40204933
M4 transitions observed in pion inelastic scattering on 15N.
Cross sections for ${\ensuremath{\pi}}^{+}$ and ${\ensuremath{\pi}}^{\mathrm{\ensuremath{-}}}$ elastic and inelastic scattering to states in $^{15}\mathrm{N}$ have been measured at an incident pion energy of 164 MeV. Transitions to states at 10.7, 12.5, 14.0, and 17.2 MeV were found to contain significant M4 strength. The M4 assignments are supported both by angular distribution shapes and by additional ${\ensuremath{\pi}}^{+}$ cross sections measured at 120 and 260 MeV. The angular distributions are compared with distorted-wave impulse-approximation calculations to extract isoscalar and isovector spectroscopic amplitudes. These amplitudes are compared with model predictions.
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.
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.
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.
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 .
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.
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.
2864348
Calculation of exclusive decay modes of the tau.
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.
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.
18057410
Flavor-changing decays of the Z into heavy neutrinos.
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.