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

Abstract

The asymmetry parameter P was measured for the elastic pion-proton scattering in the very backward angular region of θcm ≈ 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.PACS. 13.88.+e Polarization in interactions and scattering -13.75.Gx Pion-Baryon interactions

Progress towards understanding baryon resonances

“…The most recent πN elastic and charge-exchange results published after 2000 come from experiments at the Brookhaven National Laboratory (BNL) [92], the Tri-University Meson Facility (TRIUMF) [93], and the Paul Scherrer Institute (PSI) [94,95], for instance. The polarization parameter, P , and the spin-rotation parameter, A, were published recently by the ITEP-PNPI collaboration based on experiments at the Institute for Theoretical and Experimental Physics (ITEP) [96,97]. Earlier recoil polarization data were accumulated in the 1980s at Los Alamos, e.g.…”

P -wave excited baryons from pion- and photo-induced hyperon production

“…But this analysis challenges the existence of many resonances. A strong argument in favor of the Arndt analysis is the correct prediction of spin rotation parameters [14,15,16] and of the backward asymmetry [17] in the elastic pion-proton scattering from ITEP/PNPI while the predictions from [1,2] show clear discrepancies with the data. On the other hand, it is difficult to believe that the consistency between the older analyses is just fortuitous.…”

Spectroscopy of baryon resonances

“…The latter analysis included high precision data from the meson factories (see [34] for a list of data). This analysis predicted the spin rotation parameters [35][36][37] and the backward asymmetry [38] in the elastic pion-proton scattering from ITEP/PNPI very precisely while the predictions from [32,33] show clear discrepancies with the data. Hence the number of trustworthy resonances was reduced to 11 N * and 9 Δ * only.…”