emission of pions by the Δ(1232) decay in a hot compressed projectile-target residue. We calculate the momentum distribution of the pions created by the two-body Δ(1232) decay. Reabsorption is taken into account assuming a quasi-deuteron model. We argue that low-energy pions created deep inside the hot zone are likely to escape and contribute to the pion inclusive spectrum.     

Production of charged pions, kaons and antikaons in relativistic C + C and C + Au collisions

Production cross-sections of charged pions, kaons and antikaons have been measured in C+C and C+Au collisions at beam energies of 1.0 and 1.8 AGeV for different polar emission angles. The kaon and antikaon energy spectra can be described by Boltzmann distributions whereas the pion spectra exhibit an additional enhancement at low energies. The pion multiplicity per participating nucleon M(π⁺)/<A _part> is a factor of about 3 smaller in C+Au than in C+C collisions at 1.0 AGeV whereas it differs only little for the C and the Au target at a beam energy of 1.8 AGeV. The K⁺ multiplicities per participating nucleon M(K⁺)/ <A _part> are independent of the target size at 1 AGeV and at 1.8 AGeV. The K^- multiplicity per participating nucleon M(K^-)/ <A _part> is reduced by a factor of about 2 in C+Au as compared to C+C collisions at 1.8 AGeV. This effect might be caused by the absorption of antikaons in the heavy target nucleus. Transport model calculations underestimate the K^-/K⁺ ratio for C+C collisions at 1.8 AGeV by a factor of about 4 if in-medium modifications of K-mesons are neglected. Received: 10 December 1999 / Accepted: 14 November 2000     

Particle production in Pb+Pb collisions at the SPS

Experiment NA49 at the CERN SPS employs a large acceptance detector to study particle spectra, yields and correlations in nucleus-nucleus, nucleon-nucleus and nucleon-nucleon collisions. Preliminary results on pion, kaon, A and ā production in central Pb+Pb collisions at 40, 80 and 158 A·GeV beam energy are shown and compared to measurements at lower and higher energies.     

Omega- and Omega+ production in central Pb + Pb collisions at 40 and 158A GeV

Results are presented on Omega production in central Pb+Pb collisions at 40 and 158A GeV beam energy. For the first time in heavy ion reactions, rapidity distributions and total yields were measured for the sum Omega(-) + Omega(+) at 40A GeV and for Omega(-) and Omega(+) separately at 158A GeV. The yields are strongly underpredicted by the string-hadronic UrQMD model but agree better with predictions from hadron gas models.     

Kaon production in S+nucleus and Pb+Pb collisions at CERN SPS

Charged and neutral kaon production in S-nucleus and Pb-Pb collisions has been measured at CERN in the NA35 and NA49 experiments, close to mid-rapidity. The production ofK ^± in S+S, Ag, Au at 200 GeV/nucleon was measured via their one-prong (kink) topology inside a Time Projection Chamber (TPC). The resulting charged kaon yields are in agreement with other measurements done in the same experiment. TheK ⁺/K ^? ratio was found to be 1.30±0.15 in central S+Au interactions. The production ofK _S ⁰ in Pb+Pb collisions was measured using the NA49’s large (Main) TPCs outside the magnetic field. The resulting yields are compatible with other measurements performed in the same experiment, within the quoted systematic errors. The preliminary rapidity distribution in Pb+Pb scales with the number of participants if compared to S+S collisions. From this we conclude that no further strangeness enhancement (relative to nucleon-nucleon collisions) is observed in going from S+S to Pb+Pb.     

The production of high-energy protons in central relativistic nuclear collisions

We extend our model of transport theory to be applicable to the inclusive production of protons with very high energy. We then consider the angular distribution of such protons, produced in a central collision of Ar on KC1 at 800 MeV per nucleon. The slight anisotropy observed in the data can be explained by a finite value of the friction constant which in turn determines the number of collisions needed for equilibrium to be reached. We also show that these data are quite sensitive to the reaction geometry and cannot be explained by the firestreak model.     

Investigation of neutron emission in the interaction of relativistic protons and deuterons with lead targets

Measurements of neutron double-differential cross sections and yields in time-of-flight experiments with various lead targets and beams of protons and deuterons with an energy of about 2 GeV are discussed. Space and energy distribution of neutrons in an extended lead target is studied by threshold detectors in the proton energy range of 1–3.7 GeV. The average multiplicity of neutrons, neutron energy, and neutron multiplication in lead as functions of target dimension, type, and energy of the beam particle are analyzed.     

Deformation effects in the 28Si+12C and 28Si+28Si reactions

The possible occurrence of highly deformed configurations is investigated in the ⁴⁰Ca and ⁵⁶Ni di-nuclear systems as formed in the ²⁸Si + ¹²C, ²⁸Si reactions by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments and their associated light charged particles have been collected by using the ICARE charged particle multidetector array. The data are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Significant deformation effects at high spin are observed as well as an unexpected large ⁸Be cluster emission of a binary nature.     

Interferometry of direct photons in central 208Pb + 208Pb collisions at 158A GeV

Two-particle correlations of direct photons were measured in central 208Pb+208Pb collisions at 158A GeV. The invariant interferometric radii were extracted for 100相似文献   

ATLAS potential for elliptic flow measurements in Pb+Pb collisions at LHC

Study of particle azimuthal anisotropies, quantified by coefficients of the Fourier decomposition of the azimuthal angle distributions, has emerged as an important tool to probe the early stages of nucleusnucleus collisions. In this paper the ATLAS capability of measuring elliptic flow, the second Fourier coefficient, is presented. It is shown that various analysis techniques can be applied for different combinations of the detector sub-systems. A systematic comparison of various analysis methods is also shown.     

Three-pion interferometry results from central Pb+Pb collisions at 158A GeV/c

Three-particle correlations have been measured for identified pi(-) from central 158A GeV Pb+Pb collisions by the WA98 experiment at CERN. A substantial contribution of the genuine three-body correlation has been found as expected for a mainly chaotic and symmetric source.