A cluster position reconstruction method with single-crystal precision for the L1 ECAL trigger in the STCF experiment

The Super Tau-Charm Facility (STCF) is a next-generation electron-positron collider with center-of-mass energies ranging from 2 to 7 GeV and a peak luminosity of 0.5×10 35 cm -2 s -1 at 4 GeV. In the original level-1 (L1) electromagnetic calorimeter (ECAL) trigger algorithm, the cluster position is determined as the center of the trigger cell (TC) with the highest energy deposition to reduce resource consumption. Consequently, the cluster position resolution is limited by the TC size. However, the cluster-track matching window is determined by the angular resolutions of both the ECAL and the main drift chamber (MDC), which necessitates more precise cluster positioning for effective background suppression in the L1 trigger. To address this issue, this paper presents a new cluster position reconstruction method for the L1 ECAL trigger. The method uses the regular 4×4 TC configuration, but defines the cluster position as the center of the crystal with the highest energy deposition within that TC, instead of using the TC center. With this optimization, the method significantly improves the cluster positioning precision from approximately 3° to about 1°. This improvement reduces the false cluster-track matching rate by 13% to 20% and lowers the background trigger rate by 30% for the low-multiplicity charged-particle trigger channel at five times the nominal background level. Furthermore, the background suppression capability of the new method becomes more effective at higher background levels.