Measurements of R=sigma_L/sigma_T for 0.03<x<0.1 and Fit to World Data

TL;DR

This paper reports measurements of the ratio R=sigma_L/sigma_T for low x and moderate Q^2 in electron-carbon scattering at SLAC, compares results with theoretical predictions, and updates a global fit including new data.

Contribution

It provides new measurements of R in a previously unexplored kinematic range and refines the global fit with recent data.

Findings

Results agree with pQCD calculations.

Data are consistent with previous parameterizations.

Updated fit improves understanding of R at low x.

Abstract

Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5 degrees, corresponding to 0.03<x<0.1 and 1.3<Q^2<2.7 GeV^2. Values of R=sigma_L/sigma_T were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results.