1210.0634 (M. V. Galynskii et al.)

On the physical meaning of Sachs form factors and on the violation of
the dipole dependence of G_E and G_M on Q^2    [PDF]

M. V. Galynskii, E. A. Kuraev

The questions of how a dipole character of the dependence of the form factors G_E and G_M on the square of the momentum transfer to a proton, Q^2, arise and why a violation of this dependence occurs, are investigated. The answers to these questions could be obtained owing to the use of the simplest QCD concepts of the proton structure and the results obtained by calculating the matrix elements of the proton current in the case of non-spin-flip and spin-flip transitions for protons in diagonal spin basis (DSB), where the little group of Lorentz group (little Wigner group) common to the initial and final proton states is being realized. In DSB, the matrix elements of the proton current in the cases of non-spin-flip and spin-flip transitions for protons are determined by the form factors G_E and G_M. In considering the problem in question at the quark level, use is made of the model where the proton consists of three point-like quarks having identical masses and where the respective matrix element of the proton current is the product of three quark-current amplitudes. It is shown that the dipole dependence arises if the proton spin-flip is due to spin-flip for only one of the three quarks. As to violations of this dependence, they are caused by the contributions to matrix element of proton current without spin-flip from spin-flip transitions for two quarks or by the contribution to matrix element of proton current with spin-flip from spin-flip transitions for all three quarks constituting the proton.

View original: http://arxiv.org/abs/1210.0634