Jefferson Lab (JLab) 12 GeV energy upgrade provides a golden opportunity to perform precision studies of the transverse spin and transverse-momentum-dependent structure in the valence quark region for both the proton and the neutron. In this paper, we focus our discussion on a recently approved experiment on the neutron as an example of the precision studies planned at JLab. The new experiment will perform precision measurements of target Single Spin Asymmetries (SSA) from semi-inclusive electro-production of charged pions from a 40-cm long transversely polarized 3 He target in Deep-Inelastic-Scattering kinematics using 11 and 8.8 GeV electron beams. This new coincidence experiment in Hall A will employ a newly proposed solenoid spectrometer (SoLID). The large acceptance spectrometer and the high polarized luminosity will provide precise 4-D (x, z, P T and Q 2 ) data on the Collins, Sivers, and pretzelosity asymmetries for the neutron through the azimuthal angular dependence. The full 2π azimuthal angular coverage in the lab is essential in controlling the systematic uncertainties. The results from this experiment, when combined with the proton Collins asymmetry measurement and the Collins fragmentation function determined from the e + e − collision data, will allow for a quark flavor separation in order to achieve a determination of the tensor charge of the d quark to a 10% accuracy. The extracted Sivers and pretzelosity asymmetries will provide important information to understand the correlations between the quark orbital angular momentum and the nucleon spin and between the quark spin and nucleon spin.

The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E ␥ ϭ2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results. DOI: 10.1103/PhysRevC.66.042201 PACS number͑s͒: 13.75. Cs, 24.85.ϩp, 25.10.ϩs, 25.20.Ϫx Among the many challenges facing nuclear physicists is the characterization of nuclear reactions in the few GeV energy regime. Two primary schemes exist to describe nucleonnucleon interactions. The traditional approach involves meson-baryon degrees of freedom. The second employs the quark-gluon degrees of freedom of quantum chromodynamics ͑QCD͒ to describe the underlying processes of nuclear reactions. For deuteron photodisintegration at incident photon energies above 1 GeV, the existing traditional mesonbaryon descriptions fail to describe the data ͓1,2͔. This breakdown may suggest that QCD degrees of freedom are becoming more appropriate descriptors of the deuteron photodisintegration reaction in the range of a few GeV. The different models which have been developed to improve the RAPID COMMUNICATIONS PHYSICAL REVIEW C 66, 042201͑R͒ ͑2002͒

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The 2H(e,e(')p)n cross section was measured in Hall A of the Thomas Jefferson National Accelerator Facility near the top of the quasielastic peak (x(Bj)=0.964) at a four-momentum transfer squared, Q(2)=0.665 (GeV/c) (2) (omega=0.368 GeV, W=2.057 GeV), and for recoil momenta up to 550 MeV/c. The measured cross section deviates by 1-2sigma from a state-of-the-art calculation at low recoil momenta. At high recoil momenta the cross section is well described by the same calculation; however, in this region, final-state interactions and interaction currents are predicted to be large, and alternative choices of nucleon-nucleon potential and nucleon current operator may result in significant spread in the calculations.

We have measured the differential cross section for the γn → π − p and γp → π + n reactions at θcm = 90 • in the photon energy range from 1.1 to 5.5 GeV at Jefferson Lab (JLab). The data at Eγ 3.3 GeV exhibit a global scaling behavior for both π − and π + photoproduction, consistent with the constituent counting rule and the existing π + photoproduction data. Possible oscillations around the scaling value are suggested by these new data. The data show enhancement in the scaled cross section at a center-of-mass energy near 2.2 GeV. The cross section ratio of exclusive π − to π + photoproduction at high energy is consistent with the prediction based on one-hard-gluon-exchange diagrams.PACS numbers: 13.60. Le, 24.85.+p, 25.10.+s, The study of the transition region from nucleon-meson degrees of freedom to quark-gluon degrees of freedom in quantum chromodynamics (QCD) for exclusive processes is one of the most interesting subjects in nuclear physics. Scaling in the differential cross section dσ/dt, and hadron helicity conservation have been pursued experimentally as signatures of this transition for years. While global scaling behavior has been observed in many exclusive processes, no experimental evidence supports hadron helicity conservation. Furthermore, the exact nature governing the onset of the scaling behavior is not clear. The relatively large cross section of pion photoproduction allows the search for additional possible signatures: QCD oscillations and the charged pion cross section ratio. In this experiment, three signatures (scaling, QCD oscillations, charged pion ratio) for the transition are investigated.For an exclusive two-body reaction AB → CD at high energy and large momentum transfer, the constituent counting rule (or the dimensional scaling law) predicts [1]where s and t are the Mandelstam variables. The quantity n is the total number of interacting elementary fields in the reaction, and f (θ cm ) is the angular dependence of the differential cross section. This rule was originally derived from dimensional analysis [1], and later confirmed within the framework of a perturbative QCD (pQCD) analysis up to a logarithmic factor of the strong coupling constant α s [2]. Many exclusive measurements at