The Polarized Electrons for Polarized Positrons experiment at the injector of the Continuous Electron Beam Accelerator Facility has demonstrated for the first time the efficient transfer of polarization from electrons to positrons produced by the polarized bremsstrahlung radiation induced by a polarized electron beam in a high-Z target. Positron polarization up to 82% have been measured for an initial electron beam momentum of 8.19 MeV/c, limited only by the electron beam polarization. This technique extends polarized positron capabilities from GeV to MeV electron beams, and opens access to polarized positron beam physics to a wide community.

We present new, high- Q 2 measurements of inclusive electron scattering from high-momentum nucleons in nuclei. This yields an improved extraction of the strength of two-nucleon correlations for several nuclei, including light nuclei where clustering effects can, for the first time, be examined. The data extend to the kinematic regime where three-nucleon correlations are expected to dominate and we observe significantly greater strength in this region than previous measurements.

We report on a study of the longitudinal to transverse cross section ratio, R=sigmaL/sigmaT, at low values of x and Q2, as determined from inclusive inelastic electron-hydrogen and electron-deuterium scattering data from Jefferson Laboratory Hall C spanning the four-momentum transfer range 0.06<Q2<2.8 GeV2. Even at the lowest values of Q2, R remains nearly constant and does not disappear with decreasing Q2, as might be expected. We find a nearly identical behavior for hydrogen and deuterium.

The electric form factor of the neutron was determined from measurements of the d-->(e-->,e'n)p reaction for quasielastic kinematics. Polarized electrons were scattered off a polarized deuterated ammonia (15ND3) target in which the deuteron polarization was perpendicular to the momentum transfer. The scattered electrons were detected in a magnetic spectrometer in coincidence with neutrons in a large solid angle detector. We find G(n)(E)=0.0526+/-0.0033(stat)+/-0.0026(sys) and 0.0454+/-0.0054+/-0.0037 at Q(2)=0.5 and 1.0 (GeV/c)(2), respectively.

A “new” technique involving a solenoidal recoil polarimeter is proposed to measure the small, beam helicity-independent induced normal proton polarization (PN ) in e+ p elastic scattering. This observable is proportional to the imaginary part of the two-photon exchange amplitude, so the interpretation of the observed asymmetry in terms of two-photon exchange does not require a delicate kinematic separation. The combination of a magnetic spectrometer for electron detection with a recoil polarimeter in the scattering plane provides turn-key isolation of the elastic reaction, a high figure of merit, complete control of the phase of the physics signal to cancel instrumental asymmetries, and the potential for extension to neutron measurements. If current models are correct and PN is of order 1%, non-zero measurements with significance on the order of 10σ are anticipated. We thus expect to provide very tight constraints on model-dependent calculations of two-photon exchange in the most important energy region for precision electroweak measurements on the nucleon.

The ratio of the electric to the magnetic form factor of the neutron, \(g \equiv G_{En}/G_{Mn}\), was measured via recoil polarimetry (R.G. Arnold, C.E. Carlson, F. Gross, Phys. Rev. C 23, 363 (1981)) from the quasielastic 2H\((\mathop{e}\limits^{\scriptstyle\to},e' \mathop{n}\limits^{\scriptstyle\to} )\)1H reaction at three values of Q2 (viz, 0.45, 1.15, and 1.47 (GeV/c)2) in Hall C of the Thomas Jefferson National Accelerator Facility. The data reveal that GEn continues to follow the Galster parameterization up to Q2 = 1.15 (GeV/c)2 and rises above the Galster parameterization at Q2 = 1.47 (GeV/c)2.

We report the results of a new measurement of spin structure functions of the deuteron in the region of moderate momentum transfer [Q(2)=0.27-1.3 (GeV/c)(2)] and final hadronic state mass in the nucleon resonance region (W=1.08-2.0 GeV). We scattered a 2.5 GeV polarized continuous electron beam at Jefferson Lab off a dynamically polarized cryogenic solid state target ((ND3)-N-15) and detected the scattered electrons with the CEBAF large acceptance spectrometer. From our data, we extract the longitudinal double spin asymmetry A(parallel toparallel to) and the spin structure function g(1)(d). Our data are generally in reasonable agreement with existing data from SLAC where they overlap, and they represent a substantial improvement in statistical precision. We compare our results with expectations for resonance asymmetries and extrapolated deep inelastic scaling results. Finally, we evaluate the first moment of the structure function g(1)(d) and study its approach to both the deep inelastic limit at large Q(2) and to the Gerasimov-Drell-Hearn sum rule at the real photon limit (Q(2)-->0). We find that the first moment varies rapidly in the Q(2) range of our experiment and crosses zero at Q(2) between 0.5 and 0.8 (GeV/c)(2), indicating the importance of the Delta resonance at these momentum transfers.

