Neutron Electric Dipole Moment, Present Experiment at ILL, Grenoble, and Future Prospects

The Search for Neutron Electric Dipole Moment, present experiment at ILL, Grenoble, and future prospects

Plamen IAYDJIEV - INRNE – Sofia,Bulgaria and RAL, UK nEDM experiment - Rutherford Appleton Laboratory - University of Sussex - ILL C.A. Baker, K. Green, P. Geltenbort, M.G.D. van der Grinten, P.G. Harris, P.S. Iaydjiev, S.N. Ivanov, J.M. Pendlebury, D.B. Shiers, D. Wark

CryoEDM experiment - Rutherford Appleton Laboratory - University of Sussex – ILL – University of Kure – University of Oxford

R.A.L. /Sussex/ILL/ - C.A. Baker, K. Green, P. Geltenbort, M.G.D. van der Grinten, P.G. Harris, P.S. Iaydjiev, S.N. Ivanov, J.M. Pendlebury, D.B. Shiers, D.Wark

University of Kure (Japan) H. Yoshiki RAL - M.A.H Tucker, S.N. Balashov, V. Francis University of Sussex - M. Hardiman, P. Smith, J. Grozier, K. Zuber University of Oxford H. Kraus, B. Majorovits, N. Jelley, U. Divaker The Search for Neutron Electric Dipole Moment at ILL…

nEDM experiment 1.Why we need to measure neutron EDM 2.Measurement principle 3. nEDM apparatus 4.Magnetometry – Hg comagnetometer 5. Statistical and systematical errors

CryoEDM experiment 1. Why superfluid Helium 2. UCN source at H53 beam at ILL 3. CryoEDM apparatus 4. Present status and future prospects The Search for Neutron Electric Dipole Moment at ILL…

+q -q -q +q S d n dn Sn P n T

-q -q

+q +q

Sn dn Sn dn

The Neutron Electric Dipole Moment: dn ≠ dn 0 ⇒ P and T violation The Search for Neutron Electric Dipole Moment at ILL…

Why we need to measure nEDM

• ..the validity of the parity assumption must rest on experimental evidence.. • J.M.Smith, E.M.Purcell, N.F.Ramsey, Phys. Rev. 108, 120, (1957) • CP violation is observed in K and B meson systems. • CP violation outside of SM is needed to explain observed particle-antiparticle asymmetry in the Universe • Theoretical predictions beyond the SM

The neutron is not as simple as it looks… The Search for Neutron Electric Dipole Moment at ILL…

Measurement principle

B0 B0 E B0 E

ms=+1/2 ν ν ν = μ = μ + = μ − h 2 n B h 2 n B 2dn E h 2 n B 2dn E

ms=-1/2

μ Β Ε H=- n -dn ν(↑↑)-ν(↑↓)=Δν= - 4 d E / h

B0 has to be unchanged when E is reversed The Search for Neutron Electric Dipole Moment at ILL…

“Spin up” 1. neutron...

Apply π/2 2. spin flip pulse...

3. Free precession. Statistical uncertainty .. σ(d ) = h / 2 n α ET √N 4. Second π/2 spin σ -25 flip pulse. (dn) = 2 x 10 e.cm/day The Search for Neutron Electric Dipole Moment at ILL…

nEDM apparatus

Four-layer mu-metal shield High voltage lead Quartz insulating Coil for 10 mG cylinder magnetic field Upper Main storage cell electrode Hg u.v. lamp PMT to detect Hg Vacuum u.v. light wall Mercury prepolarising cell RF coil to flip spins Hg u.v. lamp Magnet S N UCN guide changeover UCN polarising foil Ultracold neutrons (UCN)

UCN detector The Search for Neutron Electric Dipole Moment at ILL…

Experimental setup The Search for Neutron Electric Dipole Moment at ILL The ILL Reactor

