/ Experiment-HEP hep-ex/0210068

Measurement of R = sigma(L) / sigma(T) in deep inelastic scattering on nuclei

Airapetian, A. ; Akopov, N. ; Akopov, Z. ; Amarian, M. ; Ammosov, V.V. ; Aschenauer, E.C. ; Avakian, R. ; Avetissian, A. ; Avetissian, E. ; Bailey, P. ; Baturin, V. ; Baumgarten, C. ; Beckmann, M. ; Belostotski, S. ; Bernreuther, S. ; Bianchi, N. ; Blok, H.P. ; Bottcher, H. ; Borissov, A. ; Bouhali, O. ; Bouwhuis, M. ; Brack, J. ; Brauksiepe, S. ; Brull, A. ; Brunn, I.

Pages: 8

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 $\epsilon$ extends to lower values than previous measurements. From the dependence of the data on $\epsilon$, values for $R_A/R_D$ with $R$ the ratio $\sigma_L / \sigma_T$ 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$^2$.

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