1 / 13

Measurement of the Proton Elastic Form Factor Ratio at Low Q 2

Measurement of the Proton Elastic Form Factor Ratio at Low Q 2. Xiaohui Zhan (MIT) On Behalf of E08-007 Collaboration June 14th 2008 Hall A Collaboration Meeting. Outline. Background Experiment Preliminary Analysis. Proton Form Factors. Electron elastic scattering from proton:.

zagiri
Télécharger la présentation

Measurement of the Proton Elastic Form Factor Ratio at Low Q 2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measurement of the Proton Elastic Form Factor Ratio at Low Q2 Xiaohui Zhan (MIT) On Behalf of E08-007 Collaboration June 14th 2008 Hall A Collaboration Meeting

  2. Outline • Background • Experiment • Preliminary Analysis

  3. Proton Form Factors Electron elastic scattering from proton: Sachs Form Factors: Electric:GE(Q2) Magnetic:GM(Q2) Q2=0 Dipole Leading order pQED (single photon exchange)

  4. Rosenbluth Separation (Unpolarized) Method: Vary at fixed Q2, fit linearly Slope G2E Intercept G2M Difficulties: • not sensitive to GE at large Q2 and to GM at small Q2 • Limited by accruaby of cross section measurement at • different settings.

  5. Recoil Polarization 2 Direct measurement of form factor ratios by measuring the ratio of the transferred polarization Pt and Pl . • Advantages: • only one measurement is needed for each Q2. • much better precision than a cross section measurement.

  6. World Data At high Q2, Rosenbluth and Polarization methods do NOT agree. We focus on low Q2 2γ exchange?

  7. E08-007 • Approved by PAC33 • Part I: a high precision survay of Proton FF ratio by recoil • polarization method • Scheduled from May 15th ~ June 9th 2008 • Succesfully completed!

  8. e’ Experiment Setup LHRS Pp : 0.5 ~ 0.9 GeV/c Ee: 1.192GeV Polarization: ~ 80% VDC + FPP S1 + S2 Pion rejector 1 Pion rejector 2 BigBite e’ Scintillator: 13 Preshower: 27x2 Shower: 27x7 LH2 target (6cm, 15cm) E’e: ~ 1 GeV

  9. BigBite • Used for electron tagging (coincidence trigger). • Turned on preshower and shower every time we changed kinematics. • Selected shower blocks were on for production to reduce background

  10. Focal Plane Polarimeter

  11. Q2[GeV2] 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.70 0.95 0.70 0.55 0.70 0.46 0.52 0.53 0.44 Preliminary Analysis • Statistical error can be smaller • after adding the weight of different • analyzing power for different • Systematic analysis : • 3 different delta settings for every Kine. • Different spin precession method: • COSY, Pentchev, Dipole • Background substraction: • Aluminum end-cap • accidental E08-007 statistical error and world data & fits

  12. Impact • Many competing effective field theories: • VMD, Lattice, RCQM, Di-Quark, CBM/LFCBM, pQCD … • Combine ratio and cross section data (Mainz). • Proton charge density • Zemach radius/hyperfine splitting • Improved isovector/isoscalar form factors • Possible impacts on other experiments: DVCS, HAPPEX & G0, …

  13. Thank you!

More Related