Status of the Search for an EDM of 225 Ra

Transcription

1 Status of the Search for an EDM of 225 Ra I. Ahmad, K. Bailey, J. Guest, R. J. Holt, Z.-T. Lu, T. O Connor, D. H. Potterveld, N. D. Scielzo Roy Holt Lepton Moments 2006 Cape Cod

2 Outline Why is an EDM interesting? Why use radium? How to detect an EDM Our plan: Source, MOT, FORT, EDM Status and Schedule 2

3 EDM Violates Both P and T A permanent EDM violates both time-reversal symmetry and parity + T + P EDM Spin EDM Spin EDM Spin Neutron, Deuteron Diamagnetic Atoms ( 199 Hg, 225 Ra, 223 Rn) Paramagnetic Atoms (Tl) Molecules (PbO) Quark EDM Quark Chromo-EDM Electron EDM Physics beyond the Standard Model: SUSY 3

4 Origin of EDM s Standard Model EDM s are due to CP violation in CKM matrix (K 0 -system) but e - and quark EDM s are zero at Tree Level. Need at least third order to get EDM s. Thus EDM s are VERY small in the Standard Model. 4

5 The LHC is on the way. Two Possibilities: The LHC doesn t see evidence for new physics. Window of opportunity for low energy tests to make discovery before ILC. The LHC observes new physics, say, SUSY. SM has many new parameters. Low energy experiments will be necessary to pin down new parameters. 5

6 Current Experiments in Nuclei Isotope Current Limit (e cm) Institution Nuclear Spin Factor of Improvement T-odd Sensitivity Technique 199Hg -(1.1 ± 0.6)E-28 Washington Washington 1/ cells 129Xe (0.7 ± 3.3)E-27 Princeton 1/2 Michigan Liquid cell 225Ra N/A Argonne KVI 1/2 ~ Hg 2100 Trap 223Rn N/A Michigan& TRIUMF 7/2 ~ Hg 2000 Cell D N/A BNL, IUCF, KVI 1 ~Hg Storage ring 6

7 EDM of 225 Ra enhanced EDM of 225 Ra enhanced: Large intrinsic Schiff moment due to octupole deformation; Closely spaced parity doublet; Relativistic atomic structure. + - Haxton & Henley (1983) Auerbach, Flambaum & Spevak (1996) Engel, Friar & Hayes (2000) Enhancement Factor: EDM ( 225 Ra) / EDM ( 199 Hg) 55 kev Ψ = ( + )/ 2 Ψ + = ( + + )/ 2 Skyrme Model Isoscalar Isovector Isotensor SkM* SkO Schiff moment of 199 Hg, de Jesus & Engel, PRC72 (2005) Schiff moment of 225 Ra, Dobaczewski & Engel, PRL94 (2005) NB: Must include quadrupole term in Schiff operator: See C.-P. Liu et al, nucl-th/

8 EDM Measurement B E B μ, s E s B E d, s hf = 2μB + + 2dE hf = 2μ B 2 de s Parameters B = 10 mgauss f = 11 Hz E = 100 kv/cm f + -f - = 10 nhz d = 1 x e cm 8

9 Expected Statistical Accuracy No. of Ra atoms: 10 mci source = 3.6 x 10 8 Ra/s N = 1 x 10 7 atoms Trap storage time = 300 s E = 100 kv/cm T = 100 days Detection efficiency = 0.05 Best experimental limit: M. C. Romalis et al, PRL 86 (2001) 2505 Enhancement factor: Ra/Hg = 375 9

10 Search for EDM of 225 Ra Advantages of an EDM measurement on 225 Ra atoms in a trap: Trap allows a long coherence time (~ 300 s). Cold atoms result in a negligible v x E systematic effect. Trap allows the efficient use of the rare and radioactive 225 Ra atoms. Small sample in an XHV allows a high electric field (> 100 kv/cm). 10 mci 225 Ra sample Magneto-Optical Trap Atomic Beam Proposed setup Oven 225 Ra Nuclear Spin = ½ Electronic Spin = 0 t 1/2 = 15 days Transverse Cooling EDM-probing region Fiber-Laser Optical Dipole Trap 10

11 5.5 ns 7p 1 P 1 38 ms 6d 1 D e- 2 2e-5 5e-7 1 Laser-cooling: 714 nm Radium Atom Energy Level Diagram 7p 3 P ns* 7p 3 P 1 7p 3 P 0 Repump: 1428 nm 1e-1 1e-9 6e-5 9e-4 6d 5e-2 3 D 3 Dzuba et al., PRA 61, (2000) 2e-2 6d 3 D 2 4e μs? 6d 3 D 1 1e-1 Laser-cooling on 1 S 0-3 P 1 : ~2x10 4 cycling transitions 422 ns lifetime* Accel ~ 3000 m/s 2 1 G/cm MOT gradient k B T= h/(2τ) ~ 10 μk 7 ms cooling w/o repump Repump on 3 D 1-1 P 1 : 8 s cooling w/ repump Transition frequency? Isotope shift? Hyperfine splitting? 7s 2 1 S 0 *N. D. Scielzo et al., PRA 73, (2006) 11

