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Penning trap measurement of the magnetic moment of the antiproton. Wolfgang Quint ([email protected]). GSI Darmstadt, Germany. Villars Meeting, Sept. 25, 2004. m p : magnetic moment g p : g-factor s: spin m N : nuclear magneton. B. g-Factor of the antiproton.

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Penning trap measurement of the

magnetic moment of the antiproton

Wolfgang Quint

([email protected])

GSI Darmstadt, Germany

Villars Meeting, Sept. 25, 2004


mp: magnetic moment

gp: g-factor

s: spin

mN: nuclear magneton

B

g-Factor of the antiproton

proton: gp = 2×2.792847337(29)*

accuracy: 10-8

antiproton: gpbar = 2×2.800(8)* accuracy: 10-3

*Particle Data Group


cyclotron frequency:

g-Factor of the antiproton

B: magnetic field in

Penning trap

Larmor precession

frequency:


Positron

(nc , )

(nc , )

(1 , )

(2 , )

CPT

(0 , )

(1 , )

(0 , )

anomaly transition

Figure of merit for CPT violation

(Bluhm, Kostelecky, Russell):

+

-

-

w

-

w

£

×

2

21

(

)

/

2

m

c

1

,

2

10

h

a

a

e

Geonium: Single electron in a Penning trap

Electron

(nc , )

(nc , )

(1 , )

(2 , )

(0 , )

(1 , )

(0 , )

anomaly transition

(nc: cyclotron quantum number)

(Dehmelt,

Van Dyck)


Antiproton

(nc , )

(nc , )

CPT

(nc , )

spinflip transition

spinflip transition

(nc , )

Figure of merit for CPT violation

(Bluhm, Kostelecky, Russell):

Single antiproton in a Penning trap

Proton

(expected

accuracy)


z = 1 MHz

B

C

R

L

U = I R

end cap

dEp/dt = Pcool = -I2R

cooling

compensation

electrode

ring electrode

compensation

electrode

end cap

Electronic detection of a single antiproton

c2-2z2+2


Cyclotron resonance of a single antiproton

measured at LEAR,

1993

(G. Gabrielse,

D. Phillips,

W. Quint)


Ion cyclotron frequency:

G-Factor of the bound electron in H-like ions

B

Larmor precession fre-

quency of bound electron:

new value for the electron mass


Quantum jumps of a single hydrogen-like ion

  • Axial frequency depends on spin direction due to continuous Stern-Gerlach effect


Continuous Stern-Gerlach effect

spin has magnetic

moment 

magnetic bottle:

B(z) = B0 + B2z2

magnetic energy:

Emagn(z) = B0B2z2

attractive or

repulsive force

axial frequency =

f (spin direction


s

e

E

n

l

i

e

l

c

d

t

r

l

i

e

c

i

f

p

c

o

i

t

t

e

e

n

n

t

g

i

a

a

l

M

s

h

a

p

e

Double-Trap Technique for g-Factor Measurements

  • Principle:

  • Excitation of spin-flip in precision trap (homogeneous magnetic field)

  • Detection of spin-flip in analysis trap (inhomogeneous magnetic field for spin-flip detection)

analysis

trap

precision

trap


G-Factor of bound electron

in highly charged ions

experiment: g(12C5+) = 2.001 041 596(1)(4)

theory: g(12C5+) = 2.001 041 591(7)

statisitical error: dg/g = 2·10-9

total error: dg/g = 2·10-9 (limited by the knowledge of me)

  • Measurement of the g-factor of the bound electron

  • with an accuracy of 7 x 10-10

T. Beier et al., PRL 88, 011603 (2002)

V. Yerokhin et al., PRL 89, 143001 (2002)



Conclusions

  • Measurement of the magnetic moment of the

  • bound electron with an accuracy of 7 x 10-10.

  • This experimental technique can be employed for

  • the measurement of the magnetic moment of the

  • antiproton.

Improvement of accuracy in gpbar by six orders of magnitude

Important test of CPT invariance for baryons


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