Searching for a nEDM at PSI P. Schmidt-Wellenburg on behalf of the PSI-nEDM collaboration

The collaboration 6 countries 14 institutions 45 members

See talk by B. Lauss UCN source at PSI nEDM UCN Source Proton Accelerator 590 MeV Cyclotron 2.2 mA beam current See talk by B. Lauss nEDM UCN Source 2 experimental areas / 3 beamlines

Outline The apparatus Ongoing measurements and results UCN - performance Magnetometers and field control High voltage and leakage currents Ideas for the next generation experiment

Apparatus overview This is a sketch of the apparatus. In the center you see both high voltage electrodes and the insulator ring. This makes up the precession volume for the neutrons. The upper electrode can be charge up to high voltage whereas the lower stays grounded. The entire setup is within an aluminum vacuum chamber. The main magnetic field coil, a cosine theta coil is wound onto the vacuum tank producing a field of 1muT. Further more whe have a total of 33 shrim coils to adjust and fine tune the field within the precession chamber. The vacuum tank is surrounded by four layers of Mu-Metal with to reduces the earth magnetic field. The neutrons coming from the source are polarised in a 5T superconducting magnet, than pass through a slit to be filled into the chamber. After the cycle the are detected inside a neutron detector. The spin analysis is done sequentially just above the detector. We use to types of magnetometers to monitor the field. Mercury gas is used to estimate the field within the chamber, Dominique Rebreyend will present this in his talk. Cesium magnetometers are used to measure the field locally around the main precession chamber. And can thus also be used as gradiometers.

The apparatus 2009 Transfer from ILL (France) to PSI (Switzerland) Setup in thermally stabilized wooden house Two independent air-conditionings Six coils for surrounding field compensation (SFC)

Outline The apparatus Ongoing measurements and results UCN - performance Magnetometers and field control High voltage and leakage currents Ideas for the next generation experiment

UCN operation Empty Filling Monitor Just before Christmas we got ready for UCN. The UCN source story has already been told today, thus I will only add a small supplement. We prepared the apparatus for UCN, the SC magnet was flown in and installed at the end of the UCN source guide. we installed our own Nickel molybdenum coated glass guides, and the switch. In a rapid test at the BOA beam line here at PSI we could show, that the detector can digest high count rates. We identified the neutron signal and learned to discriminated it from the background. The detector was then finally mounted below our apparatus. A. Serebrov et al., NIMA 545(2005)490

UCN detector 6Li doped glass scintillator stack 3H  6Li 6Li depleted 6Li enriched 110 µm 60 µm Time (ns) Signal (mV) 6Li doped glass scintillator stack 9 independent channels (PMTs +DAQ) High count rate capable > 10 M We use a 6Li based scintillator in combination with a PMT that has been developed by the collaboration. It consist of 9 individual channels to accept high rates. UCN are captured in the Li enriched region of the scintillator and the decay products of the reaction n+6Li -> 3H + He produce a signal in the PMT. The reason for the stacked scintillators allow to collect all decay products. However, two stacks have been applied upside down as one can see in the signal to background separation. 30/11/2011 Integration gate: 9 –200 ns Channel 1 & 9 scintillator upside down Channel 8 has noise G. Ban et al., NIMA 611 (2009) 280

UCN Detector Monitor mode ~70000 UCN Emptying ~30000 UCN High UCN losses High depolarization rate G. Ban et al., NIMA 611 (2009) 280

UCN emptying curve During emptying: high loss rate of stored spin component → wrong polarisation τflip = 236 s τloss =16.5 s τ↓ = 163 s τ↑ = 16.9 s N = 29185 α0 = 0.999 Best fit to data

UCN storage time We measured the storage time for neutrons in our system, as this directly influences our sensitivity (On the one hand a longer free precession time is preferable, on the other hand the number of neutrons counted decays with time du to slits, up scattering and neutron decay) Two exponentials are fitted to accommodate for the fact, that the neutron spectrum softens with time. The result was expected for setup and combination of materials.

