Measurements of the Separated Longitudinal Structure Function F_L from Hydrogen and Deuterium Targets at Low Q^2

TL;DR

This paper presents measurements of the separated longitudinal structure function F_L for hydrogen and deuterium at low Q^2, providing new data to test theoretical models and explore nucleon and nuclear structure differences.

Contribution

It provides the first separated F_L measurements at low Q^2 for hydrogen and deuterium, comparing results with models and revealing differences in nuclear effects.

Findings

Deuterium shows smaller F_L and R than hydrogen.

Data generally agree with parton distribution models at low Q^2.

Possible nuclear suppression of gluonic distributions inferred.

Abstract

Structure functions, as measured in lepton-nucleon scattering, have proven to be very useful in studying the quark dynamics within the nucleon. However, it is experimentally difficult to separately determine the longitudinal and transverse structure functions, and consequently there are substantially less data available for the longitudinal structure function in particular. Here we present separated structure functions for hydrogen and deuterium at low four--momentum transfer squared, Q^2< 1 GeV^2, and compare these with parton distribution parameterizations and a k_T factorization approach. While differences are found, the parameterizations generally agree with the data even at the very low Q^2 scale of the data. The deuterium data show a smaller longitudinal structure function, and smaller ratio of longitudinal to transverse cross section R, than the proton. This suggests either an unexpected difference in R for the proton and neutron or a suppression of the gluonic distribution in nuclei.