Nuclear spin maser and experimental search for 129 Xe atomic EDM

Transcription

1 Hyperfine Interact DOI /s z Nuclear spin maser and experimental search for 129 Xe atomic EDM T. Inoue T. Furukawa A. Yoshimi Y. Ichikawa M. Chikamori Y. Ohtomo M. Tsuchiya N. Yoshida H. Shirai M. Uchida K. Suzuki T. Nanao H. Miyatake H. Ueno Y. Matsuo T. Fukuyama K. Asahi Springer Science+Business Media Dordrecht 2013 Abstract The present status of an active spin maser which is being developed for an experimental search for 129 Xe atomic electric dipole moment (EDM) is presented. In order to realize the long term stability of maser frequency, systematic effects for the spin maser operation were investigated. The correlations in the maser frequency This work is supported in part by the Grant-in-Aid for Scientific Research on Innovative Areas (No ) and the Grant-in-Aid for Scientific Research (A) (No ) by the Ministry of Education, Culture, Sports, Science, and Technology, Japan. Proceedings of the 4th Joint International Conference on Hyperfine Interactions and International Symposium on Nuclear Quadrupole Interactions (HFI/NQI 2012), Beijing, China, September T. Inoue Y. Ichikawa M. Chikamori Y. Ohtomo M. Tsuchiya N. Yoshida H. Shirai M. Uchida K. Suzuki T. Nanao H. Miyatake K. Asahi Department of Physics, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo , Japan T. Furukawa Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji, Tokyo , Japan A. Yoshimi Research Core for Extreme Quantum World, Okayama University, Tsushimanaka, Kita, Okayama , Japan H. Ueno Y. Matsuo RIKEN Nishina Center, RIKEN, 2-1 Hirosawa, Wako, Saitama , Japan T. Fukuyama Ritsumeikan University, Nojihigashi, Kusatsu, Shiga , Japan Present Address: T. Inoue (B) Cyclotron and Radioisotope Center, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai, Miyagi , Japan

2 T. Inoue et al. with the solenoid current, the environmental field and the cell temperature were found. With the solenoid current and environmental field being stabilized and the cell temperature lowered, a frequency precision of 7.9 nhz has been achieved for the maser operation. Keywords Nuclear spin maser Electric dipole moment CP violation 1 Introduction The study of permanent electric dipole moment (EDM) of a particle is a useful probe to search for physics beyond the standard model (SM) of elementary particles [1]. The EDM directly violates the time reversal symmetry and hence the CP symmetry through the CPT theorem. The predicted size of the EDM in the SM is too small to be detected, since the CP-violating phase contained in the SM contributes only to flavor changing processes, as observed in the CP-nonconserving decays of K and B mesons [2 4]. On the other hand, the EDM is sensitive to such phases in the physics beyond the SM allowing for EDM to acquire values within the experimental reach [5]. Thus, an experimental search for EDM constitutes a crucial test discriminating between the SM and theories beyond it. In order to constrain and confirm the theories, various experiments in a variety of systems of the neutron, atoms and molecules are tried and proposed [6 11]. So far, the experimental result for 199 Hg atomic EDM has the best limit, d( 199 Hg) < ecm [8]. In the case of 129 Xe atom, on the other hand, the experimental upper limit for EDM is d( 129 Xe) < ecm, which was obtained by the preceding experiment using a conventional spin maser technique [9]. However, as presented in the next section, the experimental search for the 129 Xe atomic EDM has the potential for a significant improvement in the experimental limit by utilizing of the nuclear spin oscillator of new type [12]. 2 Nuclear spin maser The EDM is experimentally deduced from a tiny change of the spin precession frequency upon the reversal of an applied electric field E 0 along a magnetic field B 0. Therefore the EDM search experiments require the highly precise determination of the spin precession frequency. If the size of EDM is ecm, for example, the change of the spin precession frequency is 1 nhz when E 0 = 10 kv/cm is applied. In order to detect such a change, the long measurement times for the spin precession, or, the sustainment of the spin precession is advantageous. The nuclear spin maser is a mechanism to realize the sustained spin precession [13]. We developed a spin maser which is capable of operating under low static magnetic fields, an active spin maser, for use in the 129 Xe atomic EDM measurement. Figure 1 shows the schematic view of the experimental apparatus constructed for the active spin maser operation. A glass cell which contains the Xe gas and the Rb vapor is placed in the center of a magnetic shield in order to suppress effects from environmental fields. A nuclear spin polarization of 129 Xe is realized through the spin exchange interaction with spin polarized Rb atoms by the optical pumping technique [14]. Precession of 129 Xe spins is detected by observing the transmission

