Evaluation of the Higher Twist Contribution to the Moments of Proton Structure Functions

We performed the measurement of the inclusive electron scattering off the proton [1, 2] in the resonance region (W < 2.5 GeV) at momentum transfer Q below 4.5 (GeV/c) with the CLAS detector. The large acceptance of CLAS provided an access to a large, continuous two-dimensional kinematic domain in Q and x, allowing therefore an integration of the data at fixed Q over x-interval. The covered x-interval at each measured Q value is sufficient for an evaluation of the higher moments (n > 2). From these data we extracted the structure function F2 and, by including other world data, we studied the Q evolution of its moments, Mn(Q), in order to estimate the higher twist contributions. A similar experiment with polarized proton target is completed at CLAS [3]. These new data allow an accurate determination of higher moments of the proton structure function g1. A preliminary phenomenological analysis [4] indicates an excess of the higher twist contribution in the spin-dependent structure function with respect to the spin-independent one.