On the Equation of State of Nuclear Matter in 158A GeV Pb+Pb Collisions

Within a hydrodynamical approach we investigate the sensitivity of single inclusive momentum spectra of hadrons in 158A GeV Pb+Pb collisions to three different equations of state of nuclear matter. Two of the equations of state are based on lattice QCD results and include a phase transition to a quark-gluon plasma. The third equation of state has been extracted from the microscopic transport code RQMD under the assumption of complete local thermalization. All three equations of state provide reasonable fits to data taken by the NA44 and NA49 Collaborations. The initial conditions before the evolution of the fireballs and the space-time evolution pictures differ dramatically for the three equations of state when the same freeze-out temperature is used in all calculations. However, the softest of the equations of state results in transverse mass spectra that are too steep in the central rapidity region. We conclude that the transverse particle momenta are determined by the effective softness of the equation of state during the fireball expansion.Comment: 4 pages, including 4 figures and 2 tables. For a PostScript file of the manuscript, you can also goto http://t2.lanl.gov/schlei/eprint.htm

Dynamics of vortex penetration, jumpwise instabilities and nonlinear surface resistance of type-II superconductors in strong rf fields

We consider nonlinear dynamics of a single vortex in a superconductor in a strong rf magnetic field $B_0\sin\omega t$. Using the London theory, we calculate the dissipated power $Q(B_0,\omega)$, and the transient time scales of vortex motion for the linear Bardeen-Stephen viscous drag force, which results in unphysically high vortex velocities during vortex penetration through the oscillating surface barrier. It is shown that penetration of a single vortex through the ac surface barrier always involves penetration of an antivortex and the subsequent annihilation of the vortex antivortex pairs. Using the nonlinear Larkin-Ovchinnikov (LO) viscous drag force at higher vortex velocities $v(t)$ results in a jump-wise vortex penetration through the surface barrier and a significant increase of the dissipated power. We calculate the effect of dissipation on nonlinear vortex viscosity $\eta(v)$ and the rf vortex dynamics and show that it can also result in the LO-type behavior, instabilities, and thermal localization of penetrating vortex channels. We propose a thermal feedback model of $\eta(v)$, which not only results in the LO dependence of $\eta(v)$ for a steady-state motion, but also takes into account retardation of temperature field around rapidly accelerating vortex, and a long-range interaction with the surface. We also address the effect of pinning on the nonlinear rf vortex dynamics and the effect of trapped magnetic flux on the surface resistance $R_s$ calculated as a function or rf frequency and field. It is shown that trapped flux can result in a temperature-independent residual resistance $R_i$ at low $T$, and a hysteretic low-field dependence of $R_i(B_0)$, which can {\it decrease} as $B_0$ is increased, reaching a minimum at $B_0$ much smaller than the thermodynamic critical field $B_c$.Comment: 18 figure

Realistic Expanding Source Model for Invariant One-Particle Multiplicity Distributions and Two-Particle Correlations in Relativistic Heavy-Ion Collisions

We present a realistic expanding source model with nine parameters that are necessary and sufficient to describe the main physics occuring during hydrodynamical freezeout of the excited hadronic matter produced in relativistic heavy-ion collisions. As a first test of the model, we compare it to data from central Si + Au collisions at p_lab/A = 14.6 GeV/c measured in experiment E-802 at the AGS. An overall chi-square per degree of freedom of 1.055 is achieved for a fit to 1416 data points involving invariant pi^+, pi^-, K^+, and K^- one-particle multiplicity distributions and pi^+ and K^+ two-particle correlations. The 99-percent-confidence region of parameter space is identified, leading to one-dimensional error estimates on the nine fitted parameters and other calculated physical quantities. Three of the most important results are the freezeout temperature, longitudinal proper time, and baryon density along the symmetry axis. For these we find values of 92.9 +/- 4.4 MeV, 8.2 +/- 2.2 fm/c, and 0.0222 + 0.0096 / - 0.0069 fm^-3, respectively.Comment: 37 pages and 12 figures. RevTeX 3.0. Submitted to Physical Review C. Complete preprint, including device-independent (dvi), PostScript, and LaTeX versions of the text, plus PostScript files of all figures, are available at http://t2.lanl.gov/publications/publications.html or at ftp://t2.lanl.gov/publications/res

