The New Muon g2 Experiment

1
The New Muon g-2 Experiment
David Hertzog University of Illinois at
Urbana-Champaign
Workshop on Electromagnetic Probes of Fundamental
Physics Erice, Oct. 2001
2
Purpose of this talk Describe ...

• The 1999 run has produced a new result that
• has a precision of 1.3 ppm
• differs from the SM evaluation by 2.6 s
• has raised the stakes on improving the hadronic
  VP contribution evaluation
• represents a challenge for all involved to prove
  it is correct
• The 2000 run is
• about 4-6 times larger data set for m
• full of intriguing new hurdles in the analysis
• The 2001 run
• used m- to test for CPT (and for systematics)
• included numerous beam-dynamics studies

3
The g-2 Collaboration
R.M. Carey, E. Efstathiadis, M. Hare, F. Krienen,
I.Logashenko, J.P. Miller, J. Paley, O. Rind,
B.L. Roberts, L. R. Sulak, A. Trofimov Boston
University 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 Laboratory Y.
Orlov D. Winn Cornell University
Fairfield University A. Grossmann, K. Jungmann,
G. zu Putlitz, P. von Walter University of
Heidelberg P.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-Champaign P. Cushman, L.
Duong, S. Giron, J. Kindem, I. Kronkvist, R.
McNabb, C. Timmermans, D. Zimmerman University
of Minnesota V.P. Druzhinin, G.V. Fedotovich, D.
Grigoriev, B.I. Khazin, N. Ryskulov, Yu.M.
Shatunov, E. Solodov Budker Institute A.
Yamamoto M. Iwasaki, M. Kawamura
KEK 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
4
Why probe the difference of g from 2?
QED WEAK HADRONIC
5
Hadronic VP
is related to
and also
Important new data this will be updated soon
6
Experiment to Experiment Comparison
Hadronic VP Evaluations versus Muon g-2 Expt.
minus SM Calculations
CERN III
? time
References
Expt. 2001
BNL 821
recent evaluations
6500
7000
7500
8000
7
The t contribution to HVP

• At first glance, okay
• Issues
• Isospin asymmetry (pp- vs p0p-)
• Line shape choice or not?
• CLEO - ALEPH data compatibility
• e.g., (courtesy Jon Urheim)

??
W-
?-
h

• Correction for r0 - r- width opposite 1.1
  (CLEO) -1.3 (Aleph) ??
• Long-distance radiative corrections?
• Coulomb (missing) correction?
• Its not a statistics issue here
• Bottom line, can the t data contribute in the
  long run at sub level?

8
Standard Model Summary
d (ppm)
? 10-11

• Uncertainty in hadronic VP is unsettling to many
• Hadronic light-by-light also somewhat
  controversial

9
Beyond the Standard Model

• Why muons ?
• Coupling to X about 40,000 times more sensitive
  compared to electrons
• ae ? pure QED
• am ? QED Hadronic Weak New Physics

10
The Basic Idea

• Polarized muons
• Precession proportional to (g-2)
• Pm The magic momentum
• E field doesnt affect muon spin when g 29.3
• Parity violation in the decay

n p m
µ
movie
11
We measure

• (1) Precession frequency
• (2) Muon distribution
• (3) Magnetic field map

B
12
BNL Storage Ring
incoming muons
Quads
13
Storage Ring / Kicker
Radius 7112 mm Aperture 90 mm Field 1.45 T Pm
3.094 GeV/c
14
Fast Rotation
m
15
Magnetic Field
Measured in situ using an NMR trolley
Continuously monitored with gt 360 fixed probes
mounted above and below the storage region
16
Magnetic Field vs Azimuth (1999)
1999 only Inflector shield crack
17
Field Contours Averaged around Ring
1999
inflector shield problem
18
Systematic Errors wp
ppm

• 1) 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
• Total Systematic Error dwp 0.4 ppm

19
Measuring the difference frequency wa
e
lt 20 ps shifts lt 0.1 gain change
20
1998 Data
c2/dof 1.0012
N(t) N0 e-t/t 1Acos(wat f)
? 5 ppm result
21
1999 Data Fit to Simple 5-Par Function

• 1 billion events
• Getting a good c2 is a challenge

22
FFT of Residuals to 5-par Fit
23
Pileup Subtraction
24
Flashlets - AGS Background
Occasional weak, errant muon / pion bursts
introduced into ring No kick, so not stored, but
introduces dirt
25
At the detectors, one sees...
26
Coherent Betatron Oscillations
Acceptance
Radius

• Beam center swims
• Beam width breathes
• Detector acceptance notices this

27
Coherent Betatron Oscillations
FFT of difference between red and blue
28
Muon Loss Stored Protons
m
e
29
A more sophisticated functional form
30
Internal Consistency

• c2/dof good
• consistent with 1
• 4 analyses agree
• Differences
• lt 0.3 ppm
• lt 0.5 expected

31
Systematic Errors in wa

• ISSUE Uncertainty (ppm)
• Gain instability 0.02
• Pileup 0.13
• Coherent betatron oscillations 0.05
• Lost muons 0.10
• Timing Shifts 0.10
• E field and vertical CBO 0.08
• Binning and fitting procedure 0.07
• Beam debunching 0.04
• AGS background 0.10
• TOTAL wa 0.25
• SUMMARY
• Statistical 1.25
• Systematic wp 0.40
• Systematic wa 0.25

am 116 592 03(15) ? 10-10 (1.3 ppm)
32
Result and History
33
For fun Supersymmetry ?

• General Theme
• sensitive probe for supergravity grand
  unification,
• especially for large tan ?
• Chargino-Sneutrino Neutralino-Smuon
• Model with degenerate superparticle masses T.Moroi

SUSY mass (GeV)
tan b
34
2000 Data Progress Expect ? 0.7 ppm (or better)
c2 getting good ...
g-2 stable

• 25 more data yet to be included
• Several small terms in fitting function being
  added / evaluated

35
2001 Negative Muons

• Use of two fundamental tunes to study CBO effects

36
Summary / Future

• THREE ways to interpret the result
• 1) Statistical fluke ? 1 chance
• Higher if theory error is too small
• 2) Mistake !
• In either SM theory or Experiment
• 3) New Physics !!
• This would be very exciting for HEP overall
• RESOLUTION coming
• 4-6 times more positive muon data being analyzed
• 2-3 times more negative muon data just completed
• New inputs to hadronic vacuum polarization

hertzog_at_uiuc.edu
37
Gain Stability