Measurement of the spin-correlation coefficients A_x,x and A_y,y in the quasi-free np → {pp}_sπ⁻ reaction near threshold at ANKE-COSY

¹ Laboratory of Nuclear Problems, Joint Institute for Nuclear Research 141980 Dubna Russia
² Institut für Kernphysik, Forschungszentrum Jülich 52425 Jülich Germany

^a e-mail: v.shmakova@fz-juelich.de

Abstract

A kinematically complete double-polarization measurement of the quasi-free np → {pp}_sπ⁻ reaction near threshold has been performed using the ANKE spectrometer at COSY-Jülich. Here {pp}_s represents a two-proton system with an excitation energy less than 3 MeV. The transversely vector polarized deuteron beam and the internal polarized ANKE hydrogen target were used to determine the spin-correlation coefficients A_x,x and A_y,y. Events from the quasi-free np → dπ⁰ reaction were recorded simultaneously and used for both beam and target polarimetry. In addition, the product of the beam and target polarizations could be estimated from the A_y,y coefficient. The storage cell within the polarized target was the main source of background events. Dedicated runs, with no gas in the cell and with the cell filled with N₂ gas, were taken to study the backgrounds. The data analysis procedure and the initial results of the experiment are presented.