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Positrons for a New Measurement of the Positron Magnetic Moment Shannon Fogwell Hoogerheide Lepton Moments 2014 July 21, 2014

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

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2008 Electron Magnetic Moment Measurement 3 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, (2012) D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett. 100, (2008) R. Bouchendira et.al. Phys. Rev. Lett. 106, (2011) R. Van Dyck et.al. Phys. Rev. Lett (1987)

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2008 Measurement 4 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: Could be improved by 15x with 0.28 ppt positron measurement T. Aoyama, M. Hayakawa, T. Kinoshita, and M. Nio, Phys. Rev. Lett. 109, (2012) D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett. 100, (2008) R. Bouchendira et.al. Phys. Rev. Lett. 106, (2011) R. Van Dyck et.al. Phys. Rev. Lett (1987) Solution: New and Improved Apparatus with Positron Loading Capability!

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

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6 Magnetic Field: 6 T Superconducting Solenoid Electric Field: Silver trap electrodes Dilution Refrigerator: Quantum measurement h c /k B ≈ 7.2 K Run at 100 mK <<1

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New Apparatus cm

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Advantages of the New Apparatus Mechanical Stability 8

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

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Cooldown Procedure hour cooling time Sliding seal plus glove bag

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Cooldown Procedure hour cooling time Sliding seal plus glove bag

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Advantages of the New Apparatus Mechanical Stability Radial Centering 12

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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 13

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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 14

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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) 15

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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 16

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

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

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

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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 20

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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! 21

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

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Retractable Positron Source 23

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

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Comparison of Source Size and Loading Rate 25 Source SizeLoading RateLoading Rate/mCi UW ’81-’87 (resistive damping) 0.5 mCi0.4 e + /min0.8 e + /min/mCi HU ’94-’95 (resistive damping + RMOD) 10 mCi12 e + /min1.2 e + /min/mCi HU ’00 (ATRAP) (TMOD only) 2.5 mCi420 e + /min170 e + /min/mCi HU ’00 (ATRAP) (TMOD + RMOD) 2.5 mCi1700 e + /min670 e + /min/mCi HU ’03 (ATRAP) (TMOD + RMOD) 75 mCi3.2x10 4 e + /min420 e + /min/mCi This work (TMOD only).0065 mCi1-2 e + /min e + /min/mCi

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Comparison of Source Size and Loading Rate 26 Source SizeLoading RateLoading Rate/mCi UW ’81-’87 (resistive damping) 0.5 mCi0.4 e + /min0.8 e + /min/mCi HU ’94-’95 (resistive damping + RMOD) 10 mCi12 e + /min1.2 e + /min/mCi HU ’00 (TMOD only) 2.5 mCi420 e + /min170 e + /min/mCi HU ’00 (TMOD + RMOD) 2.5 mCi1700 e + /min670 e + /min/mCi HU ’03 (TMOD + RMOD) 75 mCi3.2x10 4 e + /min420 e + /min/mCi This work (TMOD only).0065 mCi1-2 e + /min e + /min/mCi

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Loading Potentials 27

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Loading Potentials 28

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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 29

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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) 30

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