Measurement of spin-transfer observables in p p-->Lambda Lambda at 1.637 GeV/c

Spin-transfer observables for p p-->Lambda Lambda have been measured using a transversely polarized frozen-spin target and a beam momentum of 1.637 GeV/c. Current models of the reaction near threshold are in good agreement with existing measurements performed with unpolarized particles in the initial state but produce conflicting predictions for the spin-transfer observables Dnn and Knn (the normal-to-normal depolarization and polarization transfer), which are measurable only with polarized target or beam. Measurements of Dnn and Knn presented here are found to be in disagreement with predictions from these models.     

Antideuteron production in 158A GeV/c Pb + Pb collisions

The invariant cross section as a function of transverse momentum for antideuterons produced in 158A GeV/c per nucleon Pb+Pb central collisions has been measured by the NA44 experiment at CERN. This measurement, together with a measurement of antiprotons, allows for the determination of the antideuteron coalescence parameter. The extracted coalescence radius is found to agree with the deuteron coalescence radius and radii determined from two particle correlations.     

Identified hadron production in √s = 130 GeV Au-Au collisions at relativistic heavy-ion collider

Identified π^±,K ^±, p and -p transverse momentum spectra at mid-rapidity in √^sNN = 130 GeV Au-Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleonsN _part similarly for all particle species. The multiplicity densities scale faster thanN _part. TheK ^± andp ^±yields per participant increase faster than the π^± yields. We combine the PHENIX neutral and charged pion measurement and find that in central collisions forp _T >-2 GeV/c,-p andp yields are comparable to or even exceed the pion yields.     

Multistrange baryon production in Au-Au collisions at sqrt[s(NN)]=130 GeV

The transverse mass spectra and midrapidity yields for Xis and Omegas are presented. For the 10% most central collisions, the (-)Xi(+)/h(-) ratio increases from the Super Proton Synchrotron to the Relativistic Heavy Ion Collider energies while the Xi(-)/h(-) stays approximately constant. A hydrodynamically inspired model fit to the Xi spectra, which assumes a thermalized source, seems to indicate that these multistrange particles experience a significant transverse flow effect, but are emitted when the system is hotter and the flow is smaller than values obtained from a combined fit to pi, K, p, and Lambdas.     

Diffraction dissociation of nuclei in 450 GeV/c proton-nucleus collisions

Diffractive dissociation of nuclei (Be, Al, W) in collisions with 450 GeV/c protons,pApX, has been measured with the HELIOS spectrometer at the CERN Super Proton synchrotron. The dependence of the single-diffraction cross-section on the nuclear massA can be parametrized as _SD mb×A ^0.35±0.02, showing the peripheral nature of the process. The differential cross-section d_SD=(3.8±0.3)mb ×A ^0.35±0.02, is exponential with the slope parameter, increasing from 6.2±0.4 (GeV/c)^–2 for beryllium to 7.9±0.5 (GeV/c)^–2 for tungsten. The slope parameter also increases with increasing massM _X of the diffractively produced state. The rapidity, multiplicity, and transverse-momentum distributions of the particles of the diffractively produced stateX show a longitudinal phase-space population and are remarkably insensitive to the nuclear mass. This, together with theA ^1/3 dependence of _SD, suggests that the dominant process of nuclear diffractive excitation is the dissociation of single nucleons.Deceased     

Search for long-lived particles in 200 GeV/c proton-nucleon collisions

A search for long-lived particles (τ ? 10^?8 sec), with changes $\text{±}\text{2}\text{3}\text{, ± 1, ±}\text{4}\text{3}\text{and}\text{± 2}$, produced in 200 GeV pN collisions was performed at the CERN-SPS in a secondary beam equipped with superconducting r.f. separators. Upper limits were obtained for the production of long-lived hadrons and leptons. For charge - 1 particles the limits are at the level of 10^?7 of the pions at a mass m = 0.2 GeV and reach the 10^?11 level from $\text{3}\text{to}\text{8}\text{GeV}$. The production of light antinuclei was measured. The cross sections for ³He production are (1.3 ± 0.3) and (1.9 ± 0.3) × 10^?34 cm²/sr · GeV/c at 21 and 47.4 GeV/c respectively; for t the cross section is (7.6 ± 0.9) × 10^?34 cm²/sr · GeV/c at 23.7 GeV/c.     

