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DHB/Illinois 9 Apr 10

From yeV to TeV : Search for the Neutron Electric Dipole Moment ASU, Berkeley, Boston, Brown, Caltech, Duke, HMI, Illinois, Indiana, Kentucky, MSU, LANL, Maryland, MIT, NCSU, ORNL, SFU, Yale. DHB/Illinois 9 Apr 10. Outline Physics T violation standard model beyond standard model

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DHB/Illinois 9 Apr 10

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  1. From yeV to TeV:Search for the Neutron Electric Dipole MomentASU, Berkeley, Boston, Brown, Caltech, Duke, HMI, Illinois, Indiana, Kentucky, MSU, LANL, Maryland, MIT, NCSU, ORNL, SFU, Yale DHB/Illinois 9 Apr10 • Outline • Physics • T violation • standard model • beyond standard model • Experiment • ultra-cold neutrons • the other small miracles • status

  2. T Violation and Neutron EDM s m T m d d s • Existence of particle EDM implies T reversal sym’y violation • spin is only orientation (vector) in problem: or • T reversal violation implies CP violation if CPT symmetry preserved • observation; requires only locality, Lorentz invariance and Hermitian Hamiltonian • EDM of complex ‘particles’, e.g. KRbor NH3 or H2O? • weak field limit of d for a pure state averages to zero • for, e.g. NH3, N equally likely to be ‘on top’ or ‘on bottom’ relative to s • when oriented by strong enough field, interaction energy eventually linear

  3. CP Violation and Weak Interactions • CP violation is observed in neutral K and B meson decays • Christenson, Cronin, Fitch, Turlay, PRL 13 (64) see 2p decay of KL • fundamental CP violating parameters difficult to determine from K decays – soft QCD! • Move to Bd & Bs systems: lattice QCD calculations better • “B factories” measure B meson decays from U(4s)

  4. CKM Matrix • Takes mass eigenstates to weak eigenstates • Generic version • Wolfenstein parameterization • h is the CP-violating phase (flavor changing couplings) • CP-violating diagrams involve mixing • “flavor diagonal” CP violation?

  5. EDMs in SUSY • Standard model assumes (local) electroweak symmetry breaking due to single Higgs doublet • radiative corrections in this model diverge at higher energies • “super” symmetry prevents these radiative corrections • gauge couplings approach same value at high energy • provides natural dark matter candidate • Assume SUSY at high energy; softly broken at accessible energies • few dozen complex ‘soft-breaking’ parameters • As example: a drastic reduction of phases to 2: CMSSM(Pospelov and Ritz, Ann. Phys. 318 (2005) 119) • all squark masses equal • single higgsino mass phase, qm • all 3-boson (squarkL Higgs squarkR) couplings have common phase qA

  6. EDMs in CMSSM • cotanb for u quarks, etc. • sometimes stated as the SUSY CP problem q q Pospelov and Ritz: MSUSY = 500 GeV, tanb = 3

  7. QCD Effects on EDMs • Simple quark model estimate • Using QCD sum rule approach for neutron structure (Pospelov and Ritz) • “color” electric dipole moments: • Similarly the corresponding expression for 199Hg would be • effects rewritten from CP-violating pNN couplings

  8. Proton/Deuteron EDM • Deuteron would be • note that • Clever idea: beam of p/D in storage ring • (vertical) holding field produces strong (radial) E field • start with longitudinally polarized beam, dp/D causes spin to rotate out-of-plane • detect spin direction with proton/deuteron polarimeter B E p/D • PROBLEM: g-2! • synchronous (de)acceleration: Gd ~ Sx(v(t)xB) • spin dressing fields (g-2  0) • radial electric field to cancel precession (BMT) 

  9. CP Violation: q Term in LQCD • New term appears in LQCD: SU(3) gauge group • sometimes called strong CP violation • note: the trace is also related to the divergence of the axial U(1) current (mh’ >> mp) • present limit on 199Hg (neutron) EDM restricts q < 3x10-10(10-10) • Why? Peccei& Quinn propose additional hidden symmetry • q ‘relaxes’ to zero • axion is hypothetical particle remnant of sym’ybreaking • experiments continue to look for evidence