UCN Spin performance Rough adjustment of trim coils UCN detection spin sequence not yet optimized

Ramsey curve taken with 250 s precession time UCN Ramsey cycles Ramsey curve taken with 250 s precession time

Sensitivity E=110/12 kV/cm N10=9838 N20=8042 T1=56.6 s T2=182.5 s α0=0.79 Tα=556.6 s Minimum: σ(219s)=5.94×10-24 e·cm → σ(1d)=4×10-25 e·cm Assuming 30 x more UCN

Outline The apparatus Ongoing measurements and results UCN - performance Magnetometers and field control High voltage and leakage currents Ideas for the next generation experiment

The measurement technique Measure the difference of precession frequencies in parallel/anti-parallel fields: For the main part of my talk I would like to concentrate on this little term there. Which makes life difficult when changing from parallel to anti parallel field configuration. RAL-Sussex-ILL: dn < 2.9 x 10–26 e cm C.A.Baker et al., PRL 97 (2006) 131801 for dn<10-26 ω < 60 nHz

Magnetic shield Four layer Mu-Metal Shielding factors: x: 12000, y: 3000, z:8000

Surrounding field compensation Surrounding field (~ 80μT) Compensation and stabilization Three coil pairs: 6m x 8m, d= 4m 9/18 windings Six current supplies (10/20 A) Ten 3-axis Fluxgates (FG)

Sensor positions Z Monitoring positions close to shield (~ 0.3…0.8 m) nEDM Coordinate system FG 9 FG 8 FG 3 FG 6 FG 1 Al frame Y FG 5 FG 7 Thermo house (first floor) Magnetic shield door FG 0 FG 2 X 21

Results Feedback with inverted & regularized Matrix Twelve sensors close to shield taken into account (for x-direction shown below: sensors 0x, 3x, 6x, and 8x are used)

Systematic effects Most important source of systematic effects →Field mapping →Online Cs-OPM measurement →Dedicated B-drift runs (ramping E-field) →Magnetic scanning at PTB, Berlin × 10-27

Hg co-magnetometer See talk by D. Rebreyend

Principle of Cs magnetometer

Monitoring of vertical magnetic gradients Cesium magnetometers Monitoring of vertical magnetic gradients Two cesium magnetometer arrays Stabilized laser PID phase locked DAQ ±140kV 1 2 3 4 5 … 11 12 I have already told you that we used cesium magnetometer for mapping. The original reason was to have a insitu magnetic field gradiometer made of an array above the high voltage electrode and one array below the bottom ground electrode. This year we have setup a power stabilized laser. It provides the laser light to both cesium magnetometer arrays by a fiber beam splitter. The cesium are read out and driven by a dedicated data acquisition system. At the moment 9 are mounted further will be added this spring.

Homogenizer and fiber bundle Fiber bundle Beam splitter mounted on the enclosure support 31 vacuum feedthroughs for optical fibers

Adjusting field gradients Measure the response of all n=17 magnetometers to changes of each m=33 individual coil current 10nT Known response allows to calculate ideal currents for given field setting (iterative process) 10pT

Gradients STD from six gradiometer pairs

Uncompensated field drift Magnetization through changing polarity Coming now back to the table I have showed you in the beginning. One systematic effect is directly correlated with the change of the polarity of the electric field. It is called uncompensated field drift and is thought to be produced by a magnetization of something by charging currents. It is called uncompensated, as most of this changed field would be compensated by the change of the co magnetometer, however a gradient would not. One can estimate the effect to be 1.8 time 10-27 e cm per fT/cm of field gradient change.

Uncompensated field drift +100 E [kV] 100 s time -100 For this purpose we have frequently ramped the electric field from +100 to minus 100 kV measuring at the same time the magnetic field with cesium magnetometers. This was done as HV did not work with cesium at vacuum. Ramping speed = 1 kV/s Charging current = 35 nA

Uncompensated field drift No effect is observed at the level of 2.8 fT/cm Translates into What I show you here is a preliminary result of this autumns test run. You see for two cesium combinations that all data scatters around zero gradient. In fact, no effect was observed on the level of 2.8 fT/cm which translates into a systematic effect of 2.5 time 10 to the minus 27 e cm. No effect is observed at the level of 2.8 fT/cm Dedicated runs (daytime)

Outline The apparatus Ongoing measurements and results UCN - performance Magnetometers and field control High voltage and leakage currents Ideas for the next generation experiment

