Mass dependence of pion double charge exchange.
Data are presented for pion double charge exchange on targets of /sup 44/Ca, /sup 56/Fe, /sup 58/Ni, /sup 80/Se, /sup 90/Zr, and /sup 118/Sn. These and earlier data are used to examine the mass dependence of double-isobaric-analog transitions and nonanalog ground-state-to-ground-state transitions in the energy region T/sub ..pi../ = 100 to 300 MeV. The implications of the mass dependence to the interpretations of the underlying reaction mechanisms of double charge exchange are discussed.

title: Status of the focal plane polarimeter for Hall A at TJNAF
abstract: The focal plane polarimeter (FPP) for Hall A at the Thomas Jefferson National Accelerator Facility (TJNAF) is ready for experiments. The ability to calibrate the FPP on-site using elastic scattering of polarized electrons from an unpolarized hydrogen target is demonstrated. The ratio of the proton electric form factor to its magnetic form factor has been measured at Q2=0.810(GeV/c)2.

title: Measurement of the high energy two-body deuteron photodisintegration differential cross section.
abstract: The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.

title: Systematics of pion double-charge-exchange reactions on T = 0 nuclei
abstract: Pion induced double charge exchange on 12 C, 16 O, 24 Mg, 28 Si, 32 S, and 40 Ca exhibits forward-angle cross sections that vary rapidly with pion energy and fall off roughly as A −4 3 . Angular distributions at 164 MeV appear diffractive for targets of 12 C, 16 O, and 40 Ca.

title: A polarized gas internal target using a storage cell in an electron storage ring
abstract: The first experiment using a storage cell to increase the thickness of an internal polarized gas target in an electron beam storage ring was performed at the VEPP-3 facility. We describe the storage cell technique as applied in this measurement of elastic and inelastic electron scattering from tensor polarized deuterium. An analysis of electron-beam-induced depolarization of the target was performed and experimental tests were carried out which verify the effect. Other effects causing depolarization of the target are discussed as well as the means by which they are overcome. The effective p zz of the target, shown to be stable over 8 months, was 0.57±0.05; the total target thickness was increased over that of a jet target by a factor of fifteen.

title: UNIFIED ANALYSIS OF PION SINGLE AND DOUBLE CHARGE EXCHANGE SCATTERING IN THE RESONANCE REGION

title: Phenomenology of an extra neutral gauge boson in electron-positron collisions.
abstract: Models with an extra neutral gauge boson (Z') are discussed. We review present limits on the properties of such a Z' which follow from requiring that the Z/sup 0/ mass not be shifted excessively through mixing, from neutral-current experiments, and from the structure of the mass matrix which follows from the Higgs-boson content of particular theories. We then examine what extensions in sensitivity can come from electron-positron annihilation experiments at the Z peak, with emphasis on the importance of cross-section measurements for final states involving lepton or quark pairs, followed by asymmetry measurements with polarized beams. Finally, we consider the additional information provided by asymmetry measurements in electron-positron collisions at energies above the Z.

title: Calculation of exclusive decay modes of the tau.
abstract: We update the calculation of the decays of the tau lepton into various modes using recent data on electron-positron annihilation into hadrons plus bounds that follow from isotopic-spin conservation. Comparison is made with exclusive branching-ratio data and inclusive charged-prong-distribution measurements in tau decays, and the difficulty in accounting for all the one-charged-prong decays as a sum of exclusive decay modes is discussed.

title: Flavor-changing decays of the Z into heavy neutrinos.
abstract: We consider flavor-changing decays of the Z boson to a fourth-generation heavy neutrino and a light neutrino, which are induced at one loop in the standard model. Such decays have a characteristic monojet signature which makes them readily distinguished experimentally, unlike flavor-changing decays involving quarks. Like other such one-loop processes, however, they are very rare when reasonable mixing angles and intermediate fermion masses are considered.

title: Extra neutral gauge bosons in electron-positron collisions at resonance.
abstract: A simple extension of the standard model to an sum x U(l)y x U(1) gauge symmetry is considered. The symmetry is broken by vacuum expectation values of one doublet and one singlet scalar field, resulting in a second massive neutral gauge boson. Electron positron collisions at this 2’ resonance are calculated. Aside from the possibility of 2’ decays into exotic fermions which fill out the irreducible representations of grand unified theories, there generally are important decay modes into W+Wand Z”Ho coming from mixing between the 2’ and the 2 of the standard model, even after imposing the constraints from experiment on the magnitude of the mixing angle.  Work supported by the Department of Energy, contract DE AC03 76SF00515.

title: Mixing of a heavy neutrino with the electron neutrino.
abstract: We show that recent monojet searches in electron-positron annihilation experiments can be used to extend significantly the limits on the mixing of a massive fourth-generation neutrino with the electron neutrino. When combined with other limits from hadron decays and secondary-vertex searches in hadron and electron-positron annihilation experiments, bounds of Vertical BarU/sub 14/Vertical Bar/sup 2/< or approx. =10/sup -6/ for neutrino masses of 10 MeV/c/sup 2/ to over 10 GeV/c/sup 2/ are obtainable by analysis of existing data.