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Status of the (g - 2)m Fermilab Project
Lee Roberts Department of Physics Boston
University
roberts _at_bu.edu http//physics.bu.edu/s
how/roberts
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New Collaborators are welcome! proposal is at
http//lss.fnal.gov/archive/test-proposal/0000/fer
milab-proposal-0989.shtml
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Self-analyzing Muon Decay

• To understand where were going, you have to
  understand where weve been.
• Muons
• born polarized
• die with information on where
  their spin was at the
  time of
  decay
• highest energy e- carry spin
• information
  

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Spin Motion difference frequency between wS and
wC
Count number of decay e- with Ee 1.8 GeV
Dirac
where a is the anomaly,
Since g gt 2, the spin gets ahead of the momentum
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e from m ? e n n are detected
Count number of e- with Ee 1.8 GeV
400 MHz digitizer gives t, E
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Our past am Experiment

• E821 at Brookhaven
• superferric storage ring, magic g, ltBgtq 1 ppm

gtm 64.4 ms (g-2)
ta 4.37 ms Cyclotron tC 149 ns
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E821 used a forward decay beam with p m ?
11large flash in the detectors at injection
Pions _at_ 3.115 GeV/c
? 80 m decay path
Decay muons _at_ 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 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 wp.
• We measure wa and wp
• Use l mm /mp as the
• fundamental constant

9
The 1 ppm uniformity in the average field is
obtained with special shimming tools.
0.5 ppm contours
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New value for l (CODATA 2006/2008)(Rev. Mod.
Phys. 80, 633 (2008))
Blind analysis
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E821 achieved 0.54 ppm ee- based theory 0.49
ppm Hint is 3.2s
Davier et al, arXiv0908.4300 hep-ph
n.b. the
experimental point does not include the new value
of l
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The Snowmass Points and Slopes give benchmarks to
test observables with model predictions
Muon g-2 is a powerful discriminator ...no
matter where the final value lands!
Present
Future?
Model
SPS Definitions
- p. 12/68
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Suppose the MSSM point SPS1a is realized and the
paramaters are determined at LHC- sgn(D) gives
sgn(m)

• sgn (m) difficult to obtain from the collider
• tan b poorly determined by the collider

New g-2
Old g-2
2s 1s
LHC (Sfitter)
from D. Stöckinger
from Dominik Stöckinger
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Fermilab am Experiment

• E821 at Brookhaven
• superferric storage ring, magic g, ltBgtq 1 ppm
• P989 at Fermilab
• move the storage ring to Fermilab, improved
  shimming, new detectors, electronics, DAQ,
• new beam structure that takes advantage of the
  multiple rings available at Fermilab, more muons
  per hour, less per fill of the ring

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Advantages of the magic g technique

• 3rd generation (CERN, E821, Fermilab)
• technique well understood
• high intensity polarized muon beam
• large storage ring has ample room for detectors,
  field mapping, etc.
• muon injection shown to work
• rates in detectors are reasonable with
  conventional technology
• many (g -2) cycles to fit over
• large decay asymmetry
• precision field techniques well understood
• need to improve monitoring and control, but path
  is straightforward, if challenging.
• systematic errors well understood and can be
  improved
• Limit of this technique ?0.07 to 0.1 ppm error

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Why Fermilab?

• The existence of many storage rings that are
  interlinked permits us to make the ideal beam
  structure.
• proton bunch structure
• BNL 5 X 1012 p/fill effective rate 4.4 Hz
• FNAL 1012 p/fill effective rate 18 Hz
• using antiproton rings as an 900m pion decay line
• 20 times less pion flash at injection than BNL
• 0o muons
• 5-10x increase m/p over BNL
• Can run parasitic to main injector experiments
  (e.g. to NOVA) or take all the booster cycles

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Polarized muons delivered and stored in the ring
at the magic momentum, 3.094 GeV/c
beam rebunched in Recycler 4 x (1 x 1012) p

• Uses 6/20 batches
• parasitic to n program
• Proton plan up to AP0 target is almost the same
  as for Mu2e
• Uses the same target and lens as the present
  p-bar program
• Modified AP2 line ( quads)
• New beam stub into ring
• Needs simple building near cryo services

Can use all 20 if MI program is off
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The 900-m long decay beam reduces the pion
flash by x20 and leads to 6 12 times more
stored muons per proton (compared to BNL)
Flash compared to BNL
parameter FNAL/BNL
p / fill 0.25
p / p 0.4
p survive to ring 0.01
p at magic P 50
Net 0.05
Stored Muons / POT
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Building Design for Fermilab
AP0
g-2
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Stable 2.5 thick reinforced floor, supported by
4 diameter caissons down to bedrock
temperature controlled 2o F (Much better than
E821)
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Upgrades at Fermilab

• New segmented detectors to reduce pileup
• W-scifi prototype under study
• New electronics
• 500 MHz 12-bit WFDs, with deep memories
• Improvements in the magnetic field calibration,
  measurement and monitoring.

