Baryon
Antibaryon
Symmetry
Experiment
Kurt Franke
IMPRS-PTFS Evaluation
Motivation
High-precision test of CPT invariance in
Baryons by comparing the proton and
antiproton magnetic moments:

µ p/ p = g p/ p
qp/ p 
S
2 mp/ p
g p = 5.585690 (24)
g p = 5.585694713 (46)
P. F. Winkler et al., Phys. Rev. A 5, p. 83 (1972).
J. DiSciacca et al., Phys. Rev. Lett. 110, 130801 (2013).
Experimental principle
• Charged particle in magnetic field:
Cyclotron Motion
Spin precession
νL

B
1 q⋅B
νc =
2π m
νL =
1 g q⋅B
2π 2 m
• g found as ratio of two frequencies
• → Stable homogeneous magnetic field
• → Long observation time
2 𝜈𝜈𝐿𝐿
g=
𝜈𝜈𝑐𝑐
The Penning trap
Ideal Penning Trap
Radial confinement
𝐵𝐵 = 𝐵𝐵0 𝑒𝑒⃗𝑧𝑧
Φ = 𝑉𝑉0 𝐶𝐶2 (𝑧𝑧 2 − 𝜌𝜌2 /2)
Axial confinement
Motion in a Penning Trap
ν+ ~ 29 MHz
νz ~ 700 kHz
ν- ~ 10 kHz
Continuous Stern-Gerlach Effect
• Measure νSF frequency to flip Sz
• “Magnetic bottle” to affect motion

Φ M = −µ p / p ⋅ B

(
Bz = B0 + B2 z 2 − ρ 2 / 2
)
Electron:
∆𝜈𝜈𝑆𝑆𝑆𝑆 = ⋯ Electron in 28Si13+:
Proton/antiproton:
228 kHz
4.4 Hz
0.17 Hz
B2=300000 T/m2
Double Trap Technique
Split up the work
B
• Detection of spin requires large B2
• High precision requires small B2
1
AT
PT
Drive until
unambiguous
spin transition
3
Determine
spin state
(spin flipped?)
(Many cycles)
2
Measure νc
Drive spin at νRF
Pflip
νRF/νc
Implementation of BASE in the AD
BASE approved by the CERN research board
Installation of BASE in the AD during LS1
BASE Apparatus
Detecting Spin State
AT as spin state detector:
A. Mooser et al., PRL 110, 140405 (2013).
State estimator using Bayesian recursive formula:
Fitting the Resonance
• Bayesian parameter-based model selection
– 𝑃𝑃(𝜇𝜇, 𝜎𝜎, 𝑛𝑛0 , 𝑛𝑛1 , … |𝜈𝜈𝑐𝑐 , 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑)
– Numerically integrate out everything except μ
– Uncertainty reduced by 30%!
• First improvement in 𝑔𝑔𝑝𝑝 in over 40 years!
A. Mooser et al, Nature (accepted)
People/Funding
Thank you for your attention!