Direct photon cross section with conversions at CDF

We present a measurement of the isolated direct photon cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.8\mathrm{T}\mathrm{e}\mathrm{V}$ and $|\eta |<0.9$ using data collected between 1994 and 1995 by the Collider Detector at Fermilab (CDF). The measurement is based on events where the photon converts into an electron-positron pair in the material of the inner detector, resulting in a two track event signature. To remove ${\pi }^0\to \gamma \gamma$ and $\eta \to \gamma \gamma$ events from the data we use a new background subtraction technique which takes advantage of the tracking information available in a photon conversion event. We find that the shape of the cross section as a function of photon $p_T$ is poorly described by next-to-leading-order QCD predictions, but agrees with previous CDF measurements.