1. Andreas Knecht1ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 A Gravitational Spectrometer for Ultracold Neutrons Andreas Knecht Paul Scherrer Institut & Universität Zürich

2. Andreas Knecht2ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Outline Ultracold Neutrons Neutron Electric Dipole Moment UCN Detection & Standard Techniques for Determining UCN Velocities Test of an Efficient Gravitational Spectrometer for Ultracold Neutrons

3. Andreas Knecht3ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Ultracold Neutrons Neutrons with properties: Kinetic energy E < 300 neV Velocity v < 7.5 m/s Wavelenghts λ > 500 Ǻ Temperature T < 3 mK Interactions: Gravitational: V g = mgh = 100 neV/m Magnetic: V m = -μB = 60 neV/T Strong: Fermi potential depending on material; V F up to 350 neV Weak: n p + e + ν

4. Andreas Knecht4ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 nEDM An EDM couples to an electric field as a MDM couples to a magnetic field: Measure EDM from the difference of precession frequencies for parallel/ anti-parallel fields: Non-zero EDM violates both parity P and time reversal T violates also CP understand mechanism of CP violation understand baryon asymmetry

5. Andreas Knecht5ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 nEDM Current best limit: d n < 2.9×10 -26 ecm (Sussex-RAL-ILL) -e +e 1μm1μm

6. Andreas Knecht6ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Systematics Several systematic effects exist in nEDM measurements which depend on the velocity of UCN (e.g. systematics stemming from magnetic field gradient) Measure nEDM as a function of velocity Need an efficient velocity dependent UCN detection system in order to reach statistics Two scenarios: No velocity dependence observable in measured EDM false velocity-dependent EDM effects under control Velocity dependence observable extrapolate to zero velocity

7. Andreas Knecht7ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 UCN Detection UCN are neutral and have only tiny kinetic energies convert them into charged products information on UCN velocity is lost in this process Most widely used reactions: 10 B + n 7 Li + α + 2.3/2.8 MeV 6 Li + n 3 H + α + 4.8 MeV 3 He + n 3 H + p + 0.8 MeV Charged decay products are detected with standard scintillators or proportional gas counters. Pulse height spectrum of 10 B-reaction 7 Li noise

8. Andreas Knecht8ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Standard Techniques Time-of-flight spectrometryAbsorbers at different heights Transmission through foils with different Fermi potentials absorbing gas at different pressures magnetic fields of different strengths inverted-U" shaped UCN guide UCN Measurement of the reach in the gravitational field

9. Andreas Knecht9ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Efficient Gravitational Spectrometer Inclined UCN guide with 4 attached detectors at different heights Large diameter of main guide: 230 mm reduces back diffusion (~10%) Guides made from NiMo coated plexiglas Extract spectrum from distribution over the 4 detectors UCN

10. Andreas Knecht10ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Simulation

11. Andreas Knecht11ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Setup at ILL 1) PF2/TES beamline at ILL 2) U-guide for calibration 3) Gas cell for calibration 4) Input guide into spectrometer 5) Main spectrometer guide 6)-9) UCN detectors 1-4 10) Vacuum equipment

12. Andreas Knecht12ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Tests with U Step in count rates due to U with different lengths Problems with slits while turning the U

13. Andreas Knecht13ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Tests with U independent of slit and related effects change in spectrum clearly visible

14. Andreas Knecht14ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Tests with Gas Cell Gas type: 3 He (also N 2, O 2, Ar) Exponential fit: exp(-p/π i ) σ abs ~ 1/v π i ~ v π 1 = 3.586(7) mbar π 2 = 3.422(3) mbar π 3 = 3.321(3) mbar π 4 = 3.258(3) mbar change of average velocity in the different detectors

15. Andreas Knecht15ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Conclusion & Outlook Determination of UCN velocity is a way to control veloctiy dependent systematics in nEDM measurements Successful test of an efficient velocity dependent UCN detection system Analysis ongoing… Need to characterise system and tune simulation to the data

16. Andreas Knecht16ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 Backup

17. Andreas Knecht17ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 TOF Measurements Spectra after U-guide, gas cell and of the direct beam also measured using TOF technique.

18. Andreas Knecht18ZH Doktorandenseminar 2009, 4. – 5. Juni 2009 nEDM Mercury used to monitor B- field fluctuations via ω=γB. Frequency visible as oscillating signal on PMT. B1B1 + B0B0 ±E±E B0B0 ±E±E B0B0 ±E±E L B1B1 + B0B0 ±E±E