Measurements of proton-proton elastic scattering by the KOALA experiment at COSY

The KOALA experiment is being built to measure the differential cross section spectrum for antiproton-proton elastic scattering in the squared 4-momentum transfer region (vertical stroke t vertical stroke ∝ [0.0008, 0.1] (GeV/c)²) at HESR. That data is an essential input to enable the PANDA luminosity determination to obtain the desired absolute precision of 3%. The complete KOALA experiment setup will be composed of one forward arm to measure the scattered projectile and two recoil arms to measure the recoil target. In a first step, one recoil detector has been constructed and commissioned at COSY by measuring proton-proton elastic scattering at 2.5, 2.8 and 3.2 GeV/c. The differential cross-section spectrum as a function of t has been reconstructed at each beam momentum after background subtraction and efficiency correction. The resulting spectra are parameterized in terms of the total cross section σ_t, the ratio of the real to imaginary part of the forward amplitude ρ and the nuclear slope b. These parameters, as well as the normalization coefficient have been extracted by analyzing the characteristic shape of the t spectra with the parameterized expression and the optical theorem. The relative differential cross sections have been obtained after normalization. The methods and the final differential cross section spectra will be presented in this talk.