Nuclear-structure aspects of nonanalog pion double charge exchange.
The sensitivity of pion double charge exchange to nuclear structure in the shell model is examined. We consider the nonanalog ground-state to ground-state (T = 0 to T = 2) transitions on a variety of nuclear targets. The reaction model, which assumes that double charge exchange is driven by a ..pi..+rho-meson--mediated, ..delta../sub 33/-nucleon interaction, reproduces the energy dependence and shape of the empirical cross section for all the (..pi../sup +/,..pi../sup -/) transitions examined. The magnitude of the cross section is particularly sensitive to collectivity in the nuclear wave functions. All parameters of the model, with the exception of the range of the meson-..delta../sub 33/ form factor, are fixed by theoretical arguments. The form factor is then determined by normalizing to the /sup 16/O(..pi../sup +/,..pi../sup -/) /sup 16/ Ne cross section. Predictions are made for a variety of other low-lying 0/sup +/ transitions.

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

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: 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: 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: 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: Splitting of the P states in heavy quarkonium systems and the nature of the spin-dependent potential.
abstract: We consider the behavior of the splittings between the L = 1 states in heavy quarkonium systems. With standard assumptions, the ratio of mass splittings, R/sub chi/ = (M/sub 2/-M/sub 1/)/(M/sub 1/-M/sub 0/) is shown to grow slowly as we go from the lowest P states to their radial excitations, a behavior which is in accord with other theoretical calculations and is consistent with experiment. This behavior is the opposite of what is expected from a naive argument which we present. We show why the naive argument fails and how the phenomenological division of the potential into components which correspond to the exchange of a Lorentz scalar and vector can be made so as to obtain other behaviors.

title: Analysis of semileptonic decays of mesons containing heavy quarks.
abstract: We analyze semileptonic decays of mesons containing heavy quarks and indicate how to extract the signs and magnitudes of the helicity amplitudes for the exclusive decay modes involving a vector meson, lepton, and neutrino by using the joint distribution of the decay products of the vector meson (into a pair of pseudoscalar mesons) and of the virtual {ital W} (into a charged lepton and its neutrino). We apply this to specific cases of charm- and bottom-meson decays with form factors calculated from quark models.

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: Standard-model predictions for CP violation in B0-meson decay.
abstract: We examine the present set of constraints on the parameters of the standard model and use the unitarity triangle to present their allowed range. We give the implications of this for {ital CP} violation in the {ital B}-meson system as a function of top-quark mass, emphasizing what luminosity of an electron-positron collider is needed to guarantee a statistically significant asymmetry in one or more {ital B} decay channels.