3D tracking at SND@LHC

The goal of this project is to reconstruct a new type of object in the SND@LHC detector, namely a 3 dimensional (3D) track. Due to readout constraints, the muon tracking inside of the SND@LHC detector is performed by splitting the recorded hits in two separate sets based on the inclination of the detector bar recording the hit. The hits are projected onto two perpendicular planes and the tracking is performed on the two projections separately. The position of the hit along the direction perpendicular to the plane of projection, that is to say along the detector bar, is unknown. These two 2 dimensional (2D) tracks can be combined into one 3D track, but not in case of multi-track events. To perform true 3D tracking, the missing third coordinate of the hits has to be retrieved. This can only be done for systems which have readout on two opposite sides. The difference between the time at which the signal reaches each of the ends of the detector bar is used for this purpose. Once the set of 3D coordinates is completed, the same set of hits can be projected onto the two perpendicular planes and the tracking performed as was done before. The result of the track reconstruction is now a 3D track. The performance of the 3D tracking is studied on Partition 9 of Run 4705. The line equations of the reconstructed tracks are computed using Hough transform for pattern recognition. When only allowing one reconstructed track per event, the tracking efficiency achieved by the new 3D tracking scheme is (75.6 ± 0.1)%. Its efficiency compared to the previous 2D scheme is (79.4 ± 0.1)%. When allowing multiple reconstructed tracks per event, the total amount of reconstructed tracks is higher with the 3D tracking than with the 2D scheme, with (1.125 ± 0.001) times more tracks with the 3D algorithm.