Evidence for a New Resonance from Polarized Neutron-Proton Scattering


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

In: Phys. Rev. Lett. 112