Measurement of the total cross section from elastic scattering in pp collisions at root s=8 TeV with the ATLAS detector

A measurement of the total pp cross section at the LHC at √s= 8TeV is presented. An integrated luminosity of 500 μb−1 was accumulated in a special run with high-β beam optics 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 0.014 GeV2 to 0.1GeV2 to extrapolate t →0, the total cross section, σtot(pp → X), is measured via the optical theorem to be σtot(pp → X)=96.07±0.18(stat.)±0.85 (exp.)±0.31 (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 t → 0. In addition, the slope of the exponential function describing the elastic cross section at small t is determined to be B = 19.74 ± 0.05 (stat.) ± 0.23 (syst.) GeV−2.