Izlaganje sa skupa
Structure of the nucleon from electromagnetic form factors
F. Iachello
; ECT*, I-38050 Villazzano (Trento), Italy, and Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520-8120, USA
Sažetak
Recent TJNAF data on the ratio of electric to magnetic elastic form factors are reviewed in light of a model of the nucleon with an intrinsic (quark-like) structure and a meson (quark-antiquark) cloud. The analysis points to the remarkable result that the proton electric form factor vanishes at Q2 ∼ 8 (GeV/c) 2 and becomes negative beyond that point. The intrinsic structure is estimated to have a r.m.s. radius of ∼ 0.34 fm, much smaller than the proton r.m.s. radius ∼ 0.87 fm. The calculations are in perfect agreement with the proton data, but deviate drastically from neutron data at Q2 > 1 (GeV/c) 2 . Relativistic invariance is a crucial ingredient responsible for the vanishing of GEp . Symmetry, rather than detailed dynamics, appears to be a determining factor in the structure of the nucleon. Scaling appears to occur at Q2 ≥ 30 (GeV/c) 2 , i.e. at much larger values than previously thought
Ključne riječi
nucleon intrinsic structure; form factors; r.m.s. radii; symmetry; scaling
Hrčak ID:
305603
URI
Datum izdavanja:
1.3.2004.
Posjeta: 101 *