The polarized longitudinal-transverse structure function sigma(LT') has been measured in the Delta(1232) resonance region at Q(2)=0.40 and 0.65 GeV2. Data for the p((e) over right arrow ,e'p)pi(0) reaction were taken at Jefferson Lab with the CEBAF large acceptance spectrometer (CLAS) using longitudinally polarized electrons at an energy of 1.515 GeV. For the first time a complete angular distribution was measured, permitting the separation of different nonresonant amplitudes using a partial wave analysis. Comparison with previous beam asymmetry measurements at MAMI indicate a deviation from the predicted Q(2) dependence of sigma(LT ') using recent phenomenological models.

We report new measurements of the ratio of the electric form factor to the magnetic form factor of the neutron, G(E)(n)/G(M)(n), obtained via recoil polarimetry from the quasielastic H-2((e) over right arrow ,e(')(n) over right arrow)H-1 reaction at Q(2) values of 0.45, 1.13, and 1.45 (GeV/c)(2) with relative statistical uncertainties of 7.6% and 8.4% at the two higher Q(2) points, which points have never been achieved in polarization measurements.

S. Stepanyan, K. Hicks, D.S. Carman, E. Pasyuk, R.A. Schumacher, E.S. Smith, D.J. Tedeschi, L. Todor, G. Adams, P. Ambrozewicz, E. Anciant, M. Anghinolfi, B. Asavapibhop, G. Audit, H. Avakian, H. Bagdasaryan, J.P. Ball, S.P. Barrow, M. Battaglieri, K. Beard, M. Bektasoglu, M. Bellis, B.L. Berman, N. Bianchi, A.S. Biselli, S. Boiarinov, S. Bouchigny, R. Bradford, D. Branford, W.J. Briscoe, W.K. Brooks, V.D. Burkert, C. Butuceanu, J.R. Calarco, B. Carnahan, S. Chen, L. Ciciani, P.L. Cole, A. Coleman, D. Cords, P. Corvisiero, D. Crabb, H. Crannell, J.P. Cummings, E. De Sanctis, P.V. Degtyarenko, H. Denizli, L. Dennis, R. De Vita, K.V. Dharmawardane, K.S. Dhuga, C. Djalali, G.E. Dodge, D. Doughty, P. Dragovitsch, M. Dugger, S. Dytman, O.P. Dzyubak, H. Egiyan, K.S. Egiyan, L. Elouadrhiri, A. Empl, P. Eugenio, R. Fatemi, R.J. Feuerbach, J. Ficenec, T.A. Forest, H. Funsten, M. Garçon, G. Gavalian, G.P. Gilfoyle, K.L. Giovanetti, C.I.O. Gordon, R. Gothe, K. Griffioen, M. Guidal, M. Guillo, L. Guo, V. Gyurjyan, C. Hadjidakis, R.S. Hakobyan, J. Hardie, ,1 D. Heddle, ,9 P. Heimberg, F.W. Hersman, R.S. Hicks, M. Holtrop, J. Hu, C.E. Hyde-Wright, M.M. Ito, D. Jenkins, K. Joo, H.G. Juengst, J.D. Kellie, M. Khandaker, K.Y. Kim, K. Kim, W. Kim, A. Klein, F.J. Klein, A.V. Klimenko, M. Klusman, M. Kossov, L.H. Kramer, Y. Kuang, V. Kubarovsky, S.E. Kuhn, J. Kuhn, J. Lachniet, D. Lawrence, J. Li, A. Lima, K. Livingston, K. Lukashin, J.J. Manak, S. McAleer, J.W.C. McNabb, B.A. Mecking, S. Mehrabyan, J.J. Melone, M.D. Mestayer, C.A. Meyer, K. Mikhailov, R. Minehart, M. Mirazita, R. Miskimen, V. Mokeev, L. Morand, S. Morrow, V. Muccifora, J. Mueller, L.Y. Murphy, G.S. Mutchler, J. Napolitano, R. Nasseripour, S. Niccolai, G. Niculescu, I. Niculescu, B.B. Niczyporuk, R.A. Niyazov, M. Nozar, J. O’Brien, G.V. O’Rielly, A.K. Opper, M. Osipenko, K. Park, G. Peterson, S.A. Philips, N. Pivnyuk, D. Pocanic, O. Pogorelko, E. Polli, S. Pozdniakov, B.M. Preedom, J.W. Price, Y. Prok, D. Protopopescu, L.M. Qin, B.A. Raue, ,1 G. Riccardi, G. Ricco, M. Ripani, B.G. Ritchie, F. Ronchetti, P. Rossi, D. Rowntree, P. Rubin, F. Sabatié, C. Salgado, J. Santoro, V. Sapunenko, V.S. Serov, Y.G. Sharabian, J. Shaw, S. Simionatto, A.V. Skabelin, L.C. Smith, D.I. Sober, I.I. Strakovsky, A. Stavinsky, P. Stoler, R. Suleiman, M. Taiuti, S. Taylor, U. Thoma, R. Thompson, C. Tur, M. Ungaro, M.F. Vineyard, A.V. Vlassov, K. Wang, L.B. Weinstein, H. Weller, D.P. Weygand, C.S. Whisnant, E. Wolin, M.H. Wood, A. Yegneswaran, J. Yun

