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
James Karamath University of Sussex 30/06/2006 10:13:34 2 S S (n)EDMs – so? I + + d d - - P- and T-violating
CPV in SM not fully understood e.g. insufficient CPV for baryon asymmetry
γ Strong CP problem π − -10 θCP < 10 rad. Axions? n × p n
James Karamath University of Sussex 30/06/2006 10:13:34 3 (n)EDMs – so? II
Estimated EDMs model dependent -31 SM dn ~ 10 ecm Other models typically 105-6 times greater
-2 e.g. SUSY: ϕCP < 10
squark γ quark electric dipole moments: qqgaugino
4 nEDM measurement principle
B0 B0 E B0 E
dn defined +ve
ν↑↑ - ν↑↓= Δν = 4dn.E / h
Ramsey NMR performed on stored Ultra Cold Neutrons (UCN) 5 nEDM statistical limit
Fundamental statistical limit
δ ()d = h n 2α NET
α = visibility [polarisation product] E = E-field strength ~10-26ecm T = NMR coherence time N = total # counted
James Karamath University of Sussex 30/06/2006 10:13:34 6 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
False signal due True nEDM to varying B signal ☺
7 h δ ()d = nEDM experiments: history n 2α NET
Beam era ΔB ≈ v x E / c2 limited
RT stored UCN era
Co-magnetometer era
Cryogenic UCN era 8 Current nEDM experiment at ILL I
Magnetic High voltage lead Create UCN, can then shielding Magnetic be guided & stored Storage field coil cell Polarise UCN E B UCN admitted into cell with E and B-
fields and stored… Approx scale 1 m Magnet & polarizing foil / S N Mercury polarised by analysing foil Hg lamp and added to
cell UCN
James Karamath University of Sussex 30/06/2006 10:13:34 9 Current nEDM experiment at ILL I
Magnetic High voltage lead Ramsey NMR shielding Magnetic field coil performed Storage Released from cell cell E B Neutrons spin analysed (# fn of
precession) Approx scale 1 m Magnet & Repeat: E=↓or 0, B=↓ polarizing foil / S N analysing foil
UCN detector
James Karamath University of Sussex 30/06/2006 10:13:34 10 Current nEDM experiment at ILL II
Mu-metal B-shields HV in
B field coils 0 Z
Neutron cell *
Mercury lamp light *
Ground electrode Neutrons in/out
James Karamath University of Sussex 30/06/2006 10:13:34 11 Systematics I h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE
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 30/06/2006 10:13:34 12 Cohabiting Mercury Systematics II Magnetometer
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 30/06/2006 10:13:34 13 Co-magnetometer Systematics III correction
29.9295
29.9290
29.9285 Electric Field 29.9280 +
29.9275 -
29.9270
Neutron resonant frequency (Hz) 29.9265
29.9260 0 5 10 15 20 25 Run duration (hours)
14 Co-magnetometer Systematics III correction
7.7890
7.7888
7.7886
7.7884 Mercury frequencyMercury (Hz)
7.7882
0 5 10 15 20 Run duration (hours)
15 Co-magnetometer Systematics III correction
29.9295 Raw neutron frequency Corrected frequency 29.9290
29.9285
29.9280 -10 ΔB = 10 T 29.9275
29.9270
29.9265
Precession frequency (Hz)Precession frequency 29.9260 0 5 10 15 20 25 Run duration (hours) 16 Systematics IV Magnetometer problems
However, not perfect correction Mercury fills cell uniformly, UCN sag under gravity, lower by ~3 mm.
