The paper presents the upgrade of the K L and muon detector for the Belle II experiment at the SuperKEKB collider. To maintain the performance under the elevated background levels associated with high luminosity, the original resistive plate chambers in the endcaps and the innermost barrel layers have been replaced with a scintillator-based system. The new technology utilizes extruded plastic scintillation strips equipped with wavelengthshifting fibers and silicon photomultipliers. The design and assembly of the detector modules, the front-end electronics based on the TARGETX ASIC, and the calibration methodology developed for the 17,000-channel system using single-photoelectron spectra are discussed. Performance tests indicate that the light yield significantly exceeds the design specifications, ensuring high reconstruction efficiency. The upgraded KLM system is currently operational and provides robust particle identification for the Belle II physics program.
T. Uglov (Wed,) studied this question.