Polarization in Hyperon Photo- and Electro- Production

Multiple polarization observables must be measured to access the amplitude structure of pseudoscalar meson photoproduction off the proton. The hyperon-producing reactions are especially attractive to study, since the weak decays allow straightforward measurement of the induced and recoil polarization observables. In this paper we emphasize $\gamma + p \to K^+ + \Lambda$, discussing recent measurements of $C_x$, $C_z$, and $P$ for this reaction. An empirical constraint on the helicity amplitudes is obtained. A simplified model involving spin-flip and spin non-flip amplitudes is presented. Finally, a semi-classical model of how the polarization may arise is presented.Comment: Invited paper at NStar2007, Accepted for EPJ A 1-21-08, 6 pages, 6 figure

First measurement of target and double spin asymmetries for e [over→] p [over→]→ epπ^{0} in the nucleon resonance region above the Δ (1232)

The exclusive channel p→(e→,e′p)π0 was studied in the first and second nucleon resonance regions in the Q2 range from 0.187 to 0.770 GeV2 at Jefferson Lab using the CEBAF Large Acceptance Spectrometer. Longitudinal target and beam-target asymmetries were extracted over a large range of center-of-mass angles of the π0 and compared to the unitary isobar model MAID, the dynamic model by Sato and Lee, and the dynamic model DMT. A strong sensitivity to individual models was observed, in particular for the target asymmetry and in the higher invariant mass region. This data set, once included in the global fits of the above models, is expected to place strong constraints on the electrocoupling amplitudes A1/2 and S1/2 for the Roper resonance N(1400)P11 and the N(1535)S11 and N(1520)D13 states

DVCS with longitudinally polarized target using CLAS at 6 GeV

Deeply Virtual Compton Scattering (DVCS) is one of the simplest processes that can be described in terms of Generalized Parton Distributions (GPDs). The target single‐spin asymmetry (target SSA) in the reaction ep⃗→epγ is directly proportional to the imaginary part of the DVCS amplitude, and gives access to a combination of GPDs namely H̃, H, and E. This asymmetry will be measured in a dedicated experiment at Jefferson Lab using the CEBAF 6‐GeV polarized electron beam, a polarized solid‐state 14NH3 target, and the CEBAF Large Acceptance Spectrometer (CLAS) together with the Inner Calorimeter (IC). The expected asymmetry from leading‐order calculations is in the range of 20% to 40%, depending on the kinematics and on the GPD model used. The DVCS amplitude will be mapped out in the Q2 region from 1 to 4 GeV2, xB from 0.15 to 0.55 and −t from 0.1 to 2 GeV2 providing new constraints on the GPDs

Neutron structure function moments at leading twist

The experimental data on F2 structure functions of the proton and deuteron were used to construct their moments. In particular, recent measurements performed with CLAS detector at Jefferson Lab allowed to extend our knowledge of structure functions in the large-x region. The phenomenological analysis of these experimental moments in terms of the Operator Product Expansion permitted to separate the leading and higher twist contributions. Applying nuclear corrections to extracted deuteron moments we obtained the contribution of the neutron. Combining leading twist moments of the neutron and proton we found d/u ratio at x->1 approaching 0, although 1/5 value could not be excluded. The twist expansion analysis suggests that the contamination of higher twists influences the extraction of the d/u ratio at x->1 even at Q2-scale as large as 12 (GeV/c)^2.Comment: To appear in proceedings of Quark Confinement and the Hadron Spectrum VII Conference, Ponta Delgada, Portugal, 2-7 September 200

New results on SIDIS SSA from Jefferson Lab

We present studies of single-spin and double-spin asymmetries in semi-inclusive electroproduction of pions using the CEBAF 6 GeV polarized electron beam. Kinematic dependences of single and double spin asymmetries have been measured in a wide kinematic range at CLAS with a polarized NH$_3$ target. Significant target-spin $\sin2\phi$ and $\sin\phi$ asymmetries have been observed. The hypothesis of factorization has been tested with $z$-dependence of the double spin asymmetry.Comment: 4 pages, 6 figure

Dynamics Of Hadronization From Nuclear Semi Inclusive Deep Inelastic Scattering

The CLAS experiment E02-104, part of the EG2 run at Jefferson Lab, was performed to study the hadronization process using semi inclusive deep inelastic scattering off nuclei. Electron beam energy of 5 GeV and the CLAS large acceptance detector were used to study charged pion production. The high luminosity available at Jefferson Lab and the CLAS large acceptance are key factors for such measurements allowing high statistics and therefore multidimensional analyses of the data. Both the multiplicity ratio and the transverse momentum broadening for carbon, iron and lead relative to deuterium are measured. Preliminary results for positive pions are discussed.Comment: 4 pages, 2 figures, CIPANP 2006 in Puerto Ric