Measurement of R=σ_L/σ_T in Deep-Inelastic Scattering on Nuclei

Abstract

Cross section ratios for deep-inelastic scattering from $^3$He, $^{14}$N and $^{84}$Kr with respect to $^2$H have been measured by the HERMES collaboration at DESY using a 27.5 GeV positron beam. The data cover a range in the Bjorken scaling variable $x$ between 0.010 and 0.65, the negative squared four-momentum transfer $Q^2$ varies from 0.5 to 15 GeV$^2$, while at small values of $x$ and $Q^2$, the virtual photon polarisation parameter $ε$ extends to lower values than previous measurements. From the dependence of the data on $ε$, values for $R_A/R_D$ with $R$ the ratio $σ_L / σ_T$ of longitudinal to transverse DIS cross sections have been derived and found to be consistent with unity. %The data are compared to measurements performed by NMC, E665, and SLAC %on $^4$He and $^{12}$C, and are found to be different for %$x <$ 0.06 and $Q^2 <$ 1.5 GeV$^2$.

Figures (7)

• Figure 1: Ratio of track reconstruction efficiencies in $^1$H, $^3$He, $^{14}$N and $^{84}$Kr with respect to $^2$H as function of $x$. The hatched areas represent the systematic uncertainties for the N/D (cross hatched) and Kr/D (slanted hatched) efficiency ratios. The systematic uncertainties for the H/D and He/D ratios are smaller than that of the N/D ratio and are not shown.
• Figure 2: Comparison between data (points) and MC simulation (histogram) for the fractional change in the cross section ratios when treating the upper and lower HERMES detector halves independently.
• Figure 3: Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus $A$ and $D$ versus $x$. The error bars represent the statistical uncertainties, the systematic uncertainties are given by the error bands. The HERMES $^3$He/D and $^{14}$N/D data have been renormalised by 0.9 %.
• Figure 4: Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nucleus $A$ and $D$ as function of $Q^2$ for fixed values of $x$. The error bars represent the statistical uncertainties. The HERMES $^{14}$N/D data have been renormalised by 0.9 %.
• Figure 5: Ratio of isoscalar Born cross sections of inclusive deep-inelastic lepton scattering from nitrogen and deuterium (renormalised by 0.9 %) as function of $\epsilon$ for fixed values of $x$. The error bars represent the statistical uncertainties.