Resonant effect of the ultrarelativistic electron–positron pair production by gamma quanta in the field of a nucleus and a pulsed light wave

Resonant electron–positron pair production by a high-energy gamma quantum ω i ≳ 10 2 GeV in the field of a nucleus and a quasi-monochromatic laser wave with the intensities I ≲ 10 16 – 10 17 W c m − 2 was theoretically studied. Under the resonant condition, an intermediate virtual electron (positron) in the laser field becomes a real particle. Due to this fact, the initial process of the second order in the fine structure constant of a laser field effectively reduces into the two successive processes of the first order: the laser-stimulated Breit–Wheeler process and the laser-assisted process of an intermediate electron (positron) scattering by a nucleus. It is shown that there is a threshold energy for the initial gamma quantum, which significantly depends on the number of absorbed wave photons. At the resonance, the electron–positron pair energies are determined by the outgoing angle between the momenta of the initial gamma quantum and the positron (for the channel A) or the electron (for the channel B). The differential cross-sections for the first few resonances with simultaneous registration of the energy and the outgoing angle of the positron or the electron were obtained. For the initial gamma quantum energy ω i = 125 G e V the resonant electron–positron pair energies for the case of the first three resonances can be measured with a very high magnitude of the differential cross-section: from ∼10 13 for the first resonance to ∼10 8 (in the units of α Z 2 r e 2 ) for the third resonance.