The Charm quark contribution to the proton structure function

The charm quark structure function F c 2 and the longitudinal structure function F p l is directly sensitive to the gluon content of proton and is therefore crucial in undersatanding of proton structure function, in particular at low momentum transfer Q2 and low Bjorken x. In the framework pf perturbative QCD the charm structure function is calculated in the leading order (LO) and the proton strcture function is investigated in the next leading order (NLO) at small x region. The valance quark distribution is obtained from the relativistic quark-exchange model.The Calculated F c 2 (x,Q 2), F p 2 (x,Q 2) and F p L(x,Q 2), are compared with theb persent avilable experimental data.