Evidence for a New Resonance from Polarized Neutron-Proton Scattering

P. Adlarson et al. (WASA-at-COSY Collaboration, SAID Data Analysis Center)

Phys. Rev. Lett. 112, 202301 – Published 23 May 2014

Abstract

Exclusive and kinematically complete high-statistics measurements of quasifree polarized $\vec{n} p$ scattering have been performed in the energy region of the narrow resonancelike structure $d^{*}$ with $I (J^{P}) = 0 (3^{+})$ , $M \approx 2380 MeV$ , and $Γ \approx 70 MeV$ observed recently in the double-pionic fusion channels $p n \to d π^{0} π^{0}$ and $p n \to d π^{+} π^{-}$ . 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 $\vec{d} p \to n p + p_{spectator}$ . This allowed the $n p$ analyzing power, $A_{y}$ , to be measured over a broad angular range. The obtained $A_{y}$ angular distributions deviate systematically from the current SAID SP07 NN partial-wave solution. Incorporating the new $A_{y}$ data into the SAID analysis produces a pole in the ${}^{3}{D_{3}} - {}^{3}{G_{3}}$ waves in support of the $d^{*}$ resonance hypothesis.