The nEDM Experiment at the SNS Christopher Crawford University of Kentucky for the nEDM Collaboration 77th Annual Meeting of the Southeastern Section of the APS, Baton Rouge, LA

Outline Introduction to neutron physics and the SNS EDM properties – scientific motivation Separated oscillatory fields – ILL experiment Properties of He – new technique Experimental setup – expected results 2

Properties of the Neutron m n = m p + m e keV  n = ± 0.8 s q n < 2 x e d n < 3 x e cm  n =  N r m = fm r e 2 = fm 2 –3 valence quarks + sea –exponential magnetization distribution –pion cloud: spin 1/2 isospin 1/2 p p n n uududdupdown Radial charge distribution – data including BLAST 3

Cold and Ultra-Cold Neutrons (UCN) 3m g Cold neutrons: λ ~ 2 – 20 Å glancing reflections along guides UCN slow enough to be completely reflected by 58 Ni optical potential kinetic: 8 m/s thermal: 4 mK wavelength: 50 nm nuclear: 335 neV ( 58 Ni) magnetic: 60 neV (1 T) gravity: 102 neV (1 m) 4

p (or d) d (or t) n γ What can we do with neutrons? Scattering / Bragg diffraction –Complementary to X-ray diffraction Neutron interferometry Fundamental symmetry tests of the standard model –Neutron decay lifetime and correlations –PV: NPDGamma, 4 He spin rotation –T reversal: electric dipole moment Electron Proton Neutrino Neutron Spin A B C nEDM 5

Spallation Neutron Source (SNS) spallation sources: LANL, SNS –pulsed -> TOF -> energy LH2 moderator: cold neutrons –thermal equilibrium in ~30 interactions Oak Ridge National Laboratory, Tennessee 6

 spallation sources: LANL, SNS pulsed -> TOF -> energy  LH2 moderator: cold neutrons thermal equilibrium in ~30 interactions Spallation Neutron Source (SNS) 7

1B - Disordered Mat’ls Commission Backscattering Spectrometer Commission High Pressure Diffractometer Commission A - Magnetism Reflectometer Commission B - Liquids Reflectometer Commission Cold Neutron Chopper Spectrometer Commission Wide Angle Chopper Spectrometer Commission High Resolution Chopper Spectrometer Commission Fundamental Physics Beamline Commission A - Powder Diffractometer Commission Single Crystal Diffractometer Commission Engineering Diffractometer IDT CFI Funded Commission SANS Commission B - Hybrid Spectrometer Commission – Spin Echo 9 – VISION Beamline 13 allocated for nuclear physics 8

SNS Fundamental Neutron Physics Beamline (FNPB) Experiments expected to run Cold neutron beamline Hadronic PV interaction  decay correlation Neutron lifetime UCN beamline Neutron EDM 9

Cold Neutron Beamline – NPDGamma expt. 10

FnPB neutron flux vs. MC simulation ~ λ -5 shifted slightly toward longer wavelengths 2.1 x neutrons/s at full power (1.4 MW) 11

Electric Dipole Moment EDM is a P and T (therefore CP) violating quantity Standard model value: d n ~ – e·cm (Small! Ideal probe for new Physics) Present limit: d n < 2.8x e·cm (PRL 97, (2006)) + - P reversal T reversal 12

Evolution of EDM Experiments J.M. Pendlebury and E.A. Hinds, NIM A 440, 471 (2000) 13

CP violation and New Physics In SM, quark EDM is zero to first order in G F (one loop), and is also zero at the two-loop level (cancellation among diagrams). d n ~ – e·cm Many extension of SM predict an extra set of particles and CP violating phases (eg SUSY, LR symmetric model) These models predict substantially larger EDMs than SM Neutron EDM is a very sensitive probe for new sources of CP violation fLfL fLfL f’  W W e +i  e -i  Standard Model SUSY 14

Cosmic ray contains –consistent with secondary production by protons Matter-antimatter symmetry would imply –both BBN and CMB anisotropy find: Sakharov conditions: –B violating interactions –CP and P violation –Departure from thermal equilibrium Baryon Asymmetry of the Universe 15

