muon (g-2): past, present and future
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B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 1/36
(g – 2)
Muon (g-2): Past, Present and Future
B. Lee RobertsOn behalf of the
E969 Collaboration
roberts @ bu.edu http://physics.bu.edu/roberts/html
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 2/36
(g – 2)
(in modern language)
(and in English)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 3/36
(g – 2)
Dirac + Pauli moment
Schwinger term
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 4/36
(g – 2)
g = 2
s = 1/2
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 5/36
(g – 2)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 6/36
(g – 2)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 7/36
(g – 2)
Standard Model Value Muon for (g-2)
e vrs. : relative contribution of heavier things
S
?
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 8/36
(g – 2)
The hadronic contribution to a comes from e+e- →hadrons
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 9/36
(g – 2)Sign Measurement a/ a sensitivity Reference
± g ≈ 2 5% g = 2 Garwin et al.
+ 0.001130.00012+0.00016 12.4% Garwin et al.
+ 0.001 145 (22) 1.9% Charpak et al.
+ 0.001 162 (5) 0.43% Charpak et al.
± 0.001 166 16 (31) 265 ppm Bailey et al.
± 0.001 165 895 (27) 23 ppm Bailey et al.
± 0.001 165 911 (11) 7.3 ppm Bailey et al.
+ 0.001 165 920 2(16) 1.3 ppm Brown et al.
+ 0.001 165 920 3(8) 0.7 ppm Bennett et al.
- 0.001 165 921 40(80)(30)
0.7 ppm Bennett et al.
± 0.001 165 920 80(63) 0.54 ppm Bennett et al.
Measurements and Sensitivity of a
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 10/36
(g – 2)
When we started in 1983, theory and experiment were known to about 10 ppm.
Theory uncertainty was ~ 9 ppm
Experimental uncertainty was 7.3 ppm
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 11/36
(g – 2)
E821 achieved 0.54 ppm and the e+e- based theory is also at the 0.6 ppm level. Both can be improved.
All E821 results were obtained with a “blind” analysis.
world average
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 12/36
(g – 2)
With an apparent discrepancy at the level of 2.9 . . . it’s interesting and you have to work
harderto improve the measurement and the
theory value ….
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 13/36
(g – 2)
BNL E969 Collaboration R.M. Carey, I. Logashenko, K.R. Lynch, J.P. Miller, B.L. Roberts
Boston University G. Bunce, W. Meng, W. Morse, P. Pile, Y.K. Semertzidis
Brookhaven National Laboratory D. Grigoriev, B.I. Khazin, S.I. Redin, Y. M. Shatunov, E. Solodov
Budker Institute of Nuclear PhysicsF.E. Gray, B. Lauss, E.P. Sichtermann
UC Berkeley and LBL Y. Orlov – Cornell University
J. Crnkovic, P. Debevec, D.W. Hertzog, P. Kammel, S. Knaack, R. McNabb
University of Illinois at Urbana-Champaign K.L. Giovanetti – James Madison University
K.P. Jungmann, C.J.G. Onderwater – KVI Groningen T.P. Gorringe, W. Korsch U. Kentucky P. Cushman – University of Minnesota
M. Aoki, Y. Arimoto, Y. Kuno, A. Sato, K. Yamada Osaka University
S. Dhawan, F.J.M. Farley – Yale UniversityThis group contains the core of E821, and we will build on our strength and experience there.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 14/36
(g – 2)
We measure the difference frequency between the spin and momentum precession
0With an electric quadrupole field for vertical focusing
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 15/36
(g – 2)
Inflector
Kicker Modules
Storagering
Central orbitInjection orbit
Pions
Target
Protons
π
(from AGS) p=3.1GeV/c
Experimental Technique
B
• Muon polarization• Muon storage ring• injection & kicking• focus by Electric Quadrupoles• 24 electron calorimeters
R=711.2cm
d=9cm
(1.45T)
Electric Quadrupoles
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 16/36
(g – 2)
Near side Far side
E821 used a “forward” decay beam, with p 1.7% above pmagic to provide a separation at K3/K4
Pions @ 3.115 GeV/c
Decay muons @ 3.094 GeV/c
Our models show that by quadrupling the quads and going further above pmagic the flash is decreased and the muon flux will grow by approximately 2-3
Pedestal vs. TimeWe base E969 on a modified version of this proven concept.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 17/36
(g – 2)The Production Target
proton beam
top view of target
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 18/36
(g – 2)Decay Channel
Plenty of room to add more quadrupoles to increase the acceptance of the beamline.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 19/36
(g – 2)
The incident beam must enter through the magnet yoke and through an inflector magnet
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 20/36
(g – 2)
Space limitations prevent matching the inflector exit to the storage aperture
Upper Pole Piece
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 21/36
(g – 2)
The E821 inflector magnet had closed ends which lost half the beam.
Length = 1.7 m
Central field = 1.45 T
Open end prototype, built and tested
→ X2 Increase in Beam
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 22/36
(g – 2)
E969 needs 5 times the muon flux that E821 stored.
