Proton and deuteron F2 structure function at low Q2

Measurements of the proton and deuteron F 2 structure functions are presented. The data, taken at Jefferson Lab Hall C, span the four-momentum transfer range 0.06 < Q 2 < 2.8 GeV 2 and Bjorken x values from 0.009 to 0.45, thus extending the knowledge of F 2 to low values of Q 2 at low x. Next-to-next-to-leading-order calculations using recent parton distribution functions start to deviate from the data for Q 2 < 2 GeV 2 at the low and high x values. Down to the lowest value of Q 2 , the structure function is in good agreement with a parametrization of F 2 based on data that have been taken at much higher values of Q 2 or much lower values of x, and which are constrained by data at the photon point. The ratio of the deuteron and proton structure functions at low x remains well described by a logarithmic dependence on Q 2 at low Q 2 .