EDM and CP Violation in QCD QDC Langrangian can in principle has a P- and T-violating term The  term can generate a neutron EDM The current neutron EDM limit gives One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed. Strong CP problem 16

B E For B ~ 10mG = 30 Hz For E = 50 kV/cm and d n = e·cm  = 5 nHz (precesses every 6.5 yr) (corresponds to a change in magnetic field of 2 x gauss) Principle of the Measurement 17

Experimental Consideration Statistical uncertainty goes as (for stored UCNs) Therefore we need: –High UCN density –Long storage time –High electric field Systematic effects: –Non-uniformity and instability of magnetic field –Leakage current –Geometric effects 18

Ramsey’s method of separated oscillatory fields — “Traditional” method for nEDM Initial state  /2 pulse Free precession Second  /2 pulse Z component of nuclear spin Spin flip oscillator frequency Slide courtesy of A. Esler and Sussex Neutron EDM group (ILL) B field Spin flip is most efficient when the spin arrives at the 2 nd coil with the right phase, i.e. the phase advance of spin rotation is the same as the RF phase advance. Frequency difference between spin flip field and spin’s Larmor precession makes the 2 nd pulse be out of phase with the 1 st. J.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957) 19

ILL Measurement P.G. Harris et al., RPL 82, 904 (1999) C. A. Baker et al., PRL 97, (2006) Precession measurement: –Ramsey’s separated oscillatory field magnetic resonance method Magnetometry: –Mercury co-magnetometer Neutron source: –Ultra-Cold Neutrons from ILL reactor, Grenoble, France Selected parameters: –E=4.5kV/cm –T storage = 130s –N=15000 Results –d n < 2.8x ecm (90%CL) 20

199 Hg Co-Magnetometer Co-magnetometer: –Magnetometer that occupies the same volume over the same precession time interval as the species on which an EDM is sought 21

Systematic effects due to the interaction of the v  E field with B field gradients Radial gradient B v = v x E field changes sign with direction Particle following roughly circular orbit with orbital frequency  r Pendlebury et al PRA (2004) Lamoreaux and Golub PRA 71, (2005) Barabanov, Golub, Lamoreaux, PRA 74, (2006) After averaging over rotational direction Need 22

EDM Experiment at SNS General strategy: perform experiment in superfluid liquid 4 He –Produce UCN in measurement cell via superthermal process –Use polarized 3 He as comagnetometer –Use 3 He-n interaction as spin precession analyzer Figure of merit: Expected gain over the ILL measurement A 2 orders of magnitude overall gain in sensitivity is expected R.Golub and S.K.Lamoreaux Phys. Rep. 237, 1 (1994) 23

8.9 Å cold neutrons get down-scattered in superfluid 4 He by exciting elementary excitation Up-scattering process is suppressed by a large Boltzman factor No nuclear absorption R.Golub and J.M.Pendlebury, Phys.Lett.A 62,337,(77) Superthermal Production of UCN Expect a production of ~ 0.3 UCN/cc/s With a 500 second lifetime,  UCN ~150/cc and N UCN ~1.2x10 6 for an 8 liter volume 24

3 He as comagnetometer Neutron n ~29 Hz 3 He 3 ~32 Hz Change in magnetic field due to the rotating magnetization of 3 He by SQUID magnetometers Pickup coils Measurement cell filled with SF 4 He  B B A dilute admixture of polarized 3He atoms is introduced to the bath of SF 4 He (x = N 3 /N 4 ~ or  3He ~ /cc) 25

3 He as spin analyzer / 4 He as a Detector 3 He-n reaction cross section 3 He-UCN reaction rate Detect Scintillation light from the reaction products traveling in LHe –Convert EUV light to blue light using wavelength shifter –Detect the blue light with PMTs Signature of EDM would appear as a shift in  3 -  n corresponding to the reversal of E with respect to B with no change in  3 4 He superfluid filled measurement cell made of acrylic and coated with wavelength shifter 3 He + n  t + p keV  J=0 = 5333 b / 0  J=1 ¼ 0 n n + n n p p p p n n p p n n + p p 26

