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Tracking with the

Tracking with the. Silicon Detectors. Th.Naumann H1 DESY Zeuthen. A short collection of experiences What would I/we do better now ?. FST. CST. BST. The H1 Si detectors :. H1 Si detectors :. 5 APC’s with 128 channels = 640 channels per disk

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Tracking with the

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

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

  3. H1 Si detectors : • 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 p/8 crossing angle • FST: 2 r planes for redundancy • BST: trigger pads BST CST FST u/r u/v Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

  4. 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 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

  5. FST CST BST 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 ! Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

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

  7. 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!) Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

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

  9. 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 Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

  10. 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 % Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

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

  12. s1 s2 HERMES recoil f measurement: E < 1 GeV: model dE/dx by decreasing sagitta si+1 < si < s i-1 heavy background: ask for same circle origin Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

  13. 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: .... Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

  14. Use all constraints : • vertex: • s ~ 1 / L2 : large gain in precision • H1 x-y run vertex: sy < 30 mm (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 ? Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

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

  16. Summary 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 ! Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.2003

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