Challenges of the world-wide experimental search for the electric dipole moment of the neutron

2 Nov 2014, 15:00 → 6 Nov 2014, 15:20 Europe/Zurich

Congressi Stefano Franscini

Bradley W. Filippone (Californian Institut of Technologies), Klaus Kirch (Paul Scherrer Institut), Maurits van der Grinten (Rutherford Appleton Laboratory), Peter Geltenbort (Institut Laue-Langevin), Philipp Schmidt-Wellenburg (Paul Scherrer Institut)

The 2nd international workshop on techniques, methods and instrumentation for searches of a neutron electric dipole moment will be held in Ascona, Switzerland, from Sunday, November 2nd to Thursday, November 6th, 2014. It is organized by the Paul Scherrer Institut (PSI), the ETH of Zurich, the Institut Laue Langevin, Grenoble and the Rutherford Appelton Laboratory, Oxford.

The biannual workshop gives researchers from around the world the opportunity to present in detail and with a special focus on experimental techniques and methods their present status for a search of the neutron electric dipole moment. Ample time for discussion will generate in depth understanding of common challenges for all next generation experiments.

The workshop will consist of invited and contributed talks and poster sessions.

nEDM2014 is the second workshop, held in the spirit of the 2012 meeting at the Oak Ridge National Laboratory, Tennesse, United States of America.

Sunday 2 November

Registration

Registration for workshop

18:00 Welcome Drink

19:00 Dinner

Restaurant

Monday 3 November

Registration

Registration for workshop

Welcome

Short welcome and introduction to the conference center.

Convener: Philipp Schmidt-Wellenburg (Paul Scherrer Institut)

1 Welcome (OC)

2 Welcome Address Monte Verità Foundation and Congressi Stefano Franscini

Speakers: Mrs Chiara Cometta, Mr Sonognini

Theory background

3 The impact of a non-vanishing nEDM

In this talk I will discuss why we theorists always knew that you wouldn't find a non-vanishing nEDM. Just in case you will measure one, it will also be discussed, why we theorists always knew that you would eventually find a non-vanishing nEDM.

Speaker: Adrian Signer

Slides as-ascona.pdf

10:10 Coffee Break

Overview: I

4 nEDM at FRMII

At the FRM-II reactor we are currently setting up a new apparatus to measure the neutron EDM with a projected sensitivity of 10-28 ecm. To reach this 100 times improved measurement precision, next to the strongest possible source of ultra-cold neutrons, also the understanding of many systematic issues on a yet unprecedented level is required. Understanding systematic effects includes the control of small magnetic fields and large electric fields. I will give an overview of the ongoing implementation of such an apparatus, including an overview of some technical advancements and milestones that actually enable this precision.

Speaker: Prof. Peter Fierlinger (Technical University München)

5 Search for a neutron edm at the Oak Ridge SNS

In the past year the design for the apparatus has undergone a major over-haul which has moved the design in the direction of more standard cryogenic practice. After a description of the concept of the experiment we will discuss the new design and the challenges associated with it.

Speaker: Prof. Robert Golub (ncsu)

Slides nedmSchweiz11_2014.pptx

12:00 Lunch

Overview: II

6 Search for the neutron electric dipole moment at the Paul Scherrer Institute

At the Paul Scherrer Institute, a collaboration of 14 institutions is conducting an experiment to search for a permanent neutron electric dipole moment. The experiment uses ultracold neutrons (UCN) stored in vacuum at room temperature. This technique provided the last (and best) limit by the RAL/Sussex/ILL collaboration in 2006: 2.9 × 10-26 e cm (90% C.L.). We aim at improving this limit using an upgrade of the same apparatus. The data taking is ongoing and an overview of the sensitivity will be given together with a status report on the control of the systematic effects. In particular I will discuss some of the most recent developments and their impact on the sensitivity and conclude with the perspectives of this collaborative work.

