In a previous publication [T. Abbott , E802 Collaboration, Phys. Rev. C 63, 064602 (2001); 64, 029901(E) (2001)], measurements of the A dependence and pseudorapidity interval (deltaeta) dependence of midrapidity E-T distributions in a half-azimuth (Deltaphi=pi) electromagnetic calorimeter were presented for p+Be, p+Au, O+Cu, Si+Au, and Au+Au collisions at the BNL-AGS. The validity of the "nuclear geometry" characterization versus deltaeta was illustrated by plots of the E-T(deltaeta) distribution in each deltaeta interval in units of the measured (p+Au) in the same deltaeta interval for p+Au collisions. These plots, with aperture corrected scale in the physically meaningful units of number of average observed p+Au collisions, were nearly universal as a function of deltaeta, confirming that the reaction dynamics for E-T production at midrapidity at AGS energies is governed by the number of projectile participants and can be well characterized by measurements in apertures as small as Deltaphi=pi,deltaeta=0.3. A key ingredient in these analyses is the probability p(0) for no signal to be detected in a given aperture deltaeta for the fundamental p+Au collision. In fact the measured (p+Au) is biased and the true (true)(p+Au) for the detector aperture is the measured value times 1-p(0). The issues and merits of measuring the E-T(deltaeta) distribution in units of (p+Au) or (true)(p+Au) in the same deltaeta interval are presented and discussed. This method has application at RHIC, where p-p data could be used as the reference distribution for two participants. The E-T distributions for B+A collisions, with E-T(deltaeta) scale normalized by (true)(p-p) in the same aperture for p-p collisions, would then be given directly in the popular unit "per participant-pair" [K. Adcox , PHENIX Collaboration, Phys. Rev. Lett. 86, 3500 (2001); I. G. Bearden , BRAHMS Collaboration, Phys. Lett. B523, 227 (2001); B. B. Back , PHOBOS Collaboration, Phys. Rev. C 65, 031901(R) (2002); C. Adler , STAR Collaboration, Phys. Rev. Lett. 89, 202301 (2002)].

Measurements of the A dependence and pseudorapidity interval (delta eta) dependence of midrapidity E-T distributions in a half-azimuth (Delta phi = pi) electromagnetic calorimeter are presented for p + Be, p + Au, O + Cu, Si + Au, and Au + Au collisions at the BNL-AGS (Alternating-Gradient Synchrotron). The shapes of the upper edges of midrapidity E-T distributions as a function of the pseudorapidity interval delta eta in the range 0.3 to 1.3, roughly centered at midrapidity, are observed to vary with delta eta. like multiplicity-the upper edges of the distributions flatten as delta eta is reduced. At the typical fixed upper percentiles of E-T distributions used for nuclear geometry characterization by centrality definition-7 percentile, 4 percentile, 2 percentile, I percentile, 0.5 percentile-the effect of this variation in shape on the measured projectile A(p) dependence for O-16, Si-28, Au-197 projectiles on an Au target is small for the ranges of delta eta and percentile examined. The E-T distributions for p + Au and p + Be change in shape with delta eta; but in each delta eta interval the shapes of the p + Au and p + Be distributions remain indentical with each other-a striking confirmation of the absence of multiple-collision effects at midrapidity at AGS energies. The validity of the nuclear geometry characterization versus delta eta is illustrated by plots of the E-T(delta eta) distribution in each delta eta interval in units of the measured (p + Au) same delta eta interval for p + Au collisions. These plots, in the physically meaningful units of "number of average p + Au collisions," are nearly universal as a function of delta eta confirming that the reaction dynamics for E-T production at midrapidity at AGS energies is governed by the number of projectile participants and can be well characterized by measurements in apertures as small as Delta phi = pi, delta eta = 0.3.

