Measurement of the total cross section in pp collisions at sqrt(s)=7 TeV with the ALFA sub-detector of ATLAS

Abstract

A measurement of the total pp cross section at the LHC at √ s = 7 TeV by the ATLAS experiment 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 subdetector 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.) GeV2.