B. Lee Roberts, SPIN2004 –Trieste -11 September 2004 - p. 1/54 New Results on Muon (g-2) Past,...

B. Lee Roberts, SPIN2004 –Trieste -11 September 2004 - p. 1/54

New Results on Muon (g-2)

Past, Present and Future

Experiments

B. Lee RobertsDepartment of Physics

Boston University

roberts@bu.edu http://physics.bu.edu/roberts.html

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The g-2 CollaborationBoston University, Brookhaven National Laboratory, Budker Institute,

Cornell University, University of Heidelberg (* KVI), University of Illinois, KEK, University of Minnesota, Tokyo Institute of Technology,

Yale University

1921-2003Vernon W. Hughes

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Outline

• Prehistory: Stern to CERN

• Theory of Muon (g-2)

• E821: from 7.3 ppm to 0.5 ppm

• The Future: E969 from 0.5 to 0.20 ppm

• Summary and Outlook

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(in modern language)

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Dirac + Pauli moment

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Dirac Equation Predicts g=2

• radiative corrections change g

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The Lowest Order Radiative Corrections

The vertex correction:

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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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• MDM (g-2) chirality changing

• EDM

Matrix Element for MDM and EDM

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The CERN Muon (g-2) Experiments

The muon was shown to be a point particle obeying QED

The final CERN precision was 7.3 ppm

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Standard Model Value for (g-2)

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Two Hadronic Issues:

• Lowest order hadronic contribution• Hadronic light-by-light

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Lowest Order Hadronic from e+e- annihilation

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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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a(had) from hadronic decay?

• Must assume CVC, no second-class currents, make the appropriate isospin breaking corrections. decay has no isoscalar piece, while e+e- does

Let’s look at the branching ratio and Fπ from the two data sets:

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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

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• Comparison with CMD-2 in the Energy Range 0.37 <s<0.93 GeV2

(375.6 0.8stat 4.9syst+theo) 10-10

(378.6 2.7stat 2.3syst+theo) 10-10

KLOECMD2

1.3% Error0.9% Error

a= (388.7 0.8stat 3.5syst

3.5theo) 10-10

2 contribution to ahadr

• KLOE has evaluated the Dispersions Integral for the 2-Pion-Channel in the Energy Range 0.35 <s<0.95 GeV2

• At large values of s (>m) KLOE is consistent with CMD and therefore

They confirm the deviation from -data!.

Pion Formfactor

CMD-2KLOE

0.4 0.5 0.6 0.7 0.8 0.9

s [GeV2]

45

40

35

30

25

20

15

10

5

45

0

KLOE Data on R(s)

Courtesy of G. Venanzone

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A. Höcker at ICHEP04

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ahad [e+e–

] = (693.4 ± 5.3 ± 3.5) 10 –10

a SM

[e+e–

] = (11 659 182.8 ± 6.3had ± 3.5LBL ± 0.3QED+EW) 10 –10

Weak contribution aweak = + (15.4 ± 0.3) 10

–10

Hadronic contribution from higher order : ahad [( /)3] = – (10.0 ± 0.6) 10

–10

Hadronic contribution from LBL scattering: ahad [LBL] = + (12.0 ± 3.5) 10

–10

a exp – a

SM =(25.2 ± 9.2)

10 –10

2.7 ”standard deviations“

Observed Difference with Experiment:

BNL E821 (2004):a

exp =(11 659 208.0 5.8) 10 10

not yet published

not yet published

preliminary

SM Theory from ICHEP04 (A. Höcker)

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Hadronic light-by-light

• This contribution must be determined by calculation.

• the knowledge of this contribution limits knowledge of theory value.

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aμ is sensitive to a wide range of new physics

• muon substructure

• anomalous couplings• SUSY (with large tanβ )

• many other things (extra dimensions, etc.)

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SUSY connection between a , Dμ , μ → e

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Courtesy K.Olivebased on Ellis, Olive, Santoso, Spanos

In CMSSM, a can be combined with b → s, cosmological relic density h2, and LEP Higgs searches to constrain mass

Allowedband a(exp) – a(e+e- theory)

Excluded by direct searches

Excluded for neutral dark matter

Preferred

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Current Discrepancy Standard Model

The CMSSM plot with error on aof 4.6 x 10-10

(assuming better theory and a new BNL g-2 experiment)

a=24(4.6) x 10-10 (discrepancy at 6 a0 (4.6) x 10-

10

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Spin Precession Frequencies:

The EDM causes the spin to precess out of plane.

