Precise%20measurement%20of%20(g-2)?

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Precise measurement of (g-2)?
Huaizhang Deng
Yale University
University of Pennsylvania
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Collaboration
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Prof. Vernon W. Hughes (1921 ? 2003)
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Outline

• What is (g-2)? and why we measure it ?

• Principle of and experimental setup for the
  measurement.

• Analysis and result from the 2000 run.

• Theory of (g-2)? and its new development.

• Preliminary result of muon electric dipole moment.

• Conclusions.

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What is g-2
For the proton ap?1.8 because the proton is
composite particle.
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g - 2 ? 0 for the muon
Other standard model contributions
Contribution from new physics
a?(exp)-a?(SM)a?(new physics)
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Why muon?

• The muon is a point particle, so far.
• (Hadrons, like p and n, are composite
  particles.)

• The muon lives long enough for us to measure.

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Principle of the measurement
When ?29.3 (p3.09 Gev/c), ?a is independent of
E.
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How to measure B
B is determined by measuring the proton
nuclear magnetic resonance (NMR) frequency ?p in
the magnetic field.
??/?p3.183 345 39(10), W. Liu et al., Phys.
Rev. Lett. 82, 711 (1999).
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How to measure ?a
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Muon storage ring
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Some numbers about the experiment
Magnetic field 1.45 T ?p 61.79MHz
Experimental sequence
t 0 beam injection
35 500 ns beam kicked onto orbit
0 15 ?s beam scraping
5 40 ?s calorimeters gated on
45 1000 ?s g-2 measurement
33 ms beam injection
repeats (12 times)
3 s circle repeats
3 day field measurement by
trolley
1 year
data-taking repeats
20 year whole
experiment repeats
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NMR trolley
The NMR system is calibrated against a standard
probe of a spherical water sample.
X. Fei, V.W. Hughes, R. Prigl, NIM A394 349
(1997)
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Trolley measurement
The B field variation at the center of the
storage region. ltBgt?1.45 T
The B field averaged Over azimuth.
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Fixed probe measurements
Calibration of the fixed probe system with
respect to the trolley measurements
The magnetic field measured by the fixed probe
system during 2000 run.
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Systematic errors for ?p
Source of errors Size ppm 2000 1999 Size ppm 2000 1999
Absolute calibration of standard probe 0.05 0.05
Calibration of trolley probe 0.15 0.20
Trolley measurements of B0 0.10 0.10
Interpolation with fixed probes 0.10 0.15
Inflector fringe field -- 0.20
Uncertainty from muon distribution 0.03 0.12
Others 0.10 0.15
Total 0.24 0.4
higher multipoles, trolley temperature and
voltage response, eddy currents from the kickers,
and time-varying stray fields.
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2000 ?a data
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Coherent betatron oscillation (cbo)
kick
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CBO effect on ?a
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Cancellation of cbo around the ring
CBO effect shown on the average energy of e
Cancellation of cbo effect after summing all
detector together.
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Error for ?a
Source of errors Size ppm 2000 1999 Size ppm 2000 1999
Coherent betatron oscillation 0.21 0.05
Pileup 0.13 0.13
Gain changes 0.13 0.02
Lost muons 0.10 0.10
Binning and fitting procedure 0.06 0.07
AGS background 0.10
Others 0.06
Total systematic error 0.31 0.3
Statistical error 0.62 1.3
Timing shifts, E field and vertical
oscillations, beam debunching/randomization.
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Blind analysis and result
After two analyses of ?p had been completed,
?p61 791 595(15) Hz (0.2ppm),
and four analyses of ?a had been completed,
?a229 074.11(14)(7) Hz (0.7ppm),
separately and independently, the anomalous
magnetic moment was evaluated,
am11 659 204(7)(5) ?10-10
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Standard model calculation of a?
a?(SM) a?(QED) a?(had) a?(weak)
a?(QED)11 658 470.57(0.29)?10-10 (0.025 ppm)
a?(weak)15.1(0.4)?10-10 (0.03 ppm)
Both QED and weak contribution has been
calculated to high accuracy. The accuracy of
a?(had) is about 0.6 ppm.
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Hadronic contribution (LO)
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Evaluation of R
M. Davier et al., hep-ph/0208177
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Comparison between ee- and ?
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Experimental and theoretical values
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Beyond standard model

• compositeness for leptons or gauge bosons.

• extra dimensions, or extra particles,

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Muon electric dipole moment

• Vertical profile of decay positrons oscillates
• with frequency of g-2
• with phase 90o different from g-2 phase
• with amplitude proportional to dµ

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Preliminary result of muon EDM
dµ(-0.11.4)10-19ecm dµlt 2.810-19ecm (95 CL)
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Conclusions

• Improve the accuracy of a? to 0.7 ppm

• Uncertainty is about half the size of the weak
• contribution.

• The discrepancy between a?(exp) and a?(SM) is
• 0.7-1.9?, depending on theory.

• We are analyzing the data for negative muons, a
  test
• of CPT.

• Factor 3.75 improvement on the upper limit of
• muon electric dipole moment.