The E-802 Collaboration at the BNL-AGS has measured charged particle multiplicity distributions from central (ZCAL) collisions of $^{16}\mathrm{O}$+Cu at 14.6A GeV/c as a function of the pseudorapidity interval \ensuremath{\delta}\ensuremath{\eta}\ensuremath{\ge}0.1 in the range 1.2\ensuremath{\le}\ensuremath{\eta}\ensuremath{\le}2.2. The fluctuations of these distributions as a function of the pseudorapidity interval have been studied by the method of normalized factorial moments and also by directly fitting the measurements to negative binomial distributions (NBD). Excellent fits to NBD were obtained in all \ensuremath{\delta}\ensuremath{\eta} bins, allowing, for the first time, a systematic formulation of the subject of intermittency in terms of distributions to complement the description based on normalized factorial moments. In agreement with all previous measurements of NBD fits to multiplicity distributions in hadron and lepton reactions, the k parameter of the NBD fit for central $^{16}\mathrm{O}$+Cu collisions is found to exhibit an apparently linear increase with the \ensuremath{\delta}\ensuremath{\eta} interval, albeit with a much steeper slope than for other reactions, and a nonzero intercept, k(0)\ensuremath{\ne}0. The evolution of the NBD parameter k(\ensuremath{\delta}\ensuremath{\eta}) is used to determine the two-particle short-range rapidity correlation length for central $^{16}\mathrm{O}$+Cu collisions, \ensuremath{\xi}=0.18\ifmmode\pm\else\textpm\fi{}0.05, which is much shorter than the value \ensuremath{\xi}\ensuremath{\sim}1--3 for hadron collisions, but this is a quantitative rather than a qualitative difference. These results lead to a simple and elegant explanation of the intermittency formalism, without resort to fractals, for all reactions, which demystifies intermittency---for $^{16}\mathrm{O}$+Cu central collisions, intermittency is nothing more than the apparent statistical independence of the multiplicity in small pseudorapidity bins, \ensuremath{\delta}\ensuremath{\eta}\ensuremath{\sim}0.2, due to the surprisingly short two-particle rapidity correlation length.

The E-802 Collaboration at the BNL-AGS has measured charged particle multiplicity distributions from central (ZCAL) collisions of O-16+Cu at 14.6A GeV/c as a function of the pseudorapidity interval delta eta greater than or equal to 0.1 in the range 1.2 less than or equal to eta less than or equal to 2.2. The fluctuations of these distributions as a function of the pseudorapidity interval have been studied by the method of normalized factorial moments and also by directly fitting the measurements to negative binomial distributions (NBD). Excellent fits to NBD were obtained in all delta eta bins, allowing, for the first time, a systematic formulation of the subject of intermittency in terms of distributions to complement the description based on normalized factorial moments. In agreement with all previous measurements of NBD fits to multiplicity distributions in hadron and lepton reactions, the k parameter of the NBD fit for central O-16+Cu collisions is found to exhibit an apparently linear increase with the Sg interval, albeit with a much steeper slope than for other reactions, and a nonzero intercept, k(0)not equal 0. The evolution of the NBD parameter k(delta eta) is used to determine the two-particle short-range rapidity correlation length for central O-16+Cu collisions, xi=0.18+/-0.05, which is much shorter than the value xi similar to 1-3 for hadron collisions, but this is a quantitative rather than a qualitative difference. These results lead to a simple and elegant explanation of the intermittency formalism, without resort to fractals, for all reactions, which demystifies intermittency-for O-16+Cu central collisions, intermittency is nothing more than the apparent statistical independence of the multiplicity in small pseudorapidity bins, delta eta similar to 0.2, due to the surprisingly short two-particle rapidity correlation length.

Fluctuations in pseudorapidity distributions of charged particles from central collisions of O-16 + Al and O-16+Cu at 14.6A GeV/c are analyzed using scaled factorial moments. A power-law growth of moments with decreasing bin size is observed down to delta eta approximately 0.1. About half the measured signal remains after making corrections based on Monte Carlo calculations with Fritiof and GEANT which include gamma-conversions, Dalitz decays and detector effects.

