Muon g 2
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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,.

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Muon (g-2)

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Muon g 2

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Magnetic moments g factors

Magnetic moments, g-factors

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


The muon trio

Lepton Flavor Violation

Muon MDM (g-2) chiral changing

Muon EDM

The Muon Trio:

Dirac,

Pauli moment

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Electric and magnetic dipole moments

Electric and Magnetic Dipole Moments

Transformation properties:

An EDM implies both PandT 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.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Present edm limits

Present EDM Limits

final limit will be better, * projected.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Unlike the edm there is a large sm value for the mdm

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Standard model value for g 2

Standard Model Value for (g-2)

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Sm value dominated by hadronic issues

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.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Lowest order hadronic contribution from e e annihilation

Lowest Order Hadronic contribution from e+e- annihilation

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


A had from hadronic t decay

a(had) from hadronic t decay?

  • Assume: CVC, no 2nd-class currents, isospin breaking corrections.

  • n.b. t decay has no isoscalar piece, while e+e- does

  • Many inconsistencies in comparison of e+e- and

    t decay:

    - Using CVC to predict t branching ratios gives 0.7 to 3.6 s discrepancies with reality.

    - Fpfrom t decayhas different shape from e+e-.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


New physics susy with large tan

New Physics; SUSY (with large tanβ )

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Susy connection between a m d e

SUSY connection between am , dμ , μ→ e

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Muon g 2 e821

Muon (g-2) : E821

  • Superconducting “superferric” storage ring

    • superconducting inflector

    • fast muon kicker

    • magic g,

    • direct muon injection with a fast non-ferric kicker

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Use an e field for vertical focusing

Use an E field for vertical focusing

0

spin difference frequency = ws - wc

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Spin precession frequencies m in b field with both an mdm and edm

Spin Precession Frequencies: m 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.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Spin precession frequencies m in b field with both an mdm and edm1

Spin Precession Frequencies: m 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.

The EDM causes the spin to precess out of plane and increases |w|

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Spin precession frequencies m in b field with both an mdm and edm2

Spin Precession Frequencies: m in B field with both an MDM and EDM

The if the EDM were 2.8 x 10-18 e cm, wa would increase by 2.9 ppm.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Muon g 2

Muon (g-2): Store m ± in a storage ring

magnetic field averaged over azumuth in the storage ring

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Muon g 2

Muon (g-2) Present precision: ± 0.5 ppm

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Can we improve the sensitivity of this confrontation between experiment and theory

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Exclusion limitations on new physics

Exclusion/Limitations on New Physics

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Susy dark matter g 2 d e821

SUSY, dark matter, (g-2) DE821

CMSSM (constrained minimal supersymmetric model)

scalar mass

gaugino mass

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Future comparison d e969 d now

Future Comparison: DE969 = Dnow

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Future comparison d e969 0

Future Comparison: DE969= 0

Historically (g-2) has played an important role in restricting models of new physics.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


E969 at bnl

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Strategy of the improved experiment

Strategy of the improved experiment

  • More muons – E821 was statistics limited sstat = 0.46 ppm, ssyst = 0.3 ppm

    • Backward-decay, higher-transmission beamline

    • Double the quadrupoles in the p decay line

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Strategy of the improved experiment1

Strategy of the improved experiment

  • New, open-end inflector

  • Upgrade detectors, electronics, DAQ

x 2 in flux

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


E969 systematic error goal

E969: Systematic Error Goal

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


A implications for the muon edm

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.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


A implications for the muon edm1

aμ implications for the muon EDM

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Dedicated edm measurement

Dedicated EDM measurement:

  • operate withg ≈ 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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Beam needs np 2

Beam Needs: NP2

= 5*10-7

  • 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.

(Up+Down)

(Up-Down)

time (ms)

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Where e821 came from

Where E821 came from:

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Today

Today:

All E821 results were obtained with a “blind” analysis.

world average

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Summary

Summary

  • (g-2)m provides a precise check of the standard model, and accesses new physics in a way complementary to other probes.

  • (g-2)m 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.

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Muon g 2

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Recent news from novosibirsk

Recent News from Novosibirsk

  • SND has just released their results (hep-ex/0506076) for the cross section e+e- → p +p - over the r.

    • Error on dispersion integral 50% higher than CMD2

    • Good agreement with CMD2

    • Completely independent from CMD2

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Improved transmission into the ring

Improved transmission into the ring

Inflectoraperture

Inflector

Storage ring aperture

E821 Closed End

P969 Proposed Open End

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Beyond e969

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


E969 systematic error goal1

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

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Evaluating the dispersion integral

Evaluating the Dispersion Integral

Agreement between Data (BES) and pQCD (within correlated systematic errors)

use data

Better agreement between exclusive and inclusive (2) data than in 1997-1998 analyses

use QCD

use QCD

from A. Höcker ICHEP04

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Tests of cvc a h cker ichep04

Tests of CVC (A. Höcker – ICHEP04)

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


Muon g 2

Shape of Fp from e+e- and hadronic t decay

Comparison between t data and e+e- data from CDM2 (Novosibirsk)

zoom

New precision data from KLOE confirms CMD2

B. Lee Roberts, PANIC05, Santa Fe,27 October, 2005


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