Lepton Moments 2014 Craigville 07/22/2014 P. Schmidt-Wellenburg PSI Searching for the electric dipole moment of the neutron

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Institutions Eight countries / 14 institutions 48 Members 11 PhD students The collaboration

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ PSI in Switzerland UCN source & EDM

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Outline Introduction How do we search for the nEDM? Status at PSI The UCN source Statistical sensitivity Neutron/mercury gyromagnetic ratio Magnetometry Preliminary Results

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ The measurement technique Measure the difference of precession frequencies in parallel/anti-parallel fields: for d n < Δ ω < 60 nHz ω L ≈30Hz for B 0 =1 μT Best nedm limit: 2.9 × ecm Baker et al., PRL97(2006)

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ The Ramsey technique Free precession at ω L Apply  /2 spin flip pulse... Spin “ down ” neutron... Second  /2 spin flip pulse. B0↑B0↑ B 0 ↑ + B rf B0↑B0↑ Ramsey resonance curve Sensitivity:  Visibility of resonance TTime of free precession NNumber of neutrons EElectric field strength

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Ultracold neutrons (UCN) Storable neutrons (UCN) E. Fermi & W.H. Zinn(1946), Y. B. Zeldovich, Sov. Phys. JETP (1959)389 Storage properties are material dependent 350 neV ↔ 8 m/s ↔ 500 Å ↔ 3 mK Magnetic ∼ 60 neV/T Magnetic ∼ 60 neV/T Gravity 102 neV/m Gravity 102 neV/m Strong V F Strong V F V & systematic effects

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Overview Introduction How do we search for the nEDM? Status at PSI The UCN source Statistical sensitivity Neutron/mercury gyromagnetic ratio Magnetometry Preliminary Results

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ PSI UCN source Protons Spallation target E n ~MeV D 2 O moderator Neutrons thermalized to 25 meV 1m Main shutter UCN storage volume Neutron guide to experiments UCN convertor (solid D 5K) 590 MeV 2.2 mA Golub, R. & Pendlebury, J. M PLA (1975)133 Anghel, et. al NIMA (2009) 272

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ UCN/cm 3 at beam exit (~ UCN/25 liter) UCN source performance Standard operating Pulse Norm Pulse UCN Counts /s VAT Cascade Detector VAT 1m glass tube - NiMo coating - Stainless steel flanges - shutter DLC coated UCN

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ The nEDM spectrometer

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Filling UCN N (after 30s storage) Polarization

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Simultaneous spin detection ~20% increase in sensitivity (for 2014)

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Storage life time Chamber made of dPS insulator ring and DLC electrodes Two exp fit: t s ~30s t f ~180s Max no. UCN measured after 180s storage:

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Transversal depolarization PSI T 2 (B 0 ↓ ) : 1158 ± 94s T 2 (B 0 ↑ ): 836 ± 63s 2013: T 2 (B 0 ↓/ B 0 ↑ )~600s PSI T 2 (B 0 ↓ ) : 1158 ± 94s T 2 (B 0 ↑ ): 836 ± 63s 2013: T 2 (B 0 ↓/ B 0 ↑ )~600s → Excellent magnetic field homogeneity

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ RAL/Sussex/ILL*PSI 2013 bestavgbestavg E-field Neutrons T free T duty Α Neutron EDM sensitivity 2013 data taking: 3266 cycles 25 days Stopped by switch break down 2013 accumulated sensitivity 6 × e.cm * Best nedm limit: Baker et al., PRL97(2006) ~7500 ~0.75 <2

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Overview Introduction How to search for the nEDM? Status at PSI The UCN source Statistical sensitivity Neutron/mercury gyromagnetic ratio Magnetometry Preliminary Results

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ The measurement technique Measure the difference of precession frequencies in parallel/anti-parallel fields: Statistical accuracy of a magnetometer correcting for a change in B should be better than the neutron sensitivity per cycle:

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Average magnetic field (volume and cycle) σ B ~ 400 fT τ > 100 s without HV s/n ~ 500 without HV Mercury co-magnetometer ¼ wave plate linear polarizer Hg lamps PM polarization cell HgO source B 0 ≈ 1 μ T τ = 140s

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Goal: Measure magnetic field drifts via optically detected nuclear magnetic resonance (ODMR) with 199 Hg atoms Mercury co-magnetometer Hg source circular polarizer unit nm UV light, circularly polarized UCN precession chamber PMT polarization chamber ( M. Fertl, PhD-Thesis 2013 ) Fourth harmonic generator (IR → VIS → UV) Toptica TA FHG ( nm) 50 m away from the nEDM setup 50m

