Measurement of the muon anomaly to high and even higher precision

David Hertzog*University of Illinois at Urbana-Champaign

* Representing the E821 Collaboration: Boston, BNL, Budker Inst., Cornell, KFI, Heidelberg,

Illinois, KEK, Minnesota, Tokyo Tech, Yale & new E969 groups: JMU, Kentucky, LBL/UC-Berkeley

OutlineThe muon is a little brother of the tau

The “old” BNL experiment With the 2004 result on -

The theoretical ingredients and overall motivation Lots will follow today by the real experts

The “new” experiment – 0.2 ppm is the new goal Some fresh new ideas and bold ambition Approved this week at BNL with Highest “Must Do” Status

(1) Precession frequency

(2) Muon distribution

(3) Magnetic field map

Muon g-2 is determined from 3 measurements

g 2 1

2 3

TIME

B

And, 4 miracles make it happen Polarized muons

Muons are created from in-flight decay and enter ring in a bunch

And, 4 miracles make it happen Polarized muons

Precession proportional to (g-2)

µ

Momentum

Spin

e

mceBg

a

22

The muon spin precesses faster than the cyclotron frequency: a is proportional to the difference frequency

And, 4 miracles make it happen Polarized muons

Precession proportional to (g-2)

P The magic momentumE field doesn’t affect muon spin when = 29.3

µ

EaBa

mce

a

1

12

BNL Storage Ring

incoming muons

Quads

KICK

0 500 ns

100kV

Only a few percent get stored!

Magnetic Field

Continuously monitored using 150 fixed probes mounted above and below the storage region

Measured in situ using an NMR trolley

1 ppm contours 0.05

0.09

0.05

0.07

0.10

0.17

2001

And, 4 miracles make it happen Polarized muons

Precession proportional to (g-2)

P The magic momentumE field doesn’t affect muon spin when = 29.3

Parity violation in the decay

µ

EaBa

mce

a

1

12

2.5 ns samples

Measuring the difference frequency “a”

e+

TIME

Co

un

ts< 20 ps shifts

< 0.1% gain change

Few billion events

Getting a good 2 is a challenge

Fit to Simple 5-Par Function

N(t) = N0 e-t/[1+Acos(at + )]

Fourier Spectrum of Residuals to 5-par Fit

fg-2 ≈229 KHz fCBO≈466 KHz

nff CCBO 11

In 2001, we adjusted the ring index to avoid overlap

Detector“Swims”

Beam into storage volume

Detector “Breathes”(smaller effect)

Coherent Betatron Oscillations

Radius

Acc

epta

nceInflector mapping

to storage volume Acceptance vs average radius

Modulation of N0, A, with fcbo

tttAetNdtdN aa

t

cos1/ 0

tfeAt cbo

t

aacbo 2cos)(

Acbo

t

A tfeAAtA cbo 2cos1)(

Ncbo

t

N tfeANtN cbo 2cos1)( 00

Pileup Subtraction

Phase shift possible

Separate when

you can ...

low rate

deadtime corrected

Energy of positrons

Extrapolate to zero deadtime on average using out-of-time resolved events

Build pileup-free histogram

with deadtime

Muon Loss & Stored Protons

Excess loss rate

Constant loss rate

Uncertainty, mostly due to protons

muon decay

hit hit hit Account for “slow effects” by correction of muon flux in ring beyond exponential decay

Do these muons have a different phase ?

Internal Consistency: Chi-Sq, Run #

Normalized 2 vs. Start Time of Fit

Precession Frequency vs. Run Number

Internal Consistency: Start Time, Detector, Energy

Precession Frequency vs. Detector #

Precession Frequency vs. Fit Start Time

Precession Frequency vs. Energy Band

Five complementary analyses of a

Low n (black), high n (clear), combined (red) data sets.

G2off production9-parameter ratio

G2Too production3 - parameter ratio with cancellation

G2off productionMulti-parameter

G2off productionMulti-parameter quad corrections

G2Too productionMulti-parameter, Eth=1.5 GeV

asymmetry-weighted,

The new result is in excellent agreement with previous measurements on +

g-2 Collaboration: PRL 92 161802 (2004)

a = 11659214.0(8)(3) 10-10 (0.7 ppm)-

g ≠ 2 because of virtual loops, many of which can be calculated very precisely

B

QED

Z

Weak

Had VP

Had LbL

Many of the next 8! talks will discuss the standard model theory

Hadronic vacuum polarization is obtained from e+e- and/or tau data

hµ

h-

h

e+

e-

muons

hadrons

ee

eesR

is related to and also

m

,had sRssK

dsa2

1 s

sK1

The - e+e- comparison

Davier, et al hep-ex/00308214 Jan 04

Difference is significant AND energy dependent

Pion Formfactor

CMD-2KLOE

0.4 0.5 0.6 0.7 0.8 0.9s [GeV2]

