Abstract. Recently, a new technique for measuring short-range NN correlations in nuclei (NN SRCs) was reported by the E850 collaboration, using data from the EVA spectrometer at the AGS at Brookhaven Nat. Lab. In this talk, we will report on a larger set of data from new measurement by the collaboration, utilizing the same technique. This technique is based on a very simple kinematic approach. For quasielastic knockout of protons from a nucleus ( 12 C(p,2p) was used for the current work), we can reconstruct the momentum p f of the struck proton in the nucleus before the reaction, from the three momenta of the two detected protons, p 1 and p 2 and the three momentum of the incident proton, p 0 :If there are significant n-p SRCs, then we would expect to find a neutron with momentum -p f in coincidence with the two protons, provided p f is larger than the Fermi momentum k F for the nucleus (∼220 MeV/c for 12 C). Our results reported here confirm the earlier results from the E850 collaboration.

The transparency of carbon for (p,2p) quasielastic events was measured at beam momenta ranging from 5.9 to 14.5 GeV/c at 90 degrees c.m. The four-momentum transfer squared (Q2) ranged from 4.7 to 12.7 (GeV/c)(2). We present the observed beam momentum dependence of the ratio of the carbon to hydrogen cross sections. We also apply a model for the nuclear momentum distribution of carbon to obtain the nuclear transparency. We find a sharp rise in transparency as the beam momentum is increased to 9 GeV/c and a reduction to approximately the Glauber level at higher energies.

We summarize the results of two experimental programs at the Alternating Gradient Synchrotron of BNL to measure the nuclear transparency of nuclei measured in the A(p,2p) quasielastic scattering process near 90 • in the pp center of mass. The incident momenta varied from 5.9 to 14.4 GeV/c, corresponding to 4.8 < Q 2 < 12.7(GeV /c) 2 . Taking into account the motion of the target proton in the nucleus, the effective incident momenta extended from 5.0 to 15.8 GeV/c. First, we describe the measurements with the newer experiment, E850, which had more complete kinematic definition of quasielastic events. E850 covered a larger range of incident momenta, and thus provided more information regarding the nature of the energy dependence of the nuclear transparency. In E850 the angular dependence of the nuclear transparency near 90 • , and the nuclear transparency for deuterons was studied. Second, we review the techniques used in an earlier experiment, E834, and show that the two experiments are consistent for the Carbon data. E834 also determines the nuclear transparencies for lithium, aluminum, copper, and lead nuclei as well as for Carbon. A determination of the (π + , π + p) transparencies is also reported. We find for both E850 and E834 that the A(p,2p) nuclear transparency, unlike that for A(e,e'p) nuclear transparency, is incompatible with a constant value versus energy as predicted by Glauber calculations. The A(p,2p) nuclear transparency for Carbon and Aluminum increases by a factor of two between 5.9 and 9.5 GeV/c incident proton momentum. At its peak the A(p,2p) nuclear transparency is ∼ 80% of the constant A(e,e'p) nuclear transparency. Then the nuclear transparency falls back to a value at least as small as that at 5.9 GeV/c, and is compatible with the Glauber level again. This oscillating behavior is generally interpreted as an interplay between two components of the pN scattering amplitude; one short ranged and perturbative, and the other long ranged and strongly absorbed in the nuclear medium. A study of the A dependent nuclear transparency indicates that the effective cross section varies with incident momentum and is considerably smaller than the free pN cross section. We suggest a number of experiments for further studies of nuclear transparency effects.

The associated phenomena of preequilibrium emission and incomplete fusion in heavy ion collisions at low impact parameter are studied in the context of inverse kinematics and of a symmetrical system. The Ar+ "C, Mg, and 'Sc reactions performed at E40 --27. 5 MeV/nucleon are Ar discussed. Heavy fragments and light particles have been detected inclusively and exclusively.

We studied the 12 C(p,2p+n) reaction at beam momenta of 5.9, 8.0 and 9.0 GeV/c. For quasielastic (p,2p) events we reconstructed p f the momentum of the knocked-out proton before the reaction; p f was then compared (event-by-event) with pn, the measured, coincident neutron momentum. For |pn| > kF = 0.220 GeV/c (the Fermi momentum) a strong back-to-back directional correlation between p f and pn was observed, indicative of short-range n-p correlations. From pn and p f we constructed the distributions of c.m. and relative motion in the longitudinal direction for correlated pairs. After correcting for detection efficiency, flux attenuation and solid angle, we determined that 49 ± 13 % of events with |p f | > kF had directionally correlated neutrons with |pn| > kF . Thus short-range 2N correlations are a major source of high-momentum nucleons in nuclei.