  10. Baryon Asymmetry of the Universe • Observation • Sakharov criteria • fundamental interactions violate baryon number, B • Universe has undergone non-equilibrium processes (phase-transitions) • there has been CP violation: distinguishes between baryons and antibaryons • Baryon asymmetry may come from lepton asymmetry • CP violation in neutrino sector may be transmitted by B-L conserving interactions at scale of heavy neutrino mass

  11. EDM Measurements

  12. nEDM Experiments/Initiatives

  13. nEDM at SNS Spallation Neutron Source Oak Ridge National Laboratory nEDM Hall Ground Breaking (ORNL, 6 Feb. 09) “Shovel Ready” nEDM Hall July 09 (now complete)

  14. Neutron EDM Measurement • Measure precession frequency • for E = 50 kV/cm, d = 2x10-28 e·cm, dE = 10 yeV! • nm= 3 Hz, nd = 10 nHz, nd/nm= 0.03 ppm • c.f. (g-2)muon: dn/n= 0.7 ppm • Challenges • trap large number of neutrons • large E • measure precession frequency • nuclear interaction: n + 3He • measure E and B accurately • Kerr effect and 3He magnetometer, respectively

  15. Neutron EDM Experiment:Trapping Neutrons n n polarized neutron v = 440 m/s phonon Incident neutrons have same energy andmomentum as phonons in superfluid helium: they interact and stop Superfluid helium

  16. Neutron EDM Experiment:Neutron Precession n n n n n Bpulse n B0 Superfluid helium

  17. Neutron EDM Experiment:Precession Measurement (1) n n n n n n 3He 3He 3He 3He 3He 3He 3He 3He Add polarized 3He atoms (nearly same magnetic moment as neutrons) B0 Superfluid helium

  18. Neutron EDM Experiment:Precession Measurement (2a) n n 3He 3He 3He, n spins parallel: “no” interaction B0 Superfluid helium

  19. Neutron EDM Experiment:Precession Measurement (2b) n p 3H 3He p and 3H give off scintillation light B0 3He, n spins anti-parallel – large reaction probabilty → p + 3H Superfluid helium

  20. Neutron EDM Experiment:EDM Measurement n n n n n n B0 E0 Superfluid helium

  21. Apparatus Overview 3He injection volume DR LHevolume (~300 liters) Dilution refrigeratormixing volume Central LHevolume (~1000 Liters) Re-entrant insert for neutron guide Measurement cell/electrode assembly

  22. little Hadron Collider

  23. Schematic Experiment B Measurement Cells E Ground HV n n Measurement cell cutaway Scintillation signal

  24. 3He Subsystem (Illinois) • Simplified measurement cycle • Complete measurement of relative precession of polarized neutrons and 3He (1000 s) • Remove (‘depolarized’) 3He from measurement cells • Move fresh polarized 3He into measurement cells • Accumulate polarized neutrons in measurement cells (1000 s) • Flip spins with p/2 pulse, begin relative precession measurement • Remove (‘depolarized’) 3He from intermediate volume • Load polarized 3He into intermediate volume

  25. Producing Polarized 3He • Low flux (1014 /s) → quadrupole spin selector (Lamoreaux) • effusive source of cold 3He atoms (0.8 K), v3 ~ 100 m/s • permanent magnet quadrupole (1.25 m long, Bmax = 0.75 T) • Spins aligned to quadrupole field at output • adiabatic change in magnetic field to solenoid • Measured flux & polarization • R3 = 4x1014 /sP3 = 99.6±0.2%

  26. Moving 3He Around Vespel builds up in a ridge above the seal line Region where surface has been scraped during closure Diamond machined surface • Developed superfluid tight, large (~ 1 in.) diameter valves • “a technical challenge that is beyond present experience” • Vespel seals (bulk Kapton) • ‘cork in bottle’ style • Body, flanges: Torlon • high performance plastic • low thermal expansion (~ Cu) • V-groove Kapton seals • glue ‘glass-loaded’ to ‘plain’ Torlon Double BeCu Bellows Vespel “plug” Vespel “close seat” • > 104 cycles, superfluid tight • 80 lb sealing force A. Esler, et al. nucl-ex0703029 P. –H. Chu et al., to be published

