Exclusive and kinematically complete high-statistics measurements of quasifree polarized $\overrightarrow{n}p$ scattering have been performed in the energy region of the narrow resonancelike structure $d^{*}$ with $I(J^P)=0(3^{+})$, $M\approx 2380\mathrm{MeV}$, and $\mathrm{\Gamma }\approx 70\mathrm{MeV}$ observed recently in the double-pionic fusion channels $pn\to d{\pi }^0{\pi }^0$ and $pn\to d{\pi }^{+}{\pi }^{-}$. 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 $\overrightarrow{d}p\to np+p_{\text{spectator}}$. This allowed the $np$ 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.

• Received 27 February 2014

DOI:https://doi.org/10.1103/PhysRevLett.112.202301