The AGS spectrometer experiment E-802 has measured transverse mass spectra for charged hadrons over a wide rapidity interval in Si+Au, Si+Cu, and Si+Al reactions at 14.6A Gev/c. These results are compared for two different trigger conditions: central collisions corresponding to 7% of the inelastic cross section selected on multiplicity of charged particles and peripheral collisions corresponding to roughly 50% of the inelastic cross section selected on high kinetic energy at zero degrees. The invariant spectra are well described by exponentials in transverse mass allowing the extraction of rapidity distributions and inverse slope parameters for each specie emitted in the different reactions.

Antiproton production cross sections have been measured in minimum bias p+Be, p+Al, p+Cu, and p+Au collisions at 14.6 GeV/c with the E-802 spectrometer at the Brookhaven Alternating Gradient Synchrotron. The antiproton multiplicity at laboratory rapidities 1.0 to 1.6 shows almost no dependence upon the target mass. The p¯ production for p+Be is somewhat lower than an estimation based upon 19–24 GeV/c p+p data. In this rapidity interval the antiproton yield scales by a factor of 28±6 from p+Au to central Si+Au collisions.Received 25 November 1992DOI:https://doi.org/10.1103/PhysRevC.47.R1351©1993 American Physical Society

The E802 Spectrometer at the Brookhaven Alternating Gradient Synchrotron has been used to measure the correlations in relative momentum between like-sign pions emitted in central Si+Al and Si+Au collisions at 14.6A GeV/c. Data are presented in terms of the correlation function for both identified pi- and pi+ pairs near the nucleon-nucleon center-of-mass rapidity. All parametrizations of the correlation function are consistent with a spherically symmetric source of rms radius R(rms), almost-equal-to 3.5 +/- 0.4 fm and lifetime tau is similar to 2 fm/c.

K+ and π+ multiplicities have been measured in magnetic spectrometer for Si++ Al, Si+ Cu and Si + Au collisions at 14.6 A GeV/c incident momentum. The multiplicities were obtained for five different windows of forward kinetic energy as detected in a zero degree calorimeter. The K+/π+ multiplicity ratio ranges from ≈9% in peripheral interactions to 19% in central Si+Au. The largest K+ / π+ ratios are observed for those events for each target that leave the least energy in the zero degree calorimeter and the ratio increases with target mass. The observations suggest that multiple interactions are important in the particle production mechanism.

Using newly-measured data from the EOS TPC, the authors study azimuthal and {vert_bar}P{sub t}{vert_bar} correlations among triplets and higher-order multiplets, and explore the extent to which all fragments contribute to the flow. Results for Au + Au from 250 to 1200 A MeV and other data will be presented.

Recent single-particle inclusive measurements and two-particle correlation data from E802 and its succesor, E859, are presented. The K+/π+ ratio observed for collisions of 14.6 A·GeV 28Si ions on various targets is presented as a function of both forward and transverse energy. Source sizes are determined via interferometry using π+, π−, K+ and proton pairs.

A systematic set of measurements of the global transverse energy distributions, d\ensuremath{\sigma}/${\mathit{dE}}_{\mathit{T}}$ and ${\mathit{dE}}_{\mathit{T}}$/d\ensuremath{\eta}, from beams of protons, $^{16}\mathrm{O}$ and $^{28}\mathrm{Si}$ at 14.6A GeV/c, incident on targets ranging from Be to Au is presented. The detector was a semicircular array of lead-glass blocks, covering polar angles 9\ifmmode^\circ\else\textdegree\fi{}32\ifmmode^\circ\else\textdegree\fi{}, whose total response provides a good measure of the produced particle yield in the central rapidity region of these reactions. Proton-nucleus spectra exhibit a similar shape on the high-energy tail, independent of target, suggesting that produced particles in such events arise mostly from the first collision of the projectile proton. For targets heavier than Cu, the high-energy edges of the oxygen-nucleus spectra, and of the silicon-nucleus spectra, reach ratios consistent with the geometry of central collisions. Angular distributions, ${\mathit{dE}}_{\mathit{T}}$/d\ensuremath{\eta}, are characterized by Gaussian fits, and an acceptance-independent form of the differential cross section is found, based on the maximum value of ${\mathit{dE}}_{\mathit{T}}$/d\ensuremath{\eta}. The projectile dependence of nucleus-nucleus spectra is studied in terms of two very different models: simple energy scaling and the wounded projectile nucleon model of p+A convolutions.

