Low Momentum Particle Detector for the NA61 Experiment at CERN

The NA61 Experiment at CERN SPS is a large acceptance hadron spectrometer, aimed at studying of hadron-hadron, hadron-nucleus, and nucleus-nucleus interactions in a fixed target environment. The present paper discusses the construction and performance of the Low Momentum Particle Detector (LMPD), a small time projection chamber unit which has been added to the original NA61 setup. The LMPD considerably extends the detector acceptance towards the backward region, surrounding the target in hadron-nucleus interactions. The LMPD features simultaneous range and ionization measurements, which allows for particle identification and momentum measurement in the 0.1 - 0.25 GeV/c momentum range for protons. The possibility of proton identification in this range is directly demonstrated.