39737388
Measurement of tensor analyzing power in electron-deuteron elastic scattering.
An internal-target technique was used to make the first measurements of the tensor analyzing power {ital T}{sub 20} of electron-deuteron elastic scattering in the four-momentum-transfer range of 2--3 fm{sup {minus}1}. Polarized deuterium atoms were confined within a storage cell in the VEPP-3 electron storage ring in Novosibirsk to achieve a total target thickness of 3{times}10{sup 12} cm{sup {minus}2}, 15 times greater than was previously possible with an atomic-beam target alone. The results for {ital T}{sub 20} are in agreement with reasonable models of the deuteron wave function.
122958281
Higher Twists and Color Polarizabilities in the Neutron
Abstract Color polarizabilities of the neutron are extracted from data on the lowest moment of the spin-dependent g 1 structure function. New data in the resonance region from Jefferson Lab at Q 2 ≲ 1 GeV 2 , in combination with world data at higher Q 2 , allow a systematic determination of the 1 / Q 2 corrections, and provide the first constraints on 1 / Q 4 corrections. The results suggest that higher-twist effects in the neutron are small, and that quark–hadron duality may be approximately valid, even down to Q 2 ∼ 1 GeV 2 .
55880852
Status of the focal plane polarimeter for Hall A at TJNAF
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.
120867307
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.
101926880
Systematics of pion double charge exchange
Differential cross sections have been measured for pion-induced double-charge-exchange (DCX) reactions leading to double-isobaric-analog states (DIAS) and low-lying nonanalog states in the residual nuclei. A description of the experimental details and data analysis is presented. The experimentally observed systematics of reactions leading to DIAS, to nonanalog ground states, and to low-lying 2 states are described. Lowest-order optical-model calculations of DIAS DCX are compared to the data. Efforts to understand the anomalies by invoking additional reaction-mechanism amplitudes and a higher-order optical potential are described. Calculations of nonanalog DCX reactions leading to J/sup / = 0 states were performed within a distorted-wave impulse-approximation framework. The sensitivities of these calculations to input parameters are discussed. 58 refs., 41 figs., 16 tabs.
124872020
Nuclear shadowing, diffractive scattering and low momentum protons in μXe interactions at 490 GeV
The production of charged hadrons is studied in μXe and μD interactions at 490 GeV beam energy. The data were taken at the Tevatron at Fermilab with the E665 spectrometer, equipped with a streamer chamber as vertex detector. Differences between the μXe and μD data are explained by cascading of hadrons in the Xe nucleus. The average multiplicity of charged hadrons in μXe scattering is compared to previously published pXe scattering data and is found to be strongly reduced. This is traced back to the low number of ‘projectile’ collisions in μXe interactions. From a study of thexBj dependence of hadron production in μXe scattering, and by considering events with a large rapidity gap, evidence is found for a significant contribution of diffractive scattering, which is enhanced in the kinematic region where shadowing of the cross section is observed. This result supports recent models in which diffractive scattering and nuclear shadowing are closely related.
14921407
Splitting of the P states in heavy quarkonium systems and the nature of the spin-dependent potential.
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.
15587279
Standard-model predictions for CP violation in B0-meson decay.
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.
17844622
Extra neutral gauge bosons in electron-positron collisions at resonance.
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. Submitted to Physical Review D * Work supported by the Department of Energy, contract DE AC03 76SF00515.
10249412
Mixing of a heavy neutrino with the electron neutrino.
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.
17582393
Analysis of semileptonic decays of mesons containing heavy quarks.
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.