The existence of a new force beyond the Standard Model is compelling because it could explain several striking astrophysical observations which fail standard interpretations. We searched for the light vector mediator of this dark force, the Uboson, with the KLOE detector at the DAFNE e+e−collider. Using an integrated luminosity of 1.54fb−1, we studied the process e+e−→Uγ, with U →e+e−, using radiative return to search for a resonant peak in the dielectron invariant-mass distribution. We did not find ev-idence for a signal, and set a 90%CL upper limit on the mixing strength between the Standard Model photon and the dark photon, ε2, at 10−6–10−4in the 5–520MeV/c2mass range

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.