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Abstract

Photons emitted in heavy-ion collisions are an important probe to study the quark–gluon plasma. In this thesis, the standard reconstruction of photon conversions into electron–positron pairs in the ALICE experiment using mainly the Time Projection Chamber (TPC) is expanded by using the Transition Radiation Detector (TRD). Because of the material budget in front and within the TRD, many conversions take place in its vicinity. To reconstruct these conversions, a stand-alone track reconstruction was implemented. The photon reconstruction was also made possible by a newly developed kinematic fit that uses automatic differentiation. This offers improved parameter estimation compared to other kinematic reconstruction methods. Using simulated and real proton–lead collision data at center-of-mass energies per nucleon–nucleon pair of sqrt(s_{NN}) = 5.02 TeV, the functionality of the approach is proven by reconstructing neutral pions in the decay channel π^0 → γγ via the photon conversion method. By reconstructing both photons in the TRD, as well as using a mixed mode with one photon in the TRD and one photon in the TPC, the neutral pion statistics could be improved by about 75% compared to using only photons in the TPC. The photons reconstructed in the TRD could be important for LHC Run 3, as the new continuous readout may cause difficulties for photon reconstruction in the TPC. In addition, an outlook is given on the detection of other interactions in the material with the TRD using graph neural networks. In particular, it is shown that the TRD can be used to search for sexaquarks and to identify inelastic interactions of light antinuclei.