Atomic Parity Violation In Cesium Research Articles

Empirical Determination of the Bohr-Weisskopf Effect in Cesium and Improved Tests of Precision Atomic Theory in Searches for New Physics.

The finite distribution of the nuclear magnetic moment across the nucleus gives a contribution to the hyperfine structure known as the Bohr-Weisskopf (BW) effect. We have obtained an empirical value of -0.24(18)% for this effect in the ground and excited s states of atomic ^{133}Cs. This value is found from historical muonic-atom measurements in combination with our muonic-atom and atomic many-body calculations. The effect differs by 0.5% in the hyperfine structure from the value found using the uniform magnetization distribution, which has been commonly employed in the precision heavy-atom community over the last several decades. We also deduce accurate values for the BW effect in other isotopes and states of cesium. These results enable cesium atomic wave functions to be tested in the nuclear region at an unprecedented 0.2% level, and are needed for the development of precision atomic many-body methods. This is important for increasing the discovery potential of precision atomic searches for new physics, in particular for atomic parity violation in cesium.

Pump-probe measurement of atomic parity violation in cesium with a precision of 2.6%

We present the atomic parity violation measurements made in Cs vapour using a pump-probe scheme. After pulsed excitation of the 6S-7S forbidden transition in the presence of a longitudinal electric field, a laser beam resonant with one of the 7S-6P transitions stimulates the 7S atom emission for a duration of 20 ns. The polarisation of the amplified probe beam is analysed. A seven-fold signature allows discrimination of the parity-violating linear dichroism, and real-time calibration by a similar, known, parity-conserving linear dichroism. The zero-field linear dichroism signal due to the magnetic dipole transition moment is observed for the first time, and used for in situ determination of the electric field. The result, Im E 1 pv = (−808±21)×10−14 ea 0, is in perfect agreement with the corresponding, more precise measurement obtained by the Boulder group. A transverse field configuration with large probe amplification could bring atomic parity violation measurements to the 0.1% accuracy level.

Atomic parity violation in cesium and implications for the 3-3-1 models

The parity violation in cesium atom is analysed in the framework of the models based on the SU(3) C ×SU(3) L ×U(1) N gauge group. It is shown that in the minimal version, the main contribution to a deviation of weak charge ΔQ W due to direct Z′ exchange is negative. New data on parity violation in the cesium atom seems not favour to the minimal version, while it gets a positive value in the version with right-handed neutrinos. We obtain a bound on the Z′ mass at a range from 1.4 TeV to 2.6 TeV. The allowed regions for the Z– Z′ mixing angle are also derived.

Leptoquark signal from global analysis

Data from HERA, LEP and the Tevatron as well as from low energy experiments are used to constrain the Yukawa couplings for scalar and vector leptoquarks in the Buchmuller–Ruckl–Wyler effective model. In the limit of very high leptoquark masses constraints on the coupling to the mass ratio \(\lambda / M\) are derived using the contact-interaction approximation. For finite masses the coupling limits are studied as a function of the leptoquark mass. Some leptoquark models are found to describe the existing experimental data much better than the standard model. The increase in the global probability observed for models including \(S_1\) or \(\tilde{V}_{0}\) leptoquark production/exchange corresponds to an effect of more than \(3\sigma\). Assuming that a real leptoquark signal is observed, the allowed region in the \(\lambda\)–M plane is calculated. The leptoquark signal mostly results from the new data on the atomic parity violation in cesium, but is also supported by recent LEP2 measurements, unitarity violation in the CKM matrix and HERA high-\(Q^2\) results.

ELECTROWEAK MEASUREMENTS FROM HADRON MACHINES

The discovery of the W and Z gauge bosons at the Sp{bar p}S in 1983 marked the beginning of direct electroweak measurements at a hadron machine. These measurements vindicated the tree level predictions of the Standard Model. The new generation of hadron collider machines now have data of such precision that the electroweak measurements are probing the quantum corrections to the Standard Model. The importance of these quantum corrections was recognized in the award of the 1999 Nobel Price. These corrections are being tested by a wide variety of measurements ranging from atomic parity violation in cesium to precision measurements at the Z pole and above in e{sup +}e{sup {minus}} collisions. In this article, the latest experimental electroweak data from hadron machines is reviewed. The author has taken a broad definition of a hadron machine to include the results from NuTeV ({nu}N collisions) and HERA (ep collisions) as well as the results of the Tevatron (p{bar p} collisions). This is not an exhaustive survey of all results, but a summary of the new results of the past year and in particular those results which have an influence on the indirect determination of the Higgs mass. This article will cover the direct determinations of the W boson and top quark masses from p{bar p} collisions at {radical}s = 1.8 TeV from the two Tevatron experiments, CDF and D0. These results are based on s-channel production of single W bosons and top quark pairs. The results presented here from the NuTeV and HERA experiments allow one to make complementary measurements and probe the electroweak interaction in the space-like domain up to large momentum transfers in the t-channel.

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.

Atomic parity violation as a probe of anomalous gauge-boson couplings.

Quantum loop corrections involving {ital CP}-conserving anomalous gauge-boson couplings are applied to the measurement of atomic parity violation in cesium. The sensitivity of the {ital W}-boson magnetic dipole and electric quadrupole moments to this measurement, for a scale of new physics of {Lambda}=1 TeV, are found to be {minus}0.04{lt}{Delta}{kappa}{sub {ital Z}}{lt}0.12, {minus}0.03{lt}{lambda}{sub {ital Z}},{lambda}{sub {gamma}}{lt}0.13 but {ital Q}{sub {ital W}} is relatively insensitive to {kappa}{sub {gamma}}. These values are better than can be achieved at the CERN {ital e}{sup +}{ital e{minus}} collider LEP 200 and are comparable to the precision that can be achieved at the Superconducting Super Collider and CERN Large Hadron Collider. Future measurements of atomic parity violation in cesium will yield sensitivities of the order of a few percent.