Session DD: Mini-Symposium on Fundamental Symmetries (Lepton EDM)

Development of a Francium Electron Electric Dipole Moment Experiment

An experiment to discover or rule out a permanent electric dipole moment (EDM) of the electron, at a sensitivity well beyond the present experimental limit, is being developed. The experiment will use $^{211}$Fr, obtainable online at TRIUMF at rates of $10^9$/s, in a laser-cooled fountain. The experiment is done in free space and free fall, with an electric field, but no applied magnetic field, between optical state preparation and analysis. The relation between an electron EDM and an EDM of a francium atom has recently been recalculated using field theory alone (Blundell, Griffith \& Sapirstein, Phys. Rev. D\textbf{86}, 025023 [2012]), confirming previous atomic physics calculations and removing any ambiguity in the experimental interpretation.   

Electric Dipole Moment Experiment Systematic from Electric Field Discharge Current

A magnetic field, in the direction of the electric field and synchronous with the electric field reversal, will mimic an EDM signal. One might expect a discharge across the electric field plates to produce magnetic fields with only small or vanishing components parallel to the electric field, minimizing its systematic effect. Our experimental model, using simulated discharge currents, found otherwise: the discharge current may be at an angle to the normal, and thus generate a normal magnetic field. Comparison of data from the experimental model with the results from calculations will be presented, along with estimates of the time-averaged normal magnetic field seen by atoms in an electron EDM experiment using a fountain of laser-cooled francium, as a function of discharge current.   

Magnetic Shielding Studies for Electric Dipole Moment Experiments

Electric dipole moment experiments are necessarily sensitive to magnetic fields and hence require effective magnetic shielding. In testing the shielding factor of single-layer Permalloy (Carpenter HyMu``80'' \textregistered) cylinders, we find time-dependent effects lasting tens of minutes to thousands of minutes when a static magnetic field is applied to a Permalloy cylinder that has been demagnetized in a region of near-zero field. A decrease in the magnetic field, measured at the center of the cylinder, of about 20 percent is observed for applied fields ranging from 0.5 A/m to 16 A/m. The latter applied field is comparable to the Earth's magnetic field. Effects that resemble these have been seen in other ferromagnetic materials.   

Towards the measurement of the electron EDM with laser cooled francium atoms

The electric dipole moment (EDM) of a particle is a probe into new physics beyond the standard model. The electron EDM might be observed with an enhancement in heavier paramagnetic atoms. Francium (Fr), whose electron structure is useful for laser-cooling and trapping, has a large enhancement factor. Fr produced at high temperature via a fusion reaction will be laser-cooled and trapped in an optical lattice where the EDM is measured. The magneto-optical trapping of Fr is required in advance of the lattice trapping. The technique observing a small number of atoms makes it easy to search for the resonant frequency of Fr. The improvement of the beam purity should lead to a more efficient trap. The techniques towards Fr trapping and EDM measurement have been developed.   

Rb atomic magnetometer toward EDM experiment with laser cooled francium atoms

A permanent electric dipole moment (EDM) of a particle or an atom is a suited observable to test the physics beyond the standard model. We plan to search for the electron EDM by using the laser cooled francium (Fr) atom, since the Fr atom has a large enhancement factor of the electron EDM and the laser cooling techniques can suppress both statistical and systematic errors. In the EDM experiment, a fluctuation of the magnetic field is a main source of the errors. In order to achieve the high precision magnetometry, a magnetometer based on the nonlinear magneto-optical rotation effect of the Rb atom is under development. A long coherence time of Rb atom is the key issue for the highly sensitive detection of the field fluctuations. The coherence time is limited due both to collisions with an inner surface of a cell contained the Rb atom and to residual field in a magnetic shield. We prepared the cell coated with an anti-relaxation material and measured the relaxation time. A degauss of the shield was performed to eliminate the residual field. We will report the present status of the magnetometer.   

Development of an electric field application system with transparent electrodes towards the electron EDM measurement with laser-cooled Fr atoms

The permanent electric dipole moment (EDM) of elementary particles is a good probe for new physics beyond the standard model. Since the francium (Fr) atom has a large enhancement factor of the electron EDM and laser-cooled atoms can have long coherence times, we plan to utilize laser-cooled Fr atoms for the electron EDM search experiment. Besides, a strong electric field is one of key issues for the EDM experiment. Recently, we have embarked on a development of the electric field application system with transparent electrodes coated by tin-doped indium oxide (ITO). The ITO electrodes break the difficulty in the coexistence of electrodes with several cooling laser lights. The actual electric field applied to the atom is evaluated by measuring the dc Stark shift for the laser-cooled rubidium atoms. In this presentation, the present status of the electric field application system will be reported.   

