Search for a Permanent Electric Dipole Moment on theXe129Atom

Abstract

A measurement of a permanent electric dipole moment on xenon atoms has yielded the null result d( 129 Xe) = ( -0.3 ± 1.1) x 10~2 6 e • cm, achieved by use of spin exchange with optically pumped rubidium atoms to determine the precession frequency of the xenon nuclear spins as a function of applied electric field. This measurement improves the limit on an atomic dipole moment by over four orders of magnitude. It is sensitive to timereversal-asymmetric forces within the atom, setting a new upper limit of 10" 6 Gp on a shortrange tensor-pseudotensor electron-nucleon coupling.PACS numbers: 32.80. Bx, 11.30.Er, 35.10.Di The discovery 1 in 1964 of CP nonconservation in the K 0 meson system provided the first and still the only evidence of time-reversal (T) symmetry violation. In attempting to find other examples of T nonconservation accurate searches have been undertaken for a permanent electric-dipole moment (edm) on an elementary particle or atomic system. Measurements on the neutron 2 ' 3 have yielded the important null value for the dipole moment, d(n) < 4xl0~2 5 e -cm. Searches for an edm on atoms and molecules have set upper limits on Tnonconserving electron-nucleon forces, and on the edm of the electron and the proton. 4 " 8 .We report here the first result in a new search 9 for an atomic edm. We observe precession of the nuclear spins of xenon atoms in a magnetic field, and measure the change in precession frequency when an applied electric field is reversed relative to the magnetic field. Thus far we have obtained the null result:where the quoted error is statistical and one standard deviation. This result is sensitive to several plausible T-nonconserving forces within the atom. For example, it improves the limit on a tensorpseudotensor interaction 5,8 between electrons and nucleons by over a factor of 10. The ground state of 129 Xe is doubly degenerate, with the states distinguished by the axial nuclearspin quantum number, mj= ± \. In external electric and magnetic^fieldsj? and B, the energy operator is H = -d • E -jZ • B, where d^d <r, /T = /x cr are the electric and magnetic dipole operators. H gives a difference^A n =AdE/K in precession_Jrequencies between E parallel and antiparallel to B. If the precession is measured for the duration of its \/e coherence lifetime r with a signal to noise ratio S/N, and the procedure is repeated for a total time T, then a dipole can be measured with an accuracy of bd^h[4E(2rT) l/2 (S/N)]-\(2)In this work, r=500 sec, S/N =5000, and E =4.5 kV/cm, requiring T =20000 sec to reach the observed uncertainty 8</=10~2 6 e-cm. A schematic diagram of the experimental apparatus is given in Fig. 1. The xenon nuclei are polarized and their precession analyzed by spin exchange with optically pumped rubidium vapor. 10,11 A relatively large pump field, B pump = 10 mG, is applied parallel to the light for about 500 sec. A semiconductor laser with a 3-mW output tuned to the Di line of Rb (795 nm) polarizes the Rb at a rate of 50 sec" 1 , while the depolarization rate, due mainly to colli...

The electric dipole moment of the electron

“…130 [25] (0.7 ± 2.2) x 10-24 [25] -0.8 X 10-3 [28,29] -1.4 X 10-2 [28,29] (4 ± 14) x 10-24 [28,32] (-0.5 ± 1.1) x 10-24 [6] for mR -+ 00 (e parameter of J.t -+ evv) [97] (nonleptonic decays) [98] (validity of Adler-Weissberger relation) [99] (KM matrixeliments for b quark) [99] · , '" .…”

Constraints on CP violating four-fermion interactions

“…In this note we point out that CP violating interactions at this level can also be constrained by the experimental bounds on the electron EDM (d e < 10 26 ecm 3]) and neutron EDM (d n < 10 25 ecm 9]). In this paper we determine these bounds on the underlying four-fermion lepton-quark and quark-quark interactions, and the implied constraints on the parameters of the interactions of equation (1). It will be seen that this analysis leads to improved bounds on pn .…”

“…Here we concentrate on constraints on CP violating electron-nucleon and nucleon-nucleon interactions and their generalization to lepton-quark and quark-quark four-fermion interactions. The CP violating electron-nucleon and nucleon-nucleon interactions can be written as: (1) where N and N 0 can be n or p. The best experimental constraints on these interactions come from bound on the EDM of 199 Hg 2,6] with jC S j < 1 10 6 and jC T j < 2 10 8 . The constraint on C P is about one order of magnitude weaker than that on C S .…”

Nucleon EDM from Atomic Systems and Constraints on Supersymmetry Parameters

“…There are also EDM measurements of atomic systems such as 129 Xe [6,7] and 199 Hg [8,9]. However, it is not very easy to extract the individual particles EDM from the atomic EDM measurements since there is the Schiff theorem [10].…”