TPEX@DESY: Test Measurements with Calorimeter Based on Lead Tungstate Crystals

In this talk we will present the results of the test measurements performed with the $3 \times 3$ PbWO$_4$ calorimeter at the DESY test beam facility. The goal of measurements was to study the performance of two data acquisition systems: trigger-based readout with a QDC and a triggerless readout based on a digitizer. Calorimeters of this type will be the key component of an experimental setup for the future Two-Photon Exchange eXperiment (TPEX), which will provide new data on the next-to-leading order term in the QED description of electron-proton scattering process up to $Q^2 =$ 4.6 (GeV/c)$^2$ (doubling the range compared to current data).