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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

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A precision measurement of g e p g m p with blast

A Precision Measurement of GEp/GMp with BLAST

Chris Crawford

MIT Laboratory for Nuclear Science

for the BLAST collaboration


Introduction
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


World data
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

    • 2g effects


World data1
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

    • 2g effects


World data2
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

    • 2g effects


Mit bates exp 01 01
MIT-Bates Exp. 01-01

Spokespersons: H. Gao, J. Calarco, H. Kolster

  • new technique

  • precision test

    of theories

    at low Q2

  • meson cloud structure


Form factor ratio @ bates
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


Asymmetry super ratio method
Asymmetry Super-ratio Method

  • Helicity Asymmetry

  • Super-ratio

  • b = 45±


Polarized beam and target

Storage Ring

E = 850 MeV

Iinj=175 mA

Pb = 0.65

Internal ABS Target

40 cm storage cell

t = 2.71013 cm-2

Pt = 0.40

Polarized Beam and Target

  • isotopically pure internal target

  • high polarization, fast spin reversal

  • L = 1.6  1031 cm-2s-1


Detector package

BLAST Coils

Backward-Angle TOF

TOF Scintillators

Drift Chambers

Čerenkov Detectors

Neutron Detectors

LADS Detectors

Detector Package



Data sets
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


Tof scintillator cuts
TOF Scintillator Cuts

TOF paddle, proton

TOF paddle, electron


Resolution and yields
Resolution and Yields

preliminary

TOF paddle #



G e g m by super ratio method
GE/GM by Super-ratio Method


G e g m by fit method
GE/GM by Fit Method

  • fit for:

    • take advantage of large acceptance

    • optional: also fit for b (spin angle)

  • super-ratio method:

    • in each Q2 bin

    • redundant measurement of polarization


Preliminary results
Preliminary Results

  • combineddatasets(77 kC)

  • preliminary results based on ¼ of the projected data


Preliminary results1
Preliminary Results

  • combineddatasets(77 kC)

  • preliminary results based on ¼ of the projected data


Conclusion
Conclusion

  • new precision measurement of GEp/GMp

  • exploits unique capabilities of BLAST

  • 2 – 4% projected errors at low Q2


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