The Letter of Intent to Measure Muon g-2 Five to Ten Times Better

P. T. DebevecLepton Moments Conference

Yarmouthport, MAJune 12, 2003

The g-2 CollaborationR.M. Carey, E. Efstathiadis, M. F. Hare, X. Huang, F. Krienen, A. Lamm, I.Logashenko, J.P. Miller,

J. Paley, Q. Peng, O. Rind, B.L. Roberts, L. R. Sulak, A. TrofimovBoston University

G. W. Bennett, H. N. Brown, G. Bunce, G.T. Danby, R. Larsen, Y.Y. Lee, W. Meng, J.-L. Mi, W.M. Morse, D. Nikas, C. Ozben, R. Prigl, Y.K. Semertzidis, D. Warburton

Brookhaven National LaboratoryY. Orlov

Cornell University A. Grossmann, G. zu Putlitz, P. von Walter

University of HeidelbergP.T. Debevec, W. Deninger, F. Gray, D.W. Hertzog, C.J.G. Onderwater, C. Polly, S. Sedykh, M. Sossong, D. Urner

University of Illinois at Urbana-ChampaignK. Jungmann

Kernfysisch Versneller Instituut, Rijksuniversiteit GroningenB. Bousquet,P. Cushman, L. Duong, S. Giron, J. Kindem, I. Kronkvist, R. McNabb, T. Qian, P. Shagin, C. Timmermans,

D. Zimmerman University of Minnesota

V.P. Druzhinin, G.V. Fedotovich, D. Grigoriev, B.I. Khazin, N. Ryskulov, Yu.M. Shatunov, E. SolodovBudker Institute

A. Yamamoto M. Iwasaki, M. KawamuraKEK Tokyo Institute of Technology

M. Deile, H. Deng, S.K. Dhawan, F.J.M. Farley, M. Grosse-Perdekamp, V.W. Hughes, D. Kawall, J. Pretz, S.I. Redin, E. Sichtermann, A. Steinmetz

Yale University

Funding from Department of Energy, National Science Foundation, National Computational Science Alliance, German Bundesminister fur Bilding und Forschung, Russian Ministry of Science, and U.S.-Japan Agreement in High-Energy Physics

The Letter of Intent to J-PARC

submitted by all institutions of the g-2 collaboration

and

K. YoshimuraKEK

M. Aoki, Y. Kuno Osaka University

Muon Anomalous Moment --The Last Word*

R. W. Williams (1978)

Muon Anomalous Moment(not ready for)The Last Word

*talk at “New Frontiers in High-Energy Physics,” Coral Gables, FL, Jan 16-18, 1978

Still no idea to measure aµ better than the g-2 experiment

aeBam

=difference frequency is directly observable ω

magnet field measured with proton NMR pωµ

a p

a p

aω ω

λ ω ω=

−spin

pµλ µ µ=withmomentum

2000 ωa data

( ) [ ]1 cos( )to aN t N e A tγ τ ω φ−= − +

4×109 events for t > 50 µs and E > 2 GeV

ωa statistical error

( ) [ ]1 cos( )to aN t N e A tτ ω φ−= − +

2a

a a A Nδωω ω τ

=phase must be

determined from data

a

AN

ω τBNL 2000

= 100

= 0.4

= 4×109

0.6 ppma

a

δωω

=

CERN III

= 100

= 0.2

= 1×108

7 ppm=

excerpts from Williams I

“Possibly the most heroic effort in the 5-year life of this massive experiment was the magnetic field, its shimming, regulation, and measurement.”

“…the final result is close to the best theoretical calculation.”

To go to higher energy, thereby raising τ, means to leave the magic value of γ...”

“…returning to weak magnetic focusing as in the case of CERN II is quite out of the question…”

Theory of aµ

( )" "NEW expt theorya a aµ µ µ= −

QED + WEAK + HADRONIC

Standard Model g-2 Relative Magnitudes*

QED 1 (0.024 ppm)Weak 1.31 ± 0.02 ppm

Hadronic 58.5 ± 0.7 ppm (e+e-)or 60.6 ± 0.6 ppm (τ)

Williams (1979)1 (2 ppm)2 ± 2 ppm57.2 ± 8.0 ppm*

*Calmet et al. RMP49(1977)21*A. Nyffeler hep-ph/0305135v1

excerpts from Williams II

“A might be raised by very careful design, by at most a factor of 2…”

“The instantaneous rate, and therefore ultimately N, is also limited by considerations of systematics…We might expect a factor of 3 in N or √3 in the error.”

“…I conclude that a super effort might lead to a determination of a to between 1 and 2 parts per million...The hope for pioneers setting out on this long and difficult road would only be that something remarkable would show up between 8 ppm and 1 ppm, and I doubt that they would make the trip. It is the end of an era…”

“Every factor of two is precious.” V. Hughes

Why would we continue?

