Experimental study of time reversal invariance and atomic final state effects in nuclear transitions

Experiments have been performed to test time reversal invariance in nuclei using gamma transitions of oriented 191Ir and 131Xe. The phase angle η associated with the imaginary part of the ratio of reduced matrix elements of the gamma transition was measured through observation of the angular distribution of the linear polarization from oriented nuclei. Interaction of the gamma ray with the atomic electron cloud can cause an additional phase shift ξ which is indistinguishable from the time-reversal phase η. Such an atomic final state effect has been observed for the 129 keV transition in 191Ir. Nuclear orientation was achieved with a large magnetic field (the hyperfine field of Ir in iron) and low temperature (20 to 30 mK obtained with a dilution refrigerator). A Compton polarimeter was used to measure linear polarization of the E2-Ml gamma ray. The matrix-element ratio was found to have an imaginary part corresponding to a phase angle (η+ξ) = (-4.8 ± 0.2) x 10-3. This measurement is in agreement with the most recent final state calculations which give ξ = (-4.3 ± 0.4) x 10-3. A limit |η| < 10-3 is deduced for the time-reversal phase. In another experiment a phase angle η = (-1.2 ± 1.1) x 10-3 was measured for the E2-Ml 364 keV transition in 131Xe, for which atomic final state effects are small. Both measurements are consistent with time reversal invariance

Model Analysis of Time Reversal Symmetry Test in the Caltech Fe-57 Gamma-Transition Experiment

The CALTECH gamma-transition experiment testing time reversal symmetry via the E2/M1 mulipole mixing ratio of the 122 keV gamma-line in Fe-57 has already been performed in 1977. Extending an earlier analysis in terms of an effective one-body potential, this experiment is now analyzed in terms of effective one boson exchange T-odd P-even nucleon nucleon potentials. Within the model space considered for the Fe-57 nucleus no contribution from isovector rho-type exchange is possible. The bound on the coupling strength phi_A from effective short range axial-vector type exchange induced by the experimental bound on sin(eta) leads to phi_A < 10^{-2}.Comment: 5 pages, RevTex 3.

Determination of the 2p-1s transition energy and strong interaction shift in pionic hydrogen using crystal diffraction

The 2p-1s atomic transition in pionic hydrogen has been studied with the help of a point-focusing graphite diffraction spectrometer. The transition energy was measured to be E(2p-1s)=2433.5±1.7 eV. From this result a strong interaction shift of -3.9±1.7 eV was derived. The Kα x-ray yield in the 2.7 atm hydrogen target at 40 K was found to be 0.025±0.013 per stopped pion

Neutrino-oscillation experiments at the Gösgen nuclear power reactor

A search for neutrino oscillations has been conducted at the 2800-MW (thermal) nuclear power reactor in Gösgen (Switzerland), providing 5×10^20 electron antineutrinos per second. The energy spectrum of the antineutrinos was measured at three distances, 37.9, 45.9, and 64.7 m, from the reactor core. The detection of the neutrinos is based on the reaction ν¯e+p→e++n. Roughly 10^4 antineutrinos were registered at each of the three measuring positions. The measured spectra are analyzed in terms of a two-neutrino oscillation model and the results are represented as exclusion plots for the oscillation parameters Δm^2 and sin^2(2theta). Two analyses are performed: Analysis A relies exclusively on the data measured at the three different distances; analysis B combines the measured data with additional information, in particular with the reactor antineutrino spectrum as derived from independent β-spectroscopic measurements. Both analyses show that the data are consistent with the absence of neutrino oscillations, and rule out large regions of parameters (Δm2,theta). The resulting limits on the oscillation parameters are Δm^25 eV^2