Neutron turbine

Vertical guide tube

Cold source Reactor core The Search for Neutron Electric Dipole Moment at ILL

Grenoble Institut Laue Langevin (Alpes) The Search for Neutron Electric Dipole Moment at ILL The Search for Neutron Electric Dipole Moment at ILL

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

d(199Hg) < 2.1 x 10-28 e cm The Search for Neutron Electric Dipole Moment at ILL

Hg co-magnetometer

Top Polarised Hg atoms view:

PMT

PMT output: 30000 T' 20000

10000

-10000

-20000

-30000

Digitised voltage (bits)

-40000

-50000 0 2000 4000 6000 8000 10000 12000 ADC reading no. The Search for Neutron Electric Dipole Moment at ILL…

nEDM measurement

Hg co-magnetometer now compensates B drift

29.9295 Raw neutron frequency Corrected frequency 29.9290

29.9285

29.9280 ΔB = 10-10 T 29.9275

29.9270

29.9265

Precession (Hz) frequency 29.9260 0 5 10 15 20 25 Run duration (hours) The Search for Neutron Electric Dipole Moment at ILL

100

60 cm] e 40 -25

-20

-40 neutron EDM [10 neutron EDM -60 1300 1400 1500 1600 1700 1800 1900

run number

3 post publication data

2 cm]

e 1.0

1 -25 cm] e 0 -25

-1

-2

-3

neutron EDM [10 -4

-5 EDM uncertainty [10 uncertainty EDM

-6

-7 0.1 105 110 115 120 125 130 135 1996 1997 1998 1999 2000 2001 2002 2003 reactor cycle number date

The Search for Neutron Electric Dipole Moment at ILL…

False effects E from Special Relativity, extra motion-induced field v r×r r =v E Bv 2 B γc v

If B0 field has vertical gradient, than

r ∂B r B ( ) = − 0z 0r r ∂z 2 The Search for Neutron Electric Dipole Moment at ILL… Geometric phase Bnet Br Bnet B v ... so particle Bottle sees additional (top view) rotating field

Frequency shift B v ∝ E

Looks like an EDM

Bnet Br Bnet The Search for Neutron Electric Dipole Moment at ILL…

Systematics

• Consider Δh = 2.73+/- 0.39 mm ν γ R = n ⋅ Hg ν γ Hg n

• Should have value 1 • R is shifted by magnetic field gradients • Plot EDM vs measured R-1: The Search for Neutron Electric Dipole Moment at ILL

B field Down B field Up

150

100 150

100 50 e.cm) e.cm) -25

-26 50 0 -40 -20 0 20 40 0

EDM (10 -10 0 10 20 30 40 -50 EDM (10 -50

-100 -100

-150 -150 R-1 (ppm) R-1 (ppm) The Search for Neutron Electric Dipole Moment at ILL… Statistical and systematical errors

± -26 dn = -0.31 1.54 x 10 e.cm preliminary

Systematical errors Dipole & quadrupole shifts Enhanced GP dipole shifts (E x v)/c2 from translation (E x v)/c2 from rotation Light shift: direct B fluctuations Light shift: GP effects E forces – distortion of bottle Tangential leakage currents AC B fields from HV ripple Others …….. The Search for Neutron Electric Dipole Moment at ILL… CryoEDM experiment

Statistical uncertainty

σ(d ) = 2 x 10-25 e.cm/day σ h / 2 n (dn) = α ET √N for “room temperature” nEDM experiment

New UCN source Superthermal UCN source: a) a medium has a very small neutron absorption; Isotopically pure HeII b) the medium has a critical energy for total reflection σ a) absorption=0 which is much smaller than that of vessel’s walls b) Vcrit=21 neV c) the medium behaves as if there were only one c) Pure coherent scattering excited state with excitation energy E >> T >> E u Ephonon=11K,

T-temperature of the medium, Eu – the UCN energy THe=0.5K, EUCN=1 mK R.Golub and J.M.Pendlebury Phys. Let. 62A, 337, (1977) The Search for Neutron Electric Dipole Moment at ILL…

