Elastic scattering of negative pions by protons at 128 and 162 MeV

Abstract

The elastic scattering distribution of negative pions by protons has been measured with a hydrogen-filled diffusion cloud chamber in a magnetic field. In a set of exposures 344 and 941 elastic scattering events were recorded at anglesθ(c.m.s.) > 10°. The total cross-sections for elastic scattering σ_e1 (128MeV) = (12.8 ± 1.0) 10⁻²⁷ cm² and σ_e1(162 MeV) = (21.4 ± 1.2) 10⁻²⁷ cm² were determined by calculating the total length of negative pion tracks in the chamber. The elastic π⁻-p-scattering angular distributions wwere obtained in the form (the SP-analysis): $\text{d}\text{σ/}\text{d}\text{Ω(128}\text{MeV}\text{) = (1.00±0.08)[(0.55±0.07)+(0.34±0.12)}\text{cos}\text{θ+(1.30±0.24)}\text{cos}{}^2\text{θ] 10}{}^{\mathrm{-27}}\text{cm}{}^2\text{/}\text{sr}$, $\text{d}\text{σ/}\text{d}\text{Ω(162}\text{MeV}\text{) = (1.00±0.06)[(0.93±0.07)+(0.51±0.12)}\text{cos}\text{θ+(2.28±0.22)}\text{cos}{}^2\text{θ]10}{}^{\mathrm{-27}}\text{cm}{}^2\text{/}\text{sr}$. The differential forward scattering cross-sections are equal to (2.20±0.32) 10⁻²⁷ cm²/sr and (3.73±0.32) 10⁻²⁷ cm²/sr respectively. The real parts of the forward scattering amplitude (in c.m.s.) have been calculated in units of ℏ/m_πc: D_^b(128 MeV) = 0.261±0.031 and D_^b(162 MeV) = 0.216±0.038. These quantities agree with those calculated from dispersion relations with the coupling constant f² = 0.08.