arXiv subjects
Publications and source records attributed to R. M. Weiner.
Invited talk at the CORR98 meeting on Correlations, Mátraháza, June 1998, to appear in the proceedings of the meeting in World Scientific. This talk is dedicated to the memory of Peter Carruthers.
Photons and mesons are both bosons and therefore satisfy the same Bose-Einstein statistics. This leads to certain similarities in the corresponding Bose-Einstein correlations which underly photon and hadron intensity interferometry. However there are also important differences between the two effects and these will be analyzed in the following.
A multiparticle system produced by a large number of independent sources is described by a gaussian density matrix W. All theoretical approach to Bose-Einstein Correlatios Cn in high energy physics use this form for W. One of the most salient consequences of this form is the fact that all higher order (n>2) moments of the current distribution can be expressed in terms of the first two. We test this property by comparing the data on C2(Q^2), C3(Q^2) and C4(Q^2) from pion-p and K-p reactions at 250 GeV/c with the predictions of a general quantum statistical space-time approach. Even a simplified version of such approach can account for the data. Previous attempts along these lines, which did not use the space-time approach, met with difficulties.
We calculate the pi-/pi+ ratio for Pb+Pb at CERN/SPS energies and for Au+Au at BNL/AGS energies using a (3+1) dimensional hydrodynamical model. Without consideration of Coulomb effect an enhancement of this ratio at low mt is found compatible with that observed in these experiments. Our calculations are based on previous (3+1) dimensional hydrodynamical simulations (HYLANDER), which described many other aspects of experimental data. In this model the observed enhancement is a consequence of baryon and strangeness conservation and of chemical equilibration of the system and is caused by the decay of produced hyperons, which leads to a difference in the total number of positive and negative pions as well. Based on the same approach, we also present results for the pi-/pi+ ratio for S+S (CERN/SPS) collisions, where we find a similar effect. The absence of the enhancement of the pi-/pi+ ratio in the S+S data presented by the NA44 Collaboration, if confirmed, could indicate that chemical equilibration has not yet been estabilished in this reaction.
It is argued that Bose-Einstein correlations constitute one of the most important and characteristic effects of strong interactions. The progress made in our understanding of this phenomenon is reviewed and a program for future research in this field is formulated.
The implications of the formation of a Bose condensate on one- and two-particle spectra are studied for ultrarelativistic nucleus-nucleus collisions in the framework of a hydrodynamic description. It is found that single particle spectra are considerably enhanced at low momenta. The Bose-Einstein correlation function has an intercept below two. For pion pairs in the central region a two-component structure may appear in the correlation function, which is different from that found in quantum optics. The chaoticity parameter is strongly momentum dependent.
It is shown that there exists an intimate relationship between Bose Einstein correlations and quantum field theory. On the one hand several essential aspects of BEC cannot be understood and even formulated without second quantization. On the other hand BEC can serve as a unique tool in the investigation of modern field theory and in particular of the standard model. Some new developments on this subject related to multiparticle production and squeezed states are also discussed.
We present a coherent theoretical study of ultrarelativistic heavy-ion data obtained at the CERN/SPS by the NA35/NA49 Collaborations using 3+1-dimensional relativistic hydrodynamics. We find excellent agreement with the rapidity spectra of negative hadrons and protons and with the correlation measurements in two experiments: $S+S$ at 200 $AGeV$ and $Pb+Pb$ at 160 $AGeV$ (preliminary results). Within our model this implies that for $Pb+Pb$ ($S+S$) a quark-gluon-plasma of initial volume 174 $fm^3$ (24 $fm^3$) with a lifetime 3.4 $fm/c$ (1.5 $fm/c$) was formed. It is found that the Bose-Einstein correlation measurements do not determine the maximal effective radii of the hadron sources because of the large contributions from resonance decay at small momenta. Also within this study we present an NA49 acceptance corrected two-pion Bose-Einstein correlation function in the invariant variable, $Q_{inv}$.
We present the first analysis of preliminary data for $Pb+Pb$ at 160 $AGeV$ using 3+1-dimensional relativistic hydrodynamics. We find excellent agreement with the rapidity spectra of negative hadrons and the correlation measurements. The data indicates a large amount of stopping; $65\%$ of the invariant energy of the collision is thermalized and $73\%$ of the baryons are contained in the central fireball. Within our model this implies that a quark-gluon-plasma of lifetime 3.4 $fm/c$ was formed.
