Searching for a neutron electric dipole moment - European efforts Bernhard Lauss Paul Scherrer Institute, Villigen, Switzerland Dec. 7, 2018 Bernhard Lauss ACFI Workshop 7/12/2018
Outline neutron electric dipole moment • & measurement techniques ultracold neutrons • nEDM experiments - European efforts • Bernhard Lauss ACFI Workshop 7/12/2018
Mainz (Germany) NC-State (USA) RCNP (Japan) PSI (Switzerland) D2 source operating ILL (France) TRIUMF (Canada) D2 source ready waiting for license He source at TRIUMF D2 source operating RT experiment R&D at TRIUMF RT Experiment finished Turbine source running He source tested RT experiment (PNPI) setup new experiment under construction RT experiment under construction and He source prototype running PNPI (Russia) J-PARC (Japan) LANL (USA) He source under construction D2 source in discussion RT experiment planned (Ship from ILL) D2 source running RT experiment in discussion RT experiment R&D TUM (Germany) D2 source under construction RT experiment shipped to ILL SNS (USA) cryo experiment in He under construction Bernhard Lauss ACFI Workshop 7/12/2018
History of nEDM results Theory Experimental limit expectation current limit: Baker et al., PRL 2006 -19 revised with largely extended systematics in 10 ORNL, Harvard MIT, BNL -20 10 LNPI -21 Sussex- RAL-ILL 10 nEDM @PSI (expected 2019) SUSY Φ ~ 1 sensitivity -22 10 n2EDM @PSI (goal ) -23 10 d n (e cm) SUSY Φ = α / π Multi Higgs Left Right recent review -24 10 -25 10 current limit -26 10 Standard Model beam stored UCN -27 10 Weak interaction SM contribution: -28 10 1 − 6 × 10 −32 e 𝑑𝑑 -31 10 C.-Y. Seng,PRC(2015)025502 -32 10 Theory values adapted from 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 Pendlebury & Hinds, NIM-A 440 (2000) 471 Publication year comparable sensitivity goals for all worldwide efforts new limit from PSI experiment expected soon ! Bernhard Lauss ACFI Workshop 7/12/2018
Ramsey method of oscillatory field Measurement of the difference of neutron precession frequencies in parallel/anti-parallel E and B fields: µ = 60 neV/T n B = 1 μT ν ≈ 29Hz B E = 11 kV/cm − < × 26 d 3 10 e cm n Drawing:Courtesy G.Bison ν < 160nHz µ E 2 2 d ν = ± n n B E n h h High-precision control and measurement of frequency and magnetic field necessary (fT level) Bernhard Lauss ACFI Workshop 7/12/2018
Experiment sensitivity ℏ σ (d n ) 𝜏 𝑔 = 2𝛽𝛽𝛽 𝑂 nEDM results are still statistically limited → the challenge: design apparatus to maximize UCN statistics and all parameters Bernhard Lauss ACFI Workshop 7/12/2018
The beam searches 𝛽 = 𝑚 𝑤 ≈ 0.015s; 𝛽 > 0.9; 𝛽 = 100kV ℏ 1 ; 𝑂̇ cm 𝜀 𝑒 n = 𝑢 = 1 × 10 6 s −1 2𝛽𝛽𝛽 𝑂̇ = 8.7 × 10 −22 𝑓 cm 1 𝑢 𝜏 = 1×10 −24 𝑓 cm Hz 1 day l = 2m 1957 OakRidge 𝜌 /2 𝜌 /2 + + + + + + + + + + + + + + E n - - - - - - - - - - - - - B Dominant systematic effect: 𝐶 𝑤 = − 𝒘 × 𝑭 𝑑 2 final result: 𝜏 𝑒 𝐨 = 1.5 × 10 −24 𝑓 cm due to misalignment of 0.1 mrad Dres et al., PRD 15( 1977 ) 9 Bernhard Lauss ACFI Workshop 7/12/2018