Critical properties of liquid helium 4 He dispersion curve –8.9 Å down-scatter to UCNs by emitting phonon 3 He spin 90% from unpaired neutron 3 He EDM ~0 by Schiff theorem –effective comagnetometer n + 3 He -> p + t keV –spin-precession analyzer 4 He is an effective scintillator 4 He dielectric constant – HV 4 He is a superfluid (T < 1.7 K) –heat flush purification n n + n n p p p p n n p p n n + p p 27

Alternative approach Dressed spin technique By applying a strong non-resonant RF field, the gyromagnetic ratios can be modified or “dressed” For a particular value of the dressing field, the neutron and 3 He magnetic moments can be made equal (  n ’=  3 ’) Can tune the dressing parameter until the relative precession is zero. Measure this parameter vs. direction of E B B rf = B rf cos(  rf t) e  B rf = 1 gauss,  rf = 2  x 3 kHz 28

3 He System Volume Displacement Purifiers Purifier isolation Valves 3He Atomic Beam Source (ABS) Polarized 3He Collection System Pressurizer Purifier Control Valve Collection Isolation Valve Pressurizer Standoff Valve Pressurizer Isolation Valve 6a6b453 21a 1b 7 ABS Shutter Measure ment Cell Cell isolation valve 29

T = s Fill 4 He with 3 He L He 3 He E, B Fill Lines T = s  /2 pulse E, B L He n 3 He T = s Precession about E & B t p 3 He L He n E, B XUV  Deuterated TPB on Walls Light to PMT SQUID T = s Remove 3 He Emptying Lines E, B Experiment Cycle T = s UCN from Cold n L He 8.9 Å neutrons Refrigerator UCN ~ 500 Å Phonon  (UCN)=P  E, B 30

Dilution Refrigerator (DR: 1 of 2) Upper Cryostat Services Port DR LHe Volume 450 Liters 3 He Polarized Source 3 He Injection Volume Central LHe Volume (300mK, ~1000 Liters) Re-entrant Insert for Neutron Guide Lower Cryostat Upper Cryostat 5.6m 4 Layer μ-metal Shield EDM Experiment Schematic Vertical Section View 31

Magnets and Magnetic Shielding Not shown:  /2 spin-flip coil and gradient coils B 0 field direction r = 61 cm r = 48 cm r = 37 cm r = 65 cm r = 62 cm 32

Electrodes Measurement cells Light guides Gain capacitor PMTs Lower Cryostat Cutaway View Cold neutron beam 33

Application: new method of designing magnetic coils (from the inside out) Standard iterative method: Create coils and simulate field. New technique: start with boundary conditions of the desired B-field, and calculate the winding configuration 1.Use scalar magnetic potential (currents only on boundaries) 2.Simulate intermediate region using FEA with Neumann boundary conditions (H n ) 3.Windings are traced along evenly spaced equipotential lines along the boundary red - transverse field lines blue - end-cap windings Magnetostatic calculation with COMSOL 34

R&D – nearing completion Activity NameInstitution Neutron storage timeLANL Beamline Monte-Carlo simulationKentucky ABS at 45°LANL 3 He relaxation timeIllinois Light collectionLANL Valve developmentIllinois Geometric phase effect in 3 HeNCState Magnet DevelopmentCaltech High voltage studiesIndiana 4 He evaporative purificationNCState SQUID NMR signalYale 3 He injectionDuke Laser induced fluorescenceYale Slow ControlsNCState 35

Summary The nEDM is sensitive to new sources of CP-violation –Physics beyond the standard model –To explain the Baryon Asymmetry in the Universe The SNS experiment based on new concept of measuring the nEDM directly in liquid 4 He doped with polarized 3 He. –Systematic sensitivity: 3 x e cm (limited by geometric phase) –Statistical sensitivity: 8 x e cm (prospect of 4.5 x higher flux) The collaboration is nearing completion of R&D. –CD2 review early next year –Begin operation ~