It is shown that a one to one correspondence between quantum fields in two different "phases" as might be realized for pions produced from a "hadron liquid" leads to squeezed states. The single and double inclusive cross sections for at chaotic superposition of such states are calculated. The correlation of identical pions is overbunched in comparison with canonical Bose-Einstein correlations.
It is argued that correlations and multiplicity distributions constitute one of the most characteristic properties of strong interactions. The progress made in the last years in our understanding of correlations is reviewed.
The variation of radii, lifetimes, correlation lengths and the chaoticity parameter of particle sources with the collision energy $\sqrt{s}$ is studied by analysing and comparing two-particle Bose-Einstein correlation data obtained by the NA22 Collaboration at $\sqrt{s}=22\ GeV$ and by the UA1-Minimum-Bias Collaboration at $\sqrt{s}=630\ GeV$. The UA1-data are found to be inconsistent with a static source, whereas both the data at $\sqrt{s}=22\ GeV$ and at $630\ GeV$ can be described in an expanding source model. In the latter model, the $s$-dependence of the data implies an increase of the transverse radius with $s$ and a decrease of the correlation lengths in longitudinal and in transverse direction. The chaoticity parameter increases or remains approximately constant as a function of the CM energy.
Using a three-dimensional hydrodynamic simulation of the collision and an equation of state containing a first order phase transition to the quark-gluon plasma, we study thermal photon production for $Au+Au$ collisions at $E_{lab}=11.5$ AGeV and for $Pb+Pb$ collisions at $160$ AGeV. We obtain surprisingly high rates of thermal photons even at the lower energy, suggesting that, contrary to what was expected so far, photon production may be an interesting topic for experimental search also at the Alternating Gradient Synchrotron. When applied to the reaction $S+Au$ at $200$ AGeV, our model can reproduce preliminary data obtained by the WA80 Collaboration without having to postulate the existence of an extremely long-lived mixed phase as was recently proposed.
A Quantum Field Theory formulation of Bose-Einstein Correlations is given. It contains as a special case the classical current approach. It is shown that the particle-antiparticle correlations are a general feature of Bose-Einstein Correlations and not an artifact of a certain approximation. Relations are provided through which the quantum corrections to the classical current approach can be determined experimentally.
We compare and analyse Bose-Einstein correlation data for $π^+ p$ and $K^+ p$ collisions at $\sqrt{s}=22\ GeV$ obtained by the NA22-Collaboration and data for $p\bar{p}$ collisions at $\sqrt{s}=630\ GeV$ obtained by the UA1-Minimum-Bias-Collaboration. Using a parametrization for a longitudinally expanding source, we observe that correlation lengths and radii extracted from fits to the data change significantly if one goes from the NA22- to the UA1-data: the transverse radius of the chaotic source increases by about $50\%$ while the correlation lengths in longitudinal and transverse directions decrease by about $50\%$ and $30\%$, respectively. The chaoticity parameter remains approximately constant or increases. DMR-THEP-94-6/W
The Bose-Einstein correlations of photons emitted {}from a longitudinally expanding system of excited matter produced in ultrarelativistic heavy ion collision are studied. Two effects found in recent calculations -- that the correlation function in longitudinal direction exhibits oscillations, and that it takes values below unity -- are demonstrated to be numerical artefacts and/or the results of inappropriate approximations. Thus, the general quantum statistical bounds for the two particle correlation function of a chaotic source with Gaussian fluctuations are confirmed. Two different expressions for the two-photon inclusive distribution are considered. Depending on which of the two expressions is used in the calculation, the width of the correlation function may vary by as much as $30\%$. PACS numbers: 05.30.Jp, 13.85.Hd, 25.75.+r, 12.40.Ee
Bounds for the correlation functions of identical bosons are discussed for the general case of a Gaussian density matrix. In particular, for a purely chaotic system the two-particle correlation function must always be greater than one. On the other hand, in the presence of a coherent component the correlation function may take values below unity. The experimental situation is briefly discussed.
A study of hadronic data up to TEVATRON energies in terms of relativistic hydrodynamics indicates an extended 1-dimensional stage of the expansion which suggests a jet like behaviour of the fireball along the collision axis.