Transcript Neutron and electron EDMs Mike Tarbutt Centre for Cold Matter, Imperial College London. PPAP meeting, Birmingham, 18th September 2012

Neutron and electron EDMs
Mike Tarbutt
Centre for Cold Matter,
Imperial College London.
PPAP meeting, Birmingham, 18th September 2012
Motivation
• EDMs are sensitive to new CP violating physics
• Could help explain the baryon asymmetry in the universe
• Great potential for discovering \ constraining physics beyond the Standard Model
• Experiments already place severe constraints on possible models of new physics
Current experimental limits
Neutron: | de | < 2.9 × 10-26 e.cm (90%) – Sussex\RAL\ILL [PRL 97, 131801 (2006)]
Predicted values for the electron edm de (e.cm)
Electron: | de | < 1.05 × 10-27 e.cm (90%) – Imperial College [Nature 473, 493 (2011)]
10-22
10-24
10-26
10-28
CMSSM
Multi
Left Higgs
Right
Other
SUSY
10-30
10-32
10-34
10-36
Standard Model
eEDM limit
Measuring the EDM – spin precession
B& E
E
Particle precessing in
anti-parallel
parallel
a magnetic
magnetic
magnetic
fieldand
and
electric
electric
fields
fields
Measure change in precession rate when electric field direction is reversed
Sensitivity
sd =
Polarization
fraction
2a ET N
Electric
field
Spin precession
time
Number of
particles
+ good control over all systematic effects
CryoEDM: Sussex\RAL\ILL\Oxford\Kure nEDM
collaboration
• For nEDM measurement, key factor is high flux of ultracold neutrons
• New technology – ultracold neutrons in a bath of LHe at 0.5K
• Much higher flux (x100) of ultracold neutrons than in previous measurement
• Also expect longer storage times and higher electric fields
• SQUID magnetometers and low-temperature solid-state neutron detectors
Neutron
Liquid helium
HV feed
HV electrode
BeO spacers
Ground electrodes
Carbon-fibre support
CryoEDM – sensitivity so far
sd =
2a ET N
Achieved 60% polarisation in
source, but must improve
Successfully applied 10 kV/cm
(same as previous expt); aiming
for 20-30 kV/cm
Successfully produced,
transported, stored UCN,
but need to reduce losses
Previous measurement: 130 s.
CryoEDM currently has 62 s cell
storage time. Expect to improve.
CryoEDM – Plans
• Mid-2013: ILL shut down for a year; no neutrons.
• Late 2014 – move to new dedicated beamline - 4x more intense
• Upcoming PPRP request for major upgrades in 2013-2015
• Pressurise the liquid helium, upgrade from 2-cell to 4-cell system, superconducting
magnetic shield, non-magnetic superfluid containment vessel
• 2015 (assuming upgrades): factor of 10 improvement in statistical sensitivity over
previous measurement with corresponding reduction in systematics
Imperial eEDM experiment – Technology
• Heavy, polar molecules enhance the electric field, Eeffective >> Eapplied.
• We use YbF molecules. Eapplied = 10 kV/cm, Eeffective = 14.5 GV/cm.
• Measure electron spin precession in a molecular beam experiment.
• Precession time, T~1ms.
Imperial eEDM – Current status
2011 result: de = (-2.4 ± 5.7stat ± 1.5syst) × 10-28 e.cm
Statistics limited
Imperfections emphasized
Probe pol.
Pump pol.
E magnitude
Stray By
Stray Bx
F=1 detect
Probe freq
Pump freq
E direction
0 1 2 3 4 5 6
Max uncertainty (10-29 e.cm)
Systematic (rf polarization control &
imperfect field-reversal)
Since 2011 measurement:
• Longer interaction region, new magnetic
shields, new high-power rf amplifiers
• Started new measurement - reduce
uncertainty by factor of 3 (mid 2013)
• Completed systematic tests (emphasizing
various imperfections)
• New data-run about to begin (~6 months)
eEDM – Next steps
In 2013, after completing current measurement:
• Upgrade to new cryogenic source of YbF molecules
• Source already developed and tested – 10x the flux at 1/3rd the speed
• Install additional magnetic shielding and investigate systematics
• Mid 2014: Measurement with uncertainty of 8 × 10-29 e.cm
• Factor 8 better than 2011, limited by systematics; Potential for 3 × 10-29 e.cm.
eEDM – Longer term
• Extend precession time from 1ms to 300ms by making a molecular fountain.
