Parity-nonconserving Transition Research Articles

Intramolecular radiationless transition or background cosmic field effect in NO2

Optical excitation induces a transition in NO2 from a ground state |a> to an excited state |b>. The state |b> is not stable. The molecule evolves irreversibly from |b> to a state |c> in a time τ0≈3μs. We investigate the transition from |b> to |c> by analysing results of molecular beam and static gas experiments, and we conclude that the irreversible evolution is either an intramolecular radiationless transition of a symmetric to an asymmetric configuration of the isolated NO2 or the effect of a background cosmic field inducing a parity nonconserving transition from |b> to |c>.

Double-core-polarization contribution to atomic parity-nonconservation and electric-dipole-moment calculations

We present a detailed study of the effect of double core polarization (the polarization of core electrons due to the simultaneous action of the electric dipole and parity-violating weak fields) for amplitudes of the $ss$ and $sd$ parity-nonconserving transitions in Rb, Cs, Ba${}^{+}$, La${}^{2+}$, Tl, Fr, Ra${}^{+}$, Ac${}^{2+}$, and Th${}^{3+}$ as well as electron electric-dipole-moment enhancement factors for the ground states of the above neutral atoms and Au. This effect is quite large and has the potential to resolve some disagreement between calculations in the literature. It also has significant consequences for the use of experimental data in the accuracy analysis.

Relations between matrix elements of different weak interactions and interpretation of the parity-nonconserving and electron electric-dipole-moment measurements in atoms and molecules

The relations between matrix elements of different ($P$,$T$)-odd weak interactions are derived. We demonstrate that similar relations hold for parity-nonconserving transition amplitudes and electron electric dipole moments (EDMs) of atoms and molecules. This allows one to express $P$- and $T$-odd effects in many-electron systems caused by different symmetry-breaking mechanisms via each other using simple analytical formulas. We use these relations for the interpretation of the anapole moment measurements in cesium and thallium and for the analysis of the relative contributions of the scalar-pseudoscalar $CP$-odd weak interaction and electron EDMs to the EDMs of Cs, Tl, Fr, and other atoms and many polar molecules (YbF, PbO, ThO, etc.). Model-independent limits on electron EDMs and the parameter of the scalar-pseudoscalar $CP$-odd interaction are found from the analysis of the EDM measurements for Tl and YbF.

Radiative and correlation effects on the parity-nonconserving transition amplitude in heavy alkali-metal atoms

The complete gauge-invariant set of the one-loop QED corrections to the parity-nonconserving (PNC) amplitude in cesium and francium is evaluated to all orders in $\ensuremath{\alpha}Z$ using a local form of the Dirac-Fock potential. The calculations are performed in both length and velocity gauges for the absorbed photon and the total binding QED correction is found to be $\ensuremath{-}0.27(3)%$ for Cs and $\ensuremath{-}0.28(5)%$ for Fr. Moreover, a high-precision calculation of the electron-correlation and Breit-interaction effects on the $7s\text{\ensuremath{-}}8s$ PNC amplitude in francium using a large-scale configuration-interaction Dirac-Fock method is performed. The obtained results are employed to improve the theoretical predictions for the PNC transition amplitude in Cs and Fr. Using an average value from two most accurate measurements of the vector transition polarizability, the weak charge of $^{133}\mathrm{Cs}$ is derived to amount to ${Q}_{W}=\ensuremath{-}72.65{(29)}_{\mathrm{exp}}{(36)}_{\mathrm{theor}}$. This value deviates by $1.1\ensuremath{\sigma}$ from the prediction of the standard model. The values of the $7s\text{\ensuremath{-}}8s$ PNC amplitude in $^{223}\mathrm{Fr}$ and $^{210}\mathrm{Fr}$ are obtained to be $\ensuremath{-}15.49(15)$ and $\ensuremath{-}14.16(14)$, respectively, in units of $i\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}11}(\ensuremath{-}{Q}_{W})∕N\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$

Radiative corrections to one-photon decays of hydrogenic ions

Radiative corrections to the decay rate of n=2 states of hydrogenic ions are calculated. The transitions considered are the M1 decay of the 2s state to the ground state and the E1(M2) decays of the $2p_{1/2}$ and $2p_{3/2}$ states to the ground state. The radiative corrections start in order $\alpha (Z \alpha)^2$, but the method used sums all orders of $Z\alpha$. The leading $\alpha (Z\alpha)^2$ correction for the E1 decays is calculated and compared with the exact result. The extension of the calculational method to parity nonconserving transitions in neutral atoms is discussed.

Radiative corrections to parity-nonconserving transitions in atoms

The matrix element of a bound electron interacting with the nucleus through exchange of a Z boson is studied for the gauge invariant case of $2s_{1/2}-2p_{1/2}$ transitions in hydrogenic ions. The QED radiative correction to the matrix element, which is $-\alpha/2\pi$ in lowest order, is calculated to all orders in $Z\alpha$ using exact propagators. Previous calculation of the first-order binding correction are confirmed both analytically and by fitting the exact function at low $Z$. Consequences for the interpretation of parity nonconservation in cesium are discussed.

Vacuum-polarization corrections to the parity-nonconserving 6s-7s transition amplitude in (133)Cs.

