The Search for a neutron EDM at the SNS

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Brent Rich
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1 The Search for a neutron EDM at the SNS Overview of experimental approach Design of experiment Advanced engineering design Technical developments Status of experiment Projected sensitivity & exp. schedule Overview of neutron EDM attack on systematic effects

2 Collaboration ( interesting mix of nuclear, atomic, particle & low temperature physicists) R. Alarcon, S. Balascuta, L. Baron-Palos Arizona State University G. Seidel Brown University, Providence A. Kolarkar, E. Hazen, V. Logashenko, J. Miller, L. Roberts Boston University D. Budker, A. Park University of California at Berkeley J. Boissevain, R. Carr, B. Filippone, M. Mendenhall, A. Perez Galvan, R. Schmid California Institute of Technology M. Ahmed, M. Busch, P. Cao, H. Gao, X. Qian, G. Swift, Q. Ye, W.Z. Zheng Duke University L. Bartoszek, D. Beck, P. Chu, C. Daurer, J.-C. Peng, S. Williamson, J. Yoder University of Illinois Urbana-Champaign C.-Y. Liu, J. Long, H.-O. Meyer, M. Snow Indiana University C. Crawford, T. Gorringe, W. Korsch, E. Martin, S. Malkowski, B. Plaster, H. Yan University of Kentucky S. Clayton, M. Cooper, M. Espy, C. Griffith, R. Hennings-Yeoman, T. Ito, M. Makela, A. Matlachov, E. Olivas, J. Ramsey, I. Savukov, W. Sondheim, S. Stanislaus, S. Tajima, J. Torgerson, P. Volegov Los Alamos National Laboratory E. Beise, H. Breuer University of Maryland K. Dow, D. Hasell, E. Ihloff, J. Kelsey, R. Milner, R. Redwine, J. Seele, E. Tsentalovich, C. Vidal Massachusetts Institute of Technology D. Dutta, E. Leggett, Mississippi State University R. Golub, C. Gould, D. Haase, A. Hawari, P. Huffman, D. Kendellen, E. Korobkina, C. Swank, A. Young North Carolina State University R. Allen, V. Cianciolo, P. Mueller, S., Penttila, W. Yao, Oak Ridge National Laboratory M. Hayden Simon-Fraser University G. Greene, N. Fomlin The University of Tennessee S. Stanislaus Valparaiso University S. Baeβler The University of Virginia S. Lamoreaux, D. McKinsey, A. Sushkov Yale University Grad students Engineers

3 Measurement Experimental Concept: Golub & Lamoreaux, PHYSICS REPORTS 237,1,1994 Use Superthermal (non-equilibrium) system to produce UCN Superfluid 4 He can yield ~ more UCN than conventional thermal UCN source Higher Electric fields in 4 He possible Achievable electric fields may be > 50 kv/cm Use Polarized 3 He as neutron detector & co-magnetometer (γ 3He = 1.1γ n ) Very small amount of polarized 3 He in 4 He ( 3 He/ 4 He ~ ) r Detect capture via scintillation in 4 He: n + r 3 He t + p (with σ >> σ ) UV photons converted to visible (in tetraphenyl butadiene - TPB) Measure difference of ω n and ω 3 r Use SQUIDs to measure 3 He precession calibrates B-field since ω 3 B 3 He comagnetometer measures B-field at same location as neutrons Independent measurement using dressed spin technique suppresses sensitivity to fluctuations in B-field Additional RF field can match 3 He and neutron precession frequency

4 New Technique for SNS nedm 1. Inject polarized neutron & polarized 3 He 2. Rotate both spins by 90 o 3. Measure n+ 3 He capture vs. time (note: σ >>σ ) 4. Flip E-field direction E-field B-field 3 He functions as co-magnetometer Since d 3He < 3 x 10 5 d n V. A. Dzuba, V. V. Flambaum, & J. S. M. Ginges PRA 76,

5 Two complementary Approaches Free precession technique SQUIDs used to measure 3 He precession frequency which measures ambient B-field Dressed spin technique r r Additional RF magnetic field B, B >> B, ω ( >> ω ) BRF 0 RF 0 RF 0 effectively modifies gyromagnetic ratio γ = ω /B γ' = γ J (γ B /ω ) 0 0 o RF RF such that if B /ω 1.2/ γ then γ ' = rf rf n n γ3' (critical dressing) Thus we need B RF ~ 3 gauss & ω RF ~ 10 khz Provides access to EDM that is independent of SQUID magnetometers and independent of variations of the ambient B-field EDM is measured by observing a shift in critical dressing when E-field is flipped

