1. 1 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Tracking with the Silicon Detectors Th.Naumann H1 DESY Zeuthen A short collection of experiences What would I/we do better now ?

2. 2 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 FSTCSTBST The H1 Si detectors :

3. 3 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 5 APC’s with 128 channels = 640 channels per disk CST: double sided double metal 2 planes BFST: single sided 12/16 phi sectors with overlap u/v planes back-to-back with  crossing angle FST: 2 r planes for redundancy BST: trigger pads u/ru/v CST FST BST H1 Si detectors :

4. 4 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 BST CST FST Planes u/v r phi z min. pitch/um 75 96 50 88 hits FST 5 2 3 BST 6 0 2 incl. bwd calorimeter CST 2 2 2 picked up by jet chamber The Silicon Trackers

5. 5 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 FSTCSTBST A high Q2 NC DIS event in the Forward Silicon Tracker E jet > 100 GeV @ x > 0.1 E e > 100 GeV @ Q2 > 10.000 GeV2 => high track densities => real redundancy => u/v + r planes !

6. 6 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 x > 0.1 => E jet > 100 GeV high track densities and multiplicities need real redundancy add r to u/v planes u/v ghost hits...... rejected by r detectors

7. 7 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 A low Q2 scattered electron in the BST : mostly only 1 scattered lepton or some hadrons @ low x < 10-3 not much redundancy needed => u/v planes only incl. bwd calorimeter + vertex: also use 2 hit tracks (acceptance gain!)

8. 8 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Track finding before pattern recognition to reject : noise and background create track candidates Track fitting : optimum track model constraints outlier rejection

9. 9 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 From charge to space information : Online readout Power PCs calculate : strip wise : pedestal + noise APC wise for 128 channels fit coherent readout problems : common mode + slope +... parabola ? Decisive and tricky procedure to get best Signal / Noise dead strips e.g. don’t follow common mode => pseudo-noisy + destroy common mode Coherent readout losses => external inefficiency ! Monitor occupancy, noise, S/N, sagitta, efficiencies as early as possible ! Clustering of strip charges by sliding window in 2 steps: in Power PCs with loose S/N cuts in reconstruction with tight cuts

10. 10 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 BFST r detectors: double metallization (as in CST) S/N ~ 13 pat rec has to fight noise cut into efficiency = > 92 % BFST u detectors: simple single sided S/N ~ 30 nearly noise free efficiency ~ 99 %

11. 11 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 S i+1 SiSi s = (x1 + x3) / 2 - x2 zero if no curvature constant on a circle : s i = s i+1 easy to calculate: can work combinatorically if nr of measurements small (HERMES recoil) biasfree: no cuts + assumptions monitors detectorwise : mapping alignment noisy channels Pat Rec: Triplet Sagitta x1 x2 x3 s

12. 12 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 s1s1 s2s2 HERMES recoil  measurement: E < 1 GeV: model dE/dx by decreasing sagitta s i+1 < s i < s i-1 heavy background: ask for same circle origin

13. 13 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Track model: 2D or not 2D... ? solenoid field => circle in x-y, linear in s-z (s = arc length) H1 Central Tracker : Jet Chamber: r-phi + z chambers: r-z + CST precisions in r-phi and r-z differ by 100 => 3D=2D+2D: circle fit in x-y, linear fit in s-z H1 B/FST: precision alignment dominated => similar in x-y-z now: combine u-v to x-y: dead u disk kills v disk no detectorwise residuals for alignment + efficiency => try: directly fit measured quantities in a u-v-z track model ! HERMES recoil:....

14. 14 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Use all constraints : vertex:  L 2 :large gain in precision H1 x-y run vertex:  y < 30  m (better than HERA prediction) H1 z event vertex: used to reject FST x-y ghost tracks momentum conservation: HERMES: pt or phi balance in elastics ?

15. 15 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Improve momentum by dE / dx ?

16. 16 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003 Si: double sided/metal vs single sided ? guarantee real redundancy get best S/N: fight for pedestal, noise, common mode clearly separate pattern recognition + track fitting design robust pattern recognition track model: think twice use all constraints Good luck, HERMES ! Summary