A 680-fold improved comparison of the antiproton and proton magnetic moments

Transcription

1 A 680-fold improved comparison of the antiproton and proton magnetic moments Eric Tardiff Gerald Gabrielse, Jack DiSciacca, Kathryn Marable, Mason Marshall Harvard University July 21, 2014

2 Testing CPT Symmetry All Lorentz-invariant local quantum field theories are symmetric under CPT CPT violation could be used to explain matter-antimatter asymmetry Aim to compare proton and antiproton magnetic moments to better than ppb

3 Penning Trap Measurement Principle Trapping Fields and Particle Motions B Field E Field Magnetron Axial Cyclotron cyclotron These frequency: fields create three harmonic Larmor motions: (spin) frequency: ν c = eb 2πm ~ 6 Tesla ν s = g eb 2 2πm we can obtain the magnetic moment through the ratio: 1/4 µ µ N = g 2 = ν s ν c µ N /µ B = m e /m p 1/2000

4 The Penning Trap 2 m experiment LHe dewar magnet LN 2 dewar magnet LHe dewar tripod and amplfiers trap electrodes magnet coils auxiliary LN 2 dewar trap inserted into the bore of a superconducting solenoid very uniform 5.7 Tesla field along the trap axis stack of gold plated copper electrodes used to generate potentials for particle control and measurement cyrogenic system trap includes a small helium dewar to lower experiment temperature to 4K

5 The Penning Trap 20 cm feedthrough pins support rods trap electrodes degrader trap vacuum enclosure trap inserted into the bore of a superconducting solenoid very uniform 5.7 Tesla field along the trap axis stack of gold plated copper electrodes used to generate potentials for particle control and measurement cyrogenic system trap includes a small helium dewar to lower experiment temperature to 4K pumpout and pinchoff port titanium foil

6 The Penning Trap degrader field emission point analysis trap precision trap 15 cm trap inserted into the bore of a superconducting solenoid very uniform 5.7 Tesla field along the trap axis stack of gold plated copper electrodes used to generate potentials for particle control and measurement cyrogenic system trap includes a small helium dewar to lower experiment temperature to 4K

7 loading a single proton 20 cm pumpout and pinchoff port titanium foil feedthrough pins support rods trap electrodes degrader trap vacuum enclosure field emission point emits a pulse of 2 kev electrons knock the electrons off hydrogen atoms on the degrader, freeing protons have a cloud of protons in the precision trap scan the cyclotron frequencies to count the number of protons drive protons to higher cyclotron energies and lower endcap voltages until only one proton remains. repeat until only one proton remains

8 loading a single proton

9 loading a single antiproton 20 cm pumpout and pinchoff port titanium foil feedthrough pins support rods trap electrodes degrader trap vacuum enclosure first, locate the experiment in the antiproton decelerator at CERN 5 MeV antiprotons lose energy passing through the degrader, catching some kev antiprotons in the penning trap antiprotons knock loose electrons from the degrader, which are trapped as well electrons cool to the electrode temperature (4K) and collisionally cool the antiprotons move the antiprotons up to the precision trap and release all but one following the same procedure as for protons

10 Trap Frequencies Electric potential near the trap center: V (r) = V 0 2 k=0,even C k ( r d ) k Pk (cos θ) Tune trap voltages for a quadrupole potential. Axial frequency is: ν z = 1 qv0 C 2 2π md 2 Trap electric field shifts the cyclotron frequency from the free-space value by the magnetron frequency: ν + = ν c ν ν = ν2 z 2ν + We can extract the free-space cyclotron frequency from the three trap frequencies: ν c = ν+ 2 + νz 2 + ν 2

11 Frequency Measurement I I image currents on electrodes provide a signal of the particle oscillation endcaps coupled to an amplification circuit for axial frequency detection split compensation electrodes coupled to an amplification circuit for cyclotron frequency detection magnitude of image current signal on the order of 25 fa

12 Coupling the spin frequency to the axial frequency (a) 3 m m ( b ) B (tesla) e n d c a p c o m p e n s a t i o n i r o n r i n g c o m p e n s a t i o n e n d c a p d i s t a n c e ( m m ) introduce magnetic bottle for an axial field that changes quadratically: µ B µz 2 so changes in the magnetic moment change the axial frequency [ ( gms ν z 2 + n + 1 ) + ν ( m l + 1 )] 2 ν c 2

13 Self-Excited Oscillator precision measurement of axial frequency using feedback of image current signal 1 change in spin state changes the axial frequency by 130 mhz out of 1 MHz change in cyclotron state changes the axial frequency by 50 mhz V signal R eff φ G 1 PRL 94, (2005); PRL 104, (2010)

14 Cyclotron Dips effective resistance changes resonantly when detection circuit is tuned particle motion shorts the noise resonance to ground, creating a dip a single cyclotron state creates a narrow dip in the noise resonance of the axial detection circuit driving cyclotron transitions on resonance while averaging the signal results in a wider dip

15 Measurement Scheme SEO on measure f z near-resonant drive off-resonant drive feedback and SB cooling time (s)

16 Allan deviations f z Hz Allan deviation Hz a 1 2 statistical spread in a sequence of frequency difference 0 3 measurements σ Allan = N 2 ( i ) 2N time hours averaging time hours b f z Hz Allan deviation Hz i= time hours averaging time hours a b

17 Proton Result µ p µ N = (7) [2.5ppm] 2 2 PRL 108, (2012)

18 Antiproton Result µ p µ N = (12) [4.4ppm] times more precise than previous results using exotic atoms 4 3 PRL 110, (2013) 4 Z. Phys. C 37, 557 (1988); Phys. Lett. B 678, 55 (2009)

19 Proton/Antiproton Comparison µ p µ p = ± [5.0 ppm] consistent with the CPT theorem First direct comparison of proton and antiproton magnetic moments using single trapped particles

20 Strategy for ppb measurements can resolve single spin flips with 96% fidelity and 26% efficiency 5 adiabatic passage should push this to essentially 100% efficiency sweep a spin drive adiabatically through the spin resonance frequency to invert the spin precision trap used for state preparation, analysis trap used for state readout f z Hz Hz a b PRL 110, (2013) time hours time hours 0.4 c Hz time hours

21 Competition from BASE Used double penning trap technique to improve single-particle proton magnetic moment measurement to the ppb level: µ p µ N = (7)(6) 6 6 Nature 509, 596 (2014)

22 Thank you ATRAP Collaboration Kathryn Marable Mason Marshall Jack DiSciacca Eric Tardiff Rita Kalra Gerald Gabrielse Stephan Ettenauer Funding Agencies Daniel Fitzakerley Matthew Weel Matthew George Cody Storry Eric Hessels Walter Oelert Dieter Grzonka Thomas Sefzick