3 Nuclear spin maser and experimental searchfor 129 Xe atomic EDM Si photo diode Magnetic shield (4 layers) Solenoid coil (B 0 = 28.4 mg) Circularly polarizing plate Heater PEM 18 mm 129 Xe gas cell Pumping and probe laser Fig. 1 Experimental apparatus for the maser operation. The Xe gas cell placed in the magnetic shield is irradiated with circularly polarized light of Rb D1 line from the diode laser to polarize the nuclear spin and detect the spin precession. The static field of 28.4 mg is produced by the solenoid coil placed in the innermost layer of the shield of a probe light in the cell, which reflects the transverse component of Rb spins repolarized by 129 Xe spins [15]. The pumping and probe lights are supplied from a tapered amplifier diode laser. A feedback field is generated according to the detected signal, and the phase of the feedback field is arranged such that the feedback field is always orthogonal to the spin. Thus, the spin precession is maintained by applying the feedback field through a coil around the cell. Since the nuclear spin precession is optically detected, the active spin maser can operate at considerably lower static field. In fact, we succeeded in operating the active spin maser at B 0 = 28.4 mg which corresponded to the 129 Xe nuclear spin precession frequency of 33.5 Hz. Detailed explanation of the maser operation is described in [12]. 3 Present status of the active spin maser After succeeding in the realization of the maser operation, the systematic effects influencing the spin maser operation, namely stability of maser frequency ν 0 to various experimental conditions, were investigated. Drifts in ν 0 were found to originate from drifts in a solenoid current I 0 for the static field, an environmental field B env of the experimental room and a temperature at the glass cell T cell.inorder to suppress the I 0 drift, a new setup implementing an improved current stability was constructed, which was composed of two current source modules, a digital voltmeter and a standard resistor [16]. In order to cancel the B env fluctuations and drifts, we constructed a set of field correction coils enclosing the magnetic shield, and installed a feedback control system for the current in the correction coils. The optically polarized Rb atoms which coexist with 129 Xe in the Xe cell affects the 129 Xe nuclear spin precession via the magnetic field produced by the Rb magnetization which is proportional to the Rb density and polarization [17]. Since the Rb vapor density is

