Evidence for a new resonance from polarized neutron-proton scattering

Abstract

Exclusive and kinematically complete high-statistics measurements of quasifree polarized n→p scattering have been performed in the energy region of the narrow resonancelike structure d* with I(JP)=0(3+), M≈2380MeV, and Γ≈70MeV observed recently in the double-pionic fusion channels pn→dπ0π0 and pn→dπ+π-. The experiment was carried out with the WASA detector setup at COSY having a polarized deuteron beam impinged on the hydrogen pellet target and utilizing the quasifree process d→p→np+pspectator. This allowed the np analyzing power, Ay, to be measured over a broad angular range. The obtained Ay angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new Ay data into the SAID analysis produces a pole in the D33-G33 waves in support of the d* resonance hypothesis. © 2014 American Physical Society.