Measurement of the total cross section from elastic scattering in pp collisions at $\sqrt{s}=7\text{TeV}$ with the ATLAS detector

Abstract

A measurement of the total pp cross section at the LHC at $\sqrt{s}=7\text{TeV}$ is presented. In a special run with high-${\beta }^{\star }$ 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 sub-detector of ATLAS. Using a fit to the differential elastic cross section in the $|t|$ range from $0.01{\text{GeV}}^2$ to $0.1{\text{GeV}}^2$ to extrapolate to $|t|\to 0$, the total cross section, ${\sigma }_{\mathrm{tot}}(pp\to X)$, is measured via the optical theorem to be:

$${\sigma }_{\mathrm{tot}}(pp\to X)=\text{95.35}\pm 0.38(\text{stat.})\pm 1.25(\text{exp.})\pm 0.37(\text{extr.})\text{mb},$$

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 $|t|\to 0$. In addition, the slope of the elastic cross section at small $|t|$ is determined to be $B=19.73\pm 0.14(\text{stat.})\pm 0.26(\text{syst.}){\text{GeV}}^{-2}$.