Production of light particles (π±,K±,p) has been measured in both Si+A and p+A collisions. Several interesting features have been observed, among which are: the enhanced K+/π+ ratio and the larger 〈mt〉 for K+ and proton. Comparisons between ≊pp, pA and SiA collisions are discussed.

Some recent results are presented from AGS E802, a survey experiment which is studying reactions of 14.6 A {center dot} GeV beams of protons, {sup 16}O and {sup 28}Si on targets ranging from {sup 9}Be to {sup 197}Au. Spectra for the global forward and transverse energy are shown; in nucleus-nucleus collisions these two quantities are anticorrelated, consistent with a large amount of stopping. Slope parameters from inclusive particle spectra are presented, with the most interesting effect being an apparent heating'' of mid-rapidity protons which emerge from the collisions of the largest nuclei. Also given are preliminary data on the production of antiprotons. 8 refs., 4 figs., 1 tab.

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 Ar + BaI2 at 1.2 GeV/nucleon are compared with predictions of a nuclear transport model.

Antiproton production cross sections have been measured for minimum bias and central Si + Al and Si + Au collisions at 14.6 A GeV/c. The data presented cover the range of transverse momentum from 0.3 to 1.2 GeV/c and lab rapidities from 1.1 to 1.7 units. The relative pBAR/pi- and pBAR/K- yields are found to be the smallest for the heaviest system measured, central Si + Au collisions. For these collisions, the pBAR/pi- ratio, determined from integrated yields for 1.1 less-than-or-equal-to y less-than-or-equal-to 1.7, is (0.84 +/- 0.07) 10(-3). In the same rapidity interval, the average antiproton inverse m perpendicular-to slope is 141 +/- 14 MeV for central Si + Al and central Si + Au collisions.

Semi-inclusive spectra of ${\ensuremath{\pi}}^{\ifmmode\pm\else\textpm\fi{}}$, ${K}^{\ifmmode\pm\else\textpm\fi{}}$, and p have been measured near midrapidity for central collisions of 14.6A-GeV/c $^{28}\mathrm{Si}$ with $^{197}\mathrm{Au}$ nuclei. The invariant cross sections are all well fit by exponential distributions in transverse mass, within the measured ranges. The \ensuremath{\pi} and K cross sections can also be fit by Boltzmann distributions. From integrated yields, at midrapidity, the kaon/pion yield ratios are (19.2\ifmmode\pm\else\textpm\fi{}3)% for ${K}^{+}$/${\ensuremath{\pi}}^{+}$ and (3.6\ifmmode\pm\else\textpm\fi{}0.8)% for ${K}^{\mathrm{\ensuremath{-}}}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$; the ${\ensuremath{\pi}}^{+}$/${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ ratio is 1.00\ifmmode\pm\else\textpm\fi{}0.04.

To probe the early, high density stage of a heavy-ion collision, it is essential to focus on observables that are minimally distorted during the subsequent processes of expansion, decay of excited states, and chemical freeze-out. It is now widely accepted that correlations characteristic of fluid-like collective behavior (“flow”) fulfill these requirements. Such correlations signal the release of compressional energy, and provide a relative measure of the peak nuclear pressure generated in the collision.