Speaker: Dr Stephanie Roccia (CSNSM)

Slides S_Roccia.pptx

7 R \& D Toward a new nEDM Experiment at LANL

Los Alamos National Laboratory (LANL) currently operates a proton-beam-driven solid-deuterium-based UCN source, providing UCN for various neutron beta decay experiments as well as R&D for the SNS nEDM experiment. An estimate shows that the combination of further optimization of the source geometry and cold moderator material, increased proton beam current, and more optimized proton pulse structure will give us a 10-fold increase in UCN source performance. With such an improvement, an nEDM experiment with a sensitivity goal of several × 10-27 e-cm based on the already proven Ramsey's separated oscillatory fields method at room temperature could be performed at the LANL UCN source. Currently, an R&D effort is under way to improve the UCN source and demonstrate a storage of the number of UCN sufficient for such an nEDM experiment in a prototype nEDM apparatus. In this talk, the current status of this R&D effort, with an emphasis on the source upgrade, will be presented.

Speaker: Dr Takeyasu Ito (Los Alamos National Laboratory)

Slides Ito_Ascona_2014.pdf

15:30 Coffee Break

Overview: III

8 The present status of nEDM at KEK-RCNP-Osaka

We have constructed a new He-II UCN source. The performance of this new UCN source will be discussed. We will also discuss technical developments for nEDM. Preparations of magnetic field and a magnetometer will be discussed.

Speaker: Prof. Yasuhiro Masuda (IPNS, KEK)

9 Present status and future prospects of nEDM experiment in Grenoble and in Gatchina

For the last few years the work on preparation and performance of an experiment on neutron EDM search with the PNPI double-chamber EDM spectrometer has been carried out by collaboration of PNPI-ILL-PTI with PF2 MAM ultra cold neutron beam at ILL. We have obtained constraint for neutron EDM value at confidence level of 90%: |dn| < 5,5 * 10-26 e*cm. The double-chamber spectrometer provides principally different possibility of controlling systematic effects. It is obvious that one should continue making measurements which were interrupted but it is required that UCN intensity determining the statistical measurement accuracy should be raised. Accuracy is likely to be increased by making PF2 EDM beam more intensive and by applying a new spectrometer scheme. On the whole, we expect to achieve estimation accuracy approximately equal to 1*10-26 e*cm. The second part of talk will be devoted to preparation of high-intensive UCN facilities with density about 10^4 ucn/cm3. We would like to concentrate efforts in the preparation of the facilities. In case of successful result we are going to continue our nEDM measurements in PNPI. At the same time we are ready to propose the facilities for other EDM collaborations.

Speaker: Prof. Anatolii Serebrov (Petersburg Nuclear Physics Institute)

Slides Serebrov-Ascona2014.pdf

10 The UCN source and EDM experiment at TRIUMF

- on behalf of the TRIUMF UCN collaboration - The 500 meV proton cyclotron at Canada's National Lab for Particle and Nuclear Physics, TRIUMF, will be used for a spallation driven ultra-cold neutron source. As a first experiment, the search of the neutron electric dipole moment (nEDM) is planned. The talk will cover design and status of the extracted superfluid helium-4 based UCN source and give an overview of the development strategy towards a next generation nEDM experiment

Speaker: Dr Ruediger Picker (TRIUMF)

Slides UCNandEDMatTRIv2.pdf

19:00 Dinner

Tuesday 4 November

Overview: Beam experiments

11 Search for a Neutron Electric Dipole Moment using a Pulsed Beam

A novel concept to search for a CP-violating neutron electric dipole moment (nEDM) has been presented [F.M. Piegsa, Phys. Rev. C 88, 045502 (2013)]. It employs a pulsed neutron beam instead of the established use of storable ultracold neutrons (UCN). The technique takes advantage of the high peak flux and the time structure of a next-generation pulsed spallation source (e.g. the planned European Spallation Source) to directly measure the previously limiting systematic vxE-effect. Such an experiment would be complementary to experiments with UCN and could compete with their sensitivities on the 5×10e-28 e cm level. In this talk, I will describe this alternative approach including possible systematic effects and first test experiments.

Speaker: Dr Florian Piegsa (ETH Zürich)

Slides Piegsa_Beam_EDM_(Ascona).pdf

12 Сrystal diffraction nEDM experiment. Present status and future progress.

