Measurement of the total cross section at the LHC at sqrt(s)=7 TeV from elastic scattering with the ATLAS detector

Abstract

In this contribution a measurement of the total $pp$ cross section with the ATLAS detector at the LHC at sqrt(s)=7 TeV is presented. In a special run with high-beta*, beam optics, the differential elastic cross section is measured 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 GeV^2 to 0.1 GeV^2 to extrapolate to |t|--> 0, the total cross section, sigmatot(pp--> X), is measured via the optical theorem to be: sigmatot(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.