NA61-LMPD

Low Momentum Particle Detector in the CERN NA61 experiment

NA61/SHINE is a fixed target experiment at CERN SPS. One of its purposes is to study high pT phenomena in p+p and p+A collisions. The Low Momentum Particle Detector (LMPD) was used as a centrality detector in proton-nucleus interactions.

LMPD is a Time Projection Chamber (TPC) type detector in wich four absorber sheets of stepwise increasing thickness have been placed with 2cm spacing. Since it's a TPC, it provides 3D measurement points of traversing particles and measures their ionization energy. Particles falling in various momentum ranges are captured by one of the absorber sheets as function of the total traversed absorbant thickness. The combination of the ionization energy and range measurement is used for particle identification.

LMPD was positioned on the two sides of the target. It was used to detect and identify slow particles (mainly protons) coming from the "break-up" of the target nuclei. In central collision (when the proton hits the center of the nucleus) more low-momentum particles are produced than in peripheral collisions. By measuring these particles, our detector was able to determine the centrality of the interaction.

The Low Momentum Particle Detector and its prototypes were designed and constructed in Budapest by the REGARD group. In 2012 and 2014, LMPD was an important part of the NA61 detector setup during the p+Pb data taking.

Fig. 1. The configuration of the Low Momentum Particle Detector (LMPD)

Fig. 2. The structure of the readout part.

Fig. 3. The "field cage" and the absorber layer.

Fig. 4. The LMPD on the two sides of the fix target of the NA61 experiment.

Author: Krisztina Márton