The proposed method to search for the neutron EDM is based on using a large crystal electric field affected the neutron in a crystal without center of symmetry during all the time of neutron stay in crystal. Value of the field can reach about $10^9$V/cm and experimentally measured value for quartz crystal is $\sim 10^8$ V/cm. The first variant of the experimental setup based on using a quartz crystal is now under construction. The accuracy of this setup is expected on a level $\sim 2 10^{-26}$ e cm. The modern status of this project and possibility to improve the accuracy for different crystal without center of symmetry will be discussed. The "storage" variant of the setup will be considered. This variant allows essentially increase the time of neutron stay in crystal and therefore the method sensitivity can reach about $2 10^{-27}$ e cm for the BSO crystal.

Speaker: Dr Vladimir Voronin (Petersburg Nuclear Physics Institute)

Slides EDM_DEDM_V.ppt

10:20 Coffee Break

Neutron: Sources

13 PULSTAR UCN source and EDM Systematic Study

The Ultra cold Neutron source at the PULSTAR reactor on the campus of NC State University is presently in the commissioning stage. Measurements of the cryostat cooling power proved that the LHe system will be able to take the predicted radiation loads in all heat exchangers of the system. In future, the source will host an experimental test-bed apparatus to study systematic EDM effects, using polarized He-3 and UCNs . At present, an engineering design of the test bed cryostat is completed and we are working on testing prototypes of some of the components.

Speaker: Dr Ekaterina Korobkina (NC State University)

Slides Ascona_2014_SS_at_PULSTAR.key.zip

14 Status of the source for ultracold neutrons (UCN) at the Paul Scherrer Institute

The UCN source at the Paul Scherrer Institute is in operation since 2011 and providing UCN e.g. to the neutron EDM experiment. The operation principle of the source and the way of UCN production will be explained. The current status of the source and the progress made since start-up, will be presented, together with ongoing optimizations and measurements to characterize individual subsystems. In addition, comparisons between Monte Carlo Simulations of the full source setup and recent measurements will be shown. This work is supported by the Swiss National Science Foundation under grant number 200020_137664.

Speaker: Mr Dieter Ries (PSI)

Slides AsconaRies.pdf

12:00 Lunch

Guided Tour

Guided tour to the history of Monte Verité

Neutron: Sources and Simulations

15 A UCN guide system for the future FRMII UCN source

Since several years a powerful UCN source is under development and construction at the FRMII reactor in munich. In order to deliver UCN produced inside the reactor (in a solid Deuterium converter) to experiments 30m away, a dedicated UCN guide System is required. In the last years available guide options were tested. This talk will give an overview on latest results obtained from the test of an almost full-size UCN guide prototype at ILL in summer 2014.

Speaker: Mr Thorsten Zechlau (FRMII)

Slides ZechlauAscona.pdf

16 Geant4 Simulations Framework for nEDM@SNS!

The nEDM@SNS simulations team has developed Geant4 based simulations of several key aspects of the experiment including: i) neutron-3He capture signal, ii) several sources of background (neutron activation, cosmic rays, neutron beta decay, etc.), iii) light collection (scintillation, wavelength shifting, and detailed photon propagation), iv) 3He spin precession, and v) UCN production in 4He. These simulations are currently being integrated into a single framework to accommodate design changes without the need for major code revisions. Many of the simulations have also been ported to an HPC environment on the Titan supercomputer at Oak Ridge. In this presentation we present several lessons learned and best practices to ensure accurate results and efficient execution of Geant4 simulations in the low energy neutron regime. Specifically, we will present ongoing work with the SNS neutronics team and Geant4 collaboration members to compare the low energy neutron scattering kernels in Geant4 against MCNP. We will also present results from a custom Geant4 process to simulate single phonon scattering of low energy neutrons in superfluid Helium.

Speaker: Dr Jed Leggett (ORNL)

Slides Leggett_Ascona_11-14.pdf

16:00 Coffee Break

Neutron: Simulation and detection

17 High Rate Detectors for Ultra Cold Neutrons at TRIUMF

A high intensity UCN source, and an experiment to measure the neutron Electric Dipole Moment (nEDM) are being developed for TRIUMF. Some new physics predict nEDM contributions both above the present limit on the nEDM leading to their abandonment, and just below the present limit there are several other models vulnerable to the same fate. This talk will present the research and development being done to design an ultra cold neutron detector which is capable of handling the proposed high instantaneous neutron rates in future nEDM measurements.

