Longitudinal Structure Function Measurements from HERA
Measurements of the longitudinal structure function FL at the ep collider HERA are presented. They are derived from inclusive deep inelastic neutral current e+p scattering cross section measurements based on data collected in 2007 with the H1 and ZEUS detectors at a positron beam energy of 27.5 GeV and proton beam energies of 920, 575 and 460 GeV. Employing the energy dependence of the cross sections, FL(x,Q2) is measured in the range of negative four-momentum transfer squared from 12 to 800 GeV2 and low Bjorken-x from 0.00028 to 0.0353. The measured longitudinal structure function is compared with higher order QCD predictions.