Measurement Of Parity Nonconservation Research Articles

Lifetime and hyperfine splitting measurements on the 7s and 6p levels in rubidium

We present lifetime measurements of the 7S1/2 level and the 6p manifold of rubidium. We use a time-correlated single-photon counting technique on a sample of 85Rb atoms confined and cooled in a magneto-optic trap. The upper state of the 5P1/2 repumping transition serves as the resonant intermediate level for two-photon excitation of the 7s level. A probe laser provides the second step of the excitation, and we detect the decay of atomic fluorescence to the 5P3/2 level at 741 nm. The decay process feeds the 6p manifold that decays to the 5s ground state emitting UV photons. We measure lifetimes of 88.07±0.40 and 120.7±1.2 ns for the 7S1/2 level and 6p manifold, respectively; the hyperfine splitting of the 7S1/2 level is 282.6±1.6 MHz. The agreement with theoretical calculations confirms the understanding of the wave functions involved and provides confidence on the possibility of extracting weak interaction constants from a parity nonconservation measurement.

Radio frequency spectroscopy with a trapped Ba+ ion: recent progress andprospects for measuring parity violation

We have employed the method of shelving to measure Zeeman resonances of asingle trapped Ba+ ion in low magnetic fields, and have observed radio frequencytransitions with linewidths of 5 Hz, limited by magnetic-field noise. We have alsoobserved the shift in the Zeeman frequency when the ion is illuminated byoff-resonant light. A simultaneous measurement of such light shifts in two atomicstates of Ba+ will permit a precise determination of the ratio of transition matrixelements. Furthermore, using this method with an ion in a standing lightwave, aproposed parity nonconservation (PNC) measurement with Ba+ or Ra+could be realized. In this paper we review methods and the status of theseexperiments and discuss the remaining challenges of the PNC experiment.

Observation of Stark-Induced Electric Dipole Transition in Atomic Samarium with Optical Double Resonance

The Stark-induced electric dipole ( E 1) transition for a high-lying odd-parity level in atomic samarium (Sm) was observed with an optical double-resonance technique as a preliminary study for measuring parity nonconservation (PNC). While a pump laser was locked to an E 1 transition from the 0-cm -1 to 15650.55-cm -1 levels, a probe laser was tuned to the parity forbidden transitions under static electric field. For the probe transition from the 15650.55-cm -1 to 28233.08-cm -1 levels, we have observed the Stark-induced E 1 transition. In order to investigate the contribution of the 28233.08-cm -1 level to the Stark-induced E 1 transition, the tensor polarizability was measured. We have found that the observed Stark-induced E 1 transition is anomalously strong compared with the one estimated from α 2 and an E 1 transition measured as a reference. The transition is one of candidates for improving the precision of the PNC measurements.

Effects of nuclear structure on parity nonconservation in atomic cesium in relativistic mean field theory

Experiments suggested in @1# for measuring parity nonconservation ~PNC! in heavy atoms have provided an important confirmation @2,3# of the SU(2)3U(1) electroweak sector of the standard model. One can explore the possibility of new physics beyond the standard model @4# by combining the very accurate measurement of PNC in atomic cesium with sophisticated many-body calculations @5,6#. A recent measurement of parity nonconservation in atomic cesium @3# has reduced significantly the uncertainty (,1%) in the determination of the weak charge QW of the Cs nucleus @3#. The latest result @7# QW 5272.06(28)expt(34)atomic theory disagrees slightly, at the 2.5s level, with the standard model prediction of QW st . 5273.1260.06. The experimental result needs input from atomic structure calculations in the vicinity of the nucleus. However, the small but nonnegligible effects of nuclear size must be addressed before an interpretation of PNC data in terms of the fundamental electroweak couplings is possible. In particular, variations in the neutron distribution among the isotopes affect the weak charge. Thus nuclear structure could become a crucial factor in the interpretation of PNC experiments of increasing accuracy @8–11#. There have been earlier studies to determine nuclear structure effects in PNC in atomic cesium using nonrelativistic potentials @10,11#. Recently a parametric approach of nuclear effects in atomic parity nonconservation has been used @12#. In this paper we present a relativistic calculation of these effects for the first time using relativistic mean field ~RMF! theory. The RMF theory first proposed by Teller and co-workers @13,14# and Durr @15# and later by Walecka @16# and developed by others has been fairly successfully applied to both finite nuclear matter and infinite nuclei. RMF theory has the advantage that, with proper relativistic kinemetics and with the mesons and their properties already known or fixed from the properties of a small number of nuclei @17–21#, the method gives a good description for binding energies, root mean square ~rms! radii, quadrupole and hexadecapole deformations, and other nuclear properties not only spherical,

