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

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: | d e | < 2.9 × e.cm (90%) – Sussex\RAL\ILL [PRL 97, (2006)] Electron: | d e | < 1.05 × e.cm (90%) – Imperial College [Nature 473, 493 (2011)] Multi Higgs Left - Right CMSSM Other SUSY Standard Model Predicted values for the electron edm d e (e.cm) eEDM limit

Measuring the EDM – spin precession B& E E Particle precessing in a magnetic field Particle precessing in parallel magnetic and electric fields Particle precessing in anti-parallel magnetic and electric fields Measure change in precession rate when electric field direction is reversed

Sensitivity Polarization fraction 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 electrode BeO spacers Ground electrodes Carbon-fibre support HV feed

Successfully produced, transported, stored UCN, but need to reduce losses Successfully applied 10 kV/cm (same as previous expt); aiming for kV/cm Achieved 60% polarisation in source, but must improve Previous measurement: 130 s. CryoEDM currently has 62 s cell storage time. Expect to improve. CryoEDM – sensitivity so far

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 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 CryoEDM – Plans

Imperial eEDM experiment – Technology Heavy, polar molecules enhance the electric field, E effective >> E applied. We use YbF molecules. E applied = 10 kV/cm, E effective = 14.5 GV/cm. Measure electron spin precession in a molecular beam experiment. Precession time, T~1ms.

Imperial eEDM – Current status 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) 2011 result: d e = (-2.4 ± 5.7 stat ± 1.5 syst ) × e.cm Statistics limited Systematic (rf polarization control & imperfect field-reversal) Stray Bx E direction E magnitude Stray By Pump pol. Probe pol. Pump freq Probe freq F=1 detect Max uncertainty ( e.cm) Imperfections emphasized

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 1/3 rd the speed Install additional magnetic shielding and investigate systematics Mid 2014: Measurement with uncertainty of 8 × e.cm Factor 8 better than 2011, limited by systematics; Potential for 3 × e.cm.

eEDM – Longer term Extend precession time from 1ms to 300ms by making a molecular fountain. Key is to cool molecules to 100  K. 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 × e.cm.

Conclusions EDMs offer great potential for discovering \ constraining new physics. Worldwide activity; many experimental searches for eEDM and nEDM (see UK teams have world-lead for both neutron and electron. Clear paths to improvement by factors of 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 Oak Ridge – expect 2020 turn on

Ongoing and future electron EDM experiments SystemWhere?Expected E eff (GV/cm) Comments YbFImperial College20Current best limit. New measurements and upgrades in progress. PbOYale26Cell expt. Fully polarized at low field. Internal co- magnetometer. Metastable state (82  s). Completed (final result expected soon). ThOHarvard & Yale collaboration (ACME) 104Cryogenic beam expt. Fully polarized at low field. Internal co-magnetometer. Metastable state (2ms). Under (rapid) development. WCMichigan54Ground-state. Fully polarized at low field. Internal co- magnetometer. Being developed. CsU. Texas & Penn. State 0.01New experiments being developed with optically trapped ultracold Cs. FrRCNP, Osaka0.1Radioactive. Experiment with ultracold 210 Fr being developed. HfF + JILA, Boulder18Ion trap experiment with rotating electric and magnetic fields. SolidsIndiana, Amherst Lots of electrons! Difficult to control systematic effects.

Precession frequency measured using Ramsey method

Neutrons in HV in CryoEDM – Technology

DateItem factorecm/year Comment 2002RT-edm 1.7E-26 Baseline 2010CryoEDM commission 1.7E Large-area detector E-25 Proven 2012HV to 70 kV E-25 OK to 50 kV, lab tests suggest should work at 70 kV 2012Repair detector valve E-25 Repair – should be fine 2012Polarisation 60% E-25 Seen in source. Should transfer ok to cells. 2012Aperture to 50 mm E-25 Will increase radiation levels slightly, but should be ok 2014New beam E-26 ILL produced this estimate 2014Ramsey time to 60 s E-26 Guaranteed with non-magnetic SCV 2014See alpha peak E-26 Peak now becoming visible above bkgd. Further development underway. 2014Recover missing input flux? E-26 Depends on geometry match to new beam. 2014Improve cell storage lifetime E-27 Not guaranteed, but haven't yet tried most obvious solutions (e.g. bakeout), so improvement likely 2014Match aperture to beam E-27 Likely 2015HV to 135 kV E-27 Requires pressurisation. Lab tests show this is realistic. 2015Four-cell system E-27 Guaranteed part of upgrade 2015Polarisation to 90% E-27 No known reason why not Inner supercond. shield Lab tests on scale model shows factor Cryogenics Included in upgrade Non-magnetic SCV Included in upgrade CryoEDM – Sensitivity timeline

CP violating term in QCD Lagrangian, parameter  Experimental nEDM limit gives |  |< For nEDM: Fine tuning of  strong CP problem Assume some mechanism suppresses  to zero Then, Standard model prediction < e.cm