Y. AKIBA, D. BEAVIS, P. BEERY, H.C. BRITT, B. BUDICK, C. CHASMAN, Z. CHEN, C.Y. CHI, Y.Y. CHU, V. CIANCIOLO, B.A. COLE, J.B. COSTALES, H.J. CRAWFORD, J.B. CUMMING R. DEBBE, J. ENGELAGE, S.Y. FUNG, M. GONIN, S. GUSHUE, H. HAMAGAKI, O. HANSEN, R.S. HAYANO, S. HAYASHI, S. HOMMA, H.HUANG,H. KANEKO, J. KANG, S. KAUFMAN, W. KEHOE, K. KURITA, R.J. LEDOUX, MJ. LEVINE, Y. MIAKE, D. MORRISON, R.J. MORSE, B. MOSKOWITZ, S. NAGAMIYA, M.N. NAMBOODIRI, T. NAYAK, J. OLNESS, C.G. PARSONS, L.P. REMSBERG, D. ROEHRICH, P. ROTHSCHILD, H. SAKURAI, T.C. SANGSTER, R. SETO, R. SOLTZ, S.G. STEADMAN, G.S.F. STEPHANS, T. SUNG, S. TANAKA, Y. TANAKA, M.J. TANNENBAUM, J. THOMAS, J.H. VAN DIJK, F. VIDEB^K, O. VOSSNACK, V. VUTSADAKIS, F.Q. WANG, Y. WANG, H.E. WEGNER, D.S. WOODRUFF, Y.D. WU, AND W. ZAJC

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)].

Two-pion correlation functions are analyzed at mid-rapidity for three systems (14.6 A-GeV Si+Al, Si+Au, and 11.6 A-GeV Au+Au), seven distinct centrality conditions, and different kT bins in the range 0.1--0.5 GeV/c. Source reference frames are determined from fits to the Yano-Koonin source parameterization. Bertsch-Pratt radius parameters are shown to scale linearly with both number of projectile and total participants as obtained from a Glauber model calculation. A finite emission duration that increases linearly with system/centrality is also reported. The mT dependence of the Bertsch-Pratt radii is measured for the central Si+Au and Au+Au systems. The system/centrality dependence is investigated separately for both high and low mT regions.

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.

Proton and deuteron distributions from 11.6A GeV/c Au + Au collisions measured by the E802 Collaboration in experiment E-866 are presented. The invariant yield of protons and deuterons is studied as a function of the transverse mass for different cuts of rapidity and centrality. At low m(t)-m(0) the proton and deuteron invariant spectra deviate from a single exponential shape. The average m(t) as function of centrality and rapidity is used to explore the effect of collective transverse flow in the reaction. The ratio of the deuteron to squared proton yield as a function of transverse momentum, rapidity, and centrality is used to probe the coalescence model of deuteron production. This ratio is constant as a function of rapidity only for the most central cuts and decreases with the centrality for every rapidity cut. The ratio of the differential cross section of the deuteron to the squared differential cross section of the proton, for the most central cut, is not constant as a function of m(t)-m(0). [S0556-2813(99)04911-0].

Charged kaon production has been measured in Si+Al and Si+Au collisions at 14.6 A GeV/c, and Au+Au collisions at 11.1 A GeV/c by Experiments 859 and 866 (the E--802 Collaboration) at the BNL AGS. Invariant transverse mass spectra and rapidity distributions for both K+ and K- are presented. The centrality dependence of rapidity-integrated kaon yields is studied. Strangeness enhancement is observed as an increase in the slope of the kaon yield with the total number of participants as well as the yield per participant. The enhancement starts with peripheral Si+Al and Si+Au collisions (relative to N+N) and appears to saturate for a moderate number of participating nucleons in Si+Au collisions. It is also observed to increase slowly with centrality in Au+Au collisions, to a level in the most central Au+Au collisions that is greater than that found in central Si+A collisions. The enhancement factor for $K^+$ production are 3.0 +-0.2(stat.) +-0.4(syst.) and 4.0 +-0.3(stat.) +-0.5(syst.), respectively, for the most central 7% Si+Au collisions and the most central 4% Au+Au collisions relative to N+N at the correponding beam energy.

In this paper Au+Au collisions at 11.6A GeV/c are characterized by two global observables: the energy measured near zero degrees (E-ZCAL) and the total event multiplicity. Particle spectra are measured for different event classes that are defined in a two-dimensional grid of both global observables. For moderately central events (sigma/sigma(int) < 12%) the proton dN/dy distributions do not depend on E-ZCAL but only on the event multiplicity. In contrast the shape of the proton transverse spectra shows little dependence on the event multiplicity. The change in the proton dN/dy distributions suggests that different conditions are formed in the collision for different event classes. These event classes are studied for signals of new physics by measuring pion and kaon spectra and yields. In the event classes doubly selected on E-ZCAL and multiplicity there is no indication of any unusual pion or kaon yields, spectra, or K/pi ratio even in the events with extreme multiplicity. [S0556-2813(99)03704-8].