45

40

35

30

25

20

15

10

5

45

0

From G. Venanzone

And, from ICHEP, A. Hocker is stepping back from the Tau result until isospin issues are fully understood:

Today, we’ll hear about the latest KLOE “confirmation” of CMD2

Comparison of final results and theory

a(world avg = 11 659 208(6) 10-10 (0.5 ppm)

ee=25±9ee=25±9

Includes new HLbL shift and KLOE result

ee- marriage

± OppsDivorce!

Opps2KLOE

Discrepancy with e+e- based theory

What might this mean? New physics or a fluctuation

7.2 10925 10

ee

Non-zero a appeals to a catalog of SM Extensions

New physics … SUSY Leptoquarks Muon substructure Anomalous W couplings

µ µ

W

µ

W

B

Sensitive for supergravity grand unification, especially for large tan

Chargino-Sneutrino Neutralino-Smuon

tan = 10

100 300 500 700 900

-50

50

0

100

a S

US

Y[1

0-10 ]

smuon mass (GeV)

ee-expt

tau-expt

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- thy)

Excluded for neutral dark matter

Preferred

tan=10

Excluded by direct searches

Same Discrepancy Standard Model

a 25(5) x 10-10 (5 a0 (5) x 10-10

Two “futures” when new experiment and improved theory are complete

E969 is a new g-2 experiment at BNLStrategy is basic:

Get more muons – E821 was statistics limited (stat = 0.46 ppm, syst = 0.3 ppm) AGS 20% more protons Backward-decay beam Higher-transmission beamline New, open-end inflector Upgrade detectors, electronics, DAQ

Reduce B, systematic uncertainty on magnetic field, B Improve calibration, field monitoring and measurement

Reduce a systematic uncertainty on precession, ωa Improve the electronics and detectors New parallel “integration” method of analysis

Keep the main ideas and ring

Expect 5 x more rate

E821 used forward decay beam, which permitted a large component to enter ring

Pions @ 3.115 GeV/c

Decay muons @ 3.094 GeV/c

Pedestal vs. Time

Near side Far side

This baseline limits how early we can fit data

New experiment uses a backward decay beam with large mismatch in momentum at final slits

Expect for both sides

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

Decay region will include more quads to capture muons

Lattice doubled

E821 lattice

x 2 more

muons

Improved transmission into the ring

InflectorInflector aperture

Storage ring aperture

E821 Closed End P969 Proposed Open End

Outscatters muons

x 2 more

muons

Systematic Error Evolution by Factor of 2

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

E969: Precession Measurement Expect 5 x more rate

Segment calorimeters 500 MHz waveform digitization Greatly increased data volume for DAQ

Introduce parallel “Q” method of data collection and analysis Integrate energy flow vs. time

T Method

Q Method

Starting ideas for new, fast, dense and segmented W-SciFi calorimeters

20-fold segmentation 0.7 cm X0

14%/Sqrt(E) Greatly constrained space

Conclusions

E821 was very successful, reaching 0.5 ppm final uncertainty

Theory has gone from 5 ppm → 0.6 ppm during same time period

Today’s status: tantalizing 2.7 discrepancy

Next phase includes new, approved experiment and continued work on hadronic issues related to theory KLOE, BaBar, Belle, radiative corrections, lattice, … Together, expect reduction in expt-thy comparison by x 2

hertzog@uiuc.edu

Extra Slides Follow

Field Uncertainties - HistorySource of

Uncertainty 1998 1999 2000 2001

Absolute Calibration 0.05 0.05 0.05 0.05

Calibration of Trolley 0.3 0.20 0.15 0.09

Trolley Measurements of B0 0.1 0.10 0.10 0.05

Interpolation with the fixed probes 0.3 0.15 0.10 0.07

Inflector fringe field 0.2 0.20 - -

uncertainty from muon distribution 0.1 0.12 0.03 0.03

Other* 0.15 0.10 0.10

Total 0.5 0.4 0.24 0.17

* higher multipoles, trolley voltage and temperature response, kicker eddy currents, and time-varying stray fields.

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 0.11

Σ* = 0.11

The - decay input to H-VP Data precise Related by CVC with corrections

Isospin asymmetry (vs

W-

Issues with mass and width raised last year Long-distance radiative corrections

Bottom line, can the data contribute in the long run at sub % level?