Strong-field Breit-Wheeler pair production in short laser pulses:   Relevance of spin effects
  Production of electron-positron pairs in the collision of a high-energy photon with a high-intensity few-cycle laser pulse is studied. By utilizing the frameworks of laser-dressed spinor and scalar quantum electrodynamics, a comparison between the production of pairs of Dirac and Klein-Gordon particles is drawn. Positron energy spectra and angular distributions are presented for various laser parameters. We identify conditions under which predictions from Klein-Gordon theory either closely resemble or largely differ from those of the proper Dirac theory. In particular, we address the question to which extent the relevance of spin effects is influenced by the short duration of the laser pulse. 
M. J. A. Jansen, J. Z. Kami\'nski, K. Krajewska, and C. M\"uller
hep-ph physics.atom-ph