Space-time extensions from space-time densities and Bose-Einstein correlations

Using a (3+1)-dimensional solution of the relativistic Euler-equations for $Pb+Pb$ at 160 $AGeV$, space-time extensions of kaon emission zones are calculated from space-time densities and compared to the inverse widths of two-kaon Bose-Einstein correlation functions. The comparison shows a satisfactory agreement and it is concluded that because of the Gaussian shape of the kaon correlation functions, the space-time parameters of the kaon source can be calculated directly from space-time densities. In the case of intensity interferometry of identical pions this simplification is not recommended when applying Gaussian fits because of the present strong effects of resonance decays. The whole discussion is based on the assumption that hadron emission in ultra-relativistic heavy-ion collisions is purely chaotic or that coherence is at least negligible.Comment: 11 pages, 2 figures (distributed on 3 Postscript files

An unidentified TeV source in the vicinity of Cygnus OB2

Deep observation (∼113 hrs) of the Cygnus region at TeV energies using the HEGRA stereoscopic system of air Čerenkov telescopes has serendipitously revealed a signal positionally inside the core of the OB association Cygnus OB2, at the edge of the 95% error circle of the EGRET source 3EG J2033+4118, and ∼0.5° north of Cyg X-3. The source centre of gravity is RA αJ2000: 20hr32m07s± 9.2stats±2.2syss, Dec δJ2000: +41°30′30″2.0stat±0.4′sys. The source is steady, has a post-trial significance of +4.6σ, indication for extension with radius 5.6′ at the ∼3σ level, and has a differential power-law flux with hard photon index of - 1.9 ± 0.3stat ± 0.3sys. The integral flux above 1 TeV amounts ∼3% that of the Crab. No counterpart for the TeV source at other wavelengths is presently identified, and its extension would disfavour an exclusive pulsar or AGN origin. If associated with Cygnus OB2, this dense concentration of young, massive stars provides an environment conducive to multi-TeV particle acceleration and likely subsequent interaction with a nearby gas cloud. Alternatively, one could envisage γ-ray production via a jet-driven termination shock.F. A. Aharonian, ... G. P. Rowell, ... [et al

Correlation search for coherent pion emission in heavy ion collisions

The methods allowing to extract the coherent component of pion emission conditioned by the formation of a quasi-classical pion source in heavy ion collisions are suggested. They exploit a nontrivial modification of the quantum statistical and final state interaction effects on the correlation functions of like and unlike pions in the presence of the coherent radiation. The extraction of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation functions and single--pion spectra is discussed in detail for large expanding systems produced in ultra-relativistic heavy ion collisions.Comment: 21 pages, 3 eps figures, ReVTeX, corrected submission abstract. Version published in PRC 65 (2002) 064904. Added is a detailed explanation of the differences between pure coherent states and charge constrained coherent states in the case of a simple example model. The expressions for two-particle spectra taking into account both the final state interaction and the coherent component of pion emission are derived in a more general and transparent wa

Various Models for Pion Probability Distributions from Heavy-Ion Collisions

Various models for pion multiplicity distributions produced in relativistic heavy ion collisions are discussed. The models include a relativistic hydrodynamic model, a thermodynamic description, an emitting source pion laser model, and a description which generates a negative binomial description. The approach developed can be used to discuss other cases which will be mentioned. The pion probability distributions for these various cases are compared. Comparison of the pion laser model and Bose-Einstein condensation in a laser trap and with the thermal model are made. The thermal model and hydrodynamic model are also used to illustrate why the number of pions never diverges and why the Bose-Einstein correction effects are relatively small. The pion emission strength $\eta$ of a Poisson emitter and a critical density $\eta_c$ are connected in a thermal model by $\eta/n_c = e^{-m/T} < 1$, and this fact reduces any Bose-Einstein correction effects in the number and number fluctuation of pions. Fluctuations can be much larger than Poisson in the pion laser model and for a negative binomial description. The clan representation of the negative binomial distribution due to Van Hove and Giovannini is discussed using the present description. Applications to CERN/NA44 and CERN/NA49 data are discussed in terms of the relativistic hydrodynamic model.Comment: 12 pages, incl. 3 figures and 4 tables. You can also download a PostScript file of the manuscript from http://p2hp2.lanl.gov/people/schlei/eprint.htm