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

Jlab high Q 2 program extensive with various decay channels. Focus on two experiments : CLAS Ebeam=5.75 GeV L~10 34 cm -1 s -1 Full cm angular coverage Q 2 continuous from 2 to 5 GeV 2 /c 2 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>10 38 Nearly full cm angular coverage at  Most angular coverage at S11 Q 2 at 2 points 6.3 and 7.5 GeV 2 /c 2 PhD thesis: Anthony Villano Hall C experiment analysis not yet complete.. Analysis complete on CLAS experiment. Thus focus rest of talk on CLAS results

Cartoon of relevant physics at different Q2 scales. Isobar model Quark model GPDpQCD

Some of the physics issues G M * is related to the isovector component of the elastic form factor. G M * vs Q 2 : Falls much faster than G MP Falls much faster than dipole Relate via GPD’s to Isovector G EP E 1+ /M 1+ : Helicity meter. =1 pQCD =0 quark model

15 bins in W - 20 MeV bin size – 1.4 GeV 7 bins in Q2 - variable bin size GeV 10 bins in cos   12 bins in   Kinematic coverage Highest in Q 2 so far Full coverage of cm angles

CLAS eg1 Experiment More than data intervals in W, Q 2, 

CLAS ability to detect large kinematic range Bethe Heitler separation:  0 selection

W=1.23, Q 2 =1.72

Structure functions extraction: bb

Structure functions Legendre expansion: bb

Different ways to extract amplitudes M 1+ dominance. Assume all multipoles are much smaller than M +1 Retain only those which multiply M 1+ 6 parameter fit. Problem: At high Q 2 M 1+ 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.

E 1+ /M 1+ S 1+ /M 1+ Preliminary Results (M Ungaro et al.)  M 1+ dominance  Isobar (JANR I. Aznauryan et al. )

G * M still falling faster than G D CLAS preliminary GPD prediction: PRL 03, issue 91, vol

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)

SOME DETAILS

Obtain E IV from fit to F 2P ( P.S. Phys.Rev.Lett.91:172303,2003) (Renormalize E IV by 1.3 to get agreement at Q 2 ~0 )

s+h s 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  G E /G M  G M * /3G D E 1+ /M 1+

H 0 E 0 t=-30 GeV 2 t=0

Polyakov, Vanderhaeghen, Frankfurt, Strickman

s+h s