The Search for the Neutron Electric Dipole Moment

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Samuel Allison
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ue Langevin R.A.L. /Sussex/ILL/Kure /Sussex/ILL collaboration Tony Baker David Shiers Keith Green Peter Geltenbort Maurits van der Grinten* Hajime Yoshiki Philip Harris Dave Wark* Plamen

1 The Search for the Neutron Electric Dipole Moment University of Sussex Rutherford Appleton Laboratory Institut Laue Langevin R.A.L. /Sussex/ILL/Kure /Sussex/ILL collaboration Tony Baker David Shiers Keith Green Peter Geltenbort Maurits van der Grinten* Hajime Yoshiki Philip Harris Dave Wark* Plamen Iaydjiev Mark Tucker Sergei Ivanov Mike Pendlebury Sergey Balashov RAL Sussex ILL Kure * joint appointment Sussex-RAL (1/3-2/3) Grenoble Institut Laue Langevin ( Alpes ) Motivation The nedm experiment on PF2: o Experiment vs Theory o Measurement principle o Experimental set-up o Data & Results Cryogenic nedm R&D running at PF1 o Superthermal UCN source o UCN production & detection in superfluid helium o Outlook Conclusions Brighton Sussex University (Fat Boy Slim) 1

2 The Neutron Electric Dipole Moment: d n d n 0 P and T violation q T reversal -q d n S +q -q d n S CP & T violation observed in K decay, Belle & BaBar d n 0 electric dipole moment d n spin S +q -q P transform. -q d n S +q d n S P & T violation CPT conservation CP violation The neutron EDM: exp. vs theory Progress at ~ order of magnitude per decade Standard Model out of reach strong constraints on e.g. Super Symmetry -e +e 1 cm d n = 1 e cm d n < e cm (90% CL) 2

3 d 26 N < 6.3 ecm Strong d 16 N ~ θ 2 ecm θ < 9 Strong CP problem Electroweak d N 2 c s c s c s sinδ CKM No problem but d N ~ 32 ecm what about baryon asymmetry? Supersymmetric GeV dn ~ 2 sin A, B m~ Φ 2 23 ecm sin ΦA, B ~ m~ ~ TeV 2 Supersymmetric CP problem Compare the precession frequency for parallel fields: Experiments: Measurement of Larmor precession frequency of polarised neutrons in a magnetic & electric field σ ( d n ) = 2 αet N α: polarisation product E: electric field T: observation time N: number of neutrons ν = E /h = [-2B 0 µ n - 2Ed n ]/h to the precession frequency for anti-parallel fields The difference is proportional to d n and E: h(ν - ν ) = 4E d n ν = E /h = [-2B 0 µ n + 2Ed n ]/h 3

4 Measuring the neutron Larmor precession frequency: Turn polarised neutron by /2 rf pulse Neutron and rf precess separately Turn neutron again by a 2 nd /2 rf pulse Analyse spin if in phase neutron ends up anti-parallel If there is a difference in ν L and ν RF a phase difference will accumulate and 2 nd rf pulse will not take the neutron fully anti-parallel to B 0 4

same volume as neutrons PMT measures signal of

5 Measuring the mercury Larmor precession frequency: Turn polarised 199 Hg by /2 rf pulse Hg precesses in same volume as neutrons PMT measures signal of reading bulb Fit signal to decaying sine curve The ILL Reactor 5

6 6

24000 Ramsey Resonance Curve 1/T s 22000 neutron spin up count 20000 18000 16000 14000

7 24000 Ramsey Resonance Curve 1/T s neutron spin up count working points resonance frequency applied frequency [Hz] 7

8 Neutron resonant frequency (Hz) T Run duration (hours) Data Analysis Fit data to pair of cosine curves. Fitted curves slide sideways to match each data point in turn: each point then yields a unique resonant frequency. Plot freq. shift vs. applied E-field: slope of fitted line yields EDM 8

9 σ ( 26 d n ) = 1.5 ecm σ ( d n ) = 2 αet N Optimum performance Further progress Electric field E = 11 kv/cm α ~ 0.85 (P = 92%) T s ~ 130 sec. N = = ev s A MUCH stronger UCN source is required 9

10 rthermal UCN production ub and J.M. Pendlebury Phys. Lett. 53A (1975) high UCN densities obtainable if medium in storage vessel 1. has small neutron absorption 2. V F medium << V F walls 3. one single state with excitation energy E >> T >> E U ub and J.M. Pendlebury Phys. Lett. 62A (1977) Isotopically pure 4 He 1. σ abs = 0 2. V F 4 He = 21 nev 3. Pure coherent scattering ρ UCN 4 7 n/cm 3 (several litres of liquid He, T < 1K, inside a 20K cold source in a reactor) ρ UCN 3 3 n/cm 3 (end of neutron guide) Energy momentum dispersion curve main process: one phonon downscattering Production rate one-phonon interaction: = Φ λ λ * cm 3 s 1 single phonon, multiple phonon & roton interaction:

11 Storing superthermal UCN limited by: Storage lifetime (one-phonon upscattering only) neutron lifetime 4 He purity storage volume wall = A exp + absorption cross section τ T τ 0 upscattering storage time vs helium temperature: 11

