Lori Rebenitsch University of Winnipeg June 17, 2014

1. Developing a Lithium Doped Glass Detector to Measure the Electric Dipole Moment of Ultra Cold Neutrons Lori Rebenitsch University of Winnipeg June 17, 2014

2. Overview • Neutron electric dipole moment (nEDM) • Experimental set-up • UCN counter • Requirements • Specifications Please note that captions appear in top right corner of slides!

3. Neutron Electric Dipole Moment • Baryogenesis • Baryon/antibaryon asymmetry in the early universe • Sakharov conditions (Sakharov, 1967) • Baryon number violation • CP-symmetry violation • Interactions outside of thermal equilibrium • Standard model has small sources of CP-violation • CKM matrix - quarks • Electric dipole moment of fundamental particles • Extensions increase CP-violation • Possible EDM in neutrons due to quark structure

4. Ultra Cold Neutrons • Properties • < 3mK • ~7m/s • Subject to gravity • Polarizable • Find neutron electric dipole moment (nEDM) by finding Larmor frequency • | e-cm for current experimental limit (Harris et. al) • |e-cm for new physics • | e-cm for CKM in Standard Model • | e-cm for

5. nEDM Experiment • Requirements • High UCN density • Stable magnetic shields • High counting efficiency • Goal • UCN/cycle • Comagnetometer ~10fT • nEDMmeasurement e-cm in first phase for new physics

6. Neutron EDM Facility Graphic of planned facility UCN detector protons

7. Detector Requirements • Handle rates >1.3 MHz for periods of few seconds • Reject background • Gammas • Thermal neutrons • 0.05% efficiency stability • Normalize UCN density

8. Lithium Doped Glass Right: Autodesk image of detector. Bottom: Diagram of dual layer glass and how UCN capture and scintillate. • Based on design from PSI (Ban et. al) • Dual layered scintillating glass • Optically bonded • Top layer – lithium depleted • Bottom layer – lithium doped • Capture full scintillation path PMTs Lithium glass UCN Lightguides

9. Measurement The four points on the graph are used to find the Ramsey resonance frequency. • Visibility of fringes • Statistical uncertainty • Formula for determining Ramsey resonance

10. High Rates • DPP-PSD • Generates analysis faster than the computer • Describes signal in few variables in place of full waveform • Reduces computation load on DAQ • DAQ • Minimal computing • Saves • PSD • Slow control • Analyzer • Separate from DAQ • Puts data into TTree

11. DPP-PSD Left: Inverted signal from Am source. Longer events are α’s and short events are γ’s. Right: Waveform with corresponding DPP-PSD gates. The long and short gates collect charge when open.

12. Background Rejection Comparison of the gate values for a thermal neutron source, . Note how the gamma background has a strong 1:1 ratio while the neutrons do not. • By comparing the PSD variables, gamma background can be removed from data. Comparison of PSD Charge Integration Gates gammas Short Integration Gate (ADC) neutrons Long Integration Gate (ADC)

13. Stability of Efficiency Top right: Scope example of a double pulse generated from pulser. Bottom right: Rate of pile-up with respect to frequency of double pulse. • Environmental – long term efficiency • Glass • Temperature • Tests in progress • Pile-up • Occurs 2-3MHz between pulses • Pile-up events have • Higher than average long gate value • Average short gate value • Can be flagged and recounted

14. Normalize UCN Density • UCN are produced in cycles • Number of UCN vary per cycle • Example to normalize UCN density • Utilize volume below cell for UCN density estimation • Factors • Volume below cell is ~10x larger • Volume presents greater probability of pile-up • Throttle the UCN and/or account for pile-up analyzer foil detector

15. Future Work • Detector in process of being built • Stability tests • RCNP proposal to take data with UCN spallation source this fall NSERC, CFI University of Winnipeg, University of Manitoba

16. Thank you