Study of the ω →π0e+e−conversion decay with the CMD-3 detector at VEPP-2000 collider B D Kutsenko1,2 on behalf of the CMD-3 collaboration 1Budker Institute of Nuclear Physics, SB RAS, Novosibirsk 630090, Russia 2Novosibirsk State University, Novosibirsk, 630090, Russia E-mail: bdkutsenko@gmail.com Abstract. The study of the conversion decay ω →π0e+e−in the decay mode π0 →γγ was performed with the CMD-3 detector at the VEPP-2000 e+e−collider in Novosibirsk. Main background processes are events of ω →π0π+π−decay, QED events, and events of the radiative decay ω →π0γ, where monochromatic photon converts on the material in front of the sensitive volume of the detector. To suppress the last type of background the deep neural network was used. Using an integrated luminosity of about 10 pb−1 collected at the c.m. energy range from 660 MeV to 840 MeV the cross-section of the process under study was measured and the preliminary result for branching ratio Br(ω →π0e+e−) was obtained. The result is more precise than any previous measurements. The current status of the analysis is presented. 1. Introduction Measurement of branching ratios and transition form factors of conversion decays provides an important test of the vector dominance model [1] and an accurate background estimation in searches of lepton pairs produced in quark-gluon plasma [2-3]. One of such decays is ω →π0e+e− was studied at CMD-3 [4]. The Cryogenic Magnetic Detector (CMD-3) is a general purpose detector for the VEPP-2000 electron-positron collider [5], which operates in Budker Institute of Nuclear Physics, Novosibirsk, Russia. The tracking system consists of a cylindrical drift chamber. The tracking system is placed inside a thin superconducting solenoid with a field of 1.3 T. Electromagnetic barrel calorimeters are placed outside the solenoid: an LXe with a thickness of 5.4 X0 and CsI crystals with a thickness of 8.1 X0. An endcap calorimeter is made of BGO scintillation crystals, with a thickness of 13.4 X0. The main aspects of the physical program of the CMD-3 experiment are precision measurements of hadronic cross-sections in the region of the center of mass energy range from 0.4 GeV up to 2 GeV. Using an integrated luminosity of about 10 pb−1 collected at the c.m. energy range from 660 MeV to 840 MeV the cross-section of the process under study was measured and the preliminary result for branching ratio Br(ω →π0e+e−) was obtained. This data sample is 2 times larger than the sample previously used for the measurements at the CMD-2 detector. 2. Data analysis The main sources of resonant background contamination are ω →π0π+π−decay, with probability three orders of magnitudes larger than signal events, and ω →π0γ followed by the Dalitz decay of the π0 or by γ conversion on the material in front of the detector. The Monte-Carlo simulation for each energy point has been performed based on the Geant4 package [6] taking into account the initial state radiation and individual parameters for each energy point. Events with two well-reconstructed tracks and two or more photons are selected. Based on the simulation, selection criteria for tracks and photons parameters were determined and applied to data. The invariant mass of e+e−γ was used to suppress QED events, tracks spatial angle and photons recoil mass were used to suppress 3π events. One of the most important criteria is presented in Fig. 1. The other notable and efficient criterion is connected with the Presented at the 30th International Symposium on Lepton Photon Interactions at High Energies, hosted by the University of Manchester, 10-14 January 2022