Direct photon cross section with conversions at CDF

TL;DR

This paper measures the isolated direct photon cross section in proton-antiproton collisions at 1.8 TeV using photon conversions, revealing discrepancies with QCD predictions but consistency with prior measurements.

Contribution

It introduces a novel background subtraction technique leveraging tracking data from photon conversions to improve cross section measurement accuracy.

Findings

Cross section shape poorly matches NLO QCD predictions.

Results align with previous CDF measurements.

Photon conversion method effectively identifies direct photons.

Abstract

We present a measurement of the isolated direct photon cross section in p-pbar collisions at sqrt(s) = 1.8 TeV 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 pi0 -> gamma gamma and eta -> gamma gamma events 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 pT is poorly described by next-to-leading-order QCD predictions, but agrees with previous CDF measurements.