  27. (Re)moving 3He with Phonons • Experiment: T ~ 0.45 K • Heat generates phonon flow • Navier-Stokes reduces to Poissieulle in pipe(with slip) • Free energy (normal fluid) Heat source • fountain pressure • Heat carried by phonons 3He distribution X Hayden et al. PRL 93 (2004) 105302

  28. (Re)moving 3He with Phonons (2) • Phonons scatter 3He • Complications S. Lamoreaux, et al. Europhys. Lett. 58 (2002) 718 • Boltzmann for phonons • Benin & Maris, Phys. Rev. 18 (1978) 3112 • Poiseuille o.k. for L > d/3 • Need Boltzmann for interacting system

  29. Limit of Large Lph (Low T) • For a pipe with a uniform temperature gradient, diffusive scattering at the walls • phonon at with momentum originating from wall at has distribution • giving the phonon drift velocity distribution • integrating to find the heat (volume) flow gives the standard Casimir thermal conductivity H. G. B. Casimir, Physica (Utrecht) 5 (1938) 495

  30. Polarized 3He Relaxation • Relaxation time >> measurement time? • magnetic field gradients (Caltech/ASU) • wall relaxation for variety of materials (acrylic cells, Torlon plumbing, etc.) • Polarize 3He (metastability exchange optical pumping @1 Torr), inject into He II (~0.5 K) • Test cell material first • dTPB/dPS coated acrylic • cell geometry different from nEDM measurement cells …

  31. Polarized 3He Relaxation Illinois Data Pd 210-7 Duke/NCSU Data Pd 510-7 1/TS (s-1) 1/TS (s-1) (Sliquid + Sfilm)/ Vliquid (cm-1) (Sliquid + Sfilm)/ Vliquid (cm-1) • Simple kinetic theory argument • Which S/V? • film covers entire surface even when cell is only partly full • Test other materials • dTPB/dPS: Pd = 1x10-7/bounce • nEDM cell lifetime ~ 2x104 s • Torlon: Pd = 1x10-6/bounce • Resin-coated BeCu: Pd = 7x10-7/bounce • Resin-coated Torlon: Pd = 2x10-7/bounce

  32. We need materials that don’t depolarize 3He Polarization Lifetime Apparatus at “the Barn” (south side of Campus) Bare Torlon Depolarization probability per bounce Coated Torlon Torlon Rod in Cell • Use NMR to measure decay of polarization • Measure down to 0.5K • Materials: • acrylic coated with scintillator (measurement cell) • Torlon (high strength plastic for valves and tubes)

  33. Spin “Dressing” • Interacting system of spins and (r.f.) photons z, B0 S • add non-resonant r.f. magnetic field, Bx(t) to B0 • precession in y-z plane y Bx(t) • time-averaged projection Sz x • effectivegyromagnetic ratio • “critical” dressing: equalize 3He and n precession rates R. Golub and S. Lamoreaux, Phys. Rep. 237 (1994) 1; E. Muskat, et al. PRL 58 (1987) 2047

  34. Spin Dressing (2) • More sophisticated treatment for general case A. Esler, et al. Phys. Rev. C (2007) 051302 P. –H. Chu et al., to be published

  35. nEDM Project • ‘Approved’ at Fundamental Neutron Physics Beamline (FNPB) at Spallation Neutron Source • DOE: CD0 – December 2005 CD1 – August 2006 • NSF: Proposal Fa07 (Beck & Filippone) • $7.25M • Current: project management LANL  ORNL • Rebaselining • Annual review: Mar 29-31 • Staged CD-2/CD-3a … ? • Expected ass’y ~ 2015

  36. Summary Physics of T reversal violation • existing CP violation connected with Higgs couplings in SM (CKM matrix) • direct realization of baryon asymmetry requires more CP violation • multi-Higgs, SUSY have many scenarios for other sources of CP violation Many challenges • small change in frequency • systematics associated with E reversal • leakage currents, orbiting spin in magnetic field gradient • materials: n trapping, n activation, polarized 3He compatibility, non-magnetic, non-superconducting, . . .

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