We present a new type of flow analysis, based on a particle-pair correlation function, in which there is no need for an event-by-event determination of the reaction plane. Consequently, the need to correct for dispersion in an estimated reaction plane does not arise. Our method also offers the option to avoid any influence from particle misidentification. Using this method, streamer chamber data for collisions of Ar+ KCl and Ari-BaI, at 1.2 GeV/nucleon are compared with predictions of a nuclear transport model.Many intermediate-energy heavy ion experiments have been directed toward the goal of inferring properties of the nuclear equation of state (EOS) [I]. In parallel with this effort, theoretical work in the area of nuclear transport models has focused on the task of identifying the most appropriate experimental observables for probing the EOS and on the related task of establishing a quantitative connection between such observables and the EOS [2]. Many factors, both theoretical and experimental, have contributed to the current lack of a Consensus on Data [3,4] from the Diogene and Plastic Ball detectors Support this assumption for rapidities other than the midrapidity region where the "squeeze-out" [5] effect can result in a more complex distribution. In the present study, we restrict our analysis to forward rapidities (see below). The maximum azimuthal anisotropy, as defined by Welke et al. [ 6 ] , is even a relatively coarse characterization of the compresl + h R=-sional potential energy at maximum density (in other 1-h ' words, a characterization of the EOS as relatively "hard" or "soft"). One such factor, for example, arises from the fact that detector inefficiencies and distortions can be difficult to simulate and quantify (particularly in the case of a 4n-detector), and this leads to systematic uncertainties in measurements of collective flow. This paper presents a new form of collective flow analysis for two data sets from the Bevalac streamer chamber. The most noteworthy feature of this new method is that it is designed to minimize the type of systematic uncertainty mentioned above; more specifically, the influences of particle misidentification and dispersion of the reaction plane can be removed.For a nonzero impact parameter, the beam direction ( z ) and the line joining the Centers of the nuclei determine the reaction plane, i.e., the X -2 plane. The azimuthal angle of a fragment in this coordinate system is We assume that the distribution function of 4 in an interval of rapidity centered on y , can be described by an expression of the form The method proposed by Welke et al. [6] for determining R in an experiment involves estimating 4 in Eqs. (1) and (2) using the relation 4=+obs-+R, where +obs is the observed azimuth of a fragment, and +R is the estimated azimuth of the reaction plane as deter.mined from the observed fragments in the final state. This method requires that the resulting R be corrected upward, to allow for the fact that 4R is distributed about + = O with a finite dispersion. Eac...

We report a particle source imaging analysis based on two-pion correlations in high multiplicity Au+Au collisions at beam energies between 2A and 8A GeV. We apply the imaging technique introduced by Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown-Twiss analysis.

Using 47r data from the Bevalac streamer chamber, we study azimuthal correlations for fragment pairs and higher-order multiplets. We point out that previous studies of sideward flow have not ruled out the possibility that the effect is dominated by a small number of correlated fragments in each event, as opposed to being a collective motion to which most or all fragments contribute. Based on a simulation, we infer that more than 70% of the forward-going fragments from collisions of Ar on Pb at OAA GeV carry a component of the collective motion.PACS numbers: 25.75.+rIn the field of heavy-ion collisions at intermediate energies, much attention has been devoted to measurements of collective sideward deflection of the reaction products ("sideward flow") [1-10]. Fluid-dynamical models had predicted such an effect and had indicated that measurements of flow can provide information about the equation of state of compressed nuclear matter [11]. More recent developments in the area of microscopic transport models have resulted in progress towards interpretation of data in terms of nuclear state variables [12]. In this Letter, we argue that a quantitative description of "collectivity" (the percentage of fragments that participate in the ordered motion) is complementary to measurements of the strength of the flow, and, for the first time, we present a study of this aspect of the flow phemonenon [13].All of the flow analyses cited above [1-10] focus on the information contained in pair correlations, even though these studies are based on multifragment data from detectors approaching 47r solid-angle acceptance. For instance, in the transverse momentum analysis devised by Danielewicz and Odyniec [4], the orientation of the reaction plane for each event is estimated from the fragment transverse momenta p+ using the vector Q = J2 w jPf> where w is a rapidity-dependent weighting factor with the property w(y c . m .) = -w(-y c . m .); the magnitude of the flow is then characterized by (p x ), the average component of p-1 in the estimated reaction plane. This flow observable is equivalent to a particle-pair correlation of the form (p^ • pf), where it is required only that both fragments in each pair belong to the same event [14]; there is no requirement that each event contribute more than one pair. Of course, the statistical uncertainty associated with the vector Q will become large if there are few measured fragments in each event, but this is immaterial to the present discussion.The concept [15] of studying flow using a detector combination that is substantially simpler [9] than one which identifies fragments and measures momenta over a large fraction of 4n is based on the fact that flow observables such as (p x ) and various differential cross sections as a function of azimuth relative to the event reaction plane utilize only correlations between fragment pairs. As demonstrated below, it is not possible for a pair analysis to distinguish between a highly collective multifragment correlation and a flowlike effect that might, to ...

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