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arXiv:2505.09023 · The European Physical Journal C

Probing arbitrary polarized photon pairs undergoing double Compton scatterings by a dedicated MC simulator validated with experimental data

Mateusz Bała, W. Krzemień, Beatrix C. Hiesmayr, Jakub Baran, K. Dulski, K. Klimaszewski, L. Raczyński, Roman Y. Shopa, W. Wiślicki

Published Oct 8, 2025• 5 citations
arXivHTMLPDF

Abstract

Abstract Quantum correlations in the polarization degree of freedom of the two-photon system have been extensively studied and form our current understanding of the quantum nature of our world. Most of the studies are concentrated on the low-energy (optical) photon pairs, for which efficient polarization measurement devices exist. However, for high-energetic (MeV) pairs of photons, e.g. produced in the decay of positronium atoms, no polarizers are available. Partial information about the polarization degree of freedom can be extracted by exploiting the measurements of photon pairs that undergo double Compton scattering. We present a Geant4-based Monte Carlo Vienna–Warsaw model capable of simulating any initial polarization state of bipartite photons. This puts us in a position to derive the behavior of the experimental observable, the angular difference $$\Delta \hat{\Phi }$$ Δ Φ ^ formed by the two scattering planes. We validate our Vienna–Warsaw simulator with the high-statistics experimental sample – based on a total of $$3 \times 10^5 $$ 3 × 10 5 event candidates – of two-photon pairs measured with the J-PET Big Barrel detector. We deduce the value of the squared visibility (interference contrast) encoding the polarization in the angle difference of the two scattering planes, $$\Delta \hat{\Phi }$$ Δ Φ ^ . The simulated spectra are in good agreement with the experimental correlation spectra and behave as predicted by theory.

DOI
10.1140/epjc/s10052-025-14862-y

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Abstract This work presents the GEANT4 simulation of the experimental setup for studying the Compton scattering of annihilation photons and compares the simulation results with the experimental data. Two 511 keV photons are born in electron-positron annihilation at rest and have mutually orthogonal polarization which is measured by the system of Compton polarimeters. Each polarimeter consists of scatterer of initial annihilation photons and NaI(Tl) detectors of scattered at 90° photons. Additionally, an intermediate scatterer of GAGG scintillator is used to produce the tagged decoherent photons. Different cases of two-photon quantum states have been simulated. In the first case, the setup response to Compton scattering of entangled photons with mutually perpendicular polarization was studied. In the second case similar study was done for decoherent photons that are produced if one of the initial photons interacts in intermediate scatterer. Distinctions in Compton scattering for these two cases have been obtained and compared to the experimental results. Energy spectra in NaI(Tl) detectors and angular distributions of scattered photons are presented for both entangled and decoherent cases.
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We present a new experimental study of the quantum entanglement of photon pairs produced in positron-electron annihilation at rest. Each annihilation photon has an energy that is five orders of magnitude higher than the energy of photons in optical experiments. It provides a unique opportunity for controlled Compton pre-scattering of initial photons before the polarization measurements. The experimental setup includes a system of Compton polarimeters to measure the angular correlations of annihilation photons in initial and thus prepared pre-scattered states. For the first time, a direct comparison of the polarization correlations of initial and pre-scattered annihilation photons has been carried out. The angular distributions of scattered in polarimeters photons turned out to be the same for both types of events. Moreover, the correlation function in the Bell's inequality is also the same for both states. We discuss the implications of our results for quantum measurement theory and for the quantum-entangled positron emission tomography.
Abstract The experimental setup for study of Compton scattering of entangled and decoherent annihilation gammas is described. These gammas are born in two-photon positron-electron annihilation. Polarizations of annihilation gammas are mutually orthogonal, while the polarization of each photon is indefinite. If one of the photons of the pair interacts with matter, the pair becomes decoherent and photons acquire the determined polarization states. The kinematics of Compton scattering depends on the polarization states and can be different for entangled and decoherent pairs of annihilation photons. The angular correlations of scattered gammas for both, entangled and decoherent states are measured and compared. It is shown, that the kinematics of Compton scattering are similar for both cases.