A measurement of the total pp cross section at the LHC at √s = 7TeV is presented. In a special run with high-Β* beam optics, an integrated luminosity of 80 µb-1 was accumulated in order to measure the differential elastic cross section as a function of the Mandelstam momentum transfer variable t. The measurement is performed with the ALFA sub-detector of ATLAS. Using a fit to the differential elastic cross section in the |t| range from 0.01 GeV2 to 0.1 GeV2 to extrapolate to |t| → 0, the total cross section, σtot (pp→X), is measured via the optical theorem to be: σtot(pp→X) = 95.35 ± 0.38 (stat.) ± 1.25 (exp.) ± 0.37 (extr.) mb, where the first error is statistical, the second accounts for all experimental systematic uncertainties and the last is related to uncertainties in the extrapolation to |t| → 0. In addition, the slope of the elastic cross section at small |t| is determined to be B = 19.73 ± 0.14 (stat.) ± 0.26 (syst.)GeV-2.
Bibliographical noteAll figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2013-10/