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The cryogenic neutron EDM experiment at ILL

The cryogenic neutron EDM experiment at ILL. and the result of the room temperature experiment. James Karamath University of Sussex. In this talk…. (n)EDM motivation & principles Room-temperature nEDM experiment at ILL Systematics CryoEDM Summary.

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The cryogenic neutron EDM experiment at ILL

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  1. The cryogenic neutron EDM experiment at ILL and the result of the room temperature experiment James Karamath University of Sussex

  2. In this talk… • (n)EDM motivation & principles • Room-temperature nEDM experiment at ILL • Systematics • CryoEDM • Summary James Karamath University of Sussex 21/08/2014 18:41:55

  3. (n)EDMs – so? I S S + + d d - - • P- and T-violating • CPV in SM not fully understood e.g. insufficient CPV for baryon asymmetry • Strong CP problem • θCP < 10-10 rad. Axions? g p  × p n n James Karamath University of Sussex 21/08/2014 18:41:55

  4. g squark quark electric dipole moments: q q gaugino (n)EDMs – so? II • Estimated EDMs model dependent • SM dn ~ 10-31ecm • Other models typically 105-6 times greater • e.g. SUSY: CP< 10-2

  5. nEDM measurement principle B0 B0 B0 E E <Sz> = + h/2 h()= 2(-μ.B-dn.E) h()= 2(-μ.B+dn.E) h(0) = -2μ.B <Sz> = - h/2 dn defined +ve ↑↑ - ↑↓= Δ = 4dn.E / h Ramsey NMR performed on stored Ultra Cold Neutrons (UCN)

  6. nEDM statistical limit • Fundamental statistical limit α = visibility [polarisation product] E = E-field strength T = NMR coherence time N = total # counted ~10-26ecm James Karamath University of Sussex 21/08/2014 18:41:55

  7. nEDM systematic limit • Main concern: changes in B-field accidentally correlated with E-field changes give false dn signal h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE True nEDM signal  False signal due to varying B 

  8. Beam era ΔB ≈ v x E / c2 limited RT stored UCN era nEDM experiments: history Co-magnetometer era Cryogenic UCN era

  9. B E Current nEDM experiment at ILL I Magnetic shielding • Create UCN, can then be guided & stored • Polarise UCN • UCN admitted into cell with E and B-fields and stored… • Mercury polarised by Hg lamp and added to cell High voltage lead Magnetic field coil Storage cell Approx scale 1 m Magnet &polarizing foil /analysing foil S N UCN James Karamath University of Sussex 21/08/2014 18:41:55

  10. B E Current nEDM experiment at ILL I Magnetic shielding • Ramsey NMR performed • Released from cell • Neutrons spin analysed (# fn of precession) • Repeat: E=↓or 0, B=↓ High voltage lead Magnetic field coil Storage cell Approx scale 1 m Magnet & polarizing foil/ analysing foil S N UCN detector James Karamath University of Sussex 21/08/2014 18:41:55

  11. Current nEDM experiment at ILL II Mu-metal B-shields HV in B0 field coils Z * Neutron cell Mercury lamp light * Neutrons in/out Ground electrode James Karamath University of Sussex 21/08/2014 18:41:55

  12. h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE Systematics I • Reminder: B-field shifts correlated with E-field changes constitute false dn signal. • Protect against incoming perturbations with mu-metal shields • Measure changes IN cell with Mercury Cohabiting Magnetometer… James Karamath University of Sussex 21/08/2014 18:41:55

  13. Cohabiting Mercury Magnetometer Systematics II • Hg EDM known to be below ~ 10-28 ecm. • Thus variations in mercury NMR signal are due to B-field fluctuations… James Karamath University of Sussex 21/08/2014 18:41:55

  14. Electric Field + - Co-magnetometer correction Systematics III

  15. Co-magnetometer correction Systematics III

  16. Co-magnetometer correction Systematics III

  17. Magnetometer problems Systematics IV • However, not perfect correction • Mercury fills cell uniformly, UCN sag under gravity, lower by ~3 mm. • Thus don’t sample EXACTLY the same B-field. Axial (z) gradients → problems… z n Hg James Karamath University of Sussex 21/08/2014 18:41:56

  18. Geometric Phase Effect (GPE) Systematics V • Two conspiring effects • v x E: motional particle in electric field experiences B-field: ΔB ≈v x E / c2 • Axial field gradient dB/dz creates radial B-field (since .B=0) proportional to r, Br r • Let’s look at motion of a mercury atom across the storage cell

  19. Geometric Phase Effect (GPE) Systematics VI Scales with E like EDM!!! B  v x E Scales with dB/dz dB/dz → B  r i.e. B0 field into page has gradient (GPEHg ~ 40GPEn) Resultant Rotating B field Using Mercury introduces error Shifts resonance  of particle E and B0 into page

  20. GPE: J Pendlebury et al., Phys Rev A 70 032102, 2004 Other Systematics VII

  21. hep-ex/0602020 www.neutronedm.org Final result • Room temperature experiment complete! • Soon to be published result (PRL): dn = (+0.61.5(stat) 0.8(syst)) x 10-26) ecm i.e. |dn| < 3.0 x 10-26ecm (90% CL) • New cryogenic experiment will eventually be x100 more sensitive…