Reconciliation of the measurement of parity nonconservation in Cs with the standard model

Contributions from the Breit interaction in atomic structure calculations account for 1.3sigma of the previously reported 2. 5sigma deviation from the standard model in the 133Cs weak charge [S. C. Bennett and C. E. Wieman, Phys. Rev. Lett. 82, 2484 (1999)]. The updated corrections for the neutron distribution reduce the discrepancy further to 1.0sigma. The updated value of the weak charge is Q(W)(133Cs) = -72.65(28)(expt)(34)(theor).

Parity violation in232Thneutron resonances above 250 eV

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.

Precision measurement of parity nonconservation in cesium

The measurement of parity nonconservation (PNC) in atomic cesium is discussed in detail. With a spin-polarized atomic beam, this experiment achieves a fractional uncertainty of 0.35% in the measurement of the PNC amplitude for the transition between the 6S and 7S states of cesium, the lowest uncertainty of atomic PNC to date. By comparing the PNC amplitude on two hyperfine transitions, we measure for the first time the nuclear-spin-dependent contribution that arises from the nuclear anapole moment. A major portion of this paper describes the characterization and elimination of systematic errors.PACS Nos.: 32.80.Ys, 11.30.Er, 12.15.Ji, 32.10.Dk

Measurement of the6S→7STransition Polarizability in Atomic Cesium and an Improved Test of the Standard Model

The ratio of the off-diagonal hyperfine amplitude to the tensor transition polarizability $({M}_{\mathrm{hf}}/\ensuremath{\beta})$ for the $6S\ensuremath{\rightarrow}7S$ transition in cesium has been measured. The value of $\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}27.024(43{)}_{\mathrm{expt}}(67{)}_{\mathrm{theor}}{a}_{0}^{3}$ is then obtained using an accurate semiempirical value of ${M}_{\mathrm{hf}}$. This is combined with a previous measurement of parity nonconservation in atomic cesium and previous atomic structure calculations to determine the value of the weak charge. The uncertainties in the atomic structure calculations are updated (and reduced) in light of new experimental tests. The result ${Q}_{W}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}72.06(28{)}_{\mathrm{expt}}(34{)}_{\mathrm{theor}}$ differs from the prediction of the standard model of elementary particle physics by 2.5 $\ensuremath{\sigma}$.

Spins of resonances in reactions of neutrons with238U and113Cd

In this paper experiments are described that have led to the assignment of spins of a large number of $s$- and $p$-wave resonances in reactions of epithermal neutrons with the nuclei ${}^{238}$U and ${}^{113}$Cd. The gamma-ray spectra of the $(n,\ensuremath{\gamma})$ reactions have been measured using the time-of-flight technique at the GELINA pulsed neutron source facility. For the present spin determinations we have exploited the fact that the population through gamma radiation of low-lying nuclear states from the compound nucleus is dependent on the resonance spin. These assignments are important for the analysis of measurements of parity nonconservation in compound nuclei.

