Measurement of the Total Cross Section and ? -Parameter From Elastic Scattering in Pp Collisions at ?s=13 Tev With the Atlas Detector

Abstract

In a special run of the LHC with ??= 2.5 km, proton–proton elastic-scattering events were recorded at s=13 TeV with an integrated luminosity of 340?b-1 using the ALFA subdetector of ATLAS in 2016. The elastic cross section was measured differentially in the Mandelstam t variable in the range from - t= 2.5 · 10 - 4 GeV 2 to - t= 0.46 GeV 2 using 6.9 million elastic-scattering candidates. This paper presents measurements of the total cross section ?tot , parameters of the nuclear slope, and the ? -parameter defined as the ratio of the real part to the imaginary part of the elastic-scattering amplitude in the limit t? 0 . These parameters are determined from a fit to the differential elastic cross section using the optical theorem and different parameterizations of the t-dependence. The results for ?tot and ? are ?tot(pp?X)=104.7±1.1mb,?=0.098±0.011. The uncertainty in ?tot is dominated by the luminosity measurement, and in ? by imperfect knowledge of the detector alignment and by modelling of the nuclear amplitude. © 2023, The Author(s).