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

摘要

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 → dπ~0 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.