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Positrons for a New Measurement of the Positron Magnetic Moment

Positrons for a New Measurement of the Positron Magnetic Moment. Shannon Fogwell Hoogerheide Lepton Moments 2014 July 21, 2014. Acknowledgements. Prof. Gerald Gabrielse Elise Novitski (PhD in progress…) Joshua Dorr (2013) Shannon Fogwell Hoogerheide (2013). New Apparatus

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Positrons for a New Measurement of the Positron Magnetic Moment

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  1. Positrons for a New Measurement of the Positron Magnetic Moment Shannon FogwellHoogerheide Lepton Moments 2014 July 21, 2014

  2. Acknowledgements • Prof. Gerald Gabrielse Elise Novitski (PhD in progress…) Joshua Dorr (2013) Shannon FogwellHoogerheide (2013) • New Apparatus • Retractable Positron Source • Positron Loading

  3. 2008 Electron Magnetic Moment Measurement Best measurement of electron g-value: → Most precise determination of fine structure constant: →Most precise test of Standard Model and QED (with independent α) However, best measurement of positron g-value is only 4.3 ppt. This limits test of CPT violation in lepton systems: Could be improved by 15x with 0.28 ppt positron measurement T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio, Phys. Rev. Lett. 109, 111808 (2012) D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett.100, 120801 (2008) R. Bouchendira et.al. Phys. Rev. Lett.106, 080801 (2011) R. Van Dyck et.al. Phys. Rev. Lett.59. 26 (1987)

  4. 2008 Measurement Best measurement of electron g-value: → Most precise determination of fine structure constant: →Most precise test of QED with independent α However, best measurement of positron g-value is only 4.3 ppt. This limits test of CPT violation in lepton systems: Solution: New and Improved Apparatus with Positron Loading Capability! Could be improved by 15x with 0.28 ppt positron measurement T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio, Phys. Rev. Lett. 109, 111808 (2012) D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett.100, 120801 (2008) R. Bouchendira et.al. Phys. Rev. Lett.106, 080801 (2011) R. Van Dyck et.al. Phys. Rev. Lett.59. 26 (1987)

  5. Magnetron Cyclotron Axial Magnetic Field: 6 T Superconducting Solenoid Electric Field: Silver trap electrodes

  6. Magnetic Field: 6 T Superconducting Solenoid Electric Field: Silver trap electrodes Dilution Refrigerator: Quantum measurement hnc/kB ≈ 7.2 K Run at 100 mK <n> <<1

  7. New Apparatus 2.5 cm

  8. Advantages of the New Apparatus • Mechanical Stability

  9. Advantages of the New Apparatus • Mechanical Stability Challenge: Lowering warm apparatus straight into a liquid helium dewar without quenching the magnet

  10. Cooldown Procedure • 4-5 hour cooling time • Sliding seal plus glove bag 10

  11. Cooldown Procedure • 4-5 hour cooling time • Sliding seal plus glove bag 11

  12. Advantages of the New Apparatus • Mechanical Stability • Radial Centering

  13. Advantages of the New Apparatus • Mechanical Stability • Radial Centering • Improved Magnetic Shielding • 6x More Cooling Power at 100 mK (300 μW vs 50 μW) • More Room for Electronics

  14. Advantages of the New Apparatus • Mechanical Stability • Radial Centering • Improved Magnetic Shielding • 6x More Cooling Power at 100 mK (300 μW vs 50 μW) • More Room for Electronics • Smaller Magnetic Bottle • Narrower resonance lines

  15. Advantages of the New Apparatus • Mechanical Stability • Radial Centering • Improved Magnetic Shielding • 6x More Cooling Power at 100 mK (300 μW vs 50 μW) • More Room for Electronics • Smaller Magnetic Bottle • Trap Cavity Mode Design • Allows for new techniques (discussed in next talk)

  16. Advantages of the New Apparatus • Mechanical Stability • Radial Centering • Improved Magnetic Shielding • 6x More Cooling Power at 100 mK (300 μW vs 50 μW) • More Room for Electronics • Smaller Magnetic Bottle • Trap Cavity Mode Design • Positron Source Access

  17. Positron Source Source: Radioactive 22Na capsule Requirements: • Smallest source activity possible • Safety considerations • Minimal disruption to high-precision environment • Reasonable loading rate

  18. Positron Source Requirements • Smallest source activity possible • Reasonable loading rate Solution: Positron Loading Trap

  19. Positron Source Requirements • Smallest source activity possible • Reasonable loading rate • Retractable source

  20. Positron Source Requirements • Smallest source activity possible • Reasonable loading rate • Retractable source • Advantages: • Preserve high-precision environment for measurement • Able to easily remove source from apparatus if desired

  21. Positron Source Requirements • Smallest source activity possible • Reasonable loading rate • Retractable source • Advantages: • Preserve high-precision environment for measurement • Able to easily remove source from apparatus if desired • Challenges: • Move source at 100 mK • Minimize heat load on Dil fridge: Dil fridge can only handle ~300 uW at 100 mK – a 1/32” (0.8 mm) hole at 300 K radiates ~200 uW at 100 mK!

  22. Retractable Positron Source • Take great care to prevent room temperature thermal radiation from reaching cryogenic environment

  23. Retractable Positron Source

  24. Positron Loading Mechanism e+ Ps* e- e+ J. Estrada et al., Phys. Rev. Lett. 84, 859 (2000)

  25. Comparison of Source Size and Loading Rate 25

  26. Comparison of Source Size and Loading Rate 26

  27. Loading Potentials 27

  28. Loading Potentials 28

  29. Positron Loading Rate • Maximum positron loading rate: 1-2 e+/min for 6.5 μCi source, or 3-5 e+/s/mCi • Similar normalized loading rate to the 2.5 mCi and 100 mCi sources used to demonstrate positronium loading method • 3-5 times higher loading rate and 75 times smaller source than used in previous e+g-value measurement

  30. Prospects for a New Positron Magnetic Moment Measurement • New high-precision apparatus complete and running well • Robust positron loading demonstrated • Work is underway on transferring positrons to the precision trap • Ready for new (and improved!) measurements (NEXT TALK)

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