Speaker: Blair Jamieson (University of Winnipeg)

Slides Blair_Ascona_UCNDetector_20141104.pdf

18 PSI - neutron detection

A fast detector (NANOSC) and a simultaneous spin analyzer (USSA) have been built for the nEDM experiment at PSI. The detector is based on 6Li depleted glass scintillators (GS30) glass stuck to the front of 6Li enriched glass scintillators (GS20). With such a combination, the edge effects, inherent to low energy neutron detection, are suppressed and a clear separation between the gamma and the neutron contributions is carried out. The scintillators rate capability is about few 105 counts/s. A multi-detector with nine channels (NANOSC) has been built in order to handle counting rate up to few 106 counts/s. A new fast acquisition system (FASTER) is coupled to the detector. In parallel, a new spin analyzer has been carried out. It is made of two arms from which a simultaneous spin analysis can be performed. Such a device allows to symmetrically treat the two spin components and reduces the UCN depolarization and losses during the counting period. It has been successfully tested below the nEDM spectrometer. An increase

Speaker: Mr thomas lefort (University of Caen)

Slides Ascona_lefort.pptx

19 Simulations for the nEDM@PSI project - The MCUCN and STARucn codes

The MCUCN and STARucn codes for tracking ultracold neutron trajectories and spin were developed in order to perform optimization studies for UCN optics, and also for simulations supporting studies on nEDM experiment systematics. In this presentation we will briefly explain capabilities, algorithms, present inter-comparison calculations and analytic benchmarks performed with both codes. Further we will focus on some applications for the nEDM experiment e.g. (i) on calculations of the depolarization and neutron frequency shift due to higher order field gradients, important to check analytical models for the R-curve analysis, and (ii) on simulations of UCN spin echo for testing the analysis method of measurements aiming to extract the neutron energy distribution, and helping to achieve a best field homogeneity in the nEDM experiment.

Speaker: Dr Geza Zsigmond (Paul Scherrer Institut)

Slides MC-Zsigmond-Ascona2014.ppt

Poster: with apero

20 Systematic effect measurements related to 199Hg in the nEDM experiment

The nEDM experiment benefits from two atomic magnetometers to characterize the magnetic field environment. The 199Hg co-magnetometer allows to correct the neutron frequency for magnetic field drift at the sub-ppm level but does not provide any magnetic field homogeneity informations. Consequently, a dedicated array of 16 Cesium magnetometers (CsM) has been built in the last 3 years allowing a control of vertical magnetic gradients at the 10pT/cm level, which is a critical point for systematic uncertainties estimation in the nEDM experiment. Since 2012, important results have been obtained combining both 199Hg and Cs magnetometers. I will present the last one: a false electric dipole moment of 199Hg atoms correlated to an electric field. In addition, in the context of the neutron to Hg magnetic moment ratio estimation, we put for the first time in the nEDM experiment, a limit on the systematic light shift effect related to the interaction of the probe light UV photons with the 199Hg atoms gas.

Speaker: Mr Yoann Kermaïdic (Laboratoire de Physique Subatomique et Cosmologie)

Slides Ascona_yk_2014.pdf

21 A combined $^3$He/Cs magnetometer for absolute measurements of magnetic fields

The experimental search for a neutron electric dipole moment (nEDM) at PSI (Switzerland) calls for the precise measurement and control of the applied magnetic field. Here, we report on a combined 3He-Cs magnetometer for the absolute measurement of a uT magnetic field. The measurement principle relies on detecting the free precession frequency of polarized 3He nuclei by a set of 8 optically pumped double-resonance M_x-cesium magnetometers. A prototype has been built and its performance was investigated in the magnetically shielded BMSR2-room at PTB (Berlin). We show that the combined magnetometer reaches a precision of better than 10E-7 in a 100s measurement time, its sensitivity for longer measurement periods being limited by the stability of the applied magnetic field.

