On the measurements of the pion-proton elastic scattering in nuclear emulsions

The scanning methods for the photographic emulsions, used in the study of the pion-proton elastic scattering, are discussed. A particular method is described, which is useful in the research of the backwards scatterings (135° <θ c.m. ⩽ 180°). It has been employed in order to detect some eventual contribution of waves withl > 1, by analysing the behaviour of dσ/dΩ in this angular interval. The analysis of dσ/dΩ for the scattering process π+ + p at 120 MeV, based on 871 events, shows that no wave withl > 1 is present in a measurable quantity. The phase-shifts of theS andP waves result: $$\alpha _3 = - 10.3 \pm 2.9; \alpha _{33} = 31.8 \pm 1.6; \alpha _{31} = - 2.6 \pm 1.6.$$