The SNS neutron EDM experiment - 8th International UCN ...

The SNS neutron EDM experiment: overviewand the Kerr-effect electric-field monitorByung Kyu Park 1 , Alex Sushkov 2 , Darwin Windes 1 , Dima Budker 1(for the nEDM collaboration)1 Department of Physics, University of California, Berkeley2 Department of Physics, Yale University7th International UCN WorkshopPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 1 / 29

Outline1 The SNS nEDM experiment: an overview2 The SNS nEDM experiment: current progress3 Kerr-effect electric field monitorPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 2 / 29

State of the neutron EDMCurrently: |d n| < 2.9 × 10 −26 e · cm, Baker et al., PRL 97, 131801 (2006)Summary of current and expected experimental limits on nEDM aCP violation instandard model (fromK 0 decay) not enoughto explain amount ofmatter in universeStringent limit onextensions to thestandard modelConstrain or verifysupersymmetrypredictions in nearfuturea Lamoreaux and Golub, “The Neutron Electric Dipole Moment: Yesterday,Today, and Tomorrow” in Lepton Dipole Moments, ed. Roberts & Marciano, 2009Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 3 / 29

State of the neutron EDMCurrently: |d n| < 2.9 × 10 −26 e · cm, Baker et al., PRL 97, 131801 (2006)Summary of current and expected experimental limits on nEDM aCP violation instandard model (fromK 0 decay) not enoughto explain amount ofmatter in universeStringent limit onextensions to thestandard modelConstrain or verifysupersymmetrypredictions in nearfuturea Lamoreaux and Golub, “The Neutron Electric Dipole Moment: Yesterday,Today, and Tomorrow” in Lepton Dipole Moments, ed. Roberts & Marciano, 2009Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 3 / 29

SNS experiment: distinguishing featuresUCN production by “superthermal” method 1 with ultrapuresuperfluid 4 He and storage in the same cellUCN storage within the helium volume:Gain in neutron density by at 2 orders of magnitudes from previousexperimentsLHe is good dielectric → higher applied electric field by factor of 4Use of 3 He:as polarizer: selectively absorbs antialigned neutrons; improvesneutron polarization from 90% to 95%as comagnetometer: precesses under B field and sees the samefield as neutrons; control systematics related to magnetic fieldsas neutron detector: if neutron is absorbed, neutron wasanti-aligned; if it is not absorebd, it was aligned1 Golub and Pendlebury, Phys. Lett. A 62, 337 (1977)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 4 / 29

EDM sensitivity: statisticsPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 5 / 29

EDM sensitivity: statistics∆EΩ L= −⃗µ·⃗B= γ B BPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 5 / 29

EDM sensitivity: statistics∆E + δE= −⃗µ·⃗B − ⃗ d·⃗EΩ L ± δΩ L = γ B B ± γ E EIf state of n completely specified byexisting quantum numbers, ⃗ d ‖ ⃗µPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 5 / 29

EDM sensitivity: statistics∆E + δE= −⃗µ·⃗B − ⃗ d·⃗EΩ L ± δΩ L = γ B B ± γ E EIf state of n completely specified byexisting quantum numbers, ⃗ d ‖ ⃗µSensitivity: δΩ L ∝1E √ NτTThe SNS experiment:E ≈ 50 kV/cmN ≈ 150 per cm 3 × 3000 cm 3τ ≈ 500 s for each measurementT ≈ 300 live days for initial duration ofthe experiment2π × δΩ L ≈ 2.6 µHzHigh electric field and density madepossible by keeping neutrons insuperfluid heliumHigh voltage (≈ 500 kV) is producedwithout an actual high voltage supply withgain capacitorsPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 5 / 29

EDM sensitivity: systematics⃗v × ⃗ E effectFor bottled UCN, only quadraticdynamic phase—linear geometricphase may remainmagnetic field fluctationcorrect with 3 He signalpseudomagnetic field in thepresence of polarized 3 Hesignificant but canceled withtwo-cell designgeometric phase aoccurs with B field inhomogeneitydoesn’t cancel between 3 He and ntemperature-dependentFrom Conceptual Design Report for the nEDM Projecta Commins. Am. J. Phys. 59, 1077 (1991),Pendlebury et al. Phys. Rev. A 70, 032102 (2004)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 6 / 29

