Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 1 GBL Tracking and Alignment with Millepede II. EUTelMilleGBL processor’s code 1.Load hits produced on the hitmaker step. 2.Load alignment constants : a)Apply the planes' shifts obtained on the pre-alignment step (a part of the hitmaker step) to correct the hits' positions; b)Consecutively apply the planes' shifts obtained on the previous alignment step(s) to correct the hits' positions, i.e. on the alignment step n, apply n-1 sets of the planes' shifts obtained during previous n-1 alignment steps. 3.Form track(s) out of the hits corrected on the step 2 : a)Make two groups of hits; each group consists of three hits corresponding to the planes of each telescope arm, i.e. three hits found on the upstream telescope arm (triplet) and three hits on the downstream arm (driplet); b)Combine triplet(s) and driplet(s) to track(s). 4.Create the GBL trajectory(ies) out of the formed tracks. 5.Pass the created GBL trajectory(ies) to Millepede-II for a fine alignment of the (telescope) planes. 6.Write the shift constants obtained by Millepede-II per each plane of interest to an *.slcio file.

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 2 Hits Selection An event snapshot of the hits distribution among the setup. 17 hits in total: Pl 0 : (0,1); (0,1) Pl 3 : (3,0); (3,1); (3,2); (3,3)Pl 6 : (6,0) Pl 1 : (1,0); (1,1); (1,2) Pl 4 : (4,0); (4,1) Pl 7 : (7,0) Pl 2 : (2,0); (2,1); (2,2) Pl 5 : (5,1) The only hits belonging to one track are being selected.

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 3 Hits Selection. Hits patterns recognition Hits pattern recognition (triplet formation): 1.Form the doublets – combinations of the hits on left (Pl 0 and Pl 2 for the triplet) and right planes (Pl 3 and Pl 5 for the driplet) through connecting each pair of hits by a straight line, doublet track pattern. Each left plane hit with each right plane hit. 2.Loop among the doubles and find an intersection point of each double track pattern with the middle plane (Pl1/Pl4 for the triplet/driplet); 3.When a middle plane hit (Pl1/ Pl4 hit for the triplet/driplet) fulfils the condition of matching to the intersection point, it is being assigned with a triplet/driplet track pattern.

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 4 Hits Selection. Straight-line tracks – triplet-driplet matching

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 5 GBL trajectories formation

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 6 GBL trajectories residuals

Dmitry Kisler | Alibava TB analysis. Tracking and alignment | Page 7 Hits Selection. Straight-line tracks – triplet-driplet matching