Measurement of spin observables in the quasi-free np-> {pp}_s pi- reaction at 353 MeV

TL;DR

This study measures spin observables in a quasi-free neutron-proton reaction at 353 MeV, providing insights into the reaction mechanism and partial wave contributions through polarization data and identifying the need for further measurements to resolve ambiguities.

Contribution

It presents new measurements of spin correlations and analyzing powers in the quasi-free np->pp_s pi- reaction, enhancing the understanding of partial wave decomposition in pion production.

Findings

Measured transverse spin correlations A_{x,x} and A_{y,y} at 353 MeV.

Extracted proton analyzing power consistent with previous results.

Identified three possible solutions for partial wave analysis, requiring further data to resolve.

Abstract

The transverse spin correlations A_{x,x} and A_{y,y} have been measured in the pol{d} pol{p} -> p_spec {pp}_s pi- reaction at COSY-ANKE at 353 MeV per nucleon. Here {pp}_s denotes a proton-proton pair with low excitation energy, which is dominantly in the 1S0 state. By measuring three protons in the final state it was possible to extract events where there was a spectator proton p_spec so that the reaction could be interpreted in terms of quasi-free pol{n} pol{p} -> {pp}_s pi-. The proton analyzing power in this reaction was also deduced from this data set by averaging over the polarization of the deuteron beam. The values of A_y^p were shown to be consistent with a refined analysis of our earlier results obtained with a polarized proton incident on a deuterium target. Taking these data in combination with our earlier measurements of the differential cross sections and analyzing powers in the pol{p} p -> {pp}_s pi^0 reaction, a more robust partial wave decomposition was achieved. Three different acceptable solutions were found and the only way of resolving this ambiguity without further theoretical input would be through a measurement of the mixed spin-correlation parameter A_{x,z}.