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HADES is a high acceptance di-electron spectrometer operating at SIS18, GSI, Germany aimed at study of hadron-proton, hadron-nucleus and nucleus-nucleus collisions at 1-4 AGeV beam energies. The new electromagnetic calorimeter (ECal) was added to the experimental setup in order to measure γ-quanta and thus extend its capabilities in study of π⁰-, η-mesons, production of neutral hyperons and to improve electron-to-hadron separation for the partcles with momenta p > 300 MeV/c. The first data taking with the ECal detector was carried out in March 2019 when Ag+Ag collisions at 1.23 AGeV and 1.58 AGeV beam energies were studied. The methods of reconstruction of the γγ invariant mass spectra from these data are discussed. The analysis includes several steps: calibration of each module of the ECal detector, identification of γ-quanta, reconstruction of γγ invariant mass spectra and subtraction of combinatorial background. The obtained results show experimental capabilities of the new detector and, after efficiency corrections, will allow to normalize yields of other particles.

5th International Conference on Particle Physics and Astrophysics will be held at MEPhI 5-9 October 2020, Moscow, Russian Federation