Semi-inclusive proton and pion distributions from central Au+Au reactions at 11.6A GeV/c have been measured. The proton rapidity distribution shows significantly increased stopping compared to lighter systems, providing strong evidence for the formation of a state of matter with baryon density substantially greater than normal nuclear matter. Unlike reactions at this energy induced by lighter heavy ions, at low m(1)-m(0) the proton invariant spect a deviate from a single exponential shape and become flatter, while pi(-) spectra are found to rise faster than the pi(+) spectra.

In this talk I report on the measured spectra and yields of K+ and K− emitted as a function of centrality in Au + Au collisions at 2, 4, 6, 8 and 10.7 AGeV. We use these data to explore three topics: the importance of secondary collisions in kaon production, the search for a small volume of baryon-rich QGP, and the constraints that K+ and K− spectra make on predicted in-medium properties of kaons.

Antiproton production in 11.7A GeV/c Au + Au collisions over a wide transverse-mass coverage was studied using the AGS-E866 experimental apparatus. The mean transverse kinetic energy increases as a function of centrality and is similar to that of protons. The antiproton yields in Si + Al, Si + Au, and Au + Au collisions are consistent with scaling with the 0.7 power of the number of participant nucleons. [S0031-9007(98)07191-9].

Systematic results are presented on proton, deuteron, and triton emission from the target spectator region in collisions of 10.20A GeV gold projectiles with a gold target. A forward hodoscope utilizes detection of projectile spectator fragments to determine the orientation of the reaction plane, event by event. The directed flow (p(x)) is determined as a function of pseudorapidity. Projectile spectator energy is used to estimate impact parameters. Results are compared to current theoretical models ARC, ART, and RQMD. In all cases good agreement with theory is obtained for calculations utilizing a pure cascade without nuclear potential contributions.

First measurements of single particle spectra of pi(+/-), K+ and p in Au-197 + Au collisions at E-kine = 4 GeV per nucleon are presented. Utilizing the 4 A GeV data set from the Forward Spectrometer at the AGS-E866 experiment, transverse mass distributions and rapidity density distributions of pi(+/-), K+ and p near the mid-rapidity region are extracted. Preliminary results are compared with those of the microscopic cascade model calculation, RQMD.

We report measurements of proton emission at target rapidities for minimum bias and central collisions of $14.6A\mathrm{GeV}/c$ ${}^{28}\mathrm{Si}$ with Al, Cu, and Au nuclei as well as minimum bias and central collisions of $11.7A\mathrm{GeV}/c$ ${}^{197}\mathrm{Au}$ with Au nuclei. Results for deuteron emission are also reported for the $\mathrm{S}\mathrm{i}+\mathrm{A}\mathrm{u}$ reaction. The spectra span the laboratory angular range of $50\ifmmode^\circ\else\textdegree\fi{}<~\ensuremath{\theta}<~130\ifmmode^\circ\else\textdegree\fi{}$ and kinetic energy range of $40\mathrm{MeV}<~{E}_{\mathrm{kin}}<~225\mathrm{MeV}.$ Inverse slopes of proton spectra and proton $dN/d\ensuremath{\eta}$ values in the kinetic energy range $50\mathrm{MeV}<~{E}_{\mathrm{kin}}<~110\mathrm{MeV}$ are reported. The inverse slopes are 40--80 MeV for the various systems, generally increasing with increasing pseudorapidity. The $dN/d\ensuremath{\eta}$ values for $A+A$ collisions within the restricted kinetic energy interval are compared to those for protons from $p+\mathrm{Au}$ in the literature. All pseudorapidity distributions have very similar shapes. The experimental results have been compared to the predictions of the nucleon-nucleon collision models ARC and RQMD. The predictions made by these two models for the distribution of protons at target rapidities are very similar to each other. However, there are significant differences between the model predictions and the experimental results in the details of the spectral slopes and the proton yields for different trigger conditions.

We report measurements of proton emission at target rapidities for minimum bias and central collisions of 14.6AGeV/c {sup 28}Si with Al, Cu, and Au nuclei as well as minimum bias and central collisions of 11.7AGeV/c {sup 197}Au with Au nuclei. Results for deuteron emission are also reported for the Si+Au reaction. The spectra span the laboratory angular range of 50{degree}{le}{theta}{le}130{degree} and kinetic energy range of 40MeV{le}E{sub kin}{le}225MeV. Inverse slopes of proton spectra and proton dN/d{eta} values in the kinetic energy range 50MeV{le}E{sub kin}{le}110MeV are reported. The inverse slopes are 40{endash}80 MeV for the various systems, generally increasing with increasing pseudorapidity. The dN/d{eta} values for A+A collisions within the restricted kinetic energy interval are compared to those for protons from p+Au in the literature. All pseudorapidity distributions have very similar shapes. The experimental results have been compared to the predictions of the nucleon-nucleon collision models ARC and RQMD. The predictions made by these two models for the distribution of protons at target rapidities are very similar to each other. However, there are significant differences between the model predictions and the experimental results in the details of the spectral slopes and the proton yields for different trigger conditions. {copyright} {ital 1997} {italmore » The American Physical Society}« less