22
Complementary ways to collect data

• t method time and energy of each event -
  pileup

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Complementary ways to collect data

• t method time and energy of each event -
  pileup
• q method integrate the energy - no pileup

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The error budget for a new experiment represents
a continuation of improvements already made
during E821
Systematic uncertainty (ppm) 1998 1999 2000 2001 E821 final P989 Goal
Magnetic field wp 0.5 0.4 0.24 0.17 0.07
Anomalous precession wa 0.8 0.3 0.31 0.21 0.07
Statistical uncertainty (ppm) 4.9 1.3 0.62 0.66 0.46 0.1
Systematic uncertainty (ppm) 0.9 0.5 0.39 0.28 0.28 0.1
Total Uncertainty (ppm) 5.0 1.3 0.73 0.72 0.54 0.14
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Systematic errors on ?a (ppm)
ssystematic 1999 2000 2001 Future
Pile-up 0.13 0.13 0.08 0.04
AGS Background 0.10 0.10 0.015
Lost Muons 0.10 0.10 0.09 0.02
Timing Shifts 0.10 0.02 0.02
E-Field, Pitch 0.08 0.03 0.06 0.03
Fitting/Binning 0.07 0.06 0.06
CBO 0.05 0.21 0.07 0.04
Beam Debunching 0.04 0.04 0.04
Gain Change 0.02 0.13 0.13 0.02
total 0.3 0.31 0.21 0.07
S 0.11
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The Precision Field Systematic errors

• Why is the error 0.11 ppm?
• Thats with existing knowledge and experience
• with RD defined in proposal, it will get better

Next (g-2)
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Ring relocation to Fermilab
Back

• Heavy-lift helicopters bring coils to a barge
• Rest of magnet is a kit that can be trucked to
  and from the barge

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Sikorsky S64F 12.5 T hook weight (Outer coil 8T)
from Chris Polly
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Possible Schedule?

• CY 2009
• PAC proposal defended in March 2009 (Well
  received, but how many?)
• Laboratory supports costing exercise July-October
• Report to PAC meeting November
• CY 2010 Approval?
• building design finished
• other preliminary engineering and RD
• CY 2011 Tevatron running finishes in Oct.
• building construction begins
• ring disassembly begins FY2012
• CY 2012
• building completed mid-year
• ring shipped
• 2013-2014
• re-construct ring
• shim magnet
• late 2014 or early 2015 Beam to experiment
• 2 year data collection on m

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Summary

• At present there appears to be a difference
  between am and the standard-model ee- based
  prediction at the 3.2 s level, post BaBar.
• We have proposed to reduce the experimental error
  by a factor of 4 at Fermilab.
• Our goal is to clarify if there is a discrepancy
  between experiment and theory, but whatever
  happens am will continue to be valuable in
  restricting physics beyond the standard model.
• It will be especially important in guiding the
  interpretation of the LHC data.

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A special thank you to our hosts!THE END
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muon (g-2) storage ring
Muon lifetime tm 64.4 ms (g-2) period
ta 4.37 ms Cyclotron period
tC 149 ns
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SPS points and slopes
Back

• SPS 1a Typical '' mSUGRA point with
  intermediate value of tan_beta.
• SPS 1b Typical '' mSUGRA point with relatively
  high tan_beta tau-rich neutralino and chargino
  decays.
• SPS 2 Focus point '' scenario in mSUGRA
  relatively heavy squarks and sleptons, charginos
  and neutralinos are fairly light the gluino is
  lighter than the squarks
• SPS 3 mSUGRA scenario with model line into
  co-annihilation region'' very small
  slepton-neutralino mass difference
• SPS 4 mSUGRA scenario with large tan_beta the
  couplings of A, H to b quarks and taus as well as
  the coupling of the charged Higgs to top and
  bottom are significantly enhanced in this
  scenario, resulting in particular in large
  associated production cross sections for the
  heavy Higgs bosons
• SPS 5 mSUGRA scenario with relatively light
  scalar top quark relatively low tan_beta
• SPS 6 mSUGRA-like scenario with non-unified
  gaugino masses
• SPS 7 GMSB scenario with stau NLSP
• SPS 8 GMSB scenario with neutralino NLSP
• SPS 9 AMSB scenario

SPS PLOT
www.ippp.dur.ac.uk/georg/sps/sps.html
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(g-2) at Fermilab Costing study concluding this
month.
Coils have to be moved by helicopter and barge
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wa Systematic Error Summary
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New value for l (CODATA 2006/2008)(Rev. Mod.
Phys. 80, 633 (2008))

• an increase by 14 of the experimental error