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We analyze recent data from high-momentum-transfer (p, pp) and (p, ppn) reactions on Carbon. For this analysis, the two-nucleon short-range correlation (NN-SRC) model for backward nucleon emission is extended to include the motion of the NN-pair in the mean field. The model is found to describe major characteristics of the data. Our analysis demonstrates that the removal of a proton from the nucleus with initial momentum 275−550 MeV/c is 92 +8 −18 % of the time accompanied by the emission of a correlated neutron that carries momentum roughly equal and opposite to the initial proton momentum. Within the NN-SRC dominance assumption the data indicate that the probabilities of pp or nn SRCs in the nucleus are at least a factor of six smaller than that of pn SRCs. Our result is the first estimate of the isospin structure of NN-SRCs in nuclei, and may have important implication for modeling the equation of state of asymmetric nuclear matter. Studies of short-range nucleon correlations (SRCs) in nuclei are important for understanding the shortdistance and large-momentum properties of nuclear ground state wave functions. The relevant distances in two-nucleon (NN)-SRCs are expected to be comparable to that in neutron stars corresponding to 4-10 times the central density of nuclei [1]. Thus SRC studies are essential in understanding the structure of cold dense nuclear matter. In this context the isospin content of SRCs (i.e. pn vs. pp and nn pairs) is important for understanding the structure of nuclear matter made of either protons or neutrons. Studies of SRCs also give the best hope of understanding the nature of the short-range NN repulsion.SRCs in nuclei have been actively investigated for over three decades (see e.g. [2]). However, experimental studies of the microscopic structure of SRCs were largely restricted due to moderate momentum-transfer kinematics in which it is difficult to resolve SRCs. Recently, several experiments [3,4,5,6,7] made noticeable progress in understanding dynamical aspects of SRCs. For Q 2 > 1 GeV 2 , Refs [4,5] observed Bjorken x B scaling for ratios of inclusive (e, e ′ ) cross sections of nuclei A to the 3 He nucleus when x B ≥ 1.4. This confirms the earlier observation of scaling for nucleus-to-deuteron cross section ratios [8,9], and indicates directly that the electrons probe high-momentum bound nucleons coming from local sources in nuclei (i.e. SRCs) with properties generally independent of the non-correlated residual nucleus.Based on the NN-SRC picture, which is expected to dominate the internal momentum range of ∼ 250 − 600 MeV/c, one predicts a strong directional (backto-back) correlation between the struck nucleon and its spectator in the SRC. Experiments [3,6,7] measured triple-coincidence events for the 3 He(e, e ′ pp)X and 12 C(p, ppn)X reactions, and clearly demonstrated the existence of such directional correlations. They also revealed a noticeable momentum distribution of the center of mass (c.m.) of the NN-SRCs.In this work we extend the NN-SRC model used in the an...

The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved

The results from the STAR Collaboration on directed flow (v 1 ), elliptic flow (v 2 ), and the fourth harmonic (v 4 ) in the anisotropic azimuthal distribution of particles from Au+Au collisions at √ s NN = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a blast-wave model. Different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v 2 , scaling with the number of constituent quarks and parton coalescence are discussed. For v 4 , scaling with v 2 2 and quark coalescence are discussed.

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