muon (g-2)
DESCRIPTION
Muon (g-2). Status and Plans for the Future. B. Lee Roberts Department of Physics Boston University. [email protected] http://physics.bu.edu/roberts.html. Magnetic moments, g-factors. Lepton Flavor Violation Muon MDM (g-2) chiral changing Muon EDM. The Muon Trio:. Dirac,. - PowerPoint PPT PresentationTRANSCRIPT
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B. Lee Roberts, PANIC05, Santa Fe, 27 October, 2005 - p. 1/35
Muon (g-2)
Status and Plans for the Future
B. Lee RobertsDepartment of Physics
Boston University
[email protected] http://physics.bu.edu/roberts.html
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Magnetic moments, g-factors
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The Muon Trio:• Lepton Flavor Violation
• Muon MDM (g-2) chiral changing
• Muon EDMDirac, Pauli moment
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Electric and Magnetic Dipole Moments
Transformation properties:
An EDM implies both P and T are violated. An EDM at a measureable level would imply non-standard model CP. The baryon/antibaryon asymmetry in the universe, needs new sources of CP.
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Present EDM Limits
Particle Present EDM limit(e-cm)
SM value(e-cm)
n
future exp 10-24 to 10-25 *
final limit will be better, * projected.
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Unlike the EDM, there is a large SM value for the MDM
The Electron: to the level of the experimental error (4ppb),
Contribution of μ, (or anything heavier than the electron) is ≤4 ppb.
For the muon, the relative contribution of heavier particles
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Standard Model Value for (g-2)
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SM value dominated by hadronic issues:
• Lowest order hadronic contribution ( ~ 60 ppm)
• Hadronic light-by-light contribution ( ~ 1 ppm)
The error on these two contributions will ultimately limit the interpretation of a more precise muon (g-2) measurement.
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Lowest Order Hadronic contribution from e+e-
annihilation
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a(had) from hadronic decay?
• Assume: CVC, no 2nd-class currents, isospin breaking corrections.
• n.b. decay has no isoscalar piece, while e+e- does• Many inconsistencies in comparison of e+e- and decay:
- Using CVC to predict branching ratios gives 0.7 to 3.6 discrepancies with reality.
- F from decay has different shape from e+e-.
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New Physics; SUSY (with large tanβ )
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SUSY connection between a , dμ , μ → e
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Muon (g-2) : E821
• Superconducting “superferric” storage ring– superconducting inflector– fast muon kicker– magic , – direct muon injection with a fast non-
ferric kicker
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Use an E field for vertical focusing
spin difference frequency = s - c
0
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Spin Precession Frequencies: in B field with both an MDM and EDM
The motional E - field, β X B, is much stronger (~GV/m) than laboratory electric fields.
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Spin Precession Frequencies: in B field with both an MDM and EDM
The EDM causes the spin to precess out of plane and increases ||
The motional E - field, β X B, is much stronger (~GV/m) than laboratory electric fields.
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Spin Precession Frequencies: in B field with both an MDM and EDM
The if the EDM were 2.8 x 10-18 e cm, a would increase by 2.9 ppm.
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Muon (g-2): Store ± in a storage ring
magnetic field averaged over azumuth in the storage ring
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Muon (g-2) Present precision: ± 0.5 ppm
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Can we improve the sensitivity of this confrontation between experiment and
theory?• Yes
– E969 at BNL has scientific approval to go from 0.5 ppm → 0.2ppm
– At a more intense muon facility we could do better.
Will Theory Improve beyond 0.6 ppm?• Yes
– better R measurements from: KLOE, BaBar, Belle, SND and CMD2 at Novosibirsk
– More work on the strong interaction
• Theory could eventually improve to ~0.2 ppm
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Exclusion/Limitations on New Physics
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SUSY, dark matter, (g-2)
CMSSM (constrained minimal supersymmetric model)
scal
ar m
ass
gaugino mass
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Future Comparison: E969 = now
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Future Comparison: E969
Historically (g-2) has played an important role in restricting models of new physics.
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E969 at BNL
• Scientific approval in September 2004– at present: no funds for construction or running
• Goal: total error = 0.2 ppm– lower systematic errors– more beam
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Strategy of the improved experiment
• More muons – E821 was statistics limited stat = 0.46 ppm, syst = 0.3 ppm– Backward-decay, higher-transmission beamline– Double the quadrupoles in the decay line
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Strategy of the improved experiment
• New, open-end inflector • Upgrade detectors, electronics, DAQ
x 2 in flux
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E969: Systematic Error Goal
Systematic uncertainty (ppm)
1998 1999 2000 2001 E969Goal
Magnetic field – p 0.5 0.4 0.24 0.17 0.1
Anomalous precession – a 0.8 0.3 0.3 0.21 0.1
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aμ implications for the muon EDM
This paper, published before our February 2001 announcement predicts a large muon EDM, and a corresponding SUSY contribution to aμ comparable to what we might be observing, with the e- EDM predicted to be 0.1 of the present limit.
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aμ implications for the muon EDM
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Dedicated EDM measurement:• operate with ≈ 5 << 29.3• use a radial E-field to turn off (g-2)
precession
• Place detectors above and below the vacuum chamber and look for an up/down asymmetry which builds up with time
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Beam Needs: NP2
• the figure of merit is Nμ times the polarization. We need
to reach the 10-24 e-cm level.• Since SUSY calculations range from 10-22 to
10-32 e cm, more muons is better.
= 5*10-7
(Up+
Dow
n)
time (s)
(Up-
Dow
n)
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Where E821 came from:
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Today:
All E821 results were obtained with a “blind” analysis.
world average
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Summary
• (g-2) provides a precise check of the standard model, and accesses new physics in a way complementary to other probes.
• (g-2) provides serious constraints on physics beyond the standard model.
• The hadronic contribution will eventually set the limit on useful precision, but substantial improvement can and will be made, both in theory and experiment beyond the present situation.
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Recent News from Novosibirsk
• SND has just released their results (hep-ex/0506076) for the cross section e+e- → + - over the . – Error on dispersion integral 50% higher
than CMD2– Good agreement with CMD2– Completely independent from CMD2
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Improved transmission into the ring
InflectorInflector aperture
Storage ring aperture
E821 Closed End P969 Proposed Open End
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Beyond E969?
• It’s not clear how far we can push the present technique.
• To get to 0.06 ppm presents many challenges.
• Perhaps a new storage ring design, and a smaller aperture. – detectors for another factor of 4 will be
very challenging.• At a proton driver/neutrino factory
we certainly we can get more muons
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E969: Systematic Error Goal
• Field improvements will involve better trolley calibrations, better tracking of the field with time, temperature stability of room, improvements in the hardware
• Precession improvements will involve new scraping scheme, lower thresholds, more complete digitization periods, better energy calibration
Systematic uncertainty (ppm)
1998 1999
2000 2001
E969
Goal
Magnetic field – p 0.5 0.4 0.24 0.17 0.1
Anomalous precession – a
0.8 0.3 0.3 0.21 0.1
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Better agreement between exclusive and inclusive (2) data than in 1997-1998 analyses
Agreement between Data (BES) and pQCD (within correlated systematic errors)
use QCD
use data
use QCD
Evaluating the Dispersion Integral
from A. Höcker ICHEP04
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Tests of CVC (A. Höcker – ICHEP04)
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Shape of F from e+e- and hadronic decay
zoom
Comparison between t data and e+e- data from CDM2 (Novosibirsk)
New precision data from KLOE confirms
CMD2