a precision measurement of g e p /g m p with blast

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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

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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 - PowerPoint PPT Presentation

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Page 1: A Precision Measurement of  G E p /G M p  with BLAST

A Precision Measurement of GE

p/GMp with BLAST

Chris Crawford

MIT Laboratory for Nuclear Science

for the BLAST collaboration

Page 2: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 3: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 4: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 5: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 6: A Precision Measurement of  G E p /G M p  with BLAST

MIT-Bates Exp. 01-01

new technique

precision testof theoriesat low Q2

meson cloud structure

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

Page 7: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 8: A Precision Measurement of  G E p /G M p  with BLAST

Asymmetry Super-ratio Method

Helicity Asymmetry

Super-ratio

±

Page 9: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 10: A Precision Measurement of  G E p /G M p  with BLAST

Detector Package

BLAST Coils

Backward-Angle TOF

TOF Scintillators

Drift Chambers

Čerenkov Detectors

Neutron Detectors

LADS Detectors

Page 11: A Precision Measurement of  G E p /G M p  with BLAST

BLAST

Page 12: A Precision Measurement of  G E p /G M p  with BLAST

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

Page 13: A Precision Measurement of  G E p /G M p  with BLAST

TOF Scintillator Cuts

TOF paddle, electron

TO

F p

add

le,

pro

ton

Page 14: A Precision Measurement of  G E p /G M p  with BLAST

Resolution and Yields

TOF paddle #

preliminary

Page 15: A Precision Measurement of  G E p /G M p  with BLAST

Experimental Spin Asymmetry

Page 16: A Precision Measurement of  G E p /G M p  with BLAST

GE/GM by Super-ratio Method

Page 17: A Precision Measurement of  G E p /G M p  with BLAST

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)

Page 18: A Precision Measurement of  G E p /G M p  with BLAST

Preliminary Results

» combineddatasets(77 kC)

» preliminary results based on ¼ of the projected data

Page 19: A Precision Measurement of  G E p /G M p  with BLAST

Preliminary Results

» combineddatasets(77 kC)

» preliminary results based on ¼ of the projected data

Page 20: A Precision Measurement of  G E p /G M p  with BLAST

Conclusion

new precision measurement of GEp/GM

p

exploits unique capabilities of BLAST 2 – 4% projected errors at low Q2