Loading in 5 sec....

Anomalous magnetic moment of the muonPowerPoint Presentation

Anomalous magnetic moment of the muon

- By
**karli** - Follow User

- 105 Views
- Updated On :

Brian Plimley • Physics 129 • November 2010. Anomalous magnetic moment of the muon. Outline. What is the anomalous magnetic moment? Why does it matter? Measurements of a µ 1974-1976: CERN 1997-2001: BNL Conclusions. What is the anomalous magnetic moment?. Magnetic moment:

Related searches for Anomalous magnetic moment of the muon

Download Presentation
## PowerPoint Slideshow about 'Anomalous magnetic moment of the muon' - karli

**An Image/Link below is provided (as is) to download presentation**

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript

### Anomalous magnetic moment of the muon

Brian Plimley • Physics 129 • November 2010

Outline

- What is the anomalous magnetic moment?
- Why does it matter?
- Measurements of aµ
- 1974-1976: CERN
- 1997-2001: BNL

- Conclusions

What is the anomalous magnetic moment?

- Magnetic moment:
- Dirac equation predicts g = 2 for e, µ
- Quantum vacuum fluctuations adjust this value
- Anomalous magnetic moment:

(for a muon)

(for a muon)

What is the anomalous magnetic moment?

x

Fundamental diagram:

(consistent with aµ = 0)

γ

µ

Corrections according to Standard Model:

γ

SM = Standard Model

had = hadronic (QCD)

EW = electroweak

What is the anomalous magnetic moment?

Fundamental diagram:

(consistent with aµ = 0)

x

x

γ

µ

γ

γ

µ

γ

γ

µ

QED

electroweak

hadronic

γ

(1st-order corrections)

Why does it matter?

- Tests theories of fundamental forces in the Standard Model (QED, weak, QCD)
- Look for new physics beyond the Standard Model, e.g. supersymmetry (SUSY)

Why does it matter?

- Why muons?
- Electrons also have an anomalous magnetic moment
- Electrons are much easier to work with (stable, easy to find)

A rare photo of an electron

Why does it matter?

- The amplitude of weak and hadronic diagrams scales with the lepton mass:
- So the muon magnetic moment is more sensitive to these forces by a factor of (mµ / me)2 ≈ 40 000!
- (QED has been tested very precisely by ae)

Measurements: CERN, 1974-76

- This is the third and most advanced measurement of aµ at CERN in the 60s and 70s

Measurements: CERN, 1974-76

- Protons on a target produce pions, which enter the storage ring and decay into muons (mostly)
- Muon spinsare highly polarized in the forward direction
- Muons circle the ring many times before decaying into electrons and neutrinos
- Detectors inside ring detect decay electrons

d = 14 m

Eµ ≈ 3 GeV

(pµ = 3.094 GeV/c)

Measurements: CERN, 1974-76

- Cyclotron frequency:
- Spin precession frequency:

Measurements: CERN, 1974-76

- Spin-cyclotron beat frequency (anomalous precession frequency):

- Decay electron preferentially emitted along spin axis of muon

Measurements: CERN, 1974-76

[figure from BNL work, 2006]

- Energy threshold selects only electrons emitted along direction of muon momentum

- Detector countrate oscillates at beat frequency, by which aµ can be calculated…

Measurements: CERN, 1974-76

- ωL is the Larmor frequency (spin precession of a muon at rest)
- ωL measured separately

Measurements: CERN, 1974-76

- CERN results agreed with theory (after theorists included certain higher-order Feynman diagrams!)

theory

Total experimental uncertainty in aµ: 10 ppm

Measurements: BNL, 1997-2001

- Same size and energy as CERN, for good reasons

Measurements: BNL, 1997-2001

- Same technique as CERN experiment, but with improved technology
- Higher muonfluence
- Pions decay before entering storage ring, reducing background
- Superconducting magnets
- Improved quadrupole focusing
- Advanced digital electronics
- et cetera

Measurements: BNL, 1997-2001

Calorimeter detectors are a mixture of lead and plastic scintillator

Measurements: BNL, 1997-2001

- Experimental aµ is 3.4 σ from the most recent Standard Model calculation

Conclusions

- The anomalous magnetic moment of the muon is very useful for testing the fundamental forces of physics
- Significant discrepancy with theory suggests physics beyond the Standard Model
- One candidate theory for extension of the Standard model is supersymmetry (SUSY)

- More work remains to be done to reduce uncertainties in both experimental and theoretical calculations

References

- Content:
- J. Bailey et al, Nuc. Phys. B150 1 (1979)
- G.W. Bennett et al, Phys. Rev. D73 072003 (2006)
- K. Hagiwara et al, Phys. Lett. B649 173-179 (2007)
- J.M. Paley, PhD dissertation (2004)
- wikipedia

- Diagrams:
- T.G. Steele et al, Phys. Rev. D44 3610-3619 (1991)
- D.W. Hertzog and W.M. Morse, Annu. Rev. Nucl. Part. Sci. 54 141-174 (2004)
- Brookhaven g-2 project website
- University of Glasgow, Particle Physics webpage
- The Particle Adventure
- Contemporary Physics Education Project

Download Presentation

Connecting to Server..