2611605
New calculations of the parity nonconservation matrix element for the J pi T 0(+)1, 0(-)1 doublet in 14N.
A new calculation of the predominantly isoscalar PNC matrix element between the [ital J][sup [pi]][ital T] 0[sup +]1,0[sup [minus]]1 ([ital E][sub [ital x]][approx]8.7 MeV) states in [sup 14]N has been carried out in a (0+1+2+3+4)[h bar][omega] model space with the Warburton-Brown interaction. The magnitude of the PNC matrix element of 0.22 to 0.54 eV obtained with the DDH PNC interaction is substantially suppressed compared with previous calculations in smaller model spaces but shows agreement with the preliminary Seattle experimental data. The calculated sign is opposite to that obtained experimentally, and the implications of this are discussed.
35436961
Predicted features of the beta decay of neutron-rich sd-shell nuclei
The Gamow-Teller beta-decay transitions of sd-shell nuclei with five or more excess neutrons are calculated from complete (0d/sub 5/2/, 1s/sub 1/2/, 0d/sub 3/2/)-space shell-model wave functions. These wave functions are obtained from diagonalizations of a model Hamiltonian formulation which reproduces observed energy-level structures throughout the sd shell. The calculations are carried out with both the ''free-nucleon'' normalization for the Gamow-Teller single-nucleon matrix elements and one based on the empirical values obtained for these quantities from a comparison of corresponding theoretical and experimental Gamow-Teller magnitudes near the line of stability. The phase-space factors f which connect the reduced Gamow-Teller strengths to the total half-lives and the individual decay probabilities are calculated both from the energies obtained in the shell-model calculations and, alternatively, from hybrid energy spectra in which available experimental energies are substituted for the corresponding calculated values wherever possible. Comparisons of the beta-decay predictions to existing experimental results are presented and discussed.
120853289
The 52,54Cr(p, n)52,54Mn and 57,58Fe(p, n)57,58Co reactions at Ep = 120 MeV
Abstract Differential cross sections for the (p, n) reaction on 52, 54 Cr and 57, 58 Fe have been measured for angles up to θ lab = 10.5° and 14.6°, respectively, using 120 MeV protons. The observed angular distributions are used to evaluate the location and strength of Gamow-Teller resonances. A shell-model calculation of this strength distribution is presented and compared with the experimental results. The M1 strength for 52 Cr is also calculated and compared with available results from (e, e') and (p, p') experiments. A comparison is made with other If 7 2 nuclei.
34139540
Shape of the beta spectra in the A=14 system.
56232513
Search for physics beyond the standard model via a polarization-asymmetry correlation experiment on In-107
We report on a new precision measurement of the longitudinal polarization of positrons emitted by polarized 107In nuclei. Preliminary results yield a lower limit of 303 GeV/c2 for the mass of a possible, predominantly right-handed, W gauge boson, if interpreted in the framework of the manifest, left-right symmetric model. In more general left-right symmetric models our result is complementary to those from muon decay experiments and to results from searches for a similar particle in collider experiments. Our data also provide new results on possible tensor contributions to the weak interaction.
