Feasibility of H̅ Annihilation-Vertex Reconstruction with Modular J-PET: A Simulation-Based Study

P. Pandeya, b, S. Sharmaa, b, P. Moskala, b, R.C. Fergusonc, d, R. Caravitac, d (on behalf of the AEgIS Collaboration), A.K. Venadana, b, G. Korcyla, b, K. Kacprzaka, b aMarian Smoluchowski Institute of Physics, Jagiellonian University, prof. S. Łojasiewicza 11, 30-348 Kraków, Poland bCentre for Theranostics, Jagiellonian University, Kopernika 40, 31-501 Kraków, Poland cDepartment of Physics, University of Trento, Via Sommarive 14, 38123 Povo, Trento, Italy dINFN/TIFPA - Trento Institute for Fundamental Physics and Applications, Via Sommarive 14, 38123 Povo, Trento, Italy

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The Antihydrogen Experiment: gravity, Interferometry, Spectroscopy at CERN aims to measure the gravitational acceleration of antihydrogen (H̅) atoms to test the weak equivalence principle for antimatter systems. In the proposed approach, a pulsed H̅ beam, produced via charge exchange between Rydberg positronium and antiprotons, traverses a moiré deflectometer comprising two equally spaced gratings followed by a position-sensitive detector. As the beam traverses the moiré setup, H̅ may annihilate on the gratings or nearby structures, producing high-energy pions, or continue towards the position-sensitive detector. For a high-accuracy gravity measurement, precise knowledge of the beam profile and annihilation points is essential. We present results from a feasibility study of vertex reconstruction using modular J-PET detectors spanning the full axial length of the moiré setup. The generated pions, being minimum-ionising particles, follow straight paths. The adapted method is based on the consecutive registration of each pion, defining individual tracks in a pair of modules placed 10 cm apart. The hit positions are used to reconstruct the track direction, which is then projected back to estimate the spatial coordinates of the H̅ annihilation vertex. For this feasibility study, we developed a customised Geant4-based simulation package and an analysis algorithm that implements a track-and-extrapolate algorithm to image the annihilation vertices.

DOI:10.12693/APhysPolA.148.S169 topics: Jagiellonian positron emission tomography (J-PET), antihydrogen and antiproton, annihilation vertex, Antihydrogen }xperiment: gravity, Interferometry, Spectroscopy (AEgIS)