Speaker: Mr Hans-Christian Koch (University of Mainz / University of Fribourg)

22 Transverse magnetic field measurements with scalar cesium magnetometers at the nEDM experiment

The nEDM experiment at the Paul Scherrer Institut uses ultra-cold neutrons (UCNs) to search for a neutron electric dipole moment using Ramsey’s method of separated oscillatory fields. In order to correct for drifts of the magnetic field, a mercury magnetometer (HgM) is present in the precession volume of the neutrons, which measures the average field. However, due to inhomogeneities in the magnetic field and the much lower kinetic energy of the UCNs relative to their gravitational potential, the UCNs feel a different average magnetic field than the mercury atoms. In order to correct for this difference, sixteen scalar cesium magnetometers (CsMs) were installed around the precession chamber. These magnetometers locally measure the field's magnitude and hence provide information about the inhomogeneity of the magnetic field. Apart from merely providing a correction on the HgM measurements, they can also be used for an explicit homogenisation of the magnetic field itself. However, homogenising the measured magnitudes was found to be insufficient for a homogenisation of the full magnetic field. Moreover, when comparing the average field readings from the HgM and the CsMs (using an approximated harmonic expansion to the second degree), the two magnetometers do not always agree. This is simply because the low order harmonic approximation is too crude. In order to improve the knowledge of the field's shape, we propose to measure the full vector components of the magnetic field at the position of each CsM, instead of merely its magnitude. We discuss a method to measure components transverse to the main field direction by using the scalar CsMs. An oscillatory field is applied in a transverse direction and the scalar CsMs are used to measure the field's instantaneous magnitude. Since the direction and magnitude of the applied field is known from field maps, one can extract the transverse components of the original field. As an interesting remark, a discrepancy was observed between the readings of the CsM and the expected magnetic field behaviour. So far, preliminary simulations have not yet found the origin of this inconsistency.

Speaker: Ms Elise Wursten (KU Leuven)

Poster Poster_TransverseFieldMeasurements_Ascona2014.pdf

23 A precise cesium vector magnetometer for the nEDM experiment

We have developed a vector magnetometer based on optical pumping of cesium atoms to assess the magnetic field distribution in the neutron Electric Dipole Moment (nEDM) experiment at the Paul Scherrer Institute. The system measures deviations from homogeneous magnetic field conditions, which are an important source of systematic errors in nEDM. We will report on progress with a new magnetometer module, which, at 1 uT, has achieved a magnetic field precision of 75 fT in less than two seconds for scalar measurements, and 10 pT for transverse vector measurements, and 380 fT tesla for longitudinal vector measurements.

Speaker: Mr Samer Afach (ETH Zürich)

Poster AsconaVCsM2014.pdf

24 Monte Carlo simulation of PNPI double chamber nEDM spectrometer

Model of PNPI double chamber nEDM spectrometer has been made for simulation by Monte Carlo method. In the model the trajectory of every neutron is simulated with taking into account gravity. The calculation has modeled the whole experimental process and performed data processing in the way it is done in the experiment. Simulation of various systematic effects has been carried out.

Speaker: Mr Alexey Fomin (Petersburg Nuclear Physics Institute)

Poster Fomin.pdf

25 Analysis of Magnetic Field Mapping of the nEDM apparatus of PSI

An improved experimental search for a neutron electric dipole moment (nEDM) is currently taking data at the Paul Scherrer Institute, Switzerland using ultra-cold neutrons (UCN). The experiment requires the holding field ($\mathbf{B}_{\text{0}}$) to be homogeneous over the UCN precession volume to maintain the polarization of the stored UCN and to suppress some of the systematic effects. The accurate knowledge of all magnetic fields generated by the trim coils located on the vacuum tank is of paramount importance to optimize the magnetic field homogeneity better than \SI{e-3}{}. The magnetic field inside the vacuum tank was mapped with a tri-axial fluxgate magnetometer and a vector cesium magnetometer. However, the mechanical limitations of the setup provoke errors in the field measurements by these sensors. These measurement errors could be up to a few tens of $\SI{}{\nano\tesla}$ without correction. We demonstrate an approach to extract and correct these errors in the offline analysis.