• Open inflector x 2
• Quadruple the quadrupoles x 2 – 3
Beam increase design factor x 4 – 6
At 3% above pmagic the reduced injection flash will permit us to begin fitting the data at earlier times (closer to the injection time) than in E821.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 23/36
(g – 2)
The 700 ton (g-2) precision storage ring
Muon lifetime t = 64.4 s
(g-2) period ta = 4.37 s
Cyclotron period tC = 149 ns
Scraping time (E821) 7 to 15 s
Total counting time ~700 s
Total number of turns ~4000
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 24/36
(g – 2)
The fast kicker is the major new feature not in the CERN experiment. Kicker Modulator is an LCR circuit, with V ~ 95 kV, I0 ~ 4200 A
oilFluorinert (FC40)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 25/36
(g – 2)
E821 Electron Detectors were Pb-scintillating fiber calorimeters read-out by 4 PMTs.
New experiment needs segmented detectors for pileup reduction.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 26/36
(g – 2)
We count high-energy e- as a function of time.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 27/36
(g – 2)
New segmented detectors of tungsten/scintillating- fiber ribbons to deal with pile-up
• System fits in available space• Prototype under construction• Again the bases will be gated.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 28/36
(g – 2)
The magnetic field is measured and controlled using pulsed NMR and the free-induction decay.
• Calibration to a spherical water sample that ties the field to the Larmor frequency of the free proton p.
• So we measure a and p
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 29/36
(g – 2)
The ± 1 ppm uniformity in the average field is obtained with special shimming tools.
We can shim the
dipole,
quadrupole
sextupole
independently
0.5 ppm contours
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 30/36
(g – 2)
The error budget for E969 represents a continuation of improvements already made during E821
• Field improvements: 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 0.31 0.21 0.1
Statistical uncertainty (ppm)
4.9 1.3 0.62 0.66 0.14
Total Uncertainty (ppm) 5.0 1.3 0.73 0.72 0.20
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 31/36
(g – 2)The Role of Muon (g-2)
• Historically (g-2) has placed a major hurdle in the path of new theories beyond the standard model.
• The (g-2) result must fit with other evidence into a consistent picture of new physics, e.g.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 32/36
(g – 2)
e.g. the (g-2) “discrepancy is quite consistent with other constraints on the SUSY LSP being the dark matter candidate. With
CMSSM (constrained minimal supersymmetric model)
scal
ar m
ass
gaugino mass
Following Ellis, Olive, Santoso, Spanos
from K. Olive
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 33/36
(g – 2)
X2 improvement: (theory and experiment)
Future Comparison for E969 = now
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 34/36
(g – 2)
X2 improvement: (theory and experiment):
Future Comparison: E969
Historically (g-2) has played an important role in restricting models of new physics.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 35/36
(g – 2)Summary• E821 Achieved a precision of ± 0.5 ppm
• There appears to be a discrepancy between experiment and e+e- based theory
• E969 proposes to push the precision down to ± 0.2 ppm
• There is lots of work worldwide on the hadronic theory piece, both experimental and theoretical.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 36/36
(g – 2)Outlook:
• E969 was considered by the national U.S. Particle Physics Project Prioritization Panel (P5) on the 27th of March; report due in September.
• Our friends in the theory, e+e- and communities will continue to work on the
hadronic contribution to a
• If both theory can improve by a factor of 2, and experiment can improve by a factor of ≥2, the stage is set for another showdown.
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 37/36
(g – 2)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 38/36
(g – 2)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
Systematic errors on ωa (ppm)
Σ* = 0.11
Cleaner beam
Beam manipulation
Detector segmentation and lower energy- threshold required for pile-up rejection with higher rates
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 39/36
(g – 2)
Systematic errors on ωp (ppm)
*higher multipoles, trolley voltage and temperature response, kicker eddy currents,
and time-varying stray fields.
E969
(i)(I)
(II)
(III)
(iv)
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 40/36
(g – 2)
Field systematic uncertainties, ordered by importance
Source E821(ppm)
E969(ppm)
Comment
Calibration of trolley probe 0.09 0.06 Improved shimming in the transfer region; improved registration of trolley location in ring
Interpolation with fixed probes 0.07 0.06 Repairs and retuning of a number of probes to improve the sampling of the ring field
Absolute calibration 0.05 0.05 Could improve if 3He based probe Trolley measurements of B0 0.05 0.02 More frequent trolley runs; mechanical
maintenance of trolley drive and garage; Extensive measurements of trolley NMR probe active volumes
Muon distribution 0.03 0.02 Simulations of storage ring; improved shimming
“Other”eddy currentshigher multipolestrolley temp and PS
response
0.10 0.05in situ measurement of eddy currentsImproved shimmingModifications to trolley and PS
Total 0.17 0.11
B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 41/36
(g – 2)
Precession frequency systematic uncertainties, ordered by importance
Source E821(ppm)
E969(ppm)
Comments
Gain stability 0.12 0.03 Full WFD samples recorded; stability of laser calibration with local reference detectors; single-phase WFDs
Lost muons 0.09 0.04 New scraping scheme; improved kickPileup:T method
Q method (not applicable)
0.08 0.07 Recording all samples, no threshold, will eliminate ambiguity from low-energy pulses
CBO: coherent betatron oscillations
0.07 0.04 Improved kick; new scraping; taller calorimeters
E and pitch correction 0.05 0.05 Should be improved with better storage ring simulation, but we keep it as is for now
Timing shifts 0.02 0.01 Laser calibration; precision determined by amount of data collected
AGS background 0.01 0.01 Sweeper magnet maintainedFit procedure and bin width 0.06 0.01 Limited by number of simulated trials
performedVertical waist 0.03 0.01 CBO related; see aboveOther small effects <
0.03<
0.02These either scale with the data set size or from the simulations demonstrating “no effect”
Total 0.21 0.11
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