Models of baryon structure predict a small quadrupole deformation of the nucleon due to residual tensor forces between quarks or distortions from the pion cloud. Sensitivity to quark versus pion degrees of freedom occurs through the Q(2) dependence of the magnetic (M1+), electric (E1+), and scalar (S1+) multipoles in the gamma* p --> Delta(+) --> ppi(0) transition. We report new experimental values for the ratios E1+/M1+ and S1+/M1+ over the range Q(2) = 0.4-1.8 GeV2, extracted from precision p(e,e'p)pi(0) data using a truncated multipole expansion. Results are best described by recent unitary models in which the pion cloud plays a dominant role.

Neutral pion photoproduction from a liquid deuterium target was measured in the energy region near 300 MeV at the LEGS facility of Brookhaven National Laboratory. The inclusive cross sections from deuterium are in agreement with measurments from Mainz, yet the exclusive cross sections and spin asymmetries for neutral pion production in coincidence with a detected nucleon are much smaller than expected from a quasi-free approximation. This may indicate that substantial final state interactions play a significant role, which will complicate the extraction of the desired amplitudes that would be measured if a free neutron target could be used.

New cross sections for the reaction e p-->e p eta are reported for total center of mass energy W = 1.5--1.86 GeV and invariant momentum transfer Q2 = 0.25--1.5 (GeV/c)(2). This large kinematic range allows extraction of important new information about response functions, photocouplings, and eta N coupling strengths of baryon resonances. Newly observed structure at W approximately 1.65 GeV is shown to come from interference between S and P waves and can be interpreted with known resonances. Improved values are derived for the photon coupling amplitude for the S11(1535) resonance.

We studied the exclusive reaction ep→eЈpЈ using the →K ϩ K Ϫ decay mode.The data were collected using a 4.2 GeV incident electron beam and the CEBAF Large Acceptance Spectrometer ͑CLAS͒ at the Thomas Jefferson National Accelerator Facility.Our experiment covers the range in Q 2 from 0.7 to 2.2 GeV 2 , and W from 2.0 to 2.6 GeV.Taken together with all previous data, we find a consistent picture of production on the proton.Our measurement shows the expected decrease of the t slope with the vector-meson formation time c⌬ below 2 fm.At ͗c⌬͘ϭ0.6 fm, we measure b ϭ2.27Ϯ0.42GeV Ϫ2 .The cross section dependence on W as W 0.2Ϯ0.1 at Q 2 ϭ1.3 GeV 2 was determined by comparison with production at HERA after correcting for threshold effects.This is the same dependence as observed in photoproduction.