Backward asymmetry measurements in the elastic pion-proton scattering at resonance energies

TL;DR

This study measures the asymmetry parameter P in elastic pion-proton scattering at backward angles near resonance energies to improve partial wave analyses and resolve baryon spectrum uncertainties.

Contribution

It provides new experimental data in a previously unmeasured kinematic domain, aiding in clarifying partial wave analysis discrepancies.

Findings

New asymmetry measurements at backward angles

Data covering resonance energy range

Improved constraints for partial wave analyses

Abstract

The asymmetry parameter P was measured for the elastic pion-proton scattering in the very backward angular region of theta_cm ~ 150-170^o at several pion beam energies in the invariant mass range containing most of the pion-proton resonances. The general goal of the experimental program was to provide new data for partial wave analyses in order to resolve their uncertainties in the baryon resonance region to allow the unambiguous baryon spectrum reconstructions. Until recently the parameter P was not measured in the examined domain that might be explained by the extremely low cross section. At the same time the predictions of various partial wave analyses are far from agreement in some kinematic areas and specifically those areas were chosen for the measurements where the disagreement is most pronouncing. The experiment was performed at the ITEP U-10 proton synchrotron, Moscow, by the ITEP-PNPI collaboration in the latest 5 years.