The motional E - field, β X B, is much stronger than laboratory electric fields.

spin difference frequency = s - c

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Inflector

Kicker Modules

Storagering

Ideal orbitInjection orbit

Pions

Target

Protons

π

(from AGS) p=3.1GeV/c

Experimental Technique

π μν

S

Spin

Momentum

B

• Muon polarization• Muon storage ring• injection & kicking• focus by Electric Quadrupoles• 24 electron calorimeters

R=711.2cm

d=9cm

(1.45T)

Electric Quadrupoles

polarized

The field values along the muon trajectory are measured several times per week with 17 NMR probes mounted on a trolley.

The field is tracked continually with ~160 out of 375 NMR probes in the top and bottom walls of the vacuum chamber.

The system is calibrated in situ against a standard* before and after data taking with beam

Experiment - Field Measurement

(I) calibration uncertainties

(II) measurement uncertainties

(III) interpolation uncertainties

(IV) apparatus response and

field perturbations (IV)

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muon (g-2) storage ring

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Field Shimming

2001

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Magnetic Field Uncertainty

Systematic uncertainty (ppm)

1998 1999 2000 2001

Magnetic field – p 0.5 0.4 0.24 0.17

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Beam Dynamics

mismatch between entrance channel and storage volume, + imperfect kick causes coherent beam oscillations

beam storage region

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Coherent Betatron Oscillations

2 is one turn around the ring

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Frequencies in the g-2 Ring

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Detectors and vacuum chamber

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Fourier Transform: residuals to 5-parameter fit

beam motion across a

scintillating fiber – ~15 turn period

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Effects of the CBO on e- spectrum

• CBO causes modulation of N, amplitude ~0.01

• CBO causes modulation of observed energy distribution

• which in turn causes oscillation in A(E), (E), with amplitudes ~0.001, ~1 mrad.

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Functional form of the time spectrum

• A1 and A2 → artificial shifts in a up to 4 ppm in individual detectors when not accounted for.

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Other Systematic Effects: a

• muon losses

• gain changes and pedistal shifts

• pulse pileup

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Muon Frequency Error

Systematic uncertainty (ppm)

1998 1999 2000 2001

Spin precession – a 0.8 0.3 0.3 0.21

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Where we came from:

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Today with e+e- based theory:

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

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Life Beyond E821?

• With a 2.7 discrepancy, you’ve got to go further.

• A new upgraded experiment was approved by the BNL PAC in September

E969• Goal: total error = 0.2 ppp

– 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– New, open-end inflector – Upgrade detectors, electronics, DAQ

• Improve knowledge of magnetic field B– Improve calibration, field monitoring and measurement

• Reduce systematic errors on ωa

– Improve the electronics and detectors – New parallel “integration” method of analysis

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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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Near side Far side

E821: forward decay beam

Pions @ 3.115 GeV/c

Decay muons @ 3.094 GeV/c

This baseline limits how early we can fit data

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E969: backward decay beam

Pions @ 5.32 GeV/c

Decay muons @ 3.094 GeV/c

No hadron-induced prompt flash

Approximately the same muon flux is realized

x 1 more

muons

Expect for both sides

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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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Summary

• g-2 continues to be at the center of interest in particle physics.

• E821 reached 0.5 ppm precision with a 2.7 discrepancy with SM – using e+e- data for the hadronic piece

• E969 has scientific approval, physics reach is x 2 to 2.5 over E821. Should clarify comparison with SM. (still need $)

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Outlook• Scenario 1

– LHC finds SUSY– (g-2) helps provide information on important

aspects of this new reality, e.g. tan • Scenario 2

– LHC finds the Standard Model Higgs at a reasonable mass, nothing else, (g-2) discrepancy and m might be the only indication of new physics

– virtual physics, e.g. (g-2), EDM, →e conversion would be even more important.

Stay tuned !

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E821 ωp systematic errors (ppm)

E969

(i)(I)

(II)

(III)

(iv)

*higher multipoles, trolley voltage and temperature response, kicker eddy currents, and time-

varying stray fields.

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Systematic errors on ωa (ppm)

σsystematic 1999 2000 2001 E969

Pile-up 0.13 0.13 0.08 0.07

AGS Background 0.10 0.10 *

Lost Muons 0.10 0.10 0.09 0.04

Timing Shifts 0.10 0.02 0.02

E-Field, Pitch 0.08 0.03 * 0.05

Fitting/Binning 0.07 0.06 *

CBO 0.05 0.21 0.07 0.04

Beam Debunching 0.04 0.04 *

Gain Change 0.02 0.13 0.13 0.03

total 0.3 0.31 0.21 0.11Σ* = 0.11