Prospects for a Million-fold Improvement in the Comparison of Antiproton and Proton Magnetic Moments

Transcription

1 Prospects for a Million-fold Improvement in the Comparison of Antiproton and Proton Magnetic Moments Nicholas Guise Harvard University Cambridge, Massachusetts, USA LEPTON MOMENTS 19 July 2010

2 Prospects for a Million-fold Improvement in the Comparison of Antiproton and Proton Magnetic Moments Nicholas Guise Harvard University Cambridge, Massachusetts, USA (ANTI)BARYON & LEPTON MOMENTS 19 July 2010

3 Overview: Measuring g p in a Penning Trap B field Electron g-factor is now known to 0.6 ppt D. Hanneke, S. Fogwell, and G. Gabrielse, Phys. Rev. Lett. 100, (2008) Can we measure the proton g-factor in the same way? Key differences from the electron experiment: Much harder to see a spin-flip, due to weak experimental challenges of strong magnetic bottle ( >50x e - expt. ) No precise theory calculation for g p key physics result will be proton/antiproton comparison

4 Outline and Highlights Motivations : first-generation ½ size and 50x bottle; expected spin-flip signal = 60 mhz shift in the axial frequency Progress towards g p : 60 mhz resolution achieved after cooling and self-excitation of one proton in the strong bottle and Future Plans

5 Novel Measurement of g p Current CODATA 2006: g p = (46) (10 ppb) electron g-factor, measured to < ppb (Harvard) bound magnetic moment ratio, measured to 10 ppb (MIT) bound / free corrections, calculated to < 1 ppb (Breit, Lamb, Lieb, Grotch, Faustov, Close, Osborn, Hegstrom, Persson, Karshenboim, Ivanov, others) proton-electron mass ratio, measured to < 1 ppb (Mainz, U Wash) CODATA 1998 ( P.J. Mohr and B.N. Taylor, Rev. Mod. Phys 72 (2000), )

6 Novel Measurement of g p Current CODATA 2006: g p = (46) (10 ppb) Proposed electron g-factor, measured to < ppb (Harvard) bound magnetic moment ratio, measured to 10 ppb (MIT) bound / free corrections, calculated to < 1 ppb (Breit, Lamb, Lieb, Grotch, Faustov, Close, Osborn, Hegstrom, Persson, Karshenboim, Ivanov, others) proton-electron mass ratio, measured to < 1 ppb (Mainz, U Wash) CODATA 1998 ( P.J. Mohr and B.N. Taylor, Rev. Mod. Phys 72 (2000), )

7 Potential Million-fold Improvement in Antiproton g Brookhaven T. Pask et al., Phys. Lett. B. 678, 55 (2009) A. Kreissl et al., Z. Phys. C: Part. Fields 37, 557 (1988)

8 Potential Million-fold Improvement in Antiproton g ω cyc has been measured to 0.1 ppb [G. Gabrielse, A. Khabbaz, D. S. Hall, C. Heimann, H. Kalinowsky and W. Jhe, Phys. Rev. Lett. 82, 3198 (1999)] ω spin is the subject of this work potential improvement by 10 6

9 New test of CPT Invariance Charge conjugation Parity transformation Time reversal Tests of CPT include: g factor ratios mass ratios charge ratios lifetime ratios charge to mass ratios

10 New test of CPT Invariance proposed ppb test of Charge conjugation Parity transformation Time reversal Tests of CPT include: g factor ratios mass ratios charge ratios lifetime ratios charge to mass ratios

11 The Open-Endcap Penning Trap B Field E Field Magnetron Endcap Electrode z r Axial Proton Frequencies Cyclotron Compensation Electrode Ring Electrode Compensation Electrode ρ Endcap Electrode B

12 Detecting a Spin-Flip: The Magnetic Bottle Trap potential on-axis is: SHO along the trap axis Introduce a bottle : term modifies axial frequency Now the axial frequency depends on the spin state of the proton: Iron ring, B 2 = T/m 2