Spallation Neutron Source (SNS) @ Oak Ridge National Lab 1 GeV proton

6 Spallation Neutron Source Oak Ridge National Lab 1 GeV proton beam 1.4 MW on spallation target Fundamental Physics Beamline Neutron EDM

7 External nedm building completed Nov. 2009

8 EDM Experiment at SNS 8.9 Å Monochrometer Cold beamline He Liquifier Isolated floor

9 EDM Experiment at SNS

10 Measurement cycle 1. Load collection volume with polarized 3 He atoms 2. Transfer polarized 3 He atoms into the measurement cell 3. Illuminate measurement cell with polarized cold neutrons to produce polarized UCN 4. Apply a π/2 pulse to rotate spins perpendicular to B 0 5. Measure precession frequency 6. Remove reduced polarization 3 He atoms from measurement cell 7. Flip E-field & Go to 1.

11 Cryovessel

13 Magnet Module Inner Dressing Coil Outer Dressing Coil 50K Heat Shield 4K Heat Shield Superconducting Lead Shield Ferromagnetic Shield Gradient and shim coils B 0 cosθ Magnet

14 Central Detector Module HV Multiplier Light Guide 1200-l G10 Container Ground Electrodes HV Electrode PMT Ground Return 3He/4He Feed Line 7.5x10x40 cm Cell V1 Valve SQUID

15 Projected nedm sensitivity Statistical sensitivity limited by neutron density in storage cells Given by 8.9Å neutron flux Free precession measured by scintillation light from neutron - 3 He capture N (counts/0.03 sec) t (sec)

16 Projected Sensitivity Optimizing measurement cycle (T fill, T meas, ρ 3He ) gives shot noise limit of 90% CL σ d < 8 x e-cm in 300 live-days with T fill = 700 s, T meas = 700 s, τ capture = 400 s Similar sensitivity limit from dressed-spin technique

17 Systematic Uncertainties Systematic Errors include Additional noise beyond counting statistics that reduces sensitivity e.g. uncompensated B-fields False EDM signals E-field correlated effects e.g. leakage currents Measure and reduce artificial correlations (e.g. EDM that changes sign with direction of B, use of 2 cells) Physics issues geometric phase Careful design of apparatus

18 Systematic Errors Error Source Systematic error (e-cm) Comments Linear vxe (geometric phase) < 2 x Uniformity of B 0 field Quadratic vxe < 0.5 x E-field reversal to <1% Pseudomagnetic Field Effects Gravitational offset < 1 x p/2 pulse, comparing 2 cells < 0.1 x With 1 na leakage currents Leakage currents < 1 x < 1 na E-field stability < 1 x ΔE/E < 0.1% Miscellaneous < 1 x Other vxe, wall losses,

19 Geometric phase effects & B-field gradients Significantly different effects for neutron vs 3 He Neutron has ω 0 >> ω T (ω T is cell traversal frequency) and is largely independent of cell geometry Can use previous analysis of geometric phase Pendlebury et al Phys Rev A (2004) 3 He has ω 0 << ω T and is sensitive to cell geometry Depends on diffusion time to walls (geometry & temperature) False EDM in rectangular geometry: Golub,Swank & Lamoreaux arxiv: Effect depends on Magnetic Field gradients d f Jh = Δω = E 2 Jhγ L 2 2c B 0 along x-direction 2 z B dz z V ψ z ( ω 0 ) + B dy y V L L 2 y 2 z ψ y ( ω 0 ) ψ z ( ω 0 ) is related to the velocity autocorrelation function

20 assuming 1 B 0 B dz z V = - 1 B 0 B dy y V Geometric phase effect for 3 He = 10-5 / cm G z Running at different temperatures & B- fields can help determine size of false EDM systematic effect G y

Possible Upgrade Paths Ultimate sensitivity appears limited by neutron flux Could move experiment to cold beam at FNPB (or vice versa) Using beam-choppers instead of monochromator could increase 8.

