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

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.

Figures (4)

• Figure 1: (a) Cross sections from this experiment (E143) for 29.1 GeV electron scattering from carbon at $4.5^\circ$. Inner (outer) error bars are statistical (systematic). The curve is calculated using the NMC fit to $F_2$f2nmc, the R1990 fit to $R$r1990, and the $A$-dependence of lepton-nucleon scattering emcfit. (b) $R$ extracted from this experiment (E143) combined with NMC. Inner (outer) error bars are statistical (systematic). The solid curve is the R1990 fit, with the dotted curves showing the error band evaluated at the $Q^2$ values of the data. The dashed curve is a pQCD calculation described in the text.
• Figure 2: Kinematic distribution of data used for the R1998 fit.
• Figure 3: $R$ as a function of $Q^2$ for: a) $0.05\leq x \leq 0.10;$ b) $0.03\leq x \leq 0.05;$ c) $0.01 \leq x \leq 0.02.$ The solid curve is the average of the new fits, $R1998$, and the dashed curve is the NNLO pQCD calculation described in the text.
• Figure 4: $R$ as a function of $x$ for: a) $3\leq Q^2 \leq 6$(GeV/c)$^2$; b) $1.5\leq Q^2 \leq 3$ (GeV/c)$^2$; c) $0.5\leq Q^2 \leq 1.5$ (GeV/c)$^2$. The solid curve is the average of the new fits, $R1998,$ and the dashed curve is the NNLO pQCD calculation described in the text.