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

2. 2 In this talk… (n)EDM motivation & principles Room-temperature nEDM experiment at ILL Systematics CryoEDM Summary James KaramathUniversity of Sussex28/06/2015 20:08:36

3. 3 (n)EDMs – so? I P- and T-violating CPV in SM not fully understood e.g. insufficient CPV for baryon asymmetry Strong CP problem  θ CP < 10 -10 rad. Axions? James KaramathUniversity of Sussex28/06/2015 20:08:36 n n  p   × S + - d S - + d

4. 4 (n)EDMs – so? II Estimated EDMs model dependent  SM d n ~ 10 -31 ecm  Other models typically 10 5-6 times greater e.g. SUSY:  CP < 10 -2 quark electric dipole moments: qq  gaugino squark

5. 5 nEDM measurement principle B0B0 E = + h/2 = - h/2 h (0) = -2μ.B h (  )= 2(-μ.B+d n.E) h (  )= 2(-μ.B-d n.E) B0B0 B0B0 E d n defined +ve ↑↑ - ↑↓ = Δ = 4d n.E / h Ramsey NMR performed on stored Ultra Cold Neutrons (UCN)

6. 6 nEDM statistical limit Fundamental statistical limit α = visibility [polarisation product] E = E-field strength T = NMR coherence time N = total # counted ~10 -26 ecm James KaramathUniversity of Sussex28/06/2015 20:08:36

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

8. 8 nEDM experiments: history Co-magnetometer era Cryogenic UCN era RT stored UCN eraBeam era ΔB ≈ v x E / c 2 limited

9. 9 Current nEDM experiment at ILL I 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 N S Storage cell Magnet & polarizing foil / analysing foil UCN Approx scale 1 m B E Magnetic field coil High voltage lead James KaramathUniversity of Sussex28/06/2015 20:08:36 Magnetic shielding

10. 10 Current nEDM experiment at ILL I Ramsey NMR performed Released from cell Neutrons spin analysed (# f n of precession) Repeat: E=↓or 0, B=↓ N S Magnetic shielding Storage cell UCN detector Approx scale 1 m Magnetic field coil B High voltage lead E Magnet & polarizing foil / analysing foil James KaramathUniversity of Sussex28/06/2015 20:08:36

11. 11 Current nEDM experiment at ILL II HV in B 0 field coils Ground electrode Neutron cell Mercury lamp light * Neutrons in/out * Mu-metal B-shields James KaramathUniversity of Sussex28/06/2015 20:08:36 Z

12. 12 Systematics I Reminder: B-field shifts correlated with E- field changes constitute false d n signal. Protect against incoming perturbations with mu-metal shields Measure changes IN cell with Mercury Cohabiting Magnetometer… James KaramathUniversity of Sussex28/06/2015 20:08:36 h( ν ↑↑ – ν ↑↓ ) = 2|μ n |(B ↑↑ –B ↑↓ ) – 4d n E

13. 13 Systematics II Hg EDM known to be below ~ 10 -28 ecm. Thus variations in mercury NMR signal are due to B-field fluctuations… Cohabiting Mercury Magnetometer James KaramathUniversity of Sussex28/06/2015 20:08:36

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

15. 15 Co-magnetometer correction Systematics III

16. 16 Co-magnetometer correction Systematics III

17. 17 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… Magnetometer problems Hg n z James KaramathUniversity of Sussex28/06/2015 20:08:36

18. 18 Systematics V Two conspiring effects  v x E: motional particle in electric field experiences B-field: ΔB ≈ v x E / c 2  Axial field gradient dB/dz creates radial B-field (since .B=0) proportional to r, B r  r Let’s look at motion of a mercury atom across the storage cell Geometric Phase Effect (GPE)

19. 19 Systematics VI Geometric Phase Effect (GPE) dB/dz → B  r B  v x E Scales with E like EDM!!! Scales with dB/dz (GPE Hg ~ 40GPE n ) Resultant i.e. B 0 field into page has gradient Shifts resonance of particle Using Mercury introduces error E and B 0 into page Rotating B field

20. 20 Systematics VII Other EffectShiftUncertainty Statistical01.51 Door cavity dipole; quadrupole fields-1.100.45 Other GP dipole shifts00.60 (E x v)/c 2 from translation00.05 (E x v)/c 2 from rotation00.10 Light shift: direct & GP0.350.08 B fluctuations00.24 E forces – distortion of bottle00.04 Tangential leakage currents00.01 AC B fields from HV ripple00.001 Hg atom EDM00.05 2 nd order Exv00.002 Total –0.751.51 stat, 0.80 sys GPE: J Pendlebury et al., Phys Rev A 70 032102, 2004

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

22. 22 The cryogenic nEDM experiment Reminder: RTCryo N /day6x10 6 ~6x10 8 T /s~130~250  0.75~0.9 E /kV/cm~12~50 (B 0 /μT15) ~10 -28 ecm * * with new beamline x20 x5* x2 x1.2 x4

23. 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 KaramathUniversity of Sussex28/06/2015 20:08:36

24. 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/cm 3 /sec). Also better guides – smoother & better neutron holding surfaces, Be / BeO / DLC → more neutrons guided/stored. Allows longer T too. James KaramathUniversity of Sussex28/06/2015 20:08:36

25. 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 KaramathUniversity of Sussex28/06/2015 20:08:36

26. 26 Polarisation and detection (α) II Detector: solid state, works in 0.5K He-II. n ( 6 Li, α) 3 H reaction - alpha and triton detected Thin, polarised Fe layer - spin analysis James KaramathUniversity of Sussex28/06/2015 20:08:36

27. 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 KaramathUniversity of Sussex28/06/2015 20:08:36

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

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

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

31. 31 Improving the E-field (↑E) IV Now have a 400 kV supply to connect to HV electrode. Will sit in 3bar SF 6.

32. 32 Magnetic field issues I Target – need ~ 100 fT stability (NMR) Need ~ 1 nT/m spatial homogeneity (GPE) Perturbations ~ 0.1 μT (buses!) Need (axial) shielding factor ~ 10 6 MMu-metal shielding~ 12 SSuperconducting shielding~ 8x10 5 AActive shielding (feedback coils)~ 15 Shielding factors

33. 33 Magnetic field issues II CRYOGENIC nEDM! Utilise superconducting shield and B 0 solenoid. MMajor part of fluctuations across whole chamber (common mode variations) MMagnetometer (zero E-field) cells see same VVery stable B 0 (t) current Holding field x5 to reduce GPE in the neutrons by factor of 25 (GPE n  1/B 0 2 ) Extra benefits James KaramathUniversity of Sussex28/06/2015 20:08:36 E

34. 34 Magnetic field issues III ~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) SQUIDS

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

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

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

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

39. 39 Schedule / Future Finish construction THIS SUMMER Start data taking THIS AUTUMN First results ~2008/9 Upgrade neutron guide to ↑N ~2009 ? James KaramathUniversity of Sussex28/06/2015 20:08:36

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

41. 41 Done! Thanks for listening