new effort at Univ.Bern: Neutron EDM Experiment using a Pulsed Beam (BEAM-EDM) ► Unique, novel, and complementary EDM approach ► Project based at University of Bern – Start: 10/2016 ► Full-scale experiment intended for the ESS / ANNI (<10 -26 e cm) ► Proof-of-principle experiments at PSI and ILL (10 -24 e cm) Ramsey Phase Time-of-Fligth ILL PF1b March 2018 Piegsa, PRC 88, 045502 (2013) Courtesy: Florian Piegsa Bernhard Lauss ACFI Workshop 7/12/2018
Crystal diffraction neutron EDM - spin rotation for neutrons close to the Bragg condition for the crystallographic plane in a non-centrosymmetric crystal. - n exposed to interatomic E-field (up to 10 9 V/cm) - a non-zero nEDM results in a spin rotation close to Bragg reflex - Polarization tensor is sensitive to nEDM which would cause a phase shift New project with Beamstop Monitor sensitivity 2 10 -25 e cm (110) plane Meissner cavity per day for quartz PG (002) outgoing incoming T=T 0 ±∆ (R~50%) crystal and PF1b beam nutator nutator Double crystal T=T 0 SM polarizer PG monochromator ILL reactor is ready. Beamstop Spin flipper PF1b H L ≈ 0 Y Information courtesy 3 He cell (110) plane Z Vladimir Voronin Casemat E n <E 0 X +P D v n +E -E nPSD -P D E n >E 0 = ⋅ 8 E 2.1 10 V cm / (1120) Experimental value for (110) quartz plane V.V. Fedorov, M. Jentschel, I.A. Kuznetsov et al., Physics Letters B 694, 25 (2010) Bernhard Lauss ACFI Workshop 7/12/2018
̇ Ultracold neutrons (UCN) CN beamline (e.g. ILL - PF1b) For highest sensitivity: 𝑂̇ ≈ 2 × 10 9 s −1 @ 440 m/s optimize 𝛽 ≈ 0.99; 𝛽 ≈ 100kV/cm ℏ 𝜏 ( 𝑢 ) = 2 m 2𝛽𝛽𝛽 𝑂𝑢 𝛽 = 𝑚 / 𝑤 = 440 m/s = 4.5ms 𝜏 (1s) = 2 × 10 −23 𝑓 cm UCN (e.g. EDM at PSI) UCN are neutrons which 𝑂̇ ≈ 1000 s −1 can be stored in material 𝛽 ≈ 0.9; bottles 𝛽 = 15kV/cm 𝛽 = 200s UCN < 300neV ~ 8m/s ~ 3 mK 𝜏 1s = 4 × 10 −24 𝑓 cm > 50 nm ! Bernhard Lauss ACFI Workshop 7/12/2018
How to increase the statistical sensitivity 𝛽 ≤ 20kV/cm : Limited by insulator ℏ 𝜏 𝑒 n = 𝛽 → 1 : Polarization of neutrons 2 𝛽𝛽𝛽 𝑂 ℏ = 𝑂 0 e −𝑈 / 𝜐 𝑜 2 𝛽𝛽𝛽 0 e −𝑈 / 𝑈 𝛽 → 𝜐 n : Minimize losses 2 𝑂 0 : Limited by transport losses 𝛽 2 → ∞ : Magnetic field inhomogeneity • Make 𝛽 2 , 𝛽 large → large high performance magnetically shielded rooms and homogeneous magnetic field • Make 𝑂 0 large → improve UCN sources • better extraction of UCN from converter • higher UCN production rates • adaptation / improvement of UCN transport • Make 𝛽𝛽 𝑂 large → cryogenic UCN storage experiment Bernhard Lauss ACFI Workshop 7/12/2018 11
