Measuring quantum radiation reaction in laser--electron-beam collisions

Today's high-intensity laser facilities produce short pulses can, in tight focus, reach peak intensities of $10^{22}\,\mathrm{Wcm}^{-2}$ and, in long focus, wakefield-accelerate electrons to GeV energies. The radiation-reaction--dominated regime, where the recoil from stochastic photon emission becomes significant, can be reached in the collision of such an electron beam with an intense short pulse. Measuring the total energy emitted in gamma rays or the presence of a prominent depletion zone in the electron beam's post-collision energy spectrum would provide strong evidence of radiation reaction, provided enough electrons penetrate the region of highest laser intensity. Constraints on the accuracy of timing necessary to achieve this are given for a head-on collision.