The Matter Density Distribution for Mesons and Baryons *

The charge and matter density distributions encode detailed information on hadron structure. In the non-relativistic limit both charge and matter density distributions reduce to the square of the wave function. Therefore differences between them give a measure of relativistic effects. Hadron deformation can be searched via the matter density distribution as well as via the charge density distribution. There are strong experimental indications from measurements of the electromagnetic transition form factors in γN to ∆ [1] that the nucleon is deformed. It is thus interesting to address the issue of hadron deformation within lattice QCD and understand its physical origin. Comparison of matter and charge density distributions can help discriminate among possible mechanisms. A number of phenomenological studies use the bag-model to describe hadron deformation. For this reason we compare the charge and matter distributions to the bag-model results.