Measurement of Parity Nonconservation and an Anapole Moment in Cesium

The amplitude of the parity-nonconserving transition between the 6S and 7S states of cesium was precisely measured with the use of a spin-polarized atomic beam. This measurement gives Im(E1pnc)/beta = -1.5935(56) millivolts per centimeter and provides an improved test of the standard model at low energy, including a value for the S parameter of -1.3(3)exp (11)theory. The nuclear spin-dependent contribution was 0.077(11) millivolts per centimeter; this contribution is a manifestation of parity violation in atomic nuclei and is a measurement of the long-sought anapole moment.

Measurement of the differences in the total cross section for antiparallel and parallel longitudinal spins and a measurement of parity nonconservation with incident polarized protons and antiprotons at 200 GeV/c

Measurement of the differences in the total cross section for antiparallel and parallel longitudinal spins and a measurement of parity nonconservation with incident polarized protons and antiprotons at 200 GeV/<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>c</mml:mi></mml:math>

Parity violation in charged-particle resonance reactions.

Parity nonconservation (PNC) measurements utilizing charged-particle resonance reactions are proposed. PNC observables have been calculated for over 300 resonance pairs (with the same angular momentum and opposite parity) in five {ital s}-{ital d} shell nuclei. Detailed numerical results are presented for the longitudinal analyzing powers in the {sup 31}P({ital p}{searrow},{alpha}{sub 0}) reaction. There is strong dependence on energy, angle, and resonance parameters. A figure of merit that includes both the relative enhancement of the parity violation and the cross section is used to identify the most promising resonances for study. A proposed detector design and experimental procedure are described. These measurements should provide information on the weak spreading width (the effective nucleon-nucleus weak interaction) in light nuclei. {copyright} {ital 1996 The American Physical Society.}

The simulation of gamma spectra of 113Cd(n,γ) for neutron resonance spin assignment

The gamma decay of the highly excited nucleus of 114Cd, formed by neutron capture, has been simulated numerically. The intensity of transitions between low-lying states was found to be dependent on the neutron resonance spin, as expected from the low-level population spin assignment method. The simulations are in excellent agreement with recent measurements of neutron p-wave resonance spin assignments in 113Cd. The simulations support the work of spin assignment necessary for the interpretation of parity nonconservation measurements.

Optical-rotation technique used for a high-precision measurement of parity nonconservation in atomic lead.

We have measured the parity-nonconserving (PNC) optical rotation near the 1.279-\ensuremath{\mu}m $^{3}$${\mathit{P}}_{0}$${\ensuremath{\rightarrow}}^{3}$${\mathit{P}}_{1}$ magnetic-dipole absorption line in atomic lead vapor. We measure the quantity scrR\ensuremath{\equiv}Im(${\mathit{scrE}}_{\mathrm{PNC}}$/scrM), where scrM is the magnetic-dipole amplitude of the absorption line and ${\mathit{scrE}}_{\mathrm{PNC}}$ is the electric-dipole amplitude coupled into the same line by the PNC interaction within the lead atom. We find scrR to be (-9.86\ifmmode\pm\else\textpm\fi{}0.04\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$, where the first error is statistical and the second is systematic. The statistical errors are due to incompletely subtracted background fluctuations, and the systematic errors are caused by line-shape uncertainties and calibration error. Our value is consistent with the atomic PNC calculations for lead, which give scrR=(-10.7\ifmmode\pm\else\textpm\fi{}0.8)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}8}$ for the standard electroweak model with ${\mathrm{sin}}^{2}$${\mathrm{\ensuremath{\theta}}}_{\mathit{W}}$=0.23 and no electroweak radiative corrections. Including radiative corrections yields the value S=-3\ifmmode\pm\else\textpm\fi{}8 for the isospin-conserving electroweak parameter, with difficulties in the atomic theory of lead presently limiting the extent to which our result tests the standard model. This same technique can also be applied to thallium, where the atomic theory is currently accurate to 3%. By searching for a difference in scrR for the two hyperfine components of $^{207}\mathrm{Pb}$, we find the amplitude of the nuclear spin-dependent PNC rotation to be less than 2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}2}$ of the nuclear spin-independent rotation.