z Hg n
Thus don’t sample EXACTLY the same B- field. Axial (z) gradients → problems…
James Karamath University of Sussex 30/06/2006 10:13:34 17 Systematics V Geometric Phase Effect (GPE)
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 α r
Let’s look at motion of a mercury atom
across the storage cell 18 Systematics VI Geometric Phase Effect (GPE)
Scales with E B α v x E like EDM!!! dB/dz → B α r Scales with
i.e. B0 field into dB/dz page has gradient (GPE ~ Resultant Hg 40GPEn) Rotating B field
Using Shifts Mercury E and B0 resonance into page introduces ν of particle error 19 GPE: J Pendlebury et al., Other Systematics VII Phys Rev A 70 032102, 2004
Effect Shift Uncertainty Statistical 0 1.51 Door cavity dipole; quadrupole fields -1.10 0.45 Other GP dipole shifts 0 0.60 (E x v)/c2 from translation 0 0.05 (E x v)/c2 from rotation 0 0.10 Light shift: direct & GP 0.35 0.08 B fluctuations 0 0.24 E forces – distortion of bottle 0 0.04 Tangential leakage currents 0 0.01 AC B fields from HV ripple 0 0.001 Hg atom EDM 0 0.05 2nd order Exv 0 0.002 Total –0.75 1.51 stat, 0.80 sys 20 hep-ex/0602020 Final result www.neutronedm.org
Room temperature experiment complete! Soon to be published result (PRL):
-26 dn = (+0.6±1.5(stat) ±0.8(syst)) x 10 ) ecm
-26 i.e. |dn| < 3.0 x 10 ecm (90% CL)
New cryogenic experiment will eventually be x100 more sensitive… 21 The cryogenic nEDM experiment
Reminder: δ ()d = h n 2α NET RT Cryo N /day 6x106 ~6x108 * x20 x5* T /s ~130 ~250 x2 -28 α 0.75 ~0.9 x1.2~10 ecm E /kV/cm ~12 ~50 x4
(B0 /μT1 5) *with new beamline 22 Improved production of UCN (↑N) I
Crosses at 0.89nm Dispersion curves for He-II and for free (cold) n. free neutrons Neutron loses all energy by phonon emission → UCN. Reverse suppressed by Boltzmann factor, He-II is at 0.5K, no 12K phonons. James Karamath University of Sussex 30/06/2006 10:13:34 23 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 30/06/2006 10:13:34 24 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 30/06/2006 10:13:34 25 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 30/06/2006 10:13:34 26 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 30/06/2006 10:13:34 27 Sussex HV Improving the E-field (↑E) II tests
Test electrodes ±HV submerged in He-II in E bath cryostat. cryostat
Studying Vmax and Ileak as function of d, T, dielectric spacers, purity… up to 130 kV. gap (d, V, spacers) Some similar(ish) past data but varied He-II (T, purity…) results. ~20cm 28 Past Improving the E-field (↑E) III literature
1000
He-I data 4.2 100 10 Breakdown Voltage /k 1 0.0001 0.001 0.01 0.1 1 10 Electrode separation /cm 29 Past Improving the E-field (↑E) III literature 1000 0.5K He-II data 2.2 10 Breakdown Voltage /k 1 0.0001 0.001 0.01 0.1 1 10 Electrode separation /cm 30 Improving the E-field (↑E) IV Now have a 400 kV supply to connect to HV electrode. Will sit in 3bar SF6. 31 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 32 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 2 neutrons by factor of 25 (GPEn α 1/B0 ) James Karamath University of Sussex 30/06/2006 10:13:34 33 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 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 And so, the cryo-nEDM experiment II HV electrode HV in Carbon fibre support z BeO spacers Ground electrodes 36 And so, the cryo-nEDM experiment III HV electrode G10 HV in Superfluid containment vessel * * z Neutrons in/out 250l He-II 0.5K Ground electrodes * BeO spacers/guides 37 The shielded region And so, the cryo-nEDM experiment IV Dynamic shielding coils Magnetic (mu- metal) shields Superconducting shield and solenoid 1m 38 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 30/06/2006 10:13:34 39 Summary (n)EDMs help study T-violation and are constraining new physics. Systematics of RT-nEDM experiment well understood. -26 Final RT result: |dn| < 3.0 x 10 ecm. 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 40 Done! Thanks for listening 41