SNS nEDM experiment: UCN sourceBeamline from SNSSuperthermal production of UCN ain ultrapure superfluid 4 He at 0.5 Kfinal neutron temperature: 3 mKa Golub and Pendlebury, Phys. Lett. A 62, 337 (1977)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 7 / 29

SNS nEDM experiment: 3 He comagnetometercomagnetometers:measure local magneticfield fluctuationsHg comagnetometerssuccessfully used before3 He occupy samevolume as neutrons insuperfluid 4 He: idealcomagnetometer forSNS experiment3 He precession signaldetected byexternally-placedSQUIDsHarris et al., Phys. Rev. Lett. 82, 904 (1999)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 8 / 29

SNS nEDM experiment: 3 He neutron detectorn + 3 He → p + 3 H + 764 keVreaction products produce UV scintillation light (80 nm) in the LHe 2UV scintillation light down-shifted (430 nm) and detectedgreater cross section (by factor of 200) in the singlet statemeasures beat frequency between Ω L, 3 He and Ω L,n (small becausegyromagnetic ratio is the same within 10%)Figure from W. Korsch’s talk at PANIC08, “The SNS Neutron EDM Experiment”2 Doyle and Lamoreaux, Europhys. Lett. 26, 253 (1994)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 9 / 29

SNS nEDM experiment: 3 He neutron detectorOptimization of initial 3 He and n angleCalculation by Pinghan Chu for nEDM collaborationChange in Ω L,n without change inΩ L, 3 He → nEDM3 He has negligible EDM:d199 Hg < 10−28 e · cm, and EDM ofdiamagnetic atom varies as Z 2Dressed spin technique amodify effective gyromagnetic ratiowith oscillating B field so thatγ n ′ = γ ′3 He(critical dressing)optimize sensitivity to d n byappropriate choice of initial angle:as much as a factor of 2 increasein sensitivitya Golub and Lamoreaux, Phys. Rep. 237, 1 (1994)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 10 / 29

SNS nEDM experiment: Measurement Cycle1 Diffuse polarized 3 He atoms into themeasurement cell2 Illuminate the measurement cell with polarizedcold neutrons to produced polarized UCNaligned with the 3 He atoms3 Apply π/2 pulse to rotate spins to beperpendicular to the magnetic field4 Make precession frequency measurements5 Remove 3 He atoms from the cryostats bydiffusion to the purifier6 Reload the collection volume with polarized 3 Hefrom the ABS7 Return to step 1100 sec1000 sec10 sec500 sec100 sec(300 sec,during othersteps)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 11 / 29

SNS nEDM Experiment: progressBasic R&D done, including:valve test: 10,000 cycles without failure3 He relaxation time: measured at Duke and UIUC; results agreeand meet project requirementUCN storage time: 300 s at 20K in vacuum with same wall coatingDielectric breakdown in superfluid 4 He: 50 kV/cm at 7-cmseparationcos θ coils tested for magnetic field homogeneityLHe scintillation test with HV: major components successfully testedDesign optimization and engineering currently in progressBuilding construction in progressPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 12 / 29

Measurement CellPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 13 / 29

3 He servicesPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 14 / 29

ApparatusPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 15 / 29

BuildingPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 16 / 29

Building (April 2009)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 17 / 29

