Color transparency effects in electron deuteron interactions at intermediateQ 2

Perturbative QCD Core of Hadrons and Color Transparency Phenomena

In the current paper, we argue that the ground state of a hadron contains a significant perturbative quantum chromodynamics (pQCD) core as the result of color gauge invariance and the values of chiral and gluon vacuum condensates. The evaluation within the method of dispersion sum rules (DSR) of the vacuum matrix elements of the correlator of local currents with the proper quantum numbers leads to the value of the radius of the pQCD core of a nucleon of about 0.4–0.5 fm. The selection of the initial and final states allows to select processes in which the pQCD core of the projectile gives the dominant contribution to the process. It is explained that the transparency of nuclear matter for the propagation of a spatially small and color-neutral wave packet of quarks and gluons—a color transparency (CT) phenomenon—for a group of hard processes off nuclear targets can be derived in the form of the QCD factorization theorem accounting for the color screening phenomenon. Based on the success of the method of DSR, we argue that a pQCD core in a hadron wave function is surrounded by the layer consisting of quarks interacting with quark and gluon condensates. As a result, in the quasi-elastic processes e+A→e′+N+(A−1)∗, the quasi-Feynman mechanism could be dominating in a wide range of the momentum transfer squared, Q2. In this scenario, a virtual photon is absorbed by a single quark, which carries a large fraction of the momentum of the nucleon and dominates in a wide range of Q2. CT should reveal itself in these processes at extremely large Q2 as the consequence of the presence of the Sudakov form factors, which squeeze a nucleon.

Nuclear C(e, e′p) Transparencies in a Relativistic Glauber Model

In light of the recent Jefferson Laboratory (JLab) data for the nuclear 12C(e,e′p) transparencies, calculations, obtained in a relativistic multiple scattering Glauber approximation, are discussed. The shell-separated 12C transparencies are shown and it is concluded that the p-shell nucleons are 75% more transparent than the s-shell ones. The presented comparisons between the calculations made here and the current 12C(e,e′p) data show no clear indication for the onset of color transparency when implemented within the color diffusion model with standard parameters.

u-Channel Color Transparency Observables

The paper proposes to study the onset of color transparency in hard exclusive reactions in the backward regime. Guided by the encouraging Jefferson Laboratory (JLab) results on backward π and ω electroproduction data at moderate virtuality Q2, which may be interpreted as the signal of an early scaling regime, where the scattering amplitude factorizes in a hard coefficient function convoluted with nucleon to meson transition distribution amplitudes, the study shows that investigations of these channels on nuclear targets opens a new opportunity to test the appearance of nuclear color transparency for a fast-moving nucleon.

Color Transparency in p¯A Reactions

Exclusive channels of antiproton annihilation on the bound nucleon are sensitive to mesonic interactions with the target residue. If the hard scale is present, then such interactions should be reduced due to color transparency (CT). In this paper, the d(p¯,π−π0)p reaction is discussed at a large center-of-mass angle. Predictions for the future PANDA (antiProton ANnihilations at DArmstadt) experiment at FAIR (Facility for Antiproton and Ion Research, Germany) are given for nuclear transparency ratios calculated within the generalized eikonal approximation and the quantum diffusion model of CT.

Probing the high momentum component of the deuteron at high Q2

The (2)H(e,e'p)n cross section at a momentum transfer of 3.5 (GeV/c)(2) was measured over a kinematical range that made it possible to study this reaction for a set of fixed missing momenta as a function of the neutron recoil angle θ(nq) and to extract missing momentum distributions for fixed values of θ(nq) up to 0.55  GeV/c. In the region of 35°≤θ(nq)≤45° recent calculations, which predict that final-state interactions are small, agree reasonably well with the experimental data. Therefore, these experimental reduced cross sections provide direct access to the high momentum component of the deuteron momentum distribution in exclusive deuteron electrodisintegration.

Nuclear shadowing and extraction of Fp2-Fn2 at small x from deuteron collider data

We demonstrate that leading twist nuclear shadowing leads to large corrections for the extraction of the neutron structure function Fn2 from the future deuteron collider data both in the inclusive and in the tagged structure function modes. We suggest several strategies to address the extraction of Fn2 and to measure at the same time the effect of nuclear shadowing via the measurement of the distortion of the proton spectator spectrum in the semi-inclusive eD-->e'pX process.