The nEDM Experiment at the SNS Christopher Crawford University of Kentucky for the nEDM Collaboration Symposium on Nuclear Physics XXXIII Cocoyoc, Morelos, México

Outline EDM properties – scientific motivation Properties of neutron – generation Measurement technique – ILL experiment Properties of He – new technique Experimental setup – expected results

Electric Dipole Moment + - P or T reversed state 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)) + -

Evolution of EDM Experiments

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

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

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

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

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 data from BLAST

Neutron sources - Reactors ILL, Grenoble, France

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

Spallation Neutron Source (SNS) at ORNL January 25, GeV, 1.4 mA Proton Linac SNS construction completed: 2006 SNS Total Project Cost: 1.411B$

Ultra-Cold Neutrons (UCN) 3m g 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)

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

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

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)

First nEDM experiment at ORNL   Permanent magnet Polarizer Analyzer Magnetic field Electric field Neutron spin Detector Neutron beam Electrodes J.H.Smith, E.M.Purcell, and N.F.Ramsey, Phys. Rev. 108, 120 (1957)

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 Selected parameters: –E=4.5kV/cm –T storage = 130s –N=15000 Results –d n < 2.8x ecm (90%CL)

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

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

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.

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

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)

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

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)

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

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

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

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

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

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

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

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

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

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

EDM Status & Schedule Approved by SNS FNPB PRAC - Fall 2005 US DOE CD0 granted - December 2005 R&D and design continue , 2007 US DOE CD1 granted - February 2007 US DOE CD2 review - late 2009 Construction starts Commissioning of the experiment expected ~ 2015

Summary The nEDM is sensitive to new sources of CP-violation The SNS experiment based on new concept of measuring the nEDM directly in liquid 4 He doped with polarized 3 He. –uses many important properties of He which contribute towards a ~100 x improvement in sensitivity –design sensitivity: 2 x e cm The collaboration is nearing completion of various R&D phase. –CD2 review later this year –Construction to be completed ~2015