Comparative Analysis of the Mechanisms of Fast Light Particle Formation in Nucleus-Nucleus Collisions at Low and Intermediate Energies

The dynamics and the mechanisms of preequilibrium-light-particle formation in nucleus-nucleus collisions at low and intermediate energies are studied on the basis of a classical four-body model. The angular and energy distributions of light particles from such processes are calculated. It is found that, at energies below 50 MeV per nucleon, the hardest section of the energy spectrum is formed owing to the acceleration of light particles from the target by the mean field of the projectile nucleus. Good agreement with available experimental data is obtained.Comment: 23 pages, 10 figures, LaTeX, published in Physics of Atomic Nuclei v.65, No. 8, 2002, pp. 1459 - 1473 translated from Yadernaya Fizika v. 65, No. 8, 2002, pp. 1494 - 150

Bose-condensation through resonance decay

We show that a system described by an equation of state which contains a high number of degrees of freedom (resonances) can create a considerable amount of superfluid (condensed) pions through the decay of short-lived resonances, if baryon number and entropy are large and the dense matter decouples from chemical equilibrium earlier than from thermal equilibrium. The system cools down faster in the presence of a condensate, an effect that may partially compensate the enhancement of the lifetime expected in the case of quark-gluon-plasma formation.Comment: 12 pages GSI-93-27 PREPRIN

Acceptance Dependence of Fluctuation in Particle Multiplicity

The effect of limiting the acceptance in rapidity on event-by-event multiplicity fluctuations in nucleus-nucleus collisions has been investigated. Our analysis shows that the multiplicity fluctuations decrease when the rapidity acceptance is decreased. We explain this trend by assuming that the probability distribution of the particles in the smaller acceptance window follows binomial distribution. Following a simple statistical analysis we conclude that the event-by-event multiplicity fluctuations for full acceptance are likely to be larger than those observed in the experiments, since the experiments usually have detectors with limited acceptance. We discuss the application of our model to simulated data generated using VENUS, a widely used event generator in heavy-ion collisions. We also discuss the results from our calculations in presence of dynamical fluctuations and possible observation of these in the actual data.Comment: To appear in Int. J. Mod. Phys.

Measurement of stopping beam distributions in the PIBETA detector

Precise calculation of the geometrical acceptance of a large solid angle detector with an integrated stopping target relies on precise knowledge of the beam geometry. We describe four alternative methods that we used to measure the beam stopping distributions in the PIBETA detector active target: (i) light response of segmented target elements to incident beam particles, (ii) back-tracking of charged particles from pi+ and mu+ decays using multi-wire proportional chambers, (iii) volume distribution of the Dalitz decay (pi0->gamma e+e-) event vertices, and (iv) the opening angle distribution of two pi0 photons originating from the beta decay of pi+ at rest. We demonstrate consistent results obtained by these four independent approaches and show how particular beam stopping distributions affect the detector's geometrical acceptance.Comment: 38 pages, 16 postscript figures, 2 tables, LaTeX, submitted to Nucl. Instrum. Meth.

New mechanism for the production of the extremely fast light particles in heavy-ion collisions in the Fermi energy domain

Employing a four-body classical model, various mechanisms responsible for the production of fast light particles in heavy ion collisions at low and intermediate energies have been studied. It has been shown that at energies lower than 50 A MeV, light particles of velocities of more than two times higher than the projectile velocities are produced due to the acceleration of the target light-particles by the mean field of the incident nucleus. It has also been shown that precision experimental reaction research in normal and inverse kinematics is likely to provide vital information about which mechanism is dominant in the production of fast light particles.Comment: 4 pages, 3 figures, LaTeX, to be published in Proceedings of VII International School-Seminar on Heavy Ion Physics, May 27 - June 1, 2002, Dubna, Russi

Design and Test of a Forward Neutron Calorimeter for the ZEUS Experiment

A lead scintillator sandwich sampling calorimeter has been installed in the HERA tunnel 105.6 m from the central ZEUS detector in the proton beam direction. It is designed to measure the energy and scattering angle of neutrons produced in charge exchange ep collisions. Before installation the calorimeter was tested and calibrated in the H6 beam at CERN where 120 GeV electrons, muons, pions and protons were made incident on the calorimeter. In addition, the spectrum of fast neutrons from charge exchange proton-lucite collisions was measured. The design and construction of the calorimeter is described, and the results of the CERN test reported. Special attention is paid to the measurement of shower position, shower width, and the separation of electromagnetic showers from hadronic showers. The overall energy scale as determined from the energy spectrum of charge exchange neutrons is compared to that obtained from direct beam hadrons.Comment: 45 pages, 22 Encapsulated Postscript figures, submitted to Nuclear Instruments and Method

Transverse Spin at PHENIX: Results and Prospects

The Relativistic Heavy Ion Collider (RHIC), as the world's first and only polarized proton collider, offers a unique environment in which to study the spin structure of the proton. In order to study the proton's transverse spin structure, the PHENIX experiment at RHIC took data with transversely polarized beams in 2001-02 and 2005, and it has plans for further running with transverse polarization in 2006 and beyond. Results from early running as well as prospective measurements for the future will be discussed.Comment: 6 pages, 2 figures, presented at Transversity 2005, Como, Ital

Search for Free Decay of Negative Pions in Water and Light Materials

We report on a search for the free decay component of pi- stopped in water and light materials. A non-zero value of this would be an indication of anomalous nu_e contamination to the nu_e and nu_mu_bar production at stopped-pion neutrino facilities. No free decay component of pi- was observed in water, Beryllium, and Aluminum, for which upper limits were established at 8.2E-4, 3.2E-3, and 7.7E-3, respectively

Dilepton-tagged jets in relativistic nucleus-nucleus collisions: A case study

We study the A+B -> l+ l- + jet +X process in nucleus-nucleus collisions at relativistic energies. The dilepton as well as the jet will pass through the matter produced in such collisions. The recoiling dilepton will carry information about the kinematical features of the jet, and will thus prove to be a very effective tool in isolating in-medium effects such as energy-loss and fragmentation function modifications. We estimate the contributions due to correlated charm and bottom decay and we identify a window where they are small as compared to pairs from the NLO Drell-Yan process.Comment: 7 pages, 9 figures Two figures modified, references adde