The dominant one-loop radiative corrections to atomic wave functions, those associated with vacuum polarization in the nuclear Coulomb field, are evaluated for the 6s-7s parity-nonconserving transition amplitude in (133)Cs. These corrections increase the size of this amplitude by 0.4% and, correspondingly, increase the difference between the experimental value of the weak charge Q(W)((133)Cs) and the value predicted by the standard model.

Atomic parity violation in cesium and implications for new physics

Recent high-precision measurements of atomic parity-nonconserving transitions between the 6S and 7S states of cesium allow for a determination of the weak nuclear charge with a precision of 1.3%, providing an improved test of the standard model at low energy. Implications for new physics are examined in terms of low energy effects on the weak charge, in particular contact interactions and scalar leptoquark limits. Prospects for further improvements are described.

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.

High-accuracy calculation of parity nonconservation in cesium and implications for particle physics.

High-precision measurements of atomic parity-nonconserving transitions in cesium when coupled with calculations of similar accuracy allow for a precise determination of ${Q}_{W}$, the weak nuclear charge. When expressed in terms of the $Z$ mass, radiative corrections to ${Q}_{W}$ are insensitive to the top-quark mass, so such a determination of ${Q}_{W}$ allows a particularly sensitive probe of radiative corrections depending on new physics. While the wave function of cesium, the atom in which the most accurate measurements have been made, is extremely complex, atomic theory has advanced to a point where predictions accurate to 1% can be made. This paper describes such a calculation with particular emphasis on the question of the reliability of the atomic theory. Particle-physics implications following from the present state of theory and experiment are discussed, and prospects for more accurate work described.

A semi-empirical evaluation of parity non-conserving E1 transitions in thallium

The authors apply their previously-developed semi-empirical potential method in the calculation of the dominant high order many-body correlation effects in thallium which can be modelled by a central potential. The authors use this method to evaluate the thallium parity non-conserving electric dipole 6p1/2 to 7p1/2 and the 6p1/2 to 6p3/2 transitions. To estimate the accuracy of the calculation the authors also calculate the parity conserving E1 transition matrix elements and the hyperfine interaction constants. For the 6p1/2 to 7p1/2 parity non-conserving transition the authors obtain -7.97*10-11 (1+or-0.07) (-iea0QW/N) and for the 6p1/2 to 6p3/2 parity non-conserving transition -31.6*10-11 (1+or-0.09) (-iea0QW/N).

Parity-nonconserving transitions in Cs and Tl: A semiempirical treatment of core-polarization effects.

The parity-nonconserving (PNC) electric dipole matrix elements (A/sub el(PNC)/) for Cs (6s/sub 1/2..-->..7s/sub 1/2) and Tl (6p/sub 1/2..-->..7p/sub 1/2) are calculated. In each case the active valence electron is assumed to move in the potential of a Hartree-Fock core augmented by a semiempirical core-polarization potential. Also included are the modifications to the core potential created by PNC effects within the core. The results we obtain are in good agreement with other calculations and measurements

Parity Non-Conservation and Pair Correlation in Heavy Atomic Systems

The increased accuracy of the experiments studying parity non-conserving effects in atoms calls for improvement also in the atomic calculations which are necessary to connect the experimental results to fundamental parameters. We show how the method of iterative solution of the two-dimensional "pair equation" can be used to treat the effect of pair correlation to all orders, also in the calculations of parity non-conserving transition elements.

Influence of the Dirac-Hartree-Fock starting potential on the parity-nonconserving electric-dipole-transition amplitudes in cesium and thallium.

The parity-nonconserving electric-dipole-transition amplitudes for the 6${s}_{1/2}$\ensuremath{\rightarrow}7${s}_{1/2}$ transition in cesium and the 6${p}_{1/2}$\ensuremath{\rightarrow}7${p}_{1/2}$ transition in thallium have been calculated by the Dirac-Hartree-Fock method. The effects of using different Dirac-Hartree-Fock atomic core potentials are examined and the transition amplitudes for both the length and velocity gauges are given. It is found that the parity-nonconserving transition amplitudes exhibit a greater dependence on the starting potential for thallium than for cesium.

Parity mixing in 19F and the weak parity non-conserving nucleon-nucleon interaction

We report calculations of the asymmetry of the 110 keV photon emitted in the decay of the polarized 1 2 − first excited state of 19F. The calculations employ short range correlations obtained by solving the Bethe-Goldstone equation in the A = 20 system, and are carried out for a wide range of weak parity non-conserving potentials suggested in the literature. Because of the large experimental error of the observed asymmetry, many of these potentials give results compatible with the experimental value. A calculation of the parity allowed E1 matrix element suggests that the standard Cabibbo potential gives results which disagree in sign with the observed asymmetry, which has also been the case in other parity non-conserving transitions.

Parity nonconservation in Tl and Bi atoms

In connection with experiments which have been carried out and are planned, we have calculated the violation of parity conservation due to neutral weak currents for transitions to the first excited states of $^{205}\mathrm{Tl}$ and $^{209}\mathrm{Bi}$. A Green's-function technique is used to evaluate the parity-nonconserving transition matrix. The dependence of the results on various input data (e.g., the Weinberg angle) is discussed.

Exchange currents in parity non conserving electromagnetic transitions

It is shown that exchange currents do not contribute significantly to parity non-conserving transitions of the electric multipole type.