Building (May 2009)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 18 / 29

The nEDM collaborationM. Ahmed 7 , R. Alarcon 1 , R. Allen 16 , A. Apostol 11 , A. Avakian 4 , S. Baessler 19 , S. Balascuta 1 , L. Bartoszek 2 , D. Beck 8 ,E. Beise 12 , J. Boissevain 11 , B. Bourque 11 , H. Breuer 12 , D. Budker 3 , M. Busch 7 , J. Chacon 11 , C.-Y. Liu 9 , P. Chu 8 ,V. Cianciolo 16 , S. Clayton 11 , M. Cooper 11 , C. Crawford 10 , K. Dow 13 , J. Dunne 14 , D. Dutta 14 , A. Esler 8 , M. Espy 11 ,B. Filippone 6 , A. P. Galvan 6 , H. Gao 7 , R. Golub 15 , T. Gorringe 10 , C. Gould 15 , G. Greene 16 , D. Haase 15 , D. Hasell 13 ,M. Hayden 17 , E. Hazen 4 , R. Hennings-Yeomans 11 , P. R. Huffman 15 , E. Ihloff 13 , T. Ito 11 , J. Kelsey 13 , A. Kolarkar 4 ,E. Korobkina 15 , W. Korsch 10 , S. Lamoreaux 20 , V. Logashenko 4 , J. Long 9 , M. Makela 11 , A. Matlachov 11 , C. M. Mauger 11 ,B. Mckeown 6 , D. McKinsey 20 , M. Mendenhall 6 , H. Meyer 9 , F. Mezei 11 , J. Miller 4 , R. Milner 13 , E. Olivas 11 , J.-C. Peng 8 ,B. K. Park 3 , S. Penttila 16 , B. Plaster 10 , J. Ramsey 11 , R. Redwine 13 , L. Roberts 3 , I. Savukov 11 , R. Schmid 6 , J. Seele 13 ,G. Seidel 5 , M. Snow 9 , W. Sondheim 11 , S. Stanislaus 18 , A. Sushkov 20 , C. Swank 15 , S. Tajima 7 , J. Torgerson 11 ,E. Tsentalovich 13 , C. Vidal 13 , P. Volegov 11 , W. S. Wilburn 11 , S. Williamson 8 , D. Windes 3 , H. Yan 10 , A. Q. Ye 7 , J. Yoder 8 ,A. R. Young 15 , W. Zheng 7 , X. Zhu 71 Arizona State University, Tuscon, AZ;2 Bartoszek Engineering, Aurora, IL;3 University of California, Berkeley, CA;4 Boston University, Boston, MA;5 Brown University, Providence, RI;6 California Institute of Technology, Pasadena, CA;7 Duke University, Durham, NC;8 University of Illinois, Urbana-Champaign, IL;9 Indiana University, Bloomington, IN;10 University of Kentucky, Lexington, KY;11 Los Alamos National Laboratory, Los Alamos, NM;12 University of Maryland, College Park, MD;13 Massachusetts Institute of Technology, Cambridge, MA;14 Mississippi State University, Mississippi State, MS;15 North Carolina State University, Raleigh, NC;16 Oak Ridge National Laboratory, Oak Ridge, TN;17 Simon Fraser University, Burnaby, BC, Canada;18 Valparaiso University, Valparaiso, IN;19 University of Virginia, Charlottesville, VA;20 Yale University, New Haven, CT90 members from 20 institutionsPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 19 / 29

Kerr-effect electric-field monitorNeed to measure electric field directlyE field requirements: at least 1% homogeneity within the cell, andprecise reversal of E field for systematics (quadratic ⃗v × ⃗ E)presence of dielectric can affect reversing electric fieldcharge accumulation on acrylic plates can affect electric fieldKerr effect probes electric field in the medium itselfPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 20 / 29

Optical access for Kerr monitorsmall LHe Kerr constant a :1.4 × 10 −20 (cm/V) 2expected ellipticity in SNSexperiment: ≈ 10 µradstress-induced birefringencein optical windows: offset onthe order of mrads and driftson the order of 100 µrad over100 secondssolution: cancel the noise outcancellation demonstratedto 1% of the noise in amock-up setup bOriginal cancellation schemea Sushkov et al., Phys. Rev. Lett. 93, 153003 (2004)b Park, Sushkov, and Budker, Rev. Sci. Instr. 79, 013108(2008)Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 21 / 29

Kerr monitor: demonstration in a mock setupCancellation in real timePark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 22 / 29

Kerr monitor: demonstration in a mock setupBetter cancellation with integration over 10 sPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 23 / 29

Kerr monitor: implementation within nEDM apparatusEarly conceptual designPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 24 / 29

Kerr monitor: implementation within nEDM apparatusEarly conceptual designPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 25 / 29

Kerr monitor: implementation within nEDM apparatusRecent design illustrations from John RamseyPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 26 / 29

Kerr monitor: implementation within nEDM apparatusRecent design illustrations from John RamseyPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 27 / 29

Kerr monitor: implementation within nEDM apparatusPark (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 28 / 29

SummaryThe nEDM collaboration plans to measure the electric dipolemoment of the neutron with precision of δd n ≈ 3 × 10 −28 e · cm, 2orders of magnitude improvement from the current limitHigh intensity neutron beam from SNS and new UCN productiontechnique gives UCN density two orders of magnitudes higherthan previous experimentsHighest applied electric field to dateLocal electric field strength to be monitored to 1% accuracy usingKerr effect in LHeStart collecting data in 2016?Park (for nEDM collaboration) (UC Berkeley) SNS nEDM experiment 7th UCN workshop 29 / 29