a precision measurement of g e p /g m p with blast
DESCRIPTION
A Precision Measurement of G E p /G M p with BLAST. Chris Crawford MIT Laboratory for Nuclear Science for the BLAST collaboration. Introduction. G E ,G M fundamental quantities describing charge/magnetization in the nucleon Test of QCD based calculations and models - PowerPoint PPT PresentationTRANSCRIPT
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A Precision Measurement of GE
p/GMp with BLAST
Chris Crawford
MIT Laboratory for Nuclear Science
for the BLAST collaboration
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Introduction
GE,GM fundamental quantities describing charge/magnetization in the nucleon
Test of QCD based calculations and models
Provide basis for understanding more complex systems in terms of quarks and gluons
QED Lamb shift
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World Data
Unpolarized Data» CEA, Bonn, DESY, SLAC» Christy et al. (JLab 2004)» Arrington et al. (JLab )
Polarization Transfer» Milbrath et al. (BATES) 1999» Jones et al. (JLab), 2000» Dieterich et al. (MAMI), 2001 » Gayou et al. (JLab), 2002
Theory» quark orbital momentum» 2 effects
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World Data
Unpolarized Data» CEA, Bonn, DESY, SLAC» Christy et al. (JLab 2004)» Arrington et al. (JLab )
Polarization Transfer» Milbrath et al. (BATES) 1999» Jones et al. (JLab), 2000» Dieterich et al. (MAMI), 2001 » Gayou et al. (JLab), 2002
Theory» quark orbital momentum» 2 effects
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Unpolarized Data» CEA, Bonn, DESY, SLAC» Christy et al. (JLab 2004)» Arrington et al. (JLab )
Polarization Transfer» Milbrath et al. (BATES) 1999» Jones et al. (JLab), 2000» Dieterich et al. (MAMI), 2001 » Gayou et al. (JLab), 2002
Theory» quark orbital momentum» 2 effects
World Data
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MIT-Bates Exp. 01-01
new technique
precision testof theoriesat low Q2
meson cloud structure
Spokespersons: H. Gao, J. Calarco, H. Kolster
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Form Factor Ratio @ BATES
Exploits unique features of BLAST» internal target: low dilution, fast spin reversal
» large acceptance: simultaneously measure all Q2 points
» symmetric detector: ratio measurement
Different systematics » also insensitive to Pb and Pt
» no spin transport
Q2 = 0.1 – 0.8 (GeV/c) 2 » overlap with JLab data
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Asymmetry Super-ratio Method
Helicity Asymmetry
Super-ratio
±
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Polarized Beam and Target
Storage Ring» E = 850 MeV» Iinj=175 mA» Pb = 0.65
Internal ABS Target» 40 cm storage cell» t = 2.71013 cm-2 » Pt = 0.40
isotopically pure internal targethigh polarization, fast spin reversal L = 1.6 1031 cm-2s-1
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Detector Package
BLAST Coils
Backward-Angle TOF
TOF Scintillators
Drift Chambers
Čerenkov Detectors
Neutron Detectors
LADS Detectors
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BLAST
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Data Sets
1H run 1, December 2003» reversed BLAST field – electrons out-bending
» 20 kC beam (3.4 pb-1) Pz=.45 480k elastic events
1H run 2, April 2004» nominal BLAST field – electrons in-bending
» 57 kC beam (9.6 pb-1) Pz=.40 950k elastic events
2D run, May – October 2004 » 450 kC beam (76 pb-1) Pz=.75
1H run 3, November 2004» ~250 kC (42 pb-1) planned
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TOF Scintillator Cuts
TOF paddle, electron
TO
F p
add
le,
pro
ton
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Resolution and Yields
TOF paddle #
preliminary
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Experimental Spin Asymmetry
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GE/GM by Super-ratio Method
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GE/GM by Fit Method
fit for:» take advantage of large acceptance
» optional: also fit for spin angle)
super-ratio method: » in each Q2 bin
» redundant measurement of polarization
AL(0.16) AR(0.16)
AL(0.26) AR(0.28)
AL(0.41) AR(0.41)
AL(0.54) AR(0.54)
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Preliminary Results
» combineddatasets(77 kC)
» preliminary results based on ¼ of the projected data
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Preliminary Results
» combineddatasets(77 kC)
» preliminary results based on ¼ of the projected data
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Conclusion
new precision measurement of GEp/GM
p
exploits unique capabilities of BLAST 2 – 4% projected errors at low Q2