High voltage Cesium work with HV HV did not work with Cs Tests HV works up to 200kV Flashovers along fiber bundles Reliable HV runs at ±150kV 3 Leakage current @ 195 kV 2 Another crucial piece of the apparatus is the high voltage system. During investigations concerning the performance of the HV cesium we found out that the cesium do fine in high voltage whereas we can’t ramp the high voltage in vacuum. We started detailed investigations taking out everything and showing, that we can operate the old apparatus up to 200kV, however, 195kV if we want leakage currents across the chamber below 1nA. The we put back in the parts we need for measuring a magnetic field. The fiber bundles from the cesium provoked flashovers already at 100 kV, taking them apart in single fibers improved things dramatically. Another problem might be the polarizing optics in the gap between high voltage and ground. However, the system does not always give very clear answers. nA 1 15:06 15:14

Testing high voltage Configuration w bundle -110 kV vacuum 145 kV He/Ne Configuration wo bundle 198 kV He/Ne 200 kV He/Ne

Leakage current Leakage currents are caused by the high voltage and appear along the surface of the insulator ring. Changing the polarity of the high voltage will change the direction of the leakage current, and hence the magnetic field produced by these currents Most contribution of the leakage currents cancel out, not so jφ. jr jφ jφ jr jz jφ A leakage current of 1 nA produces a false edm of 2 × 10 -28 e cm

Leakage current measurement 3.5600 FEMTO 3.5595 3.5590 3.5585 Current (nA) 3.5580 3.5575 3.5570 -80 -60 -40 -20 20 40 60 80 -0.9 -0.6 -0.3 0.0 0.3 0.6 0.9 ILeak (nA) UHV (kV) ILeak ≤ 0.5 nA σ ≤ 0.1 × 10-27e cm 0.75pA 3.5565 4 pA 3.5560 3.5555 2 4 6 8 10 Time (h) Monitoring of leakage currents on ground electrode Combination of protection circuit and highly sensitive current/voltage amplifier

Outline The apparatus Ongoing measurements and results UCN - performance Magnetometers High voltage and leakage currents Ideas for the next generation experiment

3He see talk by A. Kraft n2EDM: General concept Simultaneous measurement in 2 precession chambers Laser based Hg co-magnetometer 3He magnetometers Multiple Cs magnetometers for 3He readout and gradients UCN chamber position at PSI UCN beam height E 3He see talk by A. Kraft

Thermohouse2 10×6×8 m3 EMC shield made of copper Thermally stabilized

Conclusion & Outlook Apparatus is ready for data taking Presently remeasuring UCN parameters High quality adjustment of B-field gradients Excellent performance of high voltage nEDM data taking from Nov 2012 400 nights of data in 2013/2014 → σ < 5×10-27 e·cm In parallel design of next generation experiment → σ < 5×10-28 e·cm

The Neutron EDM Collaboration Physikalisch Technische Bundesanstalt, Berlin Laboratoire de Physique Corpusculaire, Caen Institute of Physics, Jagiellonian University, Cracow Henryk Niedwodniczanski Inst. Of Nucl. Physics, Cracow Joint Institute of Nuclear Reasearch, Dubna Département de physique, Université de Fribourg, Fribourg Laboratoire de Physique Subatomique et de Cosmologie, Grenoble Biomagnetisches Zentrum, Jena Katholieke Universiteit, Leuven Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay Inst. für Kernchemie, Johannes-Gutenberg-Universität, Mainz Inst. für Physik, Johannes-Gutenberg-Universität, Mainz Paul Scherrer Institut, Villigen Eidgenössische Technische Hochschule, Zürich M. Burghoff, A. Schnabel, J. Vogt G. Ban, V. Helaine1, Th. Lefort, Y. Lemiere, O. Naviliat-Cuncic, G. Quéméner K. Bodek, G. Wyszynski3, J. Zejma A. Kozela N. Khomutov Z. Grujic, M. Kasprzak, P. Knowles, H.C. Koch4, A. Weis G. Pignol, D. Rebreyend S. Afach, G. Lembke N. Severijns, P. Pataguppi S. Roccia C. Plonka-Spehr, J. Zenner1 W. Heil, A. Kraft G. Bison, Z. Chowdhuri, M. Daum, M. Fertl3 , B. Franke3, B. Lauss, A. Mtchedlishvili, D. Ries3, PSW, G. Zsigmond K. Kirch1, J. Krempel, F. Piegsa I would like to thank you all for your interest and all these colleagues for their excellent work! Thank you very much. also at: 1Paul Scherrer Institut, 2PNPI Gatchina, 3Eidgenössische Technische Hochschule, 4GUM Mainz