Precision Measurement of Trident Production in Strong Electromagnetic Fields

We demonstrate experimentally that the trident process $e^{-}\to e^{-}{e}^{+}{e}^{-}$ in a strong external field, with a spatial extension comparable to the effective radiation length, is well understood theoretically. The experiment, conducted at CERN, probes values for the strong field parameter $\chi$ up to 2.4. Experimental data and theoretical expectations using the Local Constant Field Approximation show remarkable agreement over almost 3 orders of magnitude in yield.