the cryogenic neutron edm experiment at ill and the result of the room temperature experiment james...
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The cryogenic neutron EDM experiment at ILL
and the result of the room temperature experiment
James Karamath
University of Sussex
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In this talk…
(n)EDM motivation & principles
Room-temperature nEDM experiment at ILL
Systematics
CryoEDM
Summary
James Karamath University of Sussex 18/04/23 10:06 PM
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(n)EDMs – so? I
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?
James Karamath University of Sussex 18/04/23 10:06 PM
n n
p
×
S+
-d
S
-
+
d
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(n)EDMs – so? II
Estimated EDMs model dependent SM dn ~ 10-31 ecm Other models typically 105-6 times greater
e.g. SUSY: CP < 10-2
quark electric dipole moments: q q
gaugino
squark
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nEDM measurement principle
B0 E<Sz> = + h/2
<Sz> = - h/2
h(0) = -2μ.B h()=2(-μ.B+dn.E)
h()=2(-μ.B-dn.E)
B0 B0 E
dn defined +ve
↑↑ - ↑↓= Δ = 4dn.E / h
Ramsey NMR performed on stored Ultra Cold Neutrons (UCN)
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nEDM statistical limit
Fundamental statistical limit
α = visibility [polarisation product]E = E-field strengthT = NMR coherence timeN = total # counted
NET
dn
2
~10-26ecm
James Karamath University of Sussex 18/04/23 10:06 PM
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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
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nEDM experiments: history
Co-magnetometer era
Cryogenic UCN era
RT stored UCN era
NET
hdn
2
Beam eraΔB ≈ v x E / c2 limited
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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
BE
Magnetic field coil
High voltage lead
James Karamath University of Sussex 18/04/23 10:06 PM
Magnetic shielding
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Current nEDM experiment at ILL I
Ramsey NMR performed
Released from cell Neutrons spin
analysed (# fn 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 Karamath University of Sussex 18/04/23 10:06 PM
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Current nEDM experiment at ILL II
HV in
B0 field coils
Ground electrode
Neutron cell
Mercury lamp light *
Neutrons in/out
*
Mu-metal B-shields
James Karamath University of Sussex 18/04/23 10:06 PM
Z
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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 18/04/23 10:06 PM
h(ν↑↑–ν ↑↓) = 2|μn|(B↑↑–B↑↓) – 4dnE
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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 Karamath University of Sussex 18/04/23 10:06 PM
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Co-magnetometer correction
0 5 10 15 20 2529.9260
29.9265
29.9270
29.9275
29.9280
29.9285
29.9290
29.9295
Ne
utr
on
re
son
an
t fr
eq
ue
ncy
(H
z)
Run duration (hours)
Electric Field
+-
Systematics III
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Co-magnetometer correction
0 5 10 15 20
7.7882
7.7884
7.7886
7.7888
7.7890
Run duration (hours)
Mer
cury
fre
quen
cy (
Hz)
Systematics III
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Co-magnetometer correctionSystematics III
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Systematics IV
However, not perfect correctionMercury 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 Karamath University of Sussex 18/04/23 10:06 PM
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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
Geometric Phase Effect (GPE)
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Systematics VI Geometric Phase Effect (GPE)
dB/dz → B r
B v x E Scales with E
like EDM!!!
Scales with dB/dz
(GPEHg ~ 40GPEn)
Resultant
i.e. B0 field into page has gradient
Shifts resonance of particle
Using Mercury
introduces error
E and B0 into page
Rotating B field
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Systematics VII Other
Effect Shift Uncertainty
Statistical 0 1.51Door cavity dipole; quadrupole fields -1.10 0.45Other GP dipole shifts 0 0.60(E x v)/c2 from translation 0 0.05(E x v)/c2 from rotation 0 0.10Light shift: direct & GP 0.35 0.08B fluctuations 0 0.24E forces – distortion of bottle 0 0.04Tangential leakage currents 0 0.01AC B fields from HV ripple 0 0.001Hg atom EDM 0 0.052nd order Exv 0 0.002
Total –0.75 1.51 stat, 0.80 sys
GPE: J Pendlebury et al., Phys Rev A 70 032102, 2004
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Final result
Room temperature experiment complete!Soon to be published result (PRL):
dn = (+0.61.5(stat) 0.8(syst)) x 10-26) ecm
i.e. |dn| < 3.0 x 10-26 ecm (90% CL)
New cryogenic experiment will eventually
be x100 more sensitive…
hep-ex/0602020 www.neutronedm.org
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The cryogenic nEDM experiment
Reminder: NET
dn
2
RT Cryo
N /day 6x106 ~6x108
T /s ~130 ~250
0.75 ~0.9
E /kV/cm ~12 ~50
(B0 /μT 1 5)
~10-28ecm
*
*with new beamline
x20 x5*
x2
x1.2
x4
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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 18/04/23 10:06 PM
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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 18/04/23 10:06 PM
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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 18/04/23 10:06 PM
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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 18/04/23 10:06 PM
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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 18/04/23 10:06 PM
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Improving the E-field (↑E) II
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
±HV
cryostat
He-II (T, purity…)
gap (d, V, spacers)
Sussex HV tests
~20cm
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Improving the E-field (↑E) IIIPast
literature
1
10
100
1000
0.0001 0.001 0.01 0.1 1 10
Electrode separation /cm
Bre
akd
ow
n V
olt
age
/kV
He-I data
4.2<T(K)<2.2
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Improving the E-field (↑E) IIIPast
literature
1
10
100
1000
0.0001 0.001 0.01 0.1 1 10
Electrode separation /cm
Bre
akd
ow
n V
olt
ag
e /kV
He-II data
2.2<T(K)<1.4
0.5K
1.8-2.1K
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Improving the E-field (↑E) IV
Now have a 400 kV supply to connect to HV electrode.
Will sit in 3bar SF6.
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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 ~ 106
Mu-metal shielding ~ 12 Superconducting shielding ~ 8x105
Active shielding (feedback coils) ~ 15
Shielding factors
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Magnetic field issues II
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/B0
2)
Extra benefits
James Karamath University of Sussex 18/04/23 10:06 PM
E
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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
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And so, the cryo-nEDM experiment I
n guide tubes + spin analyser
E ~ 60kV/cm
E = 0kV/cmSpin flipper coil (measure other spin)
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And so, the cryo-nEDM experiment II
HV electrode
Ground electrodes
HV in
z
Carbon fibre
support
BeO spacers
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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
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And so, the cryo-nEDM experiment IV
1m
Dynamic shielding coils
Magnetic (mu-metal) shields
Superconducting shield and solenoid
The shielded region
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Schedule / Future
Finish construction THIS SUMMERStart data taking THIS AUTUMNFirst results ~2008/9Upgrade neutron guide to ↑N ~2009 ?
James Karamath University of Sussex 18/04/23 10:06 PM
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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 10-26 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
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Done!
Thanks for listening