Speaker: Mr Prashanth Pataguppi (Paul Scherrer Institute)

26 A laser based mercury magnetometer for the nEDM experiment at PSI

The nEDM experiment requires very sensitive magnetometers to correct for systematic errors related to magnetic field fluctuations. We present progress on a laser based co-magnetometer which detects the spin precession frequency of 199-Hg atoms in the same volume as the neutrons. With the new laser system, we showed in a proof of principle measurement that we can achieve a fivefold increase of the signal compared to the light from a 204-Hg discharge lamp we have been using. In order to compare laser based and lamp based magnetometer sensitivity, we developed a statistical analysis method based on the Cramer-Rao Lower Bound. This work is supported by the SNF under grant 200020_144473.

Speaker: Ms Sybille Komposch (ETHZ)

27 Analysis of the FID signal of the Hg comagnetometer of nEDM experiment at PSI

The nEDM experiment, carried out in the Paul Scherrer Institute in Villigen, Switzerland, measures the electric dipole moment of the neutron. An important part of the set-up is an 199-Hg cohabiting magnetometer. A thorough research on the magnetometer's FID signal analysis was main topic of the author's master thesis. The poster will present main conclusions arising from the research. A method to effectively compare different approaches to the analysis is put forward and used to evaluate performance of a new approach proposed by the author. The evaluation includes discussion of systematic uncertainties due to magnetic field drifts. Also, a scheme for data analysis with the new approach is presented.

Speaker: Mr Michał Rawlik (ETH Zürich)

Poster rawlik_ascona_2014_poster.pdf

28 Cs magnetometer array in the nEDM experiment

The nEDM experiment located at the ultracold neutron source at Paul Scherrer Institut searches for a permanent electric dipole moment of the neutron (EDM) by looking for a difference of the neutron precession frequencies in parallel and antiparallel magnetic and electric fields. Changes of the magnetic field and its gradients that are correlated with the electric field reversal may mimic an EDM. Sixteen vacuum-compatible Cs magnetometers arranged in a three-layer gradiometer around the neutron precession chamber monitor temporal and spatial magnetic field changes. The sensors are driven by individual laser beams derived from a single beam produced by a frequency-stabilized diode laser. The magnetometers are routinely operated in a continuous mode and can be switched to a free induction decay mode for improving readout accuracy. I will present details of the magnetometer operation and array arrangement. ​

Speaker: Dr Malgorzata Kasprzak (University of Fribourg)

19:00 Dinner

Wednesday 5 November

Magnetic environment: Magnetic fields

Magnetic fields
Magnetic sensors

29 SNS magnetic field

The nEDM experiment at the Spallation Neutron Source (SNS) will search for a neutron electric dipole moment (EDM) with a sensitivity of <5⋅10−28 e-cm. Polarized neutrons will precess in a constant magnetic field while the electric field is varied, with a non-zero neutron EDM appearing as a variation in the precession frequency correlated with the electric field. Geometric phase and neutron polarization lifetime effects constrain the allowed magnetic field gradients to below 0.1 uG/cm. Gradients nearly satisfying this requirement have been measured using a cos(θ) coil operated at design magnetic fields inside an open-ended superconducting lead shield. I will describe the cryogenic operation of the coil and shield, the three-axis fluxgate magnetometer field-mapping system, and further efforts to improve the magnet design by partially closing the end of the superconducting shield.

Speaker: Dr Simon Slutsky (California Institute of Technology)

Slides SimonSlutsky_Ascona_SNSMagnets_11_2014.pdf

30 Magnetic Field R&D for the nEDM experiment at TRIUMF

The TRIUMF neutron electric dipole moment (nEDM) experiment is the first experiment that will use the new spallation driven superfluid helium UCN source at TRIUMF. This experiment will employ a room temperature Ramsey Resonance based EDM apparatus and aims to constrain the nEDM by an order of magnitude. In this design, inhomogeneities and lack of stability of the applied magnetic fields are expected to be leading sources of systematic errors in the measurement. This presentation will discuss recent R&D efforts toward active and passive magnetic shielding, magnetic field generation inside shielded volumes, and precision magnetometry.

