19689278
Diproton decay of nuclei on the proton drip line.
The process of direct two-proton decay of nuclei with {ital Z}=22--28 on the proton drip line is considered. On the basis of new 0{ital d}{sub 3/2}-0{ital f}{sub {ital f}/2} shell-model mass extrapolations, {sup 39}Ti, {sup 42}Cr, {sup 45}Fe, {sup 48}Ni, and {sup 49}Ni are found to be bound to single-proton decay but unbound to two-proton decay. New estimates of the spectroscopic factors and lifetimes have been made. The decays of {sup 39}Ti, {sup 45}Fe, and {sup 48}Ni are found to be promising for further experimental investigation.
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.
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
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.
39136906
Structure of C-16: Testing shell model and ab initio approaches
Excited states in C-16 were populated via the Be-9(N-17,C-16+gamma)X one-proton knockout reaction. The lifetime of the 2(1)(+) state in C-16 was measured using the recoil distance method. The extracted lifetime of tau(+)(21) = 11.4(-0.9)(+0.8)(stat) +/- 0.7(syst(B rho))(-1.5)(+0.0)(syst(feeding)) ps yields a deduced B(E2;2(1)(+) -> 0(1)(+)) = 4.21(-0.26)(+0.34)(stat)(-0.24)(+0.28)(syst(B rho))(-0.00)(+0.64)(syst(feeding)) e(2)fm(4) value in good agreement with a previous measurement. The one-proton knockout cross section is used to extract the proton amplitude of the C-16 2(1)(+) state, which confirms the neutron dominant character of this state. Gamma-ray branching ratios between the 2(2)(+) state and the 2(1)(+) and ground states were also determined. The results are compared with p-sd shell model and no-core shell model (with NN and NN + NNN) calculations. The inclusion of three-body forces are essential in order for the no-core shell model calculations to reproduce the experimental findings on the gamma-ray branching ratios.
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.
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.
37689024
Lowest order hadronic contribution to the muon g-2 value with systematic error correlations.
We have performed a new evaluation of the hadronic contribution to {ital a}{sub {mu}}=({ital g}{minus}2)/2 of the muon with explicit correlations of systematic errors among the experimental data on {sigma}({ital e}{sup +}{ital e}{sup {minus}}{r_arrow}hadrons). Our result for the lowest order hadronic vacuum polarization contribution is {ital a}{sub {mu}}{sup had}=702.6(7.8)(14.0){times}10{sup {minus}10} where the first error is statistical and the second is systematic. The total systematic error contributions from below and above {radical}{ital s}=1.4 GeV are (13.1){times}10{sup {minus}10} and (5.1){times}10{sup {minus}10}, respectively, and are hence dominated by the low energy region. Therefore, new measurements on {sigma}({ital e}{sup +}{ital e}{sup {minus}}{r_arrow}hadrons) below 1.4 GeV can significantly reduce the total error on {ital a}{sub {mu}}{sup had}. In particular, the effect on the total errors of new hypothetical data with 3{percent} statistical and 0.5{endash}1.0{percent} systematic errors is presented. {copyright} {ital 1996 The American Physical Society.}
36469643
Lorentzian path integral for minisuperspace cosmology.
The path integral for minisuperspace models of cosmology is defined as a sum over Lorentzian geometries, and is a Green function for the Wheeler-DeWitt operator. It is shown to be a symmetric function of the initial and final configurations, and its real part is a solution to the Wheeler-DeWitt equation. The Lorentzian path integral is computed explicitly for the de Sitter minisuper-space model and is convergent. The resulting Green function is then related to the solutions of the Wheeler-DeWitt equation known as the Hartle-Hawking and tunneling wave functions of the Universe. The real part of this Green function is a product of Hartle-Hawking wave functions.
13068301
Temperature, energy, and heat capacity of asymptotically anti-de Sitter black holes.
We investigate the thermodynamical properties of black holes in (3+1)- and (2+1)-dimensional Einstein gravity with a negative cosmological constant. In each case, ther thermodynamic internal energy is computed for a finite spatial region that contains the black hole. The temperature at the boundary of this regoin is defined by differentiating the energy with respect to entropy, and is equal to the product of the surface gravity (divided by 2\ensuremath{\pi}) and the Tolman redshift factor for temperature in a stationary gravitational field. We also compute the thermodynamic surface pressure and, in the case of the 2+1 black hole, show that the chemical potential conjugate to angular momentum is equal to the proper angular velocity of the black hole with respect to observers who are at rest in the stationary time slices. In 3+1 dimensions, a calculation of the heat capacity reveals the existence of a thermodynamically stable black hole solution and a negative heat capacity instanton. This result holds in the limit that the spatial boundary tends to infinity only if the cosmological constant is negative; if the cosmological constant vanishes, the stable black hole solution is lost. In 2+1 dimensions, a calculation of the heat capacity reveals the existence of a thermodynamically stable black hole solution, but no negative heat capacity instanton.