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 atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using (12)C, (27)Al, (56)Fe, and (208)Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

Measurement of two-and three-nucleon shortrange correlation probabilities in nuclei KS The ratios of inclusive electron scattering cross sections of 4 He, 12 C, and 56 Fe to 3 He have been measured at 1 < x B < 3. At Q 2 > 1:4 GeV 2 , the ratios exhibit two separate plateaus, at 1:5 < x B < 2 and at x B > 2:25. This pattern is predicted by models that include 2-and 3-nucleon short-range correlations (SRC). Relative to A 3, the per-nucleon probabilities of 3-nucleon SRC are 2.3, 3.1, and 4.4 times larger for A 4, 12, and 56. This is the first measurement of 3-nucleon SRC probabilities in nuclei.

Novel processes probing the decay of nucleus after removal of a nucleon with momentum larger than Fermi momentum by hard probes finally proved unambiguously the evidence for long sought presence of short-range correlations (SRCs) in nuclei. In combination with the analysis of large Q 2 , A(e,e')X processes at x > 1 they allow us to conclude that (i) practically all nucleons with momenta ≥ 300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii) probability of such SRCs in medium and heavy nuclei is ∼ 25%, iii) a fast removal of such nucleon practically always leads to emission of correlated nucleon with approximately opposite momentum, iv) proton removal from twonucleon SRCs in 90% of cases is accompanied by a removal of a neutron and only in 10% by a removal of another proton. We explain that observed absolute probabilities and the isospin structure of two nucleon SRCs confirm the 1 arXiv:0806.4412v2 [nucl-th] 4 Sep 2008important role that tensor forces play in internucleon interactions. We find also that the presence of SRCs requires modifications of the Landau Fermi liquid approach to highly asymmetric nuclear matter and leads to a significantly faster cooling of cold neutron stars with neutrino cooling operational even for N p /N n ≤ 0.1. The effect is even stronger for the hyperon stars. Theoretical challenges raised by the discovered dominance of nucleon degrees of freedom in SRCs and important role of the spontaneously broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are considered. We also outline directions for future theoretical and experimental studies of the physics relevant for SRCs.

The cross section of hard semiexclusive A(e,eЈN)(AϪ1) reactions for fixed missing energy and momentum is calculated within the eikonal approximation. Relativistic dynamics and kinematics of high energy processes are unambiguously accounted for by using the analysis of appropriate Feynman diagrams. A significant dependence of the final state interactions on the missing energy is found, which is important for interpretation of forthcoming color transparency experiments. A new, more stringent kinematic restriction on the region where the contribution of short-range nucleon correlations is enhanced in semiexclusive knock-out processes is derived. It is also demonstrated that the use of light-cone variables leads to a considerable simplification of the description of high energy knock-out reactions.

One of the primary goals of nuclear physics is providing a complete description of the structure of atomic nuclei. While mean-field calculations provide detailed information on the nuclear shell structure for a wide range of nuclei, they do not capture the complete structure of nuclei, in particular the impact of small, dense structures in nuclei. The strong, short-range component of the nucleon-nucleon potential yields hard interactions between nucleons which are close together, generating a high-momentum tail to the nucleon momentum distribution, with momenta well in excess of the Fermi momentum. This highmomentum component of the nuclear wave-function is one of the most poorly understood parts of nuclear structure.Utilizing high-energy probes, we can isolate scattering from high-momentum nucleons, and use these measurements to examine the structure and impact of short-range nucleon-nucleon correlations. Over the last decade we have moved from looking for evidence of such short-range structures to mapping out their strength in nuclei and examining their isospin structure. This has been made possible by high-luminosity and high-energy accelerators, coupled with an improved understanding of the reaction mechanism issues involved in studying these structures. We review the general issues related to short-range correlations, survey recent experiments aimed at probing these short-range structures, and lay out future possibilities to further these studies.

We review the present status of the theory of high energy reactions with semi-exclusive nucleon electro-production from nuclear targets. We demonstrate how the increase of transferred energies in these reactions opens a complete new window in studying the microscopic nuclear structure at small distances. The simplifications in theoretical descriptions associated with the increase of the energies are discussed. The theoretical framework for calculation of high energy nuclear reactions based on the effective Feynman diagram rules is described in details. The result of this approach is the generalized eikonal approximation (GEA), which is reduced to Glauber approximation when nucleon recoil is neglected. The method of GEA is demonstrated in the calculation of high energy electro-disintegration of the deuteron and A = 3 targets. Subsequently we generalize the obtained formulae for A > 3 nuclei. The relation of GEA to the Glauber theory is analyzed. Then based on the GEA framework we discuss some of the phenomena which can be studied in exclusive reactions, these are: nuclear transparency and short-range correlations in nuclei. We illustrate how light-cone dynamics of high-energy scattering emerge naturally in high energy electro-nuclear reactions.

Quantum chromodynamics (QCD), the microscopic theory of strong interactions, has not yet been applied to the calculation of nuclear wavefunctions. However, it certainly provokes a number of specific questions and suggests the existence of novel phenomena in nuclear physics which are not part of the traditional framework of the meson-nucleon description of nuclei. Many of these phenomena are related to high nuclear densities and the role of colour in nucleonic interactions. Quantum fluctuations in the spatial separation between nucleons may lead to local high-density configurations of cold nuclear matter in nuclei, up to four times larger than typical nuclear densities. We argue here that experiments utilizing the higher energies available upon completion of the Jefferson Laboratory energy upgrade will be able to probe the quarkgluon structure of such high-density configurations and therefore elucidate the fundamental nature of nuclear matter. We review three key experimental programmes: quasi-elastic electro-disintegration of light nuclei, deep inelastic scattering from nuclei at x > 1 and the measurement of tagged structure functions. These interrelated programmes are all aimed at the exploration of the quark structure of high-density nuclear configurations.The study of the QCD dynamics of elementary hard processes is another important research direction and nuclei provide a unique avenue to explore these dynamics. In particular, we argue that the use of nuclear targets and large values of momentum transfer at energies available with the Jefferson Laboratory upgrade would allow us to determine whether the physics of the