Speaker: Dr Russell Mammei (The University of Winnipeg)

Slides nEDM_2014_workshop_magfields_final.pdf

10:00 Coffee Break

Magnetic environment: Fields and Shields

Magnetic fields
Magnetic sensors

31 Degaussing of magnetic shields

Speaker: Mr Allard Schnabel (PTB, Berlin)

Slides Allard_Schnabel_Degaussing.pptx

32 PSI - Environment

The measurement of the nEDM requires a magnetic field that is homogeneous in space and stable in time. This presentation will focus on how to provide and maintain such a field. Assuming a stable current source and a rigid coil, it is still necessary to have a stable temperature such that the mu-metal keeps its magnetisation. Furthermore, careful relaxation (about once per day) of the mu-metal is necessary after each change of the orientation of the B-field. Trim-coils are used to obtain a homogeneous field. Off-line mapping is done to find their optimal setting and to measure residual inhomogeneities in order to correct for systematic effects. Before entering the mu-metal the neutrons need to be polarized, and then guided with a relatively strong magnetic field in order to keep the polarization. The transition into the weak field in the storage chamber is particularly difficult. Around the mu-metal shield a surrounding field compensation system consisting of 6 large coils and 30 Fluxgate sensors is installed and suppresses external magnetic fluctuations.

Speaker: Dr Jochen Krempel (ETH Zürich)

Slides 2014-11-Ascona-PSI-Environment-JKrempel.pptx

33 SNS Injection fields and coils

While input guide fields for polarized neutrons and He-3 do not have the same uniformity requirement as the main precession coil, their design faces other unique challenges. For example, the field must taper by several orders of magnitude while preserving polarization, and transition into the main field without causing additional gradients. We describe methods being developed to calculate the ideal field taper. Using the magnetic scalar potential, we design surface-current coils to produce this exact field profile.

Speaker: Dr Christopher Crawford (University of Kentucky)

Slides ascona_2014-11-04_transport.pptx

12:00 Lunch

Magnetic environment: Sensors

Magnetic fields
Magnetic sensors

34 Analytic models of shield-coupled coils

Analytic models of current structures coupled to highly-permeable magnetic enclosures provide a useful conceptual guide, as well as a numerical benchmark, for the design of coils in the presence of passive magnetic shields. We present recent analytic results and discuss their application in the design of shield-coupled coils for proposed EDM experiments in Canada and Japan.

Speaker: Prof. Christopher Bidinosti (University of Winnipeg)

Slides Bidinosti_Ascona2014.pdf

35 Magnetometry Overview for the PSI nEDM Experiment

One of the most important design criteria for an improved nEDM experiment is the realization of a stable and homogeneous main magnetic field B0. The level at which B0 can be controlled or measured is directly linked to the achievable nEDM sensitivity since uncompensated B0 fluctuations add noise to the extracted nEDM value and field inhomogeneities give rise to several systematic effects. Neutron EDM experiment uses a wide range of techniques to meet the demands on B0 control. These include a spectrum of different specialized magnetometers based on 199Hg 3He, and Cs atoms. We present an overview over currently used techniques, devices under development and approaches for future improvements.

Speaker: Dr Georg Bison (PSI)

36 Superconducting Quantum Interference Device (SQUID) applications in the SNS nEDM Experiment

The SNS nEDM experiment will have two readout methods built into the apparatus: the “dressed spin” method, in which a strong non-resonant RF field is applied to match the effective neutron and helium-3 (co-magnetometer) gyromagnetic ratios; and the “free precession” method, in which the RF field is off and the precession of the helium-3 magnetization is directly detected with SQUID-based gradiometers. In both methods, the neutron spin analysis is performed continuously by the spin-dependent n + 3He capture reaction, which creates scintillation light in the ambient superfluid 4He. In this talk, I will discuss practical considerations of implementing low-noise SQUID gradiometers into the SNS nEDM apparatus and show results of a series of tests of a candidate SQUID system in a mock-up apparatus, including a reference channel method to reduce unwanted signals from the 3He precession measurement. I will also describe a multi-channel SQUID based scanner for magnetic impurities in room-temperature samples, which could be used to qualify materials for installation into the central detector of a nEDM apparatus.