Parity nonconservation in the 6s2 1S0-->6s5d3D1 transition in atomic ytterbium.

The ${6s}^{2}^{1}S_{0}\ensuremath{\rightarrow}6s5d^{3}D_{1}$ transition in atomic Yb is proposed for use in the study of atomic parity nonconservation (PNC). This transition is shown to have a very large $E1$ amplitude arising from PNC: $|\mathrm{Im}({E1}_{\mathrm{PNC}})|\ensuremath{\cong}1.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}{\mathrm{ea}}_{0}$, and also a strongly suppressed $M1$ amplitude and a moderate Stark-induced amplitude. Extremely high-precision measurements of PNC in Yb appear possible, using experimental techniques of proven utility. Comparison of PNC in the wide range of stable isotopes of Yb may provide a unique test of the standard model of electroweak interactions.

Parity violation in charged particle resonances

Recent parity nonconservation (PNC) measurements in nuclei use the compound nucleus as a laboratory for the study of symmetry breaking, with the symmetry breaking matrix elements treated as random variables. This approach is made appealing by the observation of very large parity violation in neutron resonances. One key issue is the mass dependence of the effective nucleon-nucleus weak interaction. The neutron measurements do not appear feasible for light nuclei. We have calculated PNC observables for charged particle resonance reactions for over 100 states in five s-d shell nuclides using experimental values of the resonance parameters. Analyzing powers show strong dependence on energy and angle, and vary greatly from resonance to resonance. Proposed PNC experiments are discussed.

Precise Test of Electroweak Theory from a New Measurement of Parity Nonconservation in Atomic Thallium.

We report a new measurement of parity nonconserving (PNC) optical rotation near the 1.28 $\ensuremath{\mu}$m, ${6P}_{1/2}\ensuremath{\rightarrow}{6P}_{3/2}$ magnetic dipole transition in thallium. We find the ratio of the PNC $E1$ amplitude to the $M1$ amplitude to be $R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(\ensuremath{-}14.68\ifmmode\pm\else\textpm\fi{}0.17)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, which within the present uncertainty of atomic theory yields the thallium weak charge ${Q}_{w}(^{205}T\mathrm{l})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}114.2\ifmmode\pm\else\textpm\fi{}3.8$ and the electroweak parameter $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2.2\ifmmode\pm\else\textpm\fi{}3.0$. Separate measurements on the $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ and $F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0$ ground-state hyperfine components of the transition yield ${R}_{1}\ensuremath{-}{R}_{0}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}(0.15\ifmmode\pm\else\textpm\fi{}0.20)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$, which limits the size of nuclear spin-dependent PNC in Tl.

Parity violation in charged particle nuclear reactions.

The potential role of charged particle resonance reactions in the study of parity nonconservation (PNC) in the nucleus is examined in light of recent statistical interpretations of PNC measurements in neutron resonances. Several PNC observables have been calculated using experimental resonance parameters for five s-d shell nuclei. Longitudinal analyzing powers in (p\ensuremath{\rightarrow},${\mathrm{\ensuremath{\alpha}}}_{0}$) reactions show strong dependence on energy, angle, and resonance parameters. Measurements of analyzing powers at the ${10}^{\mathrm{\ensuremath{-}}4}$ level should provide new information on parity vaiolation in the nucleon-nucleus interaction.

Atomic parity nonconservation: Electroweak parameters and nuclear structure.

There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei.

Measurement of parity nonconservation in proton-deuteron scattering at 43 MeV

Parity nonconservation has been studied in the interaction of longitudinally polarized protons with deuterons at 43 MeV. Protons from pd elastic scattering and from part of the pd break-up spectrum were detected in the angular range 24°–61° (laboratory frame). The longitudinal analyzing power is found to be (+0.4±0.7)×10−7). For comparison with theory, the angular acceptance function of the apparatus for break-up protons is also reported.