High twist contribution to the longitudinal structure function $F_L$ at high $x$

We performed NLO QCD fit of combined SLAC/BCDMS/NMC DIS data at high $x$. Model independent x-shape of high twist contribution to structure function $F_L$ is extracted. Twist-4 contribution is found to be in fair agreement with the predictions of infrared renormalon model. Twist-6 contribution exhibits weak tendency to negative values, although in the whole is compatible with zero within errors.