Jets of nuclear matter in He-A T inelastic collisions at 4.5 A GeV/c

The problem of the nuclear matter jets in nucleus-nucleus collisions at 4.5 A GeV/c is discussed. The global analysis of experimental data, namely the sphericity tensor, is used to evidence such jets. The experimental results are compared with those obtained in the same collisions for hydrodynamic flow and thrust. The experiments have been performed in the frame of the SKM 200 Collaboration from JINR Dubna. Received: 20 March 1997 / Revised version: 20 July 1997     

Production properties of low-mass systems in pp collisions at 102 GeV/c

We examine in detail the properties of low-mass systems produced in the inclusive reaction p + p → p + anything at 102 GeV/c. We find that the internal characteristics of these low-mass nucleon-multipion systems (the “anything”), at fixed values of mass (M), are similar to those found for produced hadrons in high-energy collisions at fixed incident hadron energies $\text{(}\text{s}\text{)}$. The resemblance between the properties of the M² system and the characteristics of πp collisions at s = M² is particularly striking.     

Rapidity dependence of multiplicity distributions in proton-nucleus collisions at 360 GeV/c

Multiplicity distributions in various rapidity intervals for charged particles produced in collisions of 360 GeV/c protons with aluminium (Al) and gold (Au) targets are presented. The data were analysed separately for the forward and backward hemispheres. Each distribution is well described by a negative binomial distribution. The experimental distributions are compared with the predictions of the multichain model calculated by the Monte Carlo program MCMHA in which the intranuclear cascade process is included, and also with the Lund Monte Carlo FRITIOF. The results of MCMHA reproduce quite well the multiplicity distributions for various rapidity intervals.     

Inelastic 2-prong events in 147 GeV/cπ−p collisions

An SU(3) gauge-field non-topological soliton in three space-dimensions is discussed. Let N be the largest among the magnitudes of eigenvalues of the matrix Σ₁⁸λ_aQ_a, where the Q_a's are the eight conserved charges in the classical SU(3) gauge theory, and the λ_a's the usual 3 × 3 Gell-Mann matrices. We show that stable solitons exist if N > a critical value N_S, and if the ratio between the mass of the SU(3) gauge field and that of a relevant spin-0 field is >√6. Our trial function analysis suggests that, for large N, states with dets (Σ₁⁸λ_aQ_a) ≠ 0 are unstable against fission.     

Higher baryon resonances in carbon-carbon collisions at 4.2 GeV/c per nucleon

The production of the N(1440), the so-called Roper, and N(1520) resonances in high-energy collisions of carbon nuclei with the carbon nucleus, using a 2 m propane bubble chamber, was investigated. Attention was paid to the two-pion decay mode of the higher baryon resonances. From the invariant masses of three-particle states the mass and width of the resonances were obtained. The ratio of the resonances decay to and states was estimated.Received: 1 July 2003, Revised: 29 September 2003, Published online: 20 April 2004PACS: 25.70.Ef Resonances - 14.20.Gk Baryon resonances with S = 0     

Single-pion production in pp collisions at 0.95 GeV/c (I)

The single-pion production reactions pp → dπ⁺, pp → npπ⁺ and pp → ppπ⁰ were measured at a beam momentum of 0.95GeV/c ( T _p ≈ 400MeV) using the short version of the COSY-TOF spectrometer. The implementation of a central calorimeter provided particle identification, energy determination and neutron detection in addition to time-of-flight and angle measurements. Thus, all pion production channels were recorded with 1-4 overconstraints. The total and differential cross-sections obtained are compared to previous data and theoretical calculations. Main emphasis is put on the discussion of the ppπ⁰ channel, where we obtain angular distributions different from previous experimental results, however, partly in good agreement with recent phenomenological and theoretical predictions. In particular, we observe very large anisotropies for the π⁰ angular distributions in the kinematical region of small relative proton momenta revealing there a dominance of proton spinflip transitions associated with π⁰ s and d partial waves and emphasizing the important role of π⁰ d-waves.