21 Possible Upgrade Paths Ultimate sensitivity appears limited by neutron flux Could move experiment to cold beam at FNPB (or vice versa) Using beam-choppers instead of monochromator could increase 8.9 Å flux by ~ factor of 4 6 (d n < 4 x e-cm) Could move experiment to planned 2 nd target station at SNS 1 MW, optimized for long wavelength neutrons Could increase 8.9 Å flux by > 20 (d n < 2 x e-cm) US-DOE mission need 2009

22 Technical Challenges Progress towards development of an experiment Central detector K Magnet 4K Dressing field RF induces eddy currents in conductors (big headache at 0.4K) Superconductors distort B-fields SQUIDs can be killed by HV sparks Materials of cell and 3 He transport must maintain neutron & 3 He polarization

23 Technical Developments Polarized 3 He Atomic Beam Source tested Relaxation time of 3 He on deuterated polystyrene walls (doped with dtpb) measured Progress towards HV tests at low temperature Superfluid He valves tested Magnetic field uniformity measured HV dependence of scintillation light production measured

24 3 He Atomic Beam Polarizer Measured Flux = 1x10 14 atoms/s Polarization = (99.6 ± 0.25)%

25 Polarized 3 He wall relaxation Need T 1 > 10,000s Illinois Scaled to nedm cell, T 1 = 25,000s Duke/NCSU

26 Cryoenic non-metalic superfluid valves thermoplastics Valve body made from Torlon Valve boot & seal made from Vespel Tested for 10,000 cycles sealing superfluid He at 1.7K

27 HV Test Apparatus Variable capacitor amplifies E-field (50kV to 500kV) L V = Q/C = k X L = 50kV 500kV

28 HV test stand Cryostat with dilution fridge Dewar for HV electrodes

29 Summary of HV Studies To Do List: Confirm small scale studies (~1cm electrodes with ~ few mm gap) with large electrodes and large gaps

30 Magnet Development Spring-loaded wire tensioners

31 Averaged measured gradients extrapolated to nedm geometry Scaled gradients Volume averaged gradients Measured at 0.9 gauss (Left cell) (Right cell) (db x /dx)/b 0 < 5 ppm/cm < 9 ppm/cm (db y /dy)/b 0 < 5 ppm/cm < 5 ppm/cm (db z /dz)/b 0-6 ± 1 ppm/cm 6 ± 1 ppm/cm Gives false EDM due to geometric phase < 2 x e-cm Need to match these values at 4K and low B-field and with full scale magnet

32 n- 3 He Scintillation light at HV 20 kv HV feedthrough Ground electrode with α-source Light output reduced by ~ 50 kv/cm

33 Schedule Complete HV test: 12/2010 Critical Decision 2 (CD2): 3/2011 Cost & Schedule baselined CD3: 9/2011 final engineering design /drawings completed Begin construction: Begin cryogenic testing: 2013 Install subsystems in experiment: Start EDM commissioning: 2017

34 More than just the Sensitivity... The "known" systematic effects are part of the experimental design Tackling the unknown effects requires unique handles in the experiment that can be varied The significance of a non-zero result requires multiple approaches to unforeseen systematics SNS is unique in its use of a polarized 3 He co-magnetometer, characterization of geometric phase effects via temperature variation, as well as the dressed-spin capability

Comparison of Capabilities C R Y O E D M 1 C R Y O E D M 2 P S I E D M 1 P S I E D M 2 S N S E D M Δω via accumulated phase in n polarization Δω via light oscillation in 3 He capture Co-magnetometer

35 Comparison of Capabilities C R Y O E D M 1 C R Y O E D M 2 P S I E D M 1 P S I E D M 2 S N S E D M Δω via accumulated phase in n polarization Δω via light oscillation in 3 He capture Co-magnetometer Superconducting B-shield Dressed Spin Technique Horizontal B-field Multiple EDM cells Note that red vs green does not necessarily signify good vs bad But understanding systematics requires mix of red & green = included = not included

36 Summary Neutron EDM experiment at SNS is underway. An experiment at the SNS can incorporate powerful and novel techniques to provide significant scientific reach in the search for a neutron EDM

The SNS neutron EDM experiment: overview and the Kerr-effect electric-field monitor

The SNS neutron EDM experiment: overview and the Kerr-effect electric-field monitor Byung Kyu Park 1, Alex Sushkov 2, Darwin Windes 1, Dima Budker 1 (for the nedm collaboration) 1 Department of Physics,