Moments of the longitudinal proton structure function F_L from global data in the Q² range 0.75-45.0 (GeV/c)²

We present an extraction of the lowest three moments of the proton longitudinal structure function F_L from world data between Q^2 = 0.75 and 45 (GeV/c)^2. The availability of new F_L data at low Bjorken x from HERA and at large x from Jefferson Lab allows the first determination of these moments over a large Q^2 range, relatively free from uncertainties associated with extrapolations into unmeasured regions. The moments are found to be underestimated by leading twist structure function parameterizations, especially for the higher moments, suggesting either the presence of significant higher twist effects in F_L and/or a larger gluon distribution at high x.