  22. The cryogenic nEDM experiment • Reminder: * x20 x5* x2 ~10-28ecm x1.2 x4 *with new beamline

  23. Improved production of UCN (↑N) I • Crosses at 0.89nm for free (cold) n. Neutron loses all energy by phonon emission → UCN. • Reverse suppressed by Boltzmann factor, He-II is at 0.5K, no 12K phonons. Dispersion curves for He-II and free neutrons James Karamath University of Sussex 21/08/2014 18:41:56

  24. Improved production of UCN (↑N) II • Idea by Pendlebury and Golub in 1970’s, experimentally verified in 2002 (detected in He-II) for cold neutron beam at ILL (~1 UCN/cm3/sec). • Also better guides – smoother & better neutron holding surfaces, Be / BeO / DLC → more neutrons guided/stored. Allows longer T too. James Karamath University of Sussex 21/08/2014 18:41:56

  25. Polarisation and detection (α) I • Polarisation by Si-Fe multi-layer polarizer, 95±6% initial polarisation. • Could lose polarisation in 2 ways: • “Wall losses” magnetic impurities in walls, generally not aligned with neutron spin • Gradients in B-field, if not smooth and steady have similar effect James Karamath University of Sussex 21/08/2014 18:41:56

  26. Polarisation and detection (α) II • Detector: solid state, works in 0.5K He-II. • n (6Li, α) 3H reaction - alpha and triton detected • Thin, polarised Fe layer - spin analysis James Karamath University of Sussex 21/08/2014 18:41:56

  27. Improving the E-field (↑E) I • He-II has high dielectric strength . • However, many questions to study; • Nature of breakdown e.g. area/volume effects, purity effects… • Flow of current in/along surfaces in He-II • Effect on system of ~J energy breakdown in He-II (e.g. on electrode coatings, gas evolution) etc… James Karamath University of Sussex 21/08/2014 18:41:56

  28. Sussex HV tests Improving the E-field (↑E) II ±HV • Test electrodes submerged in He-II in bath cryostat. • Studying Vmax and Ileak as function of d, T, dielectric spacers, purity… up to 130 kV. • Some similar(ish) past data but varied results. E cryostat gap (d, V, spacers) He-II (T, purity…) ~20cm

  29. Past literature Improving the E-field (↑E) III He-I data 4.2<T(K)<2.2

  30. Past literature Improving the E-field (↑E) III 0.5K He-II data 2.2<T(K)<1.4 1.8-2.1K

  31. Improving the E-field (↑E) IV • Now have a 400 kV supply to connect to HV electrode. • Will sit in 3bar SF6.

  32. Magnetic field issues I Shielding factors • Target – need ~ 100 fT stability (NMR) • Need ~ 1 nT/m spatial homogeneity (GPE) • Perturbations ~ 0.1 μT (buses!) • Need (axial) shielding factor ~ 106 • Mu-metal shielding ~ 12 • Superconducting shielding ~ 8x105 • Active shielding (feedback coils) ~ 15

  33. E Magnetic field issues II Extra benefits • CRYOGENIC nEDM! Utilise superconducting shield and B0 solenoid. • Major part of fluctuations across whole chamber (common mode variations) • Magnetometer (zero E-field) cells see same • Very stable B0(t) current • Holding field x5 to reduce GPE in the neutrons by factor of 25 (GPEn 1/B02) James Karamath University of Sussex 21/08/2014 18:41:56

  34. Magnetic field issues III SQUIDS • ~fT sensitivity • 12 pickup loops will sit behind grounded electrodes. • Will show temporal stability of B-field at this level. • Additional sensitivity from zero-field cell(s)

  35. And so, the cryo-nEDM experiment I E ~ 60kV/cm n guide tubes + spin analyser E = 0kV/cm Spin flipper coil (measure other spin)

  36. HV electrode HV in Carbon fibre support BeO spacers Ground electrodes And so, the cryo-nEDM experiment II z

  37. G10 Superfluid containment vessel HV in HV electrode * * Neutrons in/out Ground electrodes *BeO spacers/guides And so, the cryo-nEDM experiment III z 250l He-II 0.5K

  38. The shielded region 1m And so, the cryo-nEDM experiment IV Dynamic shielding coils Magnetic (mu-metal) shields Superconducting shield and solenoid

  39. Schedule / Future • Finish construction THIS SUMMER • Start data taking THIS AUTUMN • First results ~2008/9 • Upgrade neutron guide to ↑N ~2009 ? James Karamath University of Sussex 21/08/2014 18:41:56

  40. Summary • (n)EDMs help study T-violation and are constraining new physics. • Systematics of RT-nEDM experiment well understood. • Final RT result: |dn| < 3.0 x 10-26ecm. • Cryo-nEDM project starts this Autumn, 2008/9 brings ~ mid 10-28ecm results. New beamline for low 10-28ecm. hep-ex/0602020 (RT result) www.neutronedm.org

  41. Done! • Thanks for listening

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