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We report the first precision measurement of the parity-violating asymmetry in the direction of proton momentum with respect to the neutron spin, in the reaction ^{3}He(n,p)^{3}H, using the capture of polarized cold neutrons in an unpolarized active ^{3}He target. The asymmetry is a result of the weak interaction between nucleons, which remains one of the least well-understood aspects of electroweak theory. The measurement provides an important benchmark for modern effective field theory and potential model calculations. Measurements like this are necessary to determine the spin-isospin structure of the hadronic weak interaction. Our asymmetry result is A_{PV}=[1.55±0.97(stat)±0.24(sys)]×10^{-8}, which has the smallest uncertainty of any hadronic parity-violating asymmetry measurement so far.

Parity nonconservation (PNC) was studied in {ital p}-wave resonances in Ag by measuring the helicity dependence of the neutron total cross section. Transmission measurements on natural Ag were performed in the energy range 32 to 422 eV with the time-of-flight method at the Manuel Lujan Neutron Scattering Center at Los Alamos National Laboratory. A total of 15 {ital p}-wave neutron resonances were studied in {sup 107}Ag and nine {ital p}-wave resonances in {sup 109}Ag. Statistically significant asymmetries were observed for eight resonances in {sup 107}Ag and for four resonances in {sup 109}Ag. An analysis treating the PNC matrix elements as random variables yields a weak spreading width of {Gamma}{sub w}=(2.67{sub {minus}1.21}{sup +2.65}){times}10{sup {minus}7} eV for {sup 107}Ag and {Gamma}{sub w}=(1.30{sub {minus}0.74}{sup +2.49}){times}10{sup {minus}7} eV for {sup 109}Ag. thinsp {copyright} {ital 1999} {ital The American Physical Society}

The parity-nonconserving longitudinal asymmetry [ital P] has been measured in nonresonant regions in [sup 232]Th for neutron energies in the range 6--86 eV. The measured value of [ital P][sub nonres]=(9.8[plus minus]21.7)[times]10[sup [minus]6] is consistent with statistical descriptions of parity violation.

Parity nonconservation was studied for seventeen states in {sup 239}U by measuring the helicity dependence of the total cross section for epithermal neutrons scattered from {sup 238}U. The root-mean-squared parity-violating matrix element for the mixing of {ital p}-wave and {ital s}-wave states was determined to be {ital M}=0.58{sub {minus}0.25}{sup +0.50} meV. This corresponds to a parity-violating spreading width of {Gamma}{sup PV}=1.0{times}10{sup {minus}7} eV. Under plausible assumptions this gives a value of 4{times}10{sup {minus}7} for {vert bar}{alpha}{sub {ital P}}{vert bar}, the ratio of strengths of the {ital P}-odd and {ital P}-even effective nucleon-nucleon interactions.

Hadronic parity violation uses quark-quark weak interactions to probe nonperturbative strong interaction dynamics through two nonperturbative QCD scales: [Formula: see text] and the fine-tuned MeV scales of NN bound states in low energy nuclear physics. The current and projected availability of high-intensity neutron and photon sources coupled with ongoing experiments and continuing developments in theoretical methods provide the opportunity to greatly expand our understanding of hadronic parity violation in few-nucleon systems. The current status of these efforts and future plans are discussed.

The parity nonconserving spin rotation of neutrons in the 0.734-eV p-wave resonance of $^{139}La$ was measured with the neutron transmission method. Two optically polarized $^3He$ cells were used before and behind a a 5-cm long $^{139}La$ target as a polarizer and an analyzer of neutron spin. The rotation angle was carefully measured by flipping the direction of $^3He$ polarization in the polarizer in sequence. The peak-to-peak value of the spin rotation was found to be $ (7.4 \pm 1.1) \times 10^{-3} $ rad/cm which was consistent with the previous experiments. But the result was statisticallly improved. The s-p mixing model gives the weak matrix element as $xW = (1.71 \pm 0.25)$ meV. The value agrees well with the one deduced from the parity-nonconserving longitudinal asymmetry in the same resonance.

The analysis of parity nonconservation (PNC) measurements performed on {sup 232}Th by the TRIPLE Collaboration has been extended to include the neutron energy range of 250 to 1900 eV. Below 250 eV all ten statistically significant parity violations have the same sign. However, at higher energies PNC effects of both signs were observed in the transmission of longitudinally polarized neutrons through a thick thorium target. Although the limited experimental energy resolution precluded analysis in terms of the longitudinal asymmetry, parity violations were observed and the cross section differences for positive and negative neutron helicities were obtained. For comparison, a similar analysis was performed on the data below 250 eV, for which longitudinal asymmetries were obtained previously. For energies below 250 eV, the p-wave neutron strength functions for the J=1/2 and J=3/2 states were extracted: S{sub 1/2}{sup 1}=(1.68{+-}0.61)x10{sup -4} and S{sub 3/2}{sup 1}=(0.75{+-}0.18)x10{sup -4}. The data provide constraints on the properties of local doorway states proposed to explain the PNC sign effect in thorium. (c) 2000 The American Physical Society.

Parity nonconservation was studied for 23 p-wave resonances in 113Cd up to En = 500 eV at the LANSCE pulsed neutron source using a longitudinally polarized neutron beam and the time-of-flight method. The helicity dependence of the total neutron capture cross section was measured with an enriched 113Cd target and with a target of natural cadmium. Parity violating effects were observed for several resonances in 113Cd and 111Cd. A root-mean-square value of the parity nonconserving matrix element MJ=1 = 2.9+1.3-0.9 meV was obtained for the spin J=1 levels in the compound nucleus 114Cd. This result from the 3p-peak region of the neutron strength function is compared with the parity violation results for nuclei from the 4p-peak region.

