Low Momentum Particle Detector at the NA61/SHINE Experiment

p+A interactions has an important role in understanding hadronic physics. In earlier experiments, it was found that the centrality of such collisions is related to the number of slow (“grey”) nucleons which are produced in the break-up of the nucleus. By detecting and identifying these low momentum particles in the typical kinetic energy range of 20–100MeV, one can determine the centrality of individual events. The NA61/SHINE at CERN SPS is a fixed-target experiment with rich physics program which contains the study of p+A collisions. For this experiment, the Low Momentum Particle Detector (LMPD) has been built which is a Time Projection Chamber with absorber layers in the gas volume. The detector has a key feature, namely it can positively identify protons by simultaneous measurement of ionization and range, in the momentum interval of 0.1–0.25 GeV/c. The LMPD was tested in 2011 at CERN and was used as a centrality detector in the p+Pb run of NA61 in 2012.