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Hg laser readout Sensitivity improvement from ~400fT → <100fT ( M. Fertl, PhD-Thesis 2013 )

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ There are two drawbacks using the HgM as field monitor: Center of mass offset Non-adiabaticity Frequency ratio R = f n /f Hg UCN 199 Hg + further sys. CsM - array

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Cesium gradiometer Monitoring of vertical magnetic gradients Six HV CsM Ten ground CsM Stabilized laser PID phase locked DAQ 1 2 … 6 7 … 1516 ± 120kV

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Field parameterized by 9 parameters (2 nd order) The parameters are adjusted to 12 magnetometers readings using least squares Residuals are about 30 pT (500 pT using only linear model) Jackknife procedure to estimate the error on the gradient G Gradients from CsM

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Extracting R Run 6043 Χ 2 /dof = 1.3

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ R vs gradient B0 up B0 down

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ There are two drawbacks using the HgM as field monitor: Center of mass offset Adiabatic vs Non-adiabatic field sampling Frequency ratio R = f n /f Hg UCN 199 Hg + further sys. CsM - array Field maps

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Mapping with fluxgate and vector cesium magnetometer -20<z<20, -10<r<30, Δφ = 5° Transversal fields UCNs: Adiabatic regime 199 Hg: Non-adiabatic regime

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ B 0 up λ f Earth Earth rotation correction

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Vector light shift in 199 Hg Atomic energy levels are influenced by the interaction with light Spin dependent part can be by modeled as effective magnetic field (which only alters the Larmor frequency of the Hg atoms, not of the UCN) Effective magnetic field depends on: Light intensity Light polarization Light frequency Light beam alignment All four parameters have to be under control for reliable calculations. B0B0 B LS B eff

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Change of light intensity 30% / 70% Change of relative angle B-field / light beam Hg lightshift measurement ppm

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Result (submitted to PLB) γnγn γ Hg

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Error budget

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/14 34 The UCN source delivers sufficient statistics for data taking, potential improvements are being identified The nEDM experiment is taking data, operational reliability has been improved during shutdown 2014 As a test of magnetic field control we have measured the most precise gyromagnetic ratio of mercury-199 and neutron. We expect with 300 data-days until 2016 a statistical sensitivity of σ ≲ e ⋅ cm Conclusion

Ort, Datum Philipp Schmidt- Wellenburg Thank you for your attention.

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ detector 1 Cascade UCN detector Standard operating Pulse Norm Pulse UCN Counts /s Measurements on beam West-1

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Cs OPM Servo

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Vector cesium magnetometer

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Cs vector magnetometer |B| BzBz ByBy BxBx 75 fT 400 fT 10 – 20 pT

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Analysis of a run The analysis: Ramsey Fit Mercury frequency Cut on cycles with residuals larger than 3 (10 %) Typical χ 2 =1.5 a

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ UCN depolarization Measurement of frequency ratio R as function of vertical gradient revealed unexpected polarization behavior and non-linearity for large gradients.

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Hg laser readout ( R&D for n2EDM, tested in nEDM ) Sensitivity improvement from ~400fT → ~100fT

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Ultracold neutrons with different energies average differently over the storage volume UCN with low energies, will depolarize faster: → contribute less to the average field measurement, → frequency changes non-linear Gravitationally enhanced depolarization Figures from: P. G. Harris et al, PRD89, (2014)

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Side remark: nEDM sensitivity RAL/Sx/ILL*PSI 2012PSI 2013 bestavgbestavgbestavg E-field Neutrons T free T duty α data taking: 3266 cycles 25 days Stopped by switch break down 2013 accumulated sensitivity 6 × e.cm *Best nedm limit: Baker et al., PRL97(2006)

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Magnetic fields B0B0 BTBT

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Field parameterized by 9 parameters (next-to-linear) The parameters are adjusted to 12 magnetometers readings using least squares Residuals are about 30 pT (500 pT using linear model) Jackknife procedure to estimate the error on the gradient G Gradients from CsM

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ f n /f Hg vs g z

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ B 0 up λ f Earth Earth rotation correction

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ The pseudo magnetic field

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ A new limit

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ HV performance HV (kV) Best HV performance 144 kV → 12.0 kV/cm Average E-Field while data taking: 10.3 kV/cm

Philipp Schmidt-Wellenburg Lepton Moments 2014, /24/ Hg co-magnetometer Extract B field from Larmor frequency and correct UCN frequency (lamp data) 16 h 1.5 pT