Parity nonconservation (PNC) was measured for 24 p-wave resonances from 8 to 300 eV in 232Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-mean-square PNC matrix element M=1.12 meV, which corresponds to a weak spreading widthΓw=4.7×10-7 eV. For the neighboring nuclide 238U there is no constant offset, suggesting that the sign correlation is specific to 232Th. Disciplines Atomic, Molecular and Optical Physics | Physics Authors Sharon L. Stephenson, J D. Bowman, Bret E. Crawford, P P J. Delheij, C M. Frankle, M IInuma, J N. Knudsen, L Y. Lowie, A Masaike, Y Matsuda, G E. Mitchell, S I. Penttila, H Postma, N R. Roberson, S J. Seestrom, E I. Sharapov, Y-F Yen, and V W. Yuan This article is available at The Cupola: Scholarship at Gettysburg College: http://cupola.gettysburg.edu/physfac/20 Parity nonconservation in neutron resonances in Th S. L. Stephenson,* J. D. Bowman, B. E. Crawford, P. P. J. Delheij, C. M. Frankle, M. Iinuma, J. N. Knudson, L. Y. Lowie, A. Masaike, Y. Matsuda, G. E. Mitchell, S. I. Penttila, H. Postma, N. R. Roberson, S. J. Seestrom, E. I. Sharapov, Y.-F. Yen, and V. W. Yuan North Carolina State University, Raleigh, North Carolina 27695-8202 and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708-0308 Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Duke University, Durham, North Carolina 27708 and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708-0308 TRIUMF, Vancouver, British Columbia, Canada V6T 2A3 Department of Physics, Kyoto University, Kyoto 606-8502, Japan University of Technology, Delft, 2600 GA, The Netherlands Joint Institute for Nuclear Research, 141980 Dubna, Russia ~Received 6 April 1998! Parity nonconservation ~PNC! was measured for 24 p-wave resonances from 8 to 300 eV in Th by measuring the helicity dependence of the total neutron cross section for epithermal neutrons with an improved experimental system. Ten resonances show statistically significant parity violation. For these ten resonances the analyzing powers are all positive, thus confirming the previously observed sign correlation. The data are fit to the sum of two terms, a constant asymmetry and a fluctuating asymmetry. With this ansatz the root-meansquare PNC matrix element M51.12 meV, which corresponds to a weak spreading width Gw54.7310 27 eV. For the neighboring nuclide U there is no constant offset, suggesting that the sign correlation is specific to Th. @S0556-2813~98!03608-5# PACS number~s!: 25.40.Ny, 24.80.1y, 11.30.Er, 27.90.1b

Measurements have been performed on the helicity dependence of the neutron resonance cross section for many nuclei by our TRIPLE Collaboration. A large number of parity violations are observed. Generic enhancements amplify the signal for symmetry breaking and the stochastic properties of the compound nucleus permit the strength of the symmetry-breaking interaction to be determined without knowledge of the wave functions of individual states. A total of 15 nuclei have been analyzed with this statistical approach. The results are summarized.

The parity and time‐reversal symmetries can be studied in neutron‐nucleus interactions. Parity non‐conserving asymmetries have been observed for many p‐wave resonances in a compound nucleus and measurements were performed on several nuclei in the mass region of A∼100 and A∼230. The statistical model of the compound nucleus provides a theoretical basis for extracting mean‐squared matrix elements from the experimental asymmetry data, and for interpreting the mean‐squared matrix elements. The constraints on the weak meson‐exchange couplings calculated from the compound‐nucleus asymmetry data agree qualitatively with the results from few‐body and light‐nuclei experiments. The tests of time‐reversal invariance in various experiments using thermal, epithermal, and MeV neutrons are being developed.

In this talk I describe a new generation of experiments studying the weak interaction between nucleons. Measurements of the effect of this interaction are few in number and the significance of the observed effects are generally small. It is well known that the weak interaction violates parity. This was first experimentally established by C. S. Wu through measurement of an asymmetry of electrons emitted in the beta-decay of polarized {sup 60}Co. The measured asymmetry was large because beta decay is a weak interaction process. For a process in which the strong interaction can contribute, we expect much smaller asymmetries, of order 10{sup {minus}7}. In the work I will describe here we study the effects of the weak interaction through the signal of the parity violation associated with that interaction. There are two basic classes of experiment used to detect parity violation. The first relies on the measurement of a cross section or width that would vanish if parity were conserved. One example of this type of experiment in nuclear physics is the decay of an unnatural parity state to a 0+ nucleus and an {alpha}-particle. Such measurements have been made for two nuclei: {sup 16}O(2{sup {minus}}) {implies} {sup 12} C(g.s)more » + {alpha} and {sup 20}N{var epsilon}(1{sup +}) {implies} {sup 16} O(g.s) + {alpha}. Parity-violating widths as small as of 10{sup {minus}10} eV have been measured in these experiments. The second class of experiments involves a measurement of pseudo-scalar observables which are odd under parity inversion. These involve correlations between spin and linear angular momenta, for example circular polarization of {gamma}-rays ({sigma}{sub {gamma}} {center dot} {kappa}{sub {gamma}}) or longitudinal analyzing power ({sigma}{sub p} {center dot} {kappa}{sub p}). 20 refs., 6 figs.« less