Remarks on the Parity Determination of Narrow Resonances ∗

Recently several proposals were put forward to determine the parity of narrow baryonic resonances, in particular the Θ +. In these proceedings we will briefly comment on the general problems in this task and then discuss in detail the potential of reactions of the type N N → Θ + Y , where Y denotes a hyperon (either Σ or Λ) and the arrows indicate that a polarized initial state is required. Besides reiterating the model–independent properties of this class of reactions we discuss the physics content of some model calculations. The parity of a hadron contains significant information on its substructure. Unfortunately, especially for spin–1/2 particles, the determination of the parity is a non–trivial problem especially when we talk about narrow states. To illustrate the origin of the difficulty we observe that—in leading order of the outgoing cms momentum—the decay vertex of a spin–1/2 resonance into a spin–1/2 particle and a pseudoscalar (e.g. Θ + → N K, if the Θ + were indeed a spin–1/2 particle as suggested by almost all models) reads σ · q for a positive parity resonance and 1 for a negative parity resonance. Thus, as long as we do not measure the polarization of the decay products, all observables scale as (σ · q)(σ · q) = q · q or 1, accordingly, leaving no unique trace of the intrinsic parity of the decaying object.