New Limit on the Electron Electric Dipole Moment

Abstract

We present the result of our most recent search for T-violation in 205 Tl, which is interpreted in terms of an electric dipole moment of the electron de. We find de = (6.9 ± 7.4) × 10 −28 e cm. The present apparatus is a major upgrade of the atomic beam magnetic-resonance device used to set the previous limit on de. PACS numbers: 11.30.Er, 14.60.Cd, 32.10.Dk We report a new result in the search for the electric dipole moment (EDM) of the electron, a quantity of interest in connection with CP violation and extensions to the standard model of particle physics [1][2][3]. In heavy paramagnetic atoms an electron EDM results in an atomic EDM enhanced by a factor R ≡ d atom /d e . Thus we search for a permanent EDM of atomic thallium in the 6 2 P 1/2 F = 1 ground state, where R −585 [4]. Experimental MethodLike its predecessor [5,6], the new experiment [7] uses magnetic resonance with two oscillating rf fields [8] separated by a space containing an intense electric field E, and employs laser optical pumping for state selection and analysis. To control systematic effects arising from motional magnetic fields E × v/c, the previous experiment employed a single pair of counterpropagating vertical atomic beams. The present experiment has two pairs separated by 2.54 cm, each consisting of Tl and Na (see Fig.1). The spatially separated beams are nominally exposed to identical magnetic but opposite electric fields; this provides common-mode noise rejection and control of some systematic effects. Sodium serves as a comagnetometer: it is susceptible to the same systematic effects but insensitive to d e , since R is roughly proportional to the cube of the nuclear charge. Furthermore, sodium's two 3 2 S 1/2 ground state hyperfine levels F =2, 1 have g F = ±1/2, which in principle permits the separation of two different types of motional field effects. Figure 1 shows a schematic diagram of the experiment with the up beams active. Atoms leave the trichamber oven thermally distributed among the ground state hyperfine levels. After some collimation they enter the quantizing magnetic field B, nominally in theẑ direction and typically 0.38 Gauss. Laser beams then depopulate the states with non-zero magnetic quantum numbers m F . Thus, in the first optical region 590 nm z polarized light selects the m F = 0 Zeeman sublevel of either the F = 2 or the F = 1 Na ground state. (B Tl cos ω Tl t + B Na cos ω Na t)x, where 2B Tl = B Na and 1.506ω Tl ω Na . These resonant fields apply 'π/2' pulses, creating coherent superpositions of the m F = 0 states of each species. The atoms then move into the electric field, nominally parallel or anti-parallel to B. Typically |E| = 1.23 × 10 5 V/cm. The second rf field is coherent with the first, differing only by a relative phase shift α. In the analysis regions the atoms are probed with the same laser that performed the state selection. Fluorescence photons accompanying the atomic decays are reflected by polished aluminum paraboloids into Winston cones [9] made of UV-transmitting plastic. These lightpi...

The effective theory of the light stop scenario

“…[13]. Let us stress that values of m ≫ 1 TeV are consistent with those necessary in order to suppress the one-loop contributions to the electric dipole moment of the electron and the neutron in the light stop scenario [15].…”

“…along with the wave function threshold contributions of each external leg 13) where the particles propagating in the loops are indicated inside squared brackets and the functions F (m 2 ) and E(m 2 ) are defined by 15) with a 2 = m 2 / m 2 . Because of the thresholds (A.13) the kinetic terms of the effective theory would not be canonically normalized if these wave function thresholds were not absorbed in a redefinition of the effective fields.…”

“…The light stop scenario of the MSSM is characterized by a light right-handed stop (with a mass near the top quark mass) while all other squarks and sleptons should be heavy enough in order to cope with present LEP bounds on the Higgs mass and to avoid large flavor, CP violation and electric dipole moment effects [14,15]. On the other hand, supersymmetric fermions (Higgsinos and gauginos) are required to be at the electroweak (EW) scale (this fact can be technically natural as a consequence of some partly conserved R-symmetry) in order to trigger the required CP-violating currents needed for baryogenesis [11], as well as providing a Dark Matter candidate [16].…”

Gaugino CP phases and EDMs in the extended gauge mediation SUSY breaking

“…After restricting the parameter space at the high energy scale by imposing these conditions on the weak scale values, we finally calculate the EDM of the electron and the neutron and impose their experimental bounds [19,20] |d e /e| = 1.6 × 10 −27 cm, |d n /e| = 1.2 × 10 −25 cm, to restrict the selected parameter region further.…”

“…It is well-known that the EDM of the electron and the neutron should be severely suppressed on the basis of the experimental data [7]. It has been recognized that there are two possibilities to satisfy this constraint [8].…”