CryoEDM – A Cryogenic Neutron-EDM Experiment Collaboration: Sussex University, RAL, ILL, Kure...
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Transcript of CryoEDM – A Cryogenic Neutron-EDM Experiment Collaboration: Sussex University, RAL, ILL, Kure...
CryoEDM – A Cryogenic Neutron-EDM Experiment
Collaboration:
Sussex University, RAL, ILL, Kure University, Oxford University
Hans Kraus
… but before: some advertising for
EURECA
• Based on CRESST-II and EDELWEISS-II expertise, with additional groups joining
• Baseline targets: Ge, CaWO4 (A dependence)
• Mass: above 100 kg
• Timescale: continue CRESST-II and EDELWEISS-II
• Started 17 March 2005
• EURECA R&D = demonstrate CRESST/EDELWEISS
European Underground Rare Event Calorimeter Array
• England
• Oxford (H Kraus, coordinator)
• Germany
• Max-Planck Institut f. Physik, Munich
• Technische Universität München
• Universität Tübingen
• Karlsruhe Universität
• Forschungszentrum Karlsruhe
• France
• CEA/DAPNIA Saclay
• CEA/DRECAM Saclay
• CNRS/CRTBT Grenoble
• CNRS/CSNSM Orsay
• CNRS/IPNL Lyon
• CNRS/IAP Paris
• CERN
CRESST + EDELWEISS + new forces
EURECA Collaboration
• Why EDM? - Theoretical Background
• The Method of Ramsey Resonance
• Room-temperature Experiment
• Ultra-Cold Neutrons
• The Cryogenic Experiment
Back to nEDMOverview
C particle antiparticle (Q→−Q)
P position inverted (r →−r)
T time reversed (t→−t)
Fundamental Inversions
Symmetries
Weak interactions are not symmetric under P or CNormal matter - n, , - readily breaks C and P symmetry.
The combination CP is differentNormal matter respects CP symmetry to a very high degree.
Time reversal T is equivalent to CP (CPT theorem)Normal matter respects T symmetry to a very high degree.
EDM breaks P and T Symmetry
spin
(P no big deal) (CP big deal)
+−
−+
P +−
−+T
P odd T odd
(assuming CPT invariance)
n n d ˆd sneutron EDM:
Overview • SM contribution is immeasurably small, but...
• most models beyond SM predict values about 106 greater than SM. Very low background!
• EDM measurements already constrained SUSY models.
• “Strong CP Problem”: Why does QCD not violate CP? Nobody knows.
• Finally, there is the question of baryon – anti-baryon asymmetry in the universe.
Two Motivations to Measure EDM
EDM is effectively zero in standard modelbut
big enough to measure in non-standard models
Direct test of physics beyond the standard model
EDM violates T symmetry
Deeply connected to CP violation and the matter-antimatter asymmetry of the Universe
A Bit of History E
xper
imen
tal L
imit
on
d (
e.cm
)
1960 1970 1980 1990
neutron:
electron:
2000
10-20
10-30
10-22
10-24
10-26
10-28
Left-Right
10-32
10-20
10-22
10-24
10-30
Multi Higgs
SUSY
Standard Model
Electro-magnetic
10-34
10-36
10-38
dn makes precessionfaster...
... or slower.
Measurement Principle
B E
B
Measure Larmor spin precession frequency in parallel & antiparallel B and E fields:
Measurement Principle
2 2
2 2
4 /
W
W
h
n
n
n
n
n
d
d
d
μ B E
μ B E
E
Apply constant magnetic field, alternate electric field:
Measure difference in precession frequency and find Electric Dipole Moment
The Neutron Mirror >> interatomic spacing; neutrons see Fermi potential VF
Critical velocity for reflection:
½mvc2 = VF
UCN: v 6 m/s: total internal reflection possible.n
n
ns
s
B
vc depends on orientation of neutron spin, so can polarise
by transmission.
Ramsey’s Technique
4.
3.
2.
1.
Free precession...
Apply /2 spinflip pulse...
“Spin up” neutron...
Second /2 spinflip pulse.
Ramsey Resonance Phase gives frequency offset from resonance.
The Room Temperature Experiment
N S
Four-layer mu-metal shield High voltage lead
Quartz insulating cylinder
Coil for 10 mG magnetic field
Upper electrodeMain storage cell
Hg u.v. lamp
PMT to detect Hg u.v. light
Vacuum wall
Mercury prepolarising cell
Hg u.v. lampRF coil to flip spins
Magnet
UCN polarising foil
UCN guide changeover
Ultracold neutrons
(UCN)
UCN detector
The Measurement
Mercury Magnetometry
PMT
Polarized mercury atoms
With Magnetometer
False EDM Signals
2
1 =
from div = 0 from spec. rel.
r
BB r
z c
v EB
B
Different for 199Hg and neutrons
see: Phys. Rev. A 70, 032102 (2004)
Need for precise magnetometry
Room Temperature Results E = 4.5 kV/cm
B = 1 T
Tcoherence ~ 130 s
Hg co-magnetometer
(B measured to 1 pT rms)
Neutron edm result: Phys. Rev. Lett. 82, 904 (1999)
|dn|< 6.310-26 e cm
Ultra-cold Neutron Production
1.03 meV (11K) neutrons down-scatter by emission of phonons in superfluid helium at 0.5K
Up-scattering suppressed: hardly any 11K phonons
cold neutron
ultra-cold neutron
phonon
λn = 8.9Å; E = 1.03meV
Ultra-cold Neutron Production
0.91±0.13 UCN cm−3 s−1 observed
C A Baker et al., Phys. Lett. A 308 (2002) 67
cold neutron
ultra-cold neutron
phonon
The Cryogenic Setup
The Ramsey Cell
Ultra-cold Neutron Detection • ORTEC ULTRA at 430mK temperature.
• Equipped with thin surface layer of 6Li.
• Using: n + 6Li → α + 3H2.73MeV triton-peak
α-peak in noise
Improvements on Statistics / 2
D ET N
• Polarisation+detection = 0.75 x 1.5• Electric field: E = 106 V/m x 2.0• Precession period: T = 130 s x 1.8• Neutrons counted: N = 6 x 106 /day x 14.9
(with new beamline) x 2.6
Item RT Expt Increase
Total improvement = x80 (x200)
Superconducting Shield
SQUIDS from CRESST
SQUIDs for Magnetometry
-4
-3
-2
-1
0
1
2
3
4
5
6
7
-6 -5 -4 -3 -2 -1 0
Time [s]
SQ
UID
Ou
tpu
t [V
]
Nb short
Cu short
1
LR
LR
jV j
jZ R j L R j LI
L
Motivation: no contact resistance
-0.02
-0.015
-0.01
-0.005
0
0.005
0.01
0.015
0.02
0 4 8 12 16
Time [s]
Sq
uid
4 +
Sq
uid
5 [
V]
0
1
2
3
4
5
6
0 4 8 12 16
Time [s]
Sq
uid
OP
[V
]
SQUID 5
SQUID 4
SQUID 4 + SQUID 5
Resolution 0.16 pT (1.6nG) @ 1Hz
Magnetometry Tests
Pickup Loop
SQUIDs
4 5
Reality Check
x
-e
+e
If neutrons were the size of the Earth …
… then current EDM limit means charge separation of Δx ≈ 3μm
Summary
• After half a century, no sign of an EDM …
• SUSY being squeezed. Ever-tighter limits continue to constrain physics beyond SM.
• Room-temperature experiment finished.
• CryoEDM: under construction with aim of ~100 improvement in sensitivity.