Measurement of the longitudinal structure function with ZEUS at HERA

The longitudinal structure function, F_L, was measured using data taken 
with the ZEUS detector at the ep collider HERA with different proton 
energies. The standard proton energy of HERA was 920 GeV. In 2007, HERA 
also ran with proton energies of 460 GeV and 575 GeV. The structure 
function F_L was extracted using cross sections measured at fixed Bjorken 
x and momentum transfer squared Q2, but different inelasticity y.