• Key is to cool molecules to 100mK. Requires laser cooling.
• Laser cooling applied to molecules is a new technology that we are developing.
• Not yet funded; but most technical details already worked out.
• Reduce uncertainty below 1 × 10-30 e.cm.
Conclusions
• EDMs offer great potential for discovering \ constraining new physics.
• Worldwide activity; many experimental searches for eEDM and nEDM (see
http://nedm.web.psi.ch/EDM-world-wide/).
• UK teams have world-lead for both neutron and electron.
• Clear paths to improvement by factors of 10-100 in next 5 years.
• At this level, if there is new CP-violating physics, we should discover it.
Some other nEDM experiments
• PSI experiment – old Sussex apparatus - expect higher flux of neutrons
• Japanese \ Canadian consortium - under development
• Gatchina group working at ILL – resurrecting 1990 experiment
• US consortium @ Oak Ridge – expect 2020 turn on
Ongoing and future electron EDM experiments
System Where?
Expected
Eeff (GV/cm)
Comments
YbF
Imperial College
20
Current best limit. New measurements and upgrades
in progress.
PbO
Yale
26
Cell expt. Fully polarized at low field. Internal comagnetometer. Metastable state (82 ms). Completed
(final result expected soon).
ThO
Harvard & Yale
collaboration (ACME)
104
Cryogenic beam expt. Fully polarized at low field.
Internal co-magnetometer. Metastable state (2ms).
Under (rapid) development.
WC
Michigan
54
Ground-state. Fully polarized at low field. Internal comagnetometer. Being developed.
Cs
U. Texas & Penn.
State
0.01
New experiments being developed with optically
trapped ultracold Cs.
Fr
RCNP, Osaka
0.1
Radioactive. Experiment with ultracold 210Fr being
developed.
HfF+
JILA, Boulder
18
Ion trap experiment with rotating electric and
magnetic fields.
Solids
Indiana, Amherst
0.00003
Lots of electrons! Difficult to control systematic
effects.
Precession frequency measured using Ramsey method
CryoEDM – Technology
HV in
Neutrons
in
CryoEDM – Sensitivity timeline
Date
Item
factor
ecm/year
Comment
2002 RT-edm
1.7E-26 Baseline
2010 CryoEDM commission
1.7E-24
2012 Large-area detector
3.5
2012 HV to 70 kV
1.6
2012 Repair detector valve
1.3
2012 Polarisation 60%
1.5
2012 Aperture to 50 mm
1.2
2014 New beam
2.0
2014 Ramsey time to 60 s
1.8
2014 See alpha peak
1.4
3.9E-26 Guaranteed with non-magnetic SCV
2.7E-26 Peak now becoming visible above bkgd. Further development underway.
2.2
1.2E-26
1.5
8.3E-27
1.3
6.4E-27
1.9
3.3E-27 Requires pressurisation. Lab tests show this is realistic.
2.3E-27 Guaranteed part of upgrade
2014 Recover missing input
flux?
2014 Improve cell storage
lifetime
2014 Match aperture to
beam
2015 HV to 135 kV
2015 Four-cell system
1.4
2015 Polarisation to 90%
1.5
2013-15 Inner supercond. shield
4.9E-25 Proven
3.1E-25 OK to 50 kV, lab tests suggest should work at 70 kV
2.5E-25 Repair – should be fine
1.7E-25 Seen in source. Should transfer ok to cells.
1.4E-25 Will increase radiation levels slightly, but should be ok
7.0E-26 ILL produced this estimate
Depends on geometry match to new beam.
Not guaranteed, but haven't yet tried most obvious solutions (e.g. bakeout), so
improvement likely
Likely
1.6E-27 No known reason why not
Lab tests on scale model shows factor 500
2013-15 Cryogenics
Included in upgrade
2013-15 Non-magnetic SCV
Included in upgrade
For nEDM:
CP violating term in QCD Lagrangian, parameter q
Experimental nEDM limit gives |q|<10-10
Fine tuning of q - strong CP problem
Assume some mechanism suppresses q to zero
Then, Standard model prediction < 10-32 e.cm