12 Argonne National Laboratory Radium EDM Experiment 12

13 225 Ra Source 229 Th 7300 yr α 225 Ra 15 days β 225 Ac 10 days α Fr, At, Rn ~ 4 hours α,β 209 Bi stable 10 mci 229 Th source produces 4 x 10 8 s Ra Test source: 0.5 mci 229 Th Chemical extraction of Ra from Th Reduction of Ra(NO 3 ) 2 with Ba, Al, Ti Exotic Beam Facility ~ 1 Ci 229 Th Expected yield for 225 Ra: 3 x s -1 13

14 Counts 225 Ra from the Oven October 03 experiment Window Facing Oven Aperture Unused Window 137 Cs 225 Ra 30% 70% γ 225 Ac β t 1/2 =14.9 d 225 Ra 40 kev γ-ray α 3 2 α 221 Fr Energy (kev) 50 12% γ 218 kev γ-ray Counts Fr 213 Bi 137 Cs Energy (kev) % 217 At γ 213 Po α α 213 Bi 441 kev γ-ray α 14

15 Spectroscopy and lifetime measurement ~ ns ~ ns * nm 1 7p 3 P 1 6e-5 PMT nm 6p 3 P d 3 D 2 7s 21 S 0 Radium 6d 3 D 1 6s 21 S 0 Barium 5d 3 D μci ~ 5 nano-g 225 Ra mg Ba Notch filter *H. Bucka et al., Ann. Physik 8, 329 (1961) Transverse laser beam Ba and Ra atomic beam 700 C 15

16 225 Ra Spectroscopy Fluorescence 1 S 0 F=1/2> -> 3 P 1 F=3/2> (1) cm -1 Iodine signal Laser locking transition Wavenumber (cm -1 ) 16

17 Ra 7s7p 3 P 1 lifetime measurement Lifetime measurement cycle: Fluorescence Excitation laser Fluorescence τ = 422 ns ns N. D. Scielzo et al., PRA (2006) Time (ns) 17

18 2500 Repump transition in 226 Ra beam 1 P1-1 S 0 photon counts D 1 -> 1 P (1) cm -1 ( nm) 1 P 1 1 S 0 3 P 1 3 D Wavenumber (cm -1 ) 18

19 Radium slower and trap 750 nci 226 Ra (600 nano-g) 1 mci 225 Ra (20 nano-g) Transverse cooling 1 μs Zeeman slower MOT Repump Probe phase ~50 ms Slower, Trans cooling, MOT phase ~400 ms PMT Slower 19

20 Laser-Trapping of Radium Atoms World s first laser trap of radium atoms: both 225 Ra and 226 Ra atoms are cooled and trapped! Key 225 Ra frequencies, lifetimes measured. 20

21 Laser-Trapping of Radium Atoms World s first laser trap of radium atoms: both 225 Ra and 226 Ra atoms are cooled and trapped! Key 225 Ra frequencies, lifetimes measured. 21

22 Overall Trap Efficiency 225 Ra sample Magneto-Optical Trap Atomic Beam Oven Transverse Cooling Monte Carlo estimate: 3 x 10-6 Observation: 7 x 10-7 Original proposal: 1 x 10-4 Future Improvements: Improved transverse cooling: x 2-10 Longer slower: x 2 Re-pump along slower: x 3 23

23 Optical Dipole Trap Intensity 1 H = de % = αe 4 Excitation rate ~ Trap potential ~ ( f f ) 2 ( f f ) laser atom 2 0 Intensity laser atom Erbium Fiber laser: λ = 1.5 μm, Power = 5 Watts Focused to 50 μm diameter trap depth 100 μk Excitation rate ~ 10-5 s -1 Spin relaxation rate ~ s -1 negligible M. V. Romalis and E. N. Fortson, PRA 59 (1999)

24 EDM Measurement 7p 3 P 1 F = 1/2 Fluorescence 7s 21 S 0 F = 1/2 m F = -1/2 σ - m F = -1/2 m F = +1/2 σ + Excitation m F = +1/2 1. Polarize 2. π / 2 pulse 3. Free precess 4. π / 2 pulse 5. Measure population Polarizing and probing laser beam Dipole trap beam Pol. P P P + P + + E down E up B E E field plates f drive -f atom 25

25 26

26 2003 Establish Ra lab, prepare Ra oven and beam 2004 Stabilize laser and perform laser spectroscopy of 225 Ra, improve oven 2005 Establish MOT of Ra atoms 2006 Establish optical dipole trap 2007 Begin EDM experiment Improve statistics and systematics Milestones 27

27 Summary New initiative at Argonne to search for the EDM of 225 Ra Combined advantages of optical trapping and the use of an octupole deformed nucleus Ultimate goal of at least x 100 improvement in sensitivity over previous experiments Radium-225 atoms have been optically trapped. 28

28 Desperate Trappers 29

29 Argonne 30

30 The End 31