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JLAB Program of Baryon Form Factors at High Momentum Transfer

Explore the status and future directions of baryon form factors at high momentum transfer, covering experiments, analysis, models, and predictions. Discussing GPD, isobar, and quark models in relation to GM* and Q2 scales. Examine preliminary results and the importance of a unified GPD perspective for understanding nucleon excitations. Highlighting the challenges of model dependence and suggesting refined approaches. Presenting detailed insights and future prospects for studying elastic and resonance form factors using a unified GPD framework.

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JLAB Program of Baryon Form Factors at High Momentum Transfer

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  1. JLAB Program of Baryon Form Factors at High Momentum Transfer Current Status and Future Directions. Paul Stoler Rensselaer Polytechnic Institute Milos 2005

  2. CLAS Ebeam=5.75 GeV L~1034 cm-1s-1 Full cm angular coverage Q2 continuous from 2 to 5 GeV 2/c2 W continuous from threshhod to 3 GeV Many experiments obtained in one run PhD thesis M. Ungaro Hall C focusing spectrometers Ebeam = 5.5 GeV L>1038 Nearly full cm angular coverage at  Most angular coverage at S11 Q2 at 2 points 6.3 and 7.5 GeV 2/c2 PhD thesis: Anthony Villano Jlab high Q2 program extensive with various decay channels. Focus on two experiments: Hall C experiment analysis not yet complete.. Analysis complete on CLAS experiment. Thus focus rest of talk on CLAS results

  3. GPD Isobar model Quark model pQCD Cartoon of relevant physics at different Q2 scales.

  4. Some of the physics issues • GM* is related to the isovector component of the elastic form factor. • GM* vs Q2: Falls much faster than GMP • Falls much faster than dipole • Relate via GPD’s to Isovector GEP • E1+/M1+: Helicity meter. =1 pQCD =0 quark model

  5. Kinematic coverage 15 bins in W - 20 MeV bin size - 1.1 – 1.4 GeV 7 bins in Q2 - variable bin size - 2-6 GeV 10 bins in cos q* 12 bins in f* • Highest in Q2 so far • Full coverage of cm angles

  6. CLAS eg1 Experiment More than 10000 data intervals in W, Q2, 

  7. p0 selection Bethe Heitler separation: CLAS ability to detect large kinematic range

  8. W=1.23, Q2=1.72

  9. Structure functions extraction: mb

  10. Structure functions Legendre expansion: mb

  11. Different ways to extract amplitudes M1+dominance. Assume all multipoles are much smaller thanM+1 Retain only those which multiplyM1+ 6 parameter fit. Problem: At highQ2 M1+decreases relative to other multipoles. Thus this approximation becomes less valid Better way: Isobar/Effective Lagrangian Fit all amplitudes taking into account contributions from all known resonances and backgrounds. JANR, Dynamic, DMT, MAID Problem: The result becomes model dependent.

  12. Preliminary Results (M Ungaro et al.) E1+/M1+ S1+/M1+ • M1+ dominance • Isobar (JANR I. Aznauryan et al.)

  13. GPD prediction: PRL 03, issue 91, vol 17 - 172303 G*M still falling faster than GD CLAS preliminary

  14. This can be F2 is predominantly isoscalar while F1 is predominantly related to the isovector part of the proton elactic form factor. Thus Apply GPD with chiral symmetry (see Goeke, Vanderhaeghen, Polyakov,Frankfort, Strickman)

  15. SOME DETAILS

  16. ObtainEIVfrom fit toF2P ( P.S. Phys.Rev.Lett.91:172303,2003) (Renormalize EIV by 1.3 to get agreement atQ2~0 )

  17. Future Program: Jlab g12 GeV Must study elastic and resonance form factors from he point of view of a unfied/coherent GPD picture of the nucleon and its excitations s+h GE/GM GM*/3GD E1+/M1+ s

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