Low momentum particle detector for the NA61 experiment at CERN

The NA61 Experiment at CERN SPS is a large acceptance hadron spectrometer, aimed to studying 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 NA61 setup in 2012. 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 Z=1 particle identification in this range is directly demonstrated.