Study of spectator tagging in the reaction np → ppπwith a deuteron beam.

The reaction $dp \ensuremath \rightarrow ppp \pi^-$ has been studied in a kinematically complete experiment at a single beam momentum $\ensuremath p_{d}=1.85$ GeV/ c ( T = 759MeV). All four ejectiles have been detected in the large-acceptance time-of-flight spectrometer COSY-TOF. We analyzed the data along the lines of the spectator model as a means to isolate the quasi-free $\ensuremath np\rightarrow pp\pi^-$ reaction. The spectator proton was identified by its momentum and flight direction thus yielding access to the associated Fermi motion of the bound neutron. A comparison is carried out with Monte Carlo simulations based on two different parameterizations of the deuteron wave function. Up to a Fermi momentum of roughly 150MeV/ c no significant deviations between experimental and simulated data of various observables were found from which we conclude that the deuteron can indeed be taken as a valid substitute for the neutron. [ABSTRACT FROM AUTHOR]