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Precision Measurement of G E p /G M p with BLAST. Chris Crawford MIT Laboratory for Nuclear Science Thesis Committee Review Meeting 2003/12/4. Outline. Introduction and Motivation Previous methods, world data Asymmetry super-ratio method Status of BLAST Hardware: ABS, wire chambers

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precision measurement of g e p g m p with blast

Precision Measurement of GEp/GMp with BLAST

Chris Crawford

MIT Laboratory for Nuclear Science

Thesis Committee Review Meeting

2003/12/4

outline
Outline
  • Introduction and Motivation
    • Previous methods, world data
    • Asymmetry super-ratio method
  • Status of BLAST
    • Hardware: ABS, wire chambers
    • Software, asymmetries
  • Progress
    • Contributions
    • Outlook
rosenbluth separation
Rosenbluth Separation
  • Elastic e-p cross section
  • At fixed Q2, fit dσ/dΩ vs. tan2(θ/2)
    • Measurement of absolute cross section
    • Dominated by either GE or GM
polarization transfer
Polarization Transfer
  • Recoil proton polarization
  • Focal Plane Polarimeter
    • recoil proton scatters off secondary 12C target
    • Pt, Pl measured fromφ distribution
    • Pb, and analyzing powercancel out in ratio
world data
World Data
  • Unpolarized Data
  • Polarization Transfer
    • Milbrath et al. (BATES) 1999
    • Jones et al. (JLAB), 2000
    • Dieterich et al. (MAMI), 2001
    • Gayou et al. (JLAB), 2002
  • Super-Rosenbluth
    • JLab Hall A, preliminaryresults expected soon
form factor ratio @ bates
Form Factor Ratio @ BATES
  • New technique: polarized beam and target
  • Exploits unique features of BLAST
    • internal target: low dilution, fast spin reversal
    • large acceptance: simultaneous measurement of all Q2 points
    • symmetric detector: ratio measurement
  • Different systematics
    • insensitive to Pb and Pt
  • Q2 = 0.07 – 0.9 (GeV/c) 2
    • overlap with JLab dataand RpEX (future exp.at Bates to measure rp)
asymmetry super ratio method
Asymmetry Super-ratio Method
  • Polarized cross section
  • Super-ratio
projected results
Projected Results
  • Statistics
    • A1, A2
  • Systematics
    • θ*1, θ*2 Δp, Δθ, Δβ

Errors are minimized as a function of β (target spin angle)

contributions
ep-elastic event generator

RC studies w/Mascarad

Newton-Rhapson fitter

rapid convergence

Lazy track fitter

fast and efficient, poor res.

TOF cal. – position, timing

WC cal. – in progress

Harmonic interpolation of BLAST field map

Maintained BlastLib2, CVS

standard program interface

blastrc – config file

Nsed enhancements

port to GCC-3.2

Control software

Elog–BLAST electronic logbook

Trigger, HV enhancements

ROOT enhancement

improved histogram drawing

Contributions
radiative corrections
Radiative Corrections
  • MASCARAD code
    • A. Afanasev et al., Phys.Rev.D 64,113009
    • Covariant calculation with no cutoff parameter
    • small corrections (<1%) to asymmetry
blastlib2 software
BlastLib2 Software
  • BlastLib2 v3.0 soon to be ready
    • Geometry: full 6 degrees of freedom
    • DST: for second pass reconstruction
    • Improved handling of WC noise
    • Debugged event-by-event
wire chamber tracking
Garfield drift time simulation

Newton-Rhapson track fitter

200 μm resolution

20:1 signal to noise ratio

Wire Chamber Tracking
asymmetry
very low dilution due to problems with ABSAsymmetry

left sector

right sector

45 degree holding field

left sector

right sector

left sector

right sector

0 degree holding field

180 degree holding field

atomic beam source

1

1

1

1

MFT (2->3)

3

3

2

2

nozzle

4

6-pole

6-pole

Atomic Beam Source
  • Standard technology
  • Dissociator & nozzle
  • 2 sextupole systems
  • 3 RF transitions

Spin State Selection:

abs enhancements
ABS Enhancements

Sextupole Damage

MEASURED FIELD ON THE POLE TIPS:

Magnet 1 8.3 kG

Magnet 2 9.1 kG

Magnet 3 9.9 kG

Magnet 4 11.6 kG

Magnet 5 15.6 kG

Magnet 6 15.4kG

Magnet 7 15.2 kG

BLAST Field Effect

new asymmetry results
New Asymmetry Results

previous results

previous results

left sector

right sector

left sector

0 degree holding field, ABS improvements

target z-dependence

outlook
Outlook
  • Work on hardware/software complete
  • Now taking high polarization data
  • Will concentrate on A, not GEp/GMp
  • Schedule
    • December: asymmetry analysis
    • January: start writing thesis
    • April: thesis defense