Something remarkable could happen between 1 and 0.1 ppme.g. supersymmetry

21001.1ppm tanSUSY GeVamµ β ∆ ≈ ×

W. Marciano, this meeting

Continued efforts on hadronic contributionfrom

CMD-2 & VEPP-200KLOE*

BaBarBelle

CLEO-CBES

*J. Lee Franzini, this meeting

BNL E821 Storage Ring

Injection path Central orbit

BNL E821 Beam Line

7×1012 Protons per Bunch12 Bunches per 3 s AGS Cycle104 Stored µ per Bunch

Magnetic Field Measurement

Measured in situusing an NMR trolley

trolley fixed probe comparison

Continuously monitored with > 360 fixed probes mounted above and below the storage region

Magnetic Field Averaged over Azimuth

Magnetic Field Variation versus Azimuthat center of storage ring (~ ±60 ppm)

Systematic Errors ωp1) absolute calibration 0.05

2) trolley probe calibration 0.20

3) trolley measurement of B0 0.10

4) interpolation with fixed probe 0.15

5) inflector fringe field 0.20

6) muon distribution 0.12

7) others (*) 0.15

2000 [ppm]

0.05

0.15

0.10

0.10

0.00

0.03

0.10

1999 [ppm]

Total Systematic Error δωp 0.40 0.24 ≤ 0.20

2001 [ppm]

improved

*higher multipoles, trolley temperature stability, kicker eddy currents

Alternate view of ωp systematic errorsB absolute standard: spherical probe 0.05 ppm

trolley calibration 0.15 ppmplunging probe for B

trolley probe B measurement 0.10 ppm B

Bfixed probe interpolation 0.10 ppmAll values from 2000 run.Values in red were improved in 2001 run.Total systematic error ≤ 0.20 in 2001 run.

Magnet improvements

Improved field uniformity would reduce systematic errors in field determination

Reduce azimuthal variation by

•Re-machining of poles to flatter tolerance

•Better shimming at pole boundaries

Magnet field measurement improvements I

To improve fixed probe interpolation

•Improve stability of ambient temperature to reduce drift of magnetic field

•Move probes away from pole boundaries

•Increase the number of fixed probes

Magnet field measurement improvements II

To improve trolley probe measurement of B and trolley probe calibration

•Reduce positioning error of trolley probes

•Improve field homogeneity in calibration region - typical value (0.2 ppm / cm) × (3 mm)

Magnet field measurement improvements III

•Reduce systematic error from other sources, e.g. better stabilize trolley temperature and trolley electronics power

•Absolute calibration against 3He

•Monitor and correct for kicker eddy current

Summary of ωp systematic error considerations

• Route to (some) significant improvements has been identified.

• No route has (yet) been identified to eliminate any known systematic error source.

• Very significant effort needed for improvement to level of 0.05 ppm from current level of ≤ 0.20 ppm.

•NB reducing the aperture would reduce the systematic error, but acceptance of the ring goes as the 5th power of the aperture.

statistical error considerations

2a

a a A Nδωω ω τ

=

0.07 ppma

a

δωω

≈for N = 4×1011

100 times BNL2000 or BNL2001!

Number of muons depends on 1) Intensity and duty factor of source2) Capture section of beam line3) Injection into storage ring

1) inflector2) kicker

4) Duration of the experiment

possible improvements

×8×4×3

1) bunches per cycle 12(BNL)→90(J-PARC)2) use lithium lens or magnetic horn3) increase aperture to match storage ring4) not an attractive option

Systematic Errors ωaBNL2000 BNL2001

1) Pile-up 0.13

2) Gain changes 0.13

3) Timing shifts 0.02

4) Coherent betatron oscillation 0.21

5) Lost muons 0.10

6) E field and vertical betatron motion 0.03

7) Binning and fitting 0.06

8) Beam debunching and randomization 0.04

Total Systematic Error δωa 0.31 0.2 – 0.3

dete

ctor

s an

del

ectro

nics

stor

ed b

eam

ωa systematic error reduction possibilities

1) Pile-up

2) Gain changes

3) Timing shifts

4) CBO

5) Lost muons

6) E field…

7) Binning…

8) Beam debunching…

improve calorimeter, WFD, increase segmentation

eliminate gating, better gain monitoring

improve injection, add CBO damping

better scraping, greater field homogeneity

improve muon distribution measurement

Summary of ωa systematic error considerations

• Route to (many) significant improvements has been identified.

• Some new technologies must be developed.

• Very significant effort needed for improvement to level of 0.05 ppm from current level of < 0.30 ppm.

My wish for the future•2001 data, ancillary analyses, final report first.

•Mandatory to demonstrate that the magnet can be made more homogeneous-best done before any move-best done for a new run.

•New inflector needed for a new run.

•New run also a testing ground for new electronics.

•Pursue new ideas, test untried ideas.

•More muons will be available.

•(Perhaps) we are not ready for the last word.