- Conference date: 19-23 Aug 1996
- Location: Santa Barbara,California (USA)
A signal of positrons above background has been observed in collisions of a low-emittance 46.6-GeV electron beam with terawatt pulses from a Nd:glass laser at 527 nm wavelength in an experiment at the Final Focus Test Beam at SLAC. Peak laser intensities of have been achieved corresponding to a value of 0.3 for the parameter where is the electric field strength of the laser transformed to the rest frame of the electron beam and is the QED critical field strength. The positrons are interpreted as arising from a two-step process in which laser photons are backscattered to GeV energies by the electron beam followed by a collision between the high-energy photon and several laser photons to produce an electron-positron pair. These results are the first laboratory evidence for a light-by-light scattering process involving only real photons.
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