Speaker: Dr Steven Clayton (Los Alamos National Laboratory)

Slides clayton_squids_nedm2014.pdf clayton_squids_nedm2014.pptx

Poster: with Coffee

Magnetic environment

Magnetic fields
Magnetic sensors

37 An NMOR-based magnetometer for studying magnetometry and magnetic fields

Precision magnetometers placed close to the nEDM measurement cell(s) can give additional information on field stability and homogeneity. We have developed a magnetometer based on non-linear magneto-optical rotation of laser light resonant with the D1 transition in Rb. In addition to characterizing magnetometer performance, we have used this magnetometer to measure large axial shielding factors for a set of concentric cylindrical shields with small applied external fields. I will report on the development of the magnetometer, on our results and plans for future development.

Speaker: Prof. Jeffery Martin (The University of Winnipeg)

Slides jmartin-Ascona-nov2014.pdf jmartin-Ascona-nov2014.pptx

38 Development of an optical co-magnetometer for a neutron EDM experiment at TRIUMF

on behalf of the TRIUMF UCN collaboration One of the experiments for the TRIUMF UCN new facility is the measurement of the neutron electric dipole moment (nEDM). In order to improve the present world’s best experimental result, it is desired to develop a new co-magnetometer. For this purpose, our group is proposing to use a dual-species comagnetometer with Hg-199 and Xe-129. In this method, polarized Hg-199 and Xe-129 atoms will be introduced into the nEDM cell at the same time as the neutrons, and the spin-precession frequencies of both species are measured simultaneously. The Xe and Hg atoms are probed continuously by observing the modulation of transmitted probe light, at 253.7 nm, for Hg, and emission in the near infrared (823 nm and 895 nm) for Xe by exciting a two-photon transition at 252.4 nm. This talk will present our progress on the development of the dual-species comagnetometer.

Speaker: Prof. Takamasa Momose (University of British Columbia)

19:00 Conference Dinner

Restaurant in Ascone transport back is organized.

Thursday 6 November

Electric Field

39 Electrical breakdown studies at TRIUMF

The neutron EDM experiment at TRIUMF aims to apply a dual species co-magnetometer using Xe-129 and Hg-199. Due to a two-photon transition, the Xe pressure in the EDM cell has to be rather high. The High Voltage tests at TRIUMF are investigating the high-voltage stability (around 10-15 kV/cm) in the presence of Xe-129 gas alone and in mixture with Hg-199. The dielectric properties of Xe-129 in the mTorr range of our interest are not known as this pressure region is below the Paschen and above other published data. Ultimately, we are seeking to find the optimum conditions of gas pressure/composition and electrodes separation/geometry and implement our results to the nEDM experiment at (KEK-RCNP/) TRIUMF. The talk will briefly outline the motivation of studding the electrical properties of the Xe-129 gas as this information is essential for conducting a Xe-EDM experiment and employing a dual Xe-129/Hg-199 co-magnetometer in our nEDM experiment. The main focus will be on presenting the current status of the high voltage development work at TRIUMF.

Speaker: Dr Aikaterini G. Katsika (TRIUMF)

Slides Electrical_breakdown_studies_at_TRIUMF_Katerina_Katsika.pdf

40 High Electric field development for the SNS nEDM experiment

The SNS nEDM collaboration is developing an experiment to search for the neutron’s electric dipole moment (EDM), using ultracold neutrons (UCNs) stored in superfluid liquid helium, to be run at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory. In this experiment, being able to achieve a strong and stable electric field in superfluid liquid helium in the region where UCNs are stored is of critical importance, because in EDM searches in general the sensitivity depends linearly on the strength of the applied electric field. However, the phenomenon of electric breakdown in liquid helium is poorly understood, and as such a major R&D effort is under way. The SNS nEDM collaboration has developed an apparatus to study electrical breakdown in liquid helium at temperatures as low as 0.4 K at pressures between the saturated vapor pressure and 1 atm for electrodes 12 cm in diameter with a gap size of a few cm. In this talk, the current status of the high electric field R&D and the implications of the findings on the SNS EDM experiment will be discussed.

Speaker: Dr Takeyasu Ito (Los Alamos National Laboratory)

Slides Ito_HV_Ascona.pdf

10:00 Coffee Break

Workshop wrap up

41 nEDM prospects at ILL

Speaker: Dr Peter Geltenbort (Institut Laue-Langevin)

42 Discussion "Quo vadis nEDM?"

43 CSF Award ceremony

Speaker: Mrs Chiara Cometta

12:00 Lunch