Example: solid deuterium based sources- LANL - NCSU - MAINZ - PSI PSI long UCN guides cryo-pump minimize rest gas losses - minimize UCN losses DLC coated UCN storage vessel exper. minimize UCN losses 7 m cold UCN-converter 5 kg solid D 2 at 5 K mazimize UCN production exper. minimize losses heavy water moderator → thermal neutrons 3.6m 3 D 2 O pulsed 1.3 MW p-beam 590 MeV, 2.2 mA, spallation target (Pb/Zr) 3% duty cycle (~ 8 neutrons/proton) Bernhard Lauss ACFI Workshop 7/12/2018
Worldwide efforts for higher UCN intensities UCN density after storage in 20 l external stainless-steel bottle storage times = 2s storage times = 50s, 100s Comparison of ultracold neutron sources for fundamental physics measurements G.Bison et al., Phys.Rev.C95 (2017) 045503 Suggestion of "standard" method and device for UCN density measurement and comparison: G.Bison et al., Nucl.Instrum.Meth. A 830 (2016) 449 Bernhard Lauss ACFI Workshop 7/12/2018
nEDM storage experiments First double chamber Pioneering efforts by the PNPI - Lobashev group using for the first time a double UCN storage chamber Bernhard Lauss ACFI Workshop 7/12/2018
Pioneering efforts by the RAL-Sussex-ILL collaboration using for the first time a cohabiting magnetometer - polarized 199-Hg set the present limit Bernhard Lauss ACFI Workshop 7/12/2018
Several improvements and upgrades to the original nEDM apparatus at PSI UCN Bernhard Lauss ACFI Workshop 7/12/2018
Several improvements and upgrades to the original nEDM apparatus at PSI UCN UCN source Bernhard Lauss ACFI Workshop 7/12/2018
How to improve: optimize UCN storage time and UCN statistics early run with lower statistic during setup Chamber made of dPS insulator ring and DLC electrodes ℏ 𝜏 𝑔 = 2𝛽𝛽𝛽 𝑂 Bernhard Lauss ACFI Workshop 7/12/2018
Simultaneous spin detection (also pioneered at PNPI) Spin dependent detection o • Adiabatic spinflipper • Iron coated foil 6 Li-doped scintillator GS20 o B UCN storage detection Bernhard Lauss ACFI Workshop 7/12/2018 S. Afach et al., EPJA (2015)51: 143
Neutron transversal depolarization time T2 ~ 1000s ℏ 𝜏 𝑔 = 2 𝛽𝛽𝛽 𝑂 2 𝑨 2 𝛽 2 𝛽 𝛽 = e −Γ 2 𝑈 − 𝛿 𝑜 ⋅ 𝑒ℎ 2 eff 2 in addition we found gravitational depolarization Afach et al., PRD92(2015)052008 Afach et al., PRL115(2015)162502 magnetic field homogeneity 10 -3 -> 10 -4 new variometer method of B-field homogenization Bernhard Lauss ACFI Workshop 7/12/2018
Hg co-magnetometer ν = γ ≈ Hg B 8 Hz Hg Hg lamp Photomultiplier / diode or laser precessing polarized Hg atoms Bernhard Lauss ACFI Workshop 7/12/2018
Analysis: Frequency ratio R = f n /f Hg Center of mass offset δ h Non-adiabaticity -> new systematic effects motional (false) EDM 𝛿 H 𝛿 n g 199 Hg UCN 𝜌 ≈ 8 Hz/ µT 𝜌≈ 30 Hz/ µT 2 2 𝑤 Hg ≈ 160 m/s vs. 𝑤 UCN ≈ 3 m/s + 𝐶 2⊥ 𝑆 = 𝑔 = 𝛿 n 1 ∓ 𝜖𝐶 Δℎ UCN 𝐶 0 2 ∓ 𝜀 Earth + 𝜀 Hg−lightshift 𝛿 Hg 𝜖𝜖 𝐶 0 𝑔 H g Measure R as function of dB/dz Bernhard Lauss ACFI Workshop 7/12/2018
extracting the neutron frequency / R-curve B down B up ) + new physics EXOTIC FORCE Bernhard Lauss ACFI Workshop 7/12/2018
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