Transcript Slide 1

Muon (g-2) to 0.2 ppm
(g – 2)m
B. Lee Roberts
Department of Physics
Boston University
roberts @ bu.edu
http://physics.bu.edu/roberts/html
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(g – 2)m
(in modern language)
(and in English)
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(g – 2)m
Dirac + Pauli moment
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Standard Model Value for (g-2)
(g – 2)m
?
e vrs. m : relative contribution of heavier things
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One reason that I’m here is the relationship
between e+e- annihilation and am
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When we started in 1983, theory and
experiment were known to about 10 ppm.
(g – 2)m
Theory
uncertainty was
~ 9 ppm
Experimental
uncertainty was
7.3 ppm
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E821 achieved 0.5 ppm and the e+e- based
theory is also at the 0.6 ppm level. Both can be (g – 2)
m
improved.
All E821 results
were obtained
with a “blind”
analysis.
world average
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With an apparent discrepancy at the level
(g – 2)
of 2.6 s . . .
m
it’s interesting and you have to work harder
to improve the measurement and the theory
value ….
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A (g-2)m Experiment to ± 0.2 ppm
Precision
–BNL E969 Collaboration
(g – 2)m
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; D.
Grigoriev B.I. Khazin S.I. Redin Yuri M. Shatunov, E.
Solodov – Budker Institute; F.E. Gray B. Lauss E.P.
Sichtermann – UC Berkely and LBL; Y. Orlov – Cornell
University; J. Crnkovic ,P. Debevec D.W. Hertzog, P.
Kammel S. Knaack, R. McNabb – University of Illinois
UC; K.L. Giovanetti – James Madison University; K.P.
Jungmann C.J.G. Onderwater – KVI Groningen; T.P.
Gorringe, W. Korsch – U. Kentucky, P. Cushman –
Minnesota; Y. Arimoto, Y. Kuno, A. Sato, K. Yamada –
Osaka University; S. Dhawan, F.J.M. Farley – Yale
University
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We measure the difference frequency between
(g – 2)m
the spin and momentum precession
With an electric quadrupole field for vertical focusing
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Experimental Technique

S
νμ
Protons
π
π
Pions
(from AGS)

m

Spin
polarized m
(g – 2)m
Momentum
m  m
Inflector

B
p=3.1GeV/c
(1.45T)
Target
• Muon polarization
• Muon storage ring
• injection & kicking
• focus by Electric Quadrupoles
• 24 electron calorimeters
Injection orbit
Central orbit
Kicker
Storage
Modules
ring
R=711.2cm
d=9cm
Electric Quadrupoles
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E821: used a “forward” decay beam
(g – 2)m
Pions @ 3.115 GeV/c
Decay muons @ 3.094 GeV/c
Near side
Far side
This baseline
limits how early
we can fit data
Pedestal vs. Time
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The Production Target
(g – 2)m
top
view
of
target
proton
beam
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Decay Channel
(g – 2)m
Plenty of room to add
more quadrupoles to
increase the
acceptance of the
beamline.
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E969: will use a “backward” decay beam
(g – 2)m
new front-end
Pions @ 5.32 GeV/c
increase
proton
beam
Decay muons
@of3.094
GeV/c
Approximately the same
muon flux is realized
Then we quadruple the
number of quadrupoles in
the decay channel
> x2
Expect for
both sides
No hadron-induced
prompt flash
x1
more
muons
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The incident beam must enter through the
magnet yoke and through an inflector magnet
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The mismatch between the inflector exit and
the storage aperture + imperfect kick causes
coherent beam oscillations
(g – 2)m
Upper Pole Piece
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The E821 inflector magnet had closed
ends which lost half the beam.
(g – 2)m
Length = 1.7 m
Central field = 1.45 T
Open end prototype, built and tested
→ X2 Increase in Beam
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The 700 ton (g-2)m precision storage ring
Muon lifetime
tm = 64.4 ms
(g-2) period
ta = 4.37 ms
Cyclotron period
tC = 149 ns
Scraping time (E821)
7 to 15 ms
Total counting time
~700 ms
(g – 2)m
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
Fluorinert (FC40)
(g – 2)m
oil
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E821 Electron Detectors were Pb-scintillating fiber
calorimeters read-out by 4 PMTs.
(g – 2)m
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
(g – 2)m
• 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
(g – 2)m
decay.
• Calibration to a spherical
water sample that ties the field
to the Larmor frequency of the
free proton wp.
• So we measure wa and wp
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The ± 1 ppm uniformity in the average
field is obtained with special shimming
tools.
(g – 2)m
We can shim the
dipole,
0.5 ppm
contours
quadrupole
sextupole
independently
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E969 needs 10 times more muons than
E821 stored.
• Open Inflector
• Backward Beam
• Quadruple the Quadrupoles
Beam increase design factor
(g – 2)m
X2
X1
X 2-3
X5
Absence of injection flash will permit us
to begin analyzing data much earlier
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The error budget for E969 represents a continuation
of improvements already made during E821
(g – 2)
Systematic uncertainty (ppm)
1998
1999
2000
2001
E969
Goal
Magnetic field – wp
0.5
0.4
0.24
0.17
0.1
Anomalous precession – wa
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
m
• 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
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Summary
(g – 2)
• 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.
• Thanks to all of you who are working on
these problems!
m
!
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Outlook:
(g – 2)m
• E969 will be considered by the national
U.S. Particle Physics Project Prioritization
Panel (P5) at the end of March
• We hope that our friends in the theory, e+eand t communities will continue to work on
the hadronic contribution to am
• If both theory can improve by a factor of 2,
and experiment can improve by a factor of
2.5, the stage is set for another
showdown.
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Thanks to the organizers for this
excellent workshop!
(g – 2)m
Thank you СПАСИБО
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(g – 2)m
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Systematic errors on ωa
200
2000
1
(ppm)
σsystematic
199
9
Pile-up
0.13
0.13
0.08
AGS
Background
0.10
0.10
*
Lost Muons
0.10
0.10
0.09
Timing Shifts
0.10
0.02
0.02
E-Field, Pitch
0.08
0.03
*
Fitting/Binning 0.07
0.06
*
CBO
0.05
0.21
0.07
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
E969
0.07
0.04
0.05
(g – 2)m
Detector
segmentation and
lower energythreshold required
for pile-up rejection
with higher rates
Beam
manipulation
0.04
Backward
beam
Σ* = 0.11
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Systematic errors on ωp (ppm)
(g – 2)m
E969
(i
(I)
)
(II)
(III)
(iv)
*higher multipoles, trolley voltage and temperature response, kicker eddy currents,
and time-varying stray fields.
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E969 Builds on the apparatus and Experience
of E821
(g – 2)m
1. AGS Proton Beam 12 – bunches from
the AGS 60 Tp total intensity
2. 0o p Beam
3. p decay channel
4. m Beam injected into the ring through a
superconducting inflector
5. Fast Muon Kicker
6. Precision Magnetic Storage Ring
7. Electron calorimeters, custom high-rate
electronics and wave-form digitizers
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