EDM Collaboration R. Alarcon, S. Balascuta, L. Baron-Palos Arizona State University, Tempe, AZ, USA D. Budker, B. Park University of California at Berkeley, Berkeley, CA 94720, USA G. Seidel Brown University, Providence, RI 02912, USA E. Hazen, A. Kolarkar, V. Logashenko, J. Miller, L. Roberts Boston University, Boston, MA 02215, USA A. Perez-Galvan, J. Boissevain, R. Carr, B. Filippone, M. Mendenhall, R. Schmid California Institute of Technology, Pasadena, CA 91125, USA M. Ahmed, M. Busch, W. Chen, H. Gao, X. Qian, Q. Ye, W.Z. Zheng, X. F. Zhu, X. Zong Duke University, Durham NC 27708, USA F. Mezei Hahn-Meitner Institut, D Berlin, Germany C.-Y. Liu, J. Long, H.-O. Meyer, M. Snow Indiana University, Bloomington, IN 47405, USA L. Bartoszek, D. Beck, P. Chu, C. Daurer, A. Esler, J.-C. Peng, S. Williamson, J. Yoder University of Illinois, Urbana-Champaign, IL 61801, USA C. Crawford, T. Gorringe, W. Korsch, B. Plaster, H. Yan University of Kentucky, Lexington KY 40506, USA E. Beise, H. Breuer, T. Langford University of Maryland, College Park, MD 20742, USA P. Barnes, S. Clayton, M. Cooper, M. Espy, R. Hennings- Yeomans, T. Ito, M. Makela, A. Matlachov, E. Olivas, J. Ramsey, I. Savukov, W. Sondheim, S. Tajima, J. Torgerson, P. Volegov, S. Wilburn Los Alamos National Laboratory, Los Alamos, NM 87545, USA K. Dow, D. Hassel, E. Ihloff, J. Kelsey, R. Milner, R. Redwine, J. Steele, E. Tsentalovich, C. Vidal Massachusetts Institute of Technology, Cambridge, MA 02139, USA J. Dunne, D. Dutta, E. Leggett Mississippi State University, Starkville, MS 39762, USA F. Dubose, R. Golub, C. Gould, D. Haase, P. Huffman, E. Korobkina, C. Swank, A. Young North Carolina State University, Raleigh, NC 27695, USA R. Allen, V. Cianciolo, S. Penttila Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA M. Hayden Simon-Fraser University, Burnaby, BC, Canada V5A 1S6 N. Fomin, G. Greene University of Tennessee, Knoxville, TN 37996, USA S. Stanislaus Valparaiso University, Valparaiso, IN 46383, USA S. Baessler University of Virgina, Charlottesville, VA 22902, USA S. Lamoreaux, D. McKinsey, A. Sushkov Yale University, New Haven, CT 06520, USA 37

What can we do with neutrons? scattering / diffraction –complementary to X-ray Bragg diffraction –large penetration –large H,D cross section –life sciences –fuel cell research –oil exploration fundamental tests of quantum mechanics –neutron interferometry –scattering lengths –neutron charge radius –spinor 4  periodicity –gravitational phase shift –quantum states in a gravitational potential 38

Motivation for n-EDM searches nEDM is a sensitive probe of new sources of CP violation –EDM due to the SM is small because in the SM, CP violation only occurs in quark flavor changing processes to the lowest order. –Most extension of SM naturally produce larger EDMs because of additional CP violating phases associated with additional particles introduced in the model. Strong CP problem –The limit on the CP violating term in the QDC Langrangian (from n-EDM) is very small –One proposed remedy, Peccei-Quinn symmetry, predicts axions. However, axions have not been observed. Baryon Asymmetry of the Universe –Cannot be explained by CP violation in the SM alone 39

Effect due to Hg atoms Because of the difference in the center of gravity between the UCNs and the Hg atoms, it was possible to plot the measured EDM as a function of the field gradient. 40

B. Plaster24 Technical progress: Scintillation Work by LANL, Indiana

B. Plaster25 Technical progress: Valves Work by Illinois Metallic construction would cause magnetic field non-uniformities and depolarization, Eddy currents The body is made from Torlon The boot and seat are made from Vespel Successfully tested to seal superfluid He (1.7 K) for 10,000 cycles

B. Plaster27 Technical progress: Magnetic fields acrylic tube 7.5’ length 24” O.D. Work by Caltech, ASU, LANL, Kentucky Measured Field Gradients ~ 5  10  6 /cm  5 ~ 10  8 G/cm at 10 mG Approaching optimal