The cryogenic neutron EDM experiment at ILL

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Stanley Little
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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 30/06/ :13:34 2

3 (n)edms so? I + S + S P- and T-violating - d - d CPV in SM not fully understood e.g. insufficient CPV for baryon asymmetry Strong CP problem θ CP < rad. Axions? n π p γ n James Karamath University of Sussex 30/06/ :13:34 3

4 (n)edms so? II Estimated EDMs model dependent SM d n ~ ecm Other models typically times greater e.g. SUSY: ϕ CP < 10-2 quark electric dipole moments: q squark gaugino γ q 4

5 nedm measurement principle <S z > = + h/2 B 0 B 0 E B 0 E <S z > = - h/2 hν(0) = -2μ.B hν( )= 2(-μ.B+d n.e) hν( )= 2(-μ.B-d n.e) d n defined +ve ν - ν = Δν = 4d n.e / h Ramsey NMR performed on stored Ultra Cold Neutrons (UCN) 5

6 nedm statistical limit Fundamental statistical limit δ h d = n αet ( ) 2 N α = visibility [polarisation product] E = E-field strength T = NMR coherence time N = total # counted ~10-26 ecm James Karamath University of Sussex 30/06/ :13:34 6

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 False signal due to varying B True nedm signal 7

8 nedm experiments: history δ ( ) d n = h 2αET N Beam era ΔB v x E / c 2 limited RT stored UCN era Co-magnetometer era Cryogenic UCN era 8

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 Magnetic shielding Storage cell Magnet & polarizing foil / analysing foil S E B N High voltage lead Magnetic field coil Approx scale 1 m UCN James Karamath University of Sussex 30/06/ :13:34 9

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= Magnetic shielding Storage cell Magnet & polarizing foil / analysing foil S E B N High voltage lead Magnetic field coil Approx scale 1 m UCN detector James Karamath University of Sussex 30/06/ :13:34 10

11 Current nedm experiment at ILL II Mu-metal B-shields HV in B 0 field coils Z Neutron cell * Mercury lamp light * Ground electrode Neutrons in/out James Karamath University of Sussex 30/06/ :13:34 11

12 Systematics I h(ν ν ) = 2 μ n (B B ) 4d n E 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 Karamath University of Sussex 30/06/ :13:34 12

13 Systematics II Cohabiting Mercury Magnetometer Hg EDM known to be below ~ ecm. Thus variations in mercury NMR signal are due to B-field fluctuations James Karamath University of Sussex 30/06/ :13:34 13

14 Systematics III Co-magnetometer correction Neutron resonant frequency (Hz) Electric Field Run duration (hours) 14

15 Systematics III Co-magnetometer correction Mercury frequency (Hz) Run duration (hours) 15

16 Systematics III Co-magnetometer correction Precession frequency (Hz) Raw neutron frequency Corrected frequency ΔB = T Run duration (hours) 16

Hg z n Thus don t sample EXACTLY the same B- field.

17 Systematics IV Magnetometer problems However, not perfect correction Mercury fills cell uniformly, UCN sag under gravity, lower by ~3 mm. Hg z n Thus don t sample EXACTLY the same B- field. Axial (z) gradients problems James Karamath University of Sussex 30/06/ :13:34 17

18 Systematics V Geometric Phase Effect (GPE) 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 α r Let s look at motion of a mercury atom across the storage cell 18

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

20 Systematics VII GPE: J Pendlebury et al., Other Phys Rev A , 2004 Effect Shift Uncertainty Statistical Door cavity dipole; quadrupole fields Other GP dipole shifts (E x v)/c 2 from translation (E x v)/c 2 from rotation Light shift: direct & GP B fluctuations E forces distortion of bottle Tangential leakage currents AC B fields from HV ripple Hg atom EDM 2 nd order Exv Total stat, 0.80 sys 20

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

22 The cryogenic nedm experiment Reminder: δ h d = n αet ( ) 2 N RT Cryo N /day 6x10 6 ~6x10 8 T /s ~130 ~250 α 0.75 ~0.9 E /kv/cm ~12 ~50 (B 0 /μt 1 5) * x20 x5* x2 x1.2 ~10-28 ecm x4 *with new beamline 22

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 30/06/ :13:34 23

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 Karamath University of Sussex 30/06/ :13:34 24

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 30/06/ :13:34 25

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 Karamath University of Sussex 30/06/ :13:34 26

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 30/06/ :13:34 27

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

29 Improving the E-field ( E) III Past literature 1000 He-I data 4.2<T(K)<2.2 Breakdown Voltage /kv Electrode separation /cm 29

30 Improving the E-field ( E) III Past literature 1000 He-II data 0.5K 2.2<T(K)<1.4 Breakdown Voltage /kv K Electrode separation /cm 30

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

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 ~ 10 6 Mu-metal shielding ~ 12 Superconducting shielding ~ 8x10 5 Active shielding (feedback coils) ~ 15 32

33 E Magnetic field issues II Extra benefits CRYOGENIC nedm! Utilise superconducting shield and B 0 solenoid. Major part of fluctuations across whole chamber (common mode variations) Magnetometer (zero E-field) cells see same Very stable B 0 (t) current Holding field x5 to reduce GPE in the neutrons by factor of 25 (GPE n α 1/B 02 ) James Karamath University of Sussex 30/06/ :13:34 33

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) 34

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) 35

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

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

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

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 30/06/ :13:34 39

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 ecm. Cryo-nEDM project starts this Autumn, 2008/9 brings ~ mid ecm results. New beamline for low ecm. hep-ex/ (RT result) 40

41 Done! Thanks for listening 41

CryoEDM The search for the electric dipole moment of the neutron

CryoEDM The search for the electric dipole moment of the neutron RAL, STFC Sussex University Oxford University ILL Kure University Swansea University Dr Christine Clarke1 4/19/2011 CryoEDM Motivation (CPV)