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Isolating continuum $\gamma\gamma \rightarrow \pi^+\pi^-$ production via entanglement enabled spin interference effects

Updated on Mon, 2024-10-07 10:58. Originally created by corey90 on 2024-10-07 10:58.

 In ultra-peripheral heavy ion collisions,  the highly Lorentz-contracted electromagnetic fields of the nuclei can be quantized as a flux of quasi-real photons. These photons contribute to $\pi^+\pi^-$ pair production through multiple processes, including photonuclear ($\gamma A$) and photon-photon $(\gamma \gamma)$ production. Using traditional techniques the $\gamma A$ and $\gamma \gamma $ production processes are practically indistinguishable in the continuum regime. However, the recently discovered Entanglement Enabled Spin Interference (EESI) effect allows the processes to be separated according to the orbital angular momentum of the final state $\pi^+\pi^-$ pair, leading to a novel method of isolating continuum $\gamma\gamma\rightarrow \pi^+\pi^-$ production.  

 
In this talk we present the first use of the EESI technique for measuring the interference between the $\gamma+\gamma\rightarrow\pi^{+}+\pi^{-}$ and $\gamma+A\rightarrow\pi^{+}+\pi^{-}$ processes. We present measurements using STAR Au+Au data at $\sqrt{s_{NN}}=200$ GeV and U+U data at $\sqrt{s_{NN}}=193$ GeV. The physics involved in this novel approach for isolating the $\gamma\gamma$ production process will be discussed. Additionally, application for providing novel constraints on hadronic light-by-light scattering cross sections, one of the most significant uncertainties in calculations of the muon (tau) anomalous magnetic moment, and their implications will be discussed.
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