muon (g-2): past, present and future

B. Lee Roberts, Dipole Moments In Storage Rings AGS/RHIC Workshop,7 June 2006 - p. 1/36

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Muon (g-2): Past, Present and Future

B. Lee RobertsOn behalf of the

E969 Collaboration

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


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(in modern language)

(and in English)


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Dirac + Pauli moment

Schwinger term


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g = 2

s = 1/2


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Standard Model Value Muon for (g-2)

e vrs. : relative contribution of heavier things

S

?


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The hadronic contribution to a comes from e+e- →hadrons


(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


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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


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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


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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 ….


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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.


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We measure the difference frequency between the spin and momentum precession

0With an electric quadrupole field for vertical focusing


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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


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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.


(g – 2)The Production Target

proton beam

top view of target


(g – 2)Decay Channel

Plenty of room to add more quadrupoles to increase the acceptance of the beamline.


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The incident beam must enter through the magnet yoke and through an inflector magnet


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Space limitations prevent matching the inflector exit to the storage aperture

Upper Pole Piece


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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


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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.


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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


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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)


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E821 Electron Detectors were Pb-scintillating fiber calorimeters read-out by 4 PMTs.

New experiment needs segmented detectors for pileup reduction.


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We count high-energy e- as a function of time.


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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.


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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


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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


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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


(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.


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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


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X2 improvement: (theory and experiment)

Future Comparison for E969 = now


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X2 improvement: (theory and experiment):

Future Comparison: E969

Historically (g-2) has played an important role in restricting models of new physics.


(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.


(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.


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(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


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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)


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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


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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

muon (g-2): past, present and future

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