Production rate one-phonon interaction: Φ Energy momentum dispersion curve = × −8 d −3 −1 RI 4.1 10 cm s dλ λ*

main process: one phonon downscattering The Search for Neutron Electric Dipole Moment at ILL… τ Storing superthermal UCN τ - storage time, one phonon scattering only limited by: 1 11.9 1 = A exp⎡− ⎤ + • neutron lifetime ⎢ ⎥ τ • 4He purity ⎣ T ⎦ 0 • storage volume wall absorption cross section • upscattering

storage time vs helium temperature: The Search for Neutron Electric Dipole Moment at ILL

CryoEDM overview Theα Search for Neutron Electric Dipole Moment at ILL α Neutron detection Ion-implanted Si with neutron to charged particles converter n+10B → (1.78MeV )+7Li(1.01) n+10B → (1.47MeV )+7Li(0.83MeV ) + γ (0.48MeV ) n + 6 Li → α ( 2 .05 MeV ) + 3H ( 2 .74 MeV )

6000

5000

4000

Series1 3000

2000

1000

0 0 500 1000 1500 2000 2500 The Search for Neutron Electric Dipole Moment at ILL

Pulse Height Analysis of cryogenic UCN detectors

1.0

0.9

0.8

0.7

0.6

0.5

Yield 0.4

0.3

0.2

0.1

0.0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 channel The Search for Neutron Electric Dipole Moment at ILL

1800

1600 4.5 Å 5 Å 5.5 Å 6 Å 1400 6.5 Å 7 Å 7.5 Å 1200 8 Å 8.5 Å 9.0 Å 1000 9.5 Å 10 Å 10.5 Å

800 11.0 Å no velocity selector

neutron count 600

400

200

0 0 5 10 15 wavelength [Å] The Search for Neutron Electric Dipole Moment at ILL Neutron velocity selector

Daimler-Benz Aerospace Dornier Wavelength λ 0.45 to 4.3 nm α(´) T(%) R(%) 60 79.4 11.4 The Search for Neutron Electric Dipole Moment at ILL λ UCN production rate vs n

Single-phonon production

Multiphonon production

1.19±0.18 UCN cm-3 s-1 expected, 0.91± 0.13 observed See C.A.Baker et al., Phys.Lett. A308 67-74 (2002) The Search for Neutron Electric Dipole Moment at ILL

CryoEDM overview The Search for Neutron Electric Dipole Moment at ILL

Cryogenic Ramsey chamber The Search for Neutron Electric Dipole Moment at ILL Magnetometry • SQUID Magnetometers – Developed at Oxford for CRESST – Highly sensitive: adequate to monitor field fluctuations • Also: Neutron Magnetometers... Statistical limits σ = h / 2 d α E T √N

Factor Current Increase • Polarisation+detection α = 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 Total increase = x 80 (x200 with new beamline) The Search for Neutron Electric Dipole Moment at ILL…

CryoEDM to start running in summer 2006 The Search for Neutron Electric Dipole Moment, present experiment at ILL, Grenoble, and future prospects

CryoEDM experiment - Rutherford Appleton Laboratory - University of Sussex – ILL – University of Kure – University of Oxford

R.A.L. /Sussex/ILL/ - C.A. Baker, K. Green, P. Geltenbort, M.G.D. van der Grinten, P.G. Harris, P.S. Iaydjiev, S.N. Ivanov, J.M. Pendlebury, D.B. Shiers, D.Wark University of Kure (Japan) H. Yoshiki RAL - M.A.H Tucker, S.N. Balashov, V. Francis University of Sussex - M. Hardiman, P. Smith, J. Grozier, K. Zuber University of Oxford H. Kraus, B. Majorovits, N. Jelley, U. Divaker The Search for Neutron Electric Dipole Moment at ILL CryoEDM 10-27 e.cm 2006/8 10-28 e.cm 2008/9

nEDM dn = -0.31 ± 1.54 x 10-26 e.cm preliminary