A search for paraphotons, or hidden U(1) gauge bosons, is performed using an intense X-ray beamline at SPring--8. "Light Shining through a Wall" technique is used in this search. No excess of events above background is observed. A stringent constraint is obtained on the photon--paraphoton mixing angle, $\chi < 8.06\times 10^{ -5}\ (95%\ { \rm C.L.})$ for $0.04\ { \rm eV}<m_{ \gamma^{ \prime}} < 26\ { \rm keV}$.
Categories: physics.ins-det hep-ex physics.optics