Photons continue to enlighten physicists

The cross section is presented as a function of the transverse energy of the photon.

You may be familiar with particles of light, called photons. Physicists give the name “prompt photons” to those that are produced by two particles smashing together — hard collisions — as contrasted with those resulting from the decay of other particles. The Tevatron produced prompt photons by the hard collisions between protons and antiprotons.

By: Andy Beretvas and Alessandra Lucà

The article is here: http://news.fnal.gov/2017/12/photons-continue-to-enlighten-physicists/