Characterization of the SIDDHARTA-2 second level trigger detector prototype based on scintillators coupled to a prism reflector light guide

The SIDDHARTA experiment at the DAΦNE collider of LNF-INFN performed in 2009 high precision measurements of kaonic hydrogen and kaonic helium atomic transitions. To determine the K-bar N isospin dependent scattering lenghts an important measurement, namely the kaonic deuterium one, is, however, still missing. Due to the very low expected yield of the kaonic deuterium Kα transition, a major improvement in the signal over background ratio is needed. To achieve a further background reduction, a second level trigger, based on the detection of charged pions produced by the K− absorption on various materials, including the target gas nuclei, is planned to be implemented in the future SIDDHARTA-2 experiment. For shielding-related geometrical limitations, a single side of the scintillators can be accessed; in order to reach a good time resolution and uniform efficiency, a both-end readout was then realized with complex multi-reflection light guides. In this work, the results of the tests made on a detector prototype, performed on the πM−1 beamline of the Paul Scherrer Institute (Switzerland), are presented. The tests had the goal to determine the efficiency and the time resolution for pions, which should comply with the minimum required values of 90% and 1 ns (FWHM) respectively. The obtained results, 96% efficiency and 750 ps FWHM for 170 MeV/c momentum pions, qualify the prototype as an excellent second level trigger for the SIDDHARTA-2 experiment. Similar results for 170 MeV/c momentum muons and electrons are also presented