Nucleon Form Factors John Arrington Argonne National Lab

Nucleon Form Factors John Arrington Argonne National Lab Hall A Collaboration Meeting 4 Jan 2007 Early History of the Proton 2 Electron Scattering and Form Factors 3 Proton Form Factors 4 Nucleon Form Factors  Fundamental properties of the nucleon – Connected to charge, magnetization distribution – Crucial testing ground for models of the nucleon internal structure – Necessary input for experiments probing nuclear structure, or trying to understand modification of nucleon structure in nuclear medium  Early measurements found: – Neutron form factor small – Others well approximated by dipole form – Only proton magnetic form factor measured precisely over large Q2 range 5 Significant Program Over Next 40+ Years 6 Unpolarized Elastic e-N Scattering  Nearly all of these measurements used Rosenbluth separation sR = ds/dW [e(1+t)/sMott] = tGM2 + eGE2 Reduced sensitivity to… • GM if t<<1 (low Q2) t = Q2/4M2 • GE if t>>1 • GE if GE2<