X-ray photon pairs with highly suppressed background

We describe an experiment demonstrating the possibility to generate collinear indistinguishable x-ray photon pairs with a highly suppressed background. By choosing angles near 90 degrees between the detectors and the pump beam, where the pump polarization is in the scattering plane, we improve the signal-to-noise ratio by 2 orders of magnitude. We measure the pure coincidence spectrum without any energy discrimination with a bandwidth of 1.5 keV at the full width at half maximum.