Development of a neutralizer and the magneto optical trap system toward the EDM search

If a non-zero electric dipole moment (EDM) is discovered, it suggests a CP violation that is important to explain the generation of matter dominant universe. To search for the electron EDM, we use Fr atoms that have a relatively simple electronic structure and a large enhancement factor of electron EDM. It is necessary to trap Fr atoms in a magneto-optical trap for EDM experiment. At present, searching for the resonance frequency of Fr atoms is undertaken. The experimental technique to trap and observe a small number of atoms is needed to search the resonance frequency. We have searched for parameters for trapping and observing the small number of atoms using Rb atoms whose resonance frequency is able to be fixed by using reference cell. In addition to this, studying of an yttrium neutralizer that is used for changing ions to neutral atoms is needed to trap as much Fr atoms as possible.   

Effect of electron electric dipole moment on the spin dynamics of the YbF molecule

The existence of the large value of the electron electric dipole moment (EDM) is predicted in extensions of the standard model (SM). To find or exclude physics beyond SM, the EDM is studied in many experiments, where the precession motion of the electron spin is used for the detection. This motion depends on the internal effective electric field (EEF). The accurate prediction of the relation between the EDM and the spin motion is mandatory for deriving the constraint of the EDM. In addition to the computation of EEF, our group studies the spin dynamics by the equation of motion (EOM) of spin. In our group, we have studied the spin motion based on quantum field theory (QFT). In QFT, the spin motion is governed by the spin torque and zeta force. The latter gives local effects and cannot be described in quantum mechanics (QM). Hence, in our approach, there is a difference from ordinary treatment of the spin motion based on QM. In this work, we show that the existence of the EDM modifies our EOM of the spin, that is, the EDM gives the additional contribution to the spin torque. This torque is induced by not only electric field but also magnetic field as a result of relativistic generalization. Then we show our results of the local spin torque distribution for the YbF molecule.   

Effective electric field of molecules of observation experiment of electron electric dipole moment

Heavy polar diatomic molecules are the most promising candidates for experiments of the electric dipole moment (EDM) of the electron, which is a hopeful and inexpensive probe of physics beyond the standard model. The upper bound of the electron EDM, $d_e$, is determined by the energy shift by the EDM, which is the product of $d_e$ and the effective electric field $E_{\rm eff}$. $E_{\rm eff}$, which cannot be measured experimentally, must be determined by ab initio computations for each molecule based on relativistic quantum theory. Relativistic and correlation effects are essentially important for accurate computations of heavy atoms and molecules. For the former effects, the four-component Dirac equation should be solved for the inclusion of the relativistic term, such as the spin-orbit interaction, while post Hartree-Fock computations, such as configuration interaction (CI), are required for the latter effects. These two treatments consume large computational resources, and hence the value of the effective electric field has not been settled yet. In this work, we investigate the effective electric field for the electron EDM in diatomic molecules such as YbF, which is a representative one for experiments of the electron EDM.   

Search for muon EDM with ultra-cold muon beam at J-PARC

The J-PARC experiment E34 aims to measure the anomalous magnetic moment ($g$-2) and electric dipole moment (EDM) of the positive muon with a novel technique utilizing an ultra-cold muons accelerated to 300MeV/$c$ and a 66 cm-diameter compact muon storage ring without focusing-electric field. This measurement will be complementary to the previous BNL E821 experiment and upcoming FNAL E989 experiment with the muon beam at the magic momentum 3.1GeV/$c$ in a 14 m-diameter storage ring. The experiment aims to achieve the sensitivity down to 0.1 ppm for $g$-2, and $10^{-21}$ $e\cdot$cm for EDM. In this presentation, I'd like to discuss the technical achievements and prospects for realization of the experiment.   

Precision measurement of muonium hyperfine splitting at J-PARC

Muonium is the bound state of a positive muon and an electron. Because neither muon nor electron has internal structure, muonium's ground state hyperfine splitting (MuHFS) can be the most precise probe for the test of the bound state QED and for the determination of the ratio of magnetic moments of muon and proton. At J-PARC, we plan to perform a precision measurement of the MuHFS via microwave spectroscopy of muonium. Muonium is formed in Kr gas target and state transition between energy levels is induced by microwave resonance. Spectroscopy of the muonium states can be performed by measurement of positron asymmetry from muonium decay. Precision of the most recent experimental result (LAMPF1999) was mostly statistically limited. Hence, improved statistics is essential for higher precision of the measurement. Our goal is to improve accuracy by an order of magnitude compared to the most recent experiment. In order to achieve the goal, we utilize J-PARC's highest-intensity pulsed muon beam (expected intensity is $1\times10^8\ \mu^{+}/\rm{s}$), highly segmented positron detector with SiPM (Silicon PhotoMultiplier), and an online/offline muon beam profile monitor. In this presentation, we discuss the experimental overview and development status of each components.   

Search for CP Violation in Positronium Decay

We present a new experiment to search for CP violation in the charged lepton sector by studying positronium decays. Positronium, a bound state of an electron and positron, occurs in both a singlet and triplet state. The triplet state, orthopositronium, decays primarily into three photons. Our experiment searches for CP-violating correlations between the directions of the three gamma-rays using the APEX annular array of NaI detectors, combined with a tagged source. This array will increase the angular acceptance by a factor 25 over previous experiments. We will present the current status of the experiment and a projected sensitivity.