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

A measurement of the total pp cross section at the LHC at √s=8 TeV 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 0.1 GeV² to extrapolate t→0 , the total cross section, σ tot (pp→X) , is measured via the optical theorem to be:
σ tot (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.