Measurement of e+e- Momentum and Angular Distributions from Linearly Polarized Photon Collisions

The Breit-Wheeler process which produces matter and antimatter from photon collisions is experimentally investigated through the observation of 6085 exclusive electron-positron pairs in ultraperipheral Au + Au collisions at root s(NN) = 200 GeV. The measurements reveal a large fourth-order angular modulation of cos4 Delta phi = (16.8 +/- 2.5)% and smooth invariant mass distribution absent of vector mesons (phi, omega, and rho) at the experimental limit of <= 0.2% of the observed yields. The differential cross section as a function of e(+)e(-) pair transverse momentum P-perpendicular to peaks at low value with root < P-perpendicular to(2)> = 38.1 +/- 0.9 MeV and displays a significant centrality dependence. These features are consistent with QED calculations for the collision of linearly polarized photons quantized from the extremely strong electromagnetic fields generated by the highly charged Au nuclei at ultrarelativistic speed. The experimental results have implications for vacuum birefringence and for mapping the magnetic field which is important for emergent QCD phenomena.

Automated summary

The experimental investigation of the Breit-Wheeler process in ultra-peripheral Au + Au collisions revealed a large fourth-order angular modulation and smooth invariant mass distribution. Additionally, the differential cross section as a function of e(+)e(-) pair transverse momentum showed important features, such as peak values and centrality dependence.