13 Detecting a Spin-Flip: The Magnetic Bottle Trap potential on-axis is: SHO along the trap axis Introduce a bottle : term modifies axial frequency Now the axial frequency depends on the spin state of the proton: Iron ring, B 2 = T/m 2 ( ~4 Hz in the e- expt. )

14 Detecting the Axial and Cyclotron Motions RLC tuned circuits convert proton image currents to voltages Endcap Ring I Vsignal I Vsignal noise Endcap Axial Inductor Cyclotron Inductor ~ 100 NbTi wire ~ 2.5 mh ~ 10 silver wire ~ 0.18 µh

15 Analysis Penning Trap Electrode Stack and Full Hat Adjustable Spacer Thermal Isolation Stages Experiment LHe Dewar 7 feet Precision Penning Trap Tripod Pinbase Electrode Stack Trap Can Magnet Windings Magnet LHe Dewar Main LN 2 Dewar Pump-Out Port 1 inch Double-Trap scheme, cf. H. Häffner et al., Phys. Rev. Lett. 85, 5308 (2000) Magnet Bore Tube Auxiliary LN 2 Dewar

16 Complications of a Strong Bottle Any proton radial motion produces a magnetic moment and causes a frequency shift Besides the desired 60 mhz from a spin-flip, we also get unwanted effects: Cyclotron Shifts: 21 mhz per (~200 Hz per µm) Magnetron Shifts: 0.5 µhz per (~40 mhz per µm) cooling (both z and ρ) is essential

17 Axial Feedback Cooling R signal Demonstrated previously only with one electron B. D'Urso, B. Odom and G. Gabrielse, Phys. Rev. Lett. 90, (2003) Apply feedback drive to modify damping rate: φ G

18 Radial Cooling to the Sideband Cooling Limit Axial-Magnetron sideband cooling in our large bottle reveals the axial temperature: We measure T z = 8 ± 2 K Feedback heating increases to T z ~ 20 K Feedback cooling reduces to T z ~ 4 K Magnetron motion cooled to T m ~ 14 mk ρ m ~ 6 µm

19 One-Proton Self-Excited Oscillator R signal Demonstrated previously only with one electron B. D'Urso, R. Van Handel, B. Odom and G. Gabrielse, Phys. Rev. Lett. 94, (2005) φ G Self-excitation at G=1 Phase Optimization Anharmonicity Tuning

20 Self-Excited Oscillator vs. Axial Dips 160 Second SEO 160 Second Axial Dip Dramatic improvement in signal-to-noise Significant reduction in linewidth

21 Axial Frequency Resolution SEO Frequency Stability Frequency resolution requires both line-splitting and low scatter of repeated measurements Overnight Drift

22 Spin-Flip Resolution Achieved with the SEO A well-tuned proton SEO now achieves axial frequency resolution at the 60 mhz level which would indicate a single-proton spin flip.

23 Summary Goal: Demonstrate feasibility of a new ppb comparison of proton/antiproton magnetic moments : First realization of single-proton feedback techniques for self-excitation and axial/radial cooling within a strong magnetic bottle gradient : Axial frequency resolution achieved at the 60 mhz level, sufficient in principle to detect a spin-flip Future Plans: Improve resolution, drive spin-flips, proceed to g- factor measurements

24 Future: Optimize for Antiproton Measurement First-Generation Trap Second-Generation Trap 1/4 Spin Flip Size: 60 mhz Spin Flip Size: 220 mhz Freq. Resolution: ~60 mhz Freq. Resolution:? Antiproton - smaller trap if suggested by proton results - access port for low-energy antiprotons from AD at CERN

25 Advertising and Acknowledgements 1 Funding: AFOSR and NSF Poster Wednesday 1. Current address: Atomic Spectroscopy Group, NIST, Gaithersburg MD