4 T. Inoue et al. Frequency (Hz) (a) Time (s) Temperature ( o C) (b) Time (s) Fig. 2 Observed time-variations of the maser frequency (a) and the cell temperature (b) averaged over 100 s duration. The maser frequency was evaluated by using the spin precession phase data, while the cell temperature measured by a resistance temperature detector a function of the cell temperature, we lowered T cell from 70 Cto50 C to reduce the effect of the T cell drifts. Figure 2 shows the typical correlation between ν 0 and T cell. In the maser operation after T cell was lowered and the I 0 and B env stabilized, a frequency precision δν was evaluated by fitting the observed precession phase signal with a simple linear function. The obtained frequency precision was 7.9 nhz for the measurement time T m = 30,000 s. The obtained frequency precision would correspond to an expected sensitivity for EDM of δd ecm, when the application of an electric field E 0 = 10 kv/cm will be realized. However, beyond appeared, suggesting that drifts of some factors which caused the frequency drift still remain. Origins of these drifts are being investigated. One of the candidates for them is the T cell fluctuation, since the T cell was only lowered without a stabilization. Under the present experimental condition, the T cell fluctuation at T cell = 50 C of about 0.2 C makes the frequency fluctuation of about 50 μhz. Further improvement in the frequency precision will be expected by stabilizing the cell temperature. In the EDM measurement, the Allan standard deviation σ Allan also is an important parameter. The Allan deviation evaluated for a time interval τ = 30,000 s, for example, was σ Allan = 30 μhz. This indicates that in an actual stage for EDM search a kind of co-magnetometer will be needed. T m = 10,000 s, a deviation from the expected dependence δν T 3/2 m 4 Summary and future We aim to search for 129 Xe atomic EDM by using the active spin maser technique. The systematic effects affecting the maser frequency were investigated to improve the frequency stability. Each drift in the solenoid current, the environmental field and the cell temperature were found as the sources of the frequency drift. The frequency precision of 7.9 nhz was achieved with the measurement time of 30,000 s in the maser operation under the low cell temperature and the solenoid current and the environmental filed stabilizations. In order to proceed to the EDM search experiment, we start to construct a 3 He co-magnetometer to monitor directly the B 0 field, and develop a Rb-magnetometer based on the nonlinear magneto-optical rotation (NMOR) effect to monitor the B 0 field around the Xe cell [18].

5 Nuclear spin maser and experimental searchfor 129 Xe atomic EDM References 1. Kriplovich, I.B., Lamoreaux, S.K.: CP Violation Without Strangeness. Springer, Heidelberg (1997) 2. Christenson, J.H., et al.: Evidence for the 2π decay of the K 0 2 meson. Phys. Rev. Lett. 13, (1964) 3. Aubert, B., et al.: Observation of CP violation in the B 0 meson system. Phys. Rev. Lett. 87, (2001) 4. Abe, K., et al.: Observation of large CPviolation in the neutral B meson system. Phys. Rev. Lett. 87, (2001) 5. Pospelov, M., Ritz, A.: Electric dipole moments as probes of new physics. Ann. Phys. 318, 119 (2005) 6. Baker, C.A., et al.: Improved experimental limit on the electric dipole moment of the neutron. Phys. Rev. Lett. 97, (2006) 7. Regan, B.C., et al.: New limit on the electron electric dipole moment. Phys. Rev. Lett. 88, (2002) 8. Griffith, W.C., et al.: Improved limit on the permanent electric dipole moment of 199 Hg. Phys. Rev. Lett. 102, (2009) 9. Rosenberry, M.A., Chupp, T.E.: Atomic electric dipole moment measurement using spin exchange pumped masers of 129 Xe and 3 He. Phys. Rev. Lett. 86, (2001) 10. Hudson, J.J., et al.: Improved measurement of the shape of the electron. Nature 473, (2011) 11. Yoshimi, A., et al.: Low-frequency 129 Xe nuclear spin oscillator with optical spin detection. Phys. Lett. A 376, (2012) 12. Yoshimi, A., et al.: Nuclear spin maser with an artificial feedback mechanism. Phys. Lett. A 304, (2002) 13. Richards, M.G., et al.: The 3 He nuclear Zeeman maser. J. Phys. B 21, 665 (1988) 14. Happer, W.: Optical pumping. Rev. Mod. Phys. 44, (1972) 15. Volk, C.H., et al.: Mark, measurement of the 87 Rb- 129 Xe spin-exchange cross section. Phys. Rev. A 21, 1549 (1980) 16. Furukawa, T., et al.: Magnetic field stabilization for 129 Xe EDM search experiment. J. Phys. Conf. Ser. 312, (2011) 17. Ma, Z.L., et al.: Collisional 3 He and 129 Xe frequency shifts in Rb-noble-gas mixtures. Phys. Rev. Lett. 106, (2011) 18. Yoshimi, A., et al.: Development of NMOR magnetometer for spin-maser EDM experiment. Phys. Proc. 17, 245 (2011)