Measurement of the total cross section from elastic scattering in pp collisions at [formula omitted] with the ATLAS detector

Hasko Stenzel

doi:10.1016/j.nuclphysbps.2015.09.333

Abstract

In this contribution a measurement of the total pp cross section with the ATLAS detector at the LHC at s=7 TeV is presented. In a special run with high-β⋆ beam optics, the differential elastic cross section is measured 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 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.) GeV-2.

Highlights

The total cross section is a fundamental parameter of strong interactions, setting the scale for the interaction strength for all processes at a given energy
A measurement of the total cross section can still be performed via elastic scattering by using the optical theorem, which relates the imaginary part of the forward elastic-scattering amplitude to the total cross section: σtot ∝ Im [ fel (t → 0)], (1)
The amount of background is varied by the difference between the yields obtained from different methods and different background shapes obtained from variations of the anti-golden method

Summary

Introduction

The total cross section is a fundamental parameter of strong interactions, setting the scale for the interaction strength for all processes at a given energy. A calculation of the total cross section from first principles, based upon quantum chromodynamics (QCD), is not possible, since large distances are involved. A measurement of the total cross section can still be performed via elastic scattering by using the optical theorem, which relates the imaginary part of the forward elastic-scattering amplitude to the total cross section: σtot ∝ Im [ fel (t → 0)] , (1). Where ρ represents a small correction arising from the ratio of the real to imaginary part of the elasticscattering amplitude in the forward direction and is taken from theory. More details on the results presented in this paper are given in Ref. The quantities measured and reported here have been measured at the LHC by the TOTEM experiment [2, 3]

Results

Discussion

Conclusion