41679008
Proton capture to excited states of O 16 : M 1 , E 1 , and Gamow-Teller transitions and shell model calculations
We have measured excitation functions of the ..gamma..-rays resulting from the bombardment of /sup 15/N by polarized and unpolarized protons in the energy range E/sub p/ = 2.5 to 9.5 MeV with emphasis on identifying dipole decays to the first (0/sup +/) and second (3/sup -/) excited states in /sup 16/O. Resonances in ..gamma../sub 12/ are observed at E/sub x/ = 16.21, 16.45, 16.82, 17.12, 18.03, 18.98, 19.90 and 20.41 MeV. The 16.21 and 17.12 MeV resonances in ..gamma../sub 12/ are identified as M1-decays of the 1/sup +/ T = 1 states to the 6.05 MeV 0/sup +/ state in /sup 16/O. The measured ratio of reduced strengths B(m1,..gamma../sub 1/)/(B(M1,..gamma../sub 0/) is 0.48 +- 0.03 for decays from the 16.21 MeV state and 0.55 +- 0.04 for decays from the 17.12 MeV state. The 18.03 MeV resonance is due to a 3/sup -/ T = 1 state in /sup 16/O with a strength Gamma/sup p/Gamma/sub gamma 2//Gamma = (1.96 +- 0.27) eV and the 18.98 MeV resonance is due to the 4/sup -/ T = 1 stretched particle-hole state with a strength of (0.85 +- 0.10) eV. We determine absolute particle and ..gamma.. widths for these states. The M1 ..gamma../submore » 2/-width of the 18.98 MeV state, (7.1 +- 3.1) eV, is in agreement with a shell-model calculation. Resonances in ..gamma../sub 3/ are observed at 16.82 and 17.27 MeV and in ..gamma../sub 4/ at 17.88 MeV. The excitation energies and widths of these levels as well as the strengths of the ..gamma.. transitions suggest T = 1 character for all of the resonances for which capture ..gamma..-rays are observed. Correspondences of our resonances to levels in /sup 16/N are given. We compare ..gamma.. widths, including ground-state M1 decays, and allowed ..beta.. transition rate in A = 16 nuclei with shell model calculations and obtain rough agreement. Additional shell model calculations for M1 and GT (Gamow-Teller) decays in the A-14, 15, 17 and 18 nuclei are presented, which indicate that GT matrix elements are quenched by approx. 20% relative to shell model predictions and also relative to the spin part of the M1 matrix elements.« less
28894226
Proton-nucleus scattering and density dependent meson masses in the nucleus.
The influence of density dependent meson masses, proposed in many previous papers, on proton-nucleus scattering in the several hundred MeV region is investigated. Introduction of this density dependence is found to remove the nuclear radius discrepancy which persistently occurred in analyses with the nonrelativistic impulse approximation when empirical nuclear densities obtained from electron scattering were employed. Nonlocality, suggested by earlier derivations of the density dependent masses, had to be introduced. Taking the estimated range of nonlocality from the earlier calculations, agreement with experiment was significantly improved by this introduction. Effects on the spin-orbit interaction and imaginary part of the optical model are qualitatively discussed. The density dependent meson masses aid in increasing the strength of the spin-orbit interaction. Preliminary results calculated in a relativistic impulse approximation (IA2) formalism for the spin observables are shown and discussed.
1772289
Temporal development of the plasma phase transition.
We present a simple argument to show why a high entropy phase must exhibit an extended pion source lifetime. The plasmas that would be formed under the conditions of the recent heavy ion experiments would emit pions over a time of the order of 10 fm/{ital c} or longer, if the plasma has an entropy density larger than that of a pion gas by an order of magnitude.
45820359
Strength of the rho meson coupling to nucleons.
In his recent publication of a [ital NN] phase shift analysis below 160 MeV, Henneck reports relatively large values for the mixing parameter [epsilon][sub 1]. Based on these results, Henneck suggests that the strength of the [rho]-meson coupling to the nucleon may be weaker than used in present day [ital NN] interactions, like the Paris, Nijmegen, or Bonn potentials. We point out that at low enegies ([approx lt] 100 MeV) there is rather little sensitivity to the strength of the [rho] coupling, due to the compensating effect of the second-order tensor term. In order to establish sensitivity, one has to go to energies [approx gt]200 MeV, where the second-order contribution has gone out. As it happens, the [epsilon][sub 1] mixing parameter is well determined in the region of energies 200--300 MeV, and there is agreement with the predictions by the Paris and Bonn potentials; the weak-[rho] model is about 50% above the data. This and additional considerations in triplet [ital P] waves reconfirm that [ital NN] scattering requires the strong [rho], consistent with the [pi][pi]-[ital N[bar N]] partial-wave analysis by Hoehler and Pietarinen.
36218377
Spin of the proton and the chiral bag.
Measurement of the spin carried by the quarks in the proton can be very important in distinguishing between low-energy models of the hadron. Topological soliton models have rather little or no spin in the quarks, in agreement with present experimental indications.
42999511
Effect of chiral restoration on kaon production in relativistic heavy-ion collisions.
Kaon production from meson-meson annihilation is enhanced significantly because of the decrease of hadron masses in hot and dense matter as a result of the restoration of chiral symmetry. We show that this can lead to enhanced kaon yield in high-energy heavy-ion collisions.