  The longitudinal proton structure function (FL) has been measured at the HERA
collider in positron-proton deep inelastic scattering collisions with the H1
and ZEUS detectors. This measurement is achieved by using multiple
center-of-mass energies (sqrt(s)) via a reduction of the proton beam energy.
The energies used for this measurement are sqrt(s) = 318, 251, 225 GeV. The
kinematic region studied is 2.5<Q^2<800 GeV^2. H1 and ZEUS data have been
combined to increase statistical precision and reduce systematic effects. The
impact of the low proton beam energy cross sections to the proton PDFs is being
investigated.

High Energy Physics - Experiment