A 125 (1987) the factor of 50 discrepancy between the production rate deduced from the present upscattering measurements and that from the UCN measurements is thought to be due to the losses in the

12 ILL Sussex Experiments on superthermal UCN production in 4 He P. Ageron et al. Phys. Lett. 66A (1978) transmission of 0.17 ±?? C. Jewell et al. Physica 7B (1981) we have not measured the transmission of this UCN transport system R. Golub et al. Z. Phys. B 51 (1983) transmission of windows 0.08 ±?? I. Kilvington et al. Phys. Lett. A 125 (1987) the factor of 50 discrepancy between the production rate deduced from the present upscattering measurements and that from the UCN measurements is thought to be due to the losses in the UCN extraction system H. Yoshiki et al. Phys. Rev. Lett. 68 (1992) attenuation aluminium windows 0.25 ±?? the poor ratio of the detected UCN to the expected UCN in this experiment is not well understood. We are left with an unresolved attenuation factor of about 0 in order of magnitude UCN produced alright extraction uncertainties absolute production rate? Good basis for new nedm exp t??? 12

isotopically pure superfluid He Contain ultracold neutrons within Be Detect UCN in situ stainless

13 7 mm cold neutron beam 326 mm Be foil Be foil 6 LiF UCN production volume superfluid 4 He superconducting level meter detector assembly electric feedthrough Cold neutron beam through isotopically pure superfluid He Contain ultracold neutrons within Be Detect UCN in situ stainless steel Ø=67mm, L=326mm Ø=mm escape aperture 2500 Å beryllium coating 0.25mm beryllium windows 1.2mm 6 LiF plastic (67%) 13

14 Solid state UCN detectors: n 3 H surface barrier detector B & 6 Li converters EDM UCN flux monitor UCN spectrum analysis α 6 LiF foil MCA α 3 H 2.05 MeV 2.73 MeV shutter closed open cold neutrons UCN phonon Record the number of neutrons as a function of time during filling/emptying 14

Pulse Height Analysis of cryogenic UCN detectors 1.0 0.9 0.8 0.7 0.6 Yield 0.5 0.4 0.3 0.2 0.1 0.

15 Pulse Height Analysis of cryogenic UCN detectors Yield channel neutron count K 2.05 K UCN/cycle to detection chamber ρ ~ 2 UCN/cc [τ = sec] cold neutron beam open to liquid helium time [sec] cold neutron beam closed to liquid helium 15

16 00 0 storage time-temperature T=0.43K T=1.00K T=1.30 K T=1.44K storage time τ [sec] experimental data single phonon interaction only 9 single & multiple phonon 8 & roton interaction temperature [K] 1800 neutron count Å 5 Å 5.5 Å 6 Å 6.5 Å 7 Å 7.5 Å 8 Å 8.5 Å 9.0 Å 9.5 Å Å.5 Å 11.0 Å no velocity selector wavelength [Å] 16

200 UCN produced at 8.9 Å at 2 UCN/sec neutron count 150 0 50 4.5 Å 6.0 Å 8.5 Å 9.0 Å R = (0.91 ± 0.13) cm -3 sec -1 Expected rate: R I = (1.19± 0.

17 200 UCN produced at 8.9 Å at 2 UCN/sec neutron count Å 6.0 Å 8.5 Å 9.0 Å R = (0.91 ± 0.13) cm -3 sec -1 Expected rate: R I = (1.19± 0.18) UCN cm -3 s -1 (gold foil activation measurements dφ/dλ = (2.88 ± 0.39) 7 neutrons cm -2 s -1 Å -1 ) channel ~ 25% of UCN produced by multiple phonon/roton interaction UCN count wavelength [Å] Superthermal UCN created at ~ 50 UCN/cc higher densities within reach Cryogenic UCN detectors have been developed and are operational within superfluid helium 80% efficient UCN production mechanism established ~75% from 9Å neutrons ~25% from 4Å - 7Å Polarisation of UCN in superthermal source Separate filling/storing/emptying of production volume long depolarisation times cryogenic UCN valve system UCN spectrum as produced by down-scattering extracting UCN into room temp. apparatus Enlarge production volume minimise dilution effect Superconducting magnetic shielding, B 0 NMR with neutrons 17

In conclusion: Room temperature: close to concluding data acquisition sensitivity ~ 1.

method demonstrated 3 years of capital construction phase sensitivity ~ -27-28 ecm

18 In conclusion: Room temperature: close to concluding data acquisition sensitivity ~ ecm cryoedm: superthermal UCN production/detection R&D concluded viability of method demonstrated 3 years of capital construction phase sensitivity ~ ecm capital constr./exploitation a very big effort for a very small number The impact is HUGE 18

CryoEDM: a cryogenic experiment to measure the neutron Electric Dipole Moment

CryoEDM: a cryogenic experiment to measure the neutron Electric Dipole Moment C A Baker, S N Balashov, V Francis, K Green, M G D van der Grinten, P S Iaydjiev 1, S N Ivanov 2, A Khazov 3, M A H Tucker