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.