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

STAR Collaboration,; Abdallah, M.S.; Schmitz, N.; Seyboth, P.; et al.,

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

MPS-Authors

STAR Collaboration,
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

Abdallah, M.S.
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

Schmitz, N.
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

Seyboth, P.
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

et al.,
Max Planck Institute for Physics, Max Planck Society and Cooperation Partners;

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Citation

STAR Collaboration, Abdallah, M., Schmitz, N., Seyboth, P., & et al. (2021). Measurement of e+e- Momentum and Angular Distributions from Linearly Polarized Photon Collisions. Physical Review Letters, 127, 052302. Retrieved from https://publications.mppmu.mpg.de/?action=search&mpi=MPP-2021-254.

Cite as: https://hdl.handle.net/21.11116/0000-000A-1B14-2

Abstract

The Breit-Wheeler process which produces matter and anti-matter from photon collisions is investigated experimentally through the observation of 6085 exclusive electron-positron pairs in ultra-peripheral Au+Au collisions at sqrt{s_NN}=200 GeV. The measurements reveal a large fourth-order angular modulation of cos{4\Delta\phi}=(16.8\pm2.5)\ and smooth invariant mass distribution absent of vector mesons (phi, omega and rho) at the experimental limit of le 0.2\ of the observed yields. The differential cross section as a function of e^+e^- pair transverse momentum P_\perp peaks at low value with sqrt{ langle P_\perp^2 \rangle } = 38.1\pm0.9 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 ultra-relativistic speed. The experimental results have implications for vacuum birefringence and for mapping the magnetic field which is important for emergent QCD phenomena.