Measurement of the total cross section from elastic scattering in pp collisions at <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.gif" overflow="scroll"><mml:msqrt><mml:mi>s</mml:mi></mml:msqrt><mml:mo>=</mml:mo><mml:mn>8</mml:mn><mml:mtext> </mml:mtext><mml:mtext>TeV</mml:mtext></mml:math> with the ATLAS detector

A measurement of the total ppcross section at the LHC at √s=8TeVis presented. An integrated luminosity of 500μb−1was 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 −trange from 0.014GeV2to 0.1GeV2to extrapolate t→0, the total cross section, σtot(pp →X), is measured via the optical theorem to be&#13;\nσtot(pp→ X) = 96.07±0.18 (stat.)±0.85 (exp.)± 0.31 (extr.) mb,&#13;\nwhere 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 tis determined to be B =19.74 ±0.05 (stat.) ±0.23 (syst.) GeV−2.