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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 - PowerPoint PPT Presentation
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Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.20031
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, 27.03.20032
FST CST BST
The H1 Si detectors :
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.20033
• 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/r u/v
CST
FST
BST
H1 Si detectors :
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.20034
BST CST FST
Planes u/v r phi z min.
pitch/um 75 96 50 88 hits
FST 5 2 3BST 6 0 2 incl. bwd calorimeterCST 2 2 2 picked up by jet chamber
The Silicon Trackers
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.20035
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, 27.03.20036
• x > 0.1 => E jet > 100 GeV
• high track densitiesand multiplicities
• need real redundancy
• add r to u/v planes
u/v ghost hits ...
... rejected by r detectors
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.20037
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, 27.03.20038
Track finding before
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, 27.03.20039
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 bestSignal / 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, 27.03.200310
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, 27.03.200311
Si+1Si
• s = (x1 + x3) / 2 - x2
• zero if no curvature• constant on a circle : si = si+1
• easy to calculate:can work combinatoricallyif nr of measurements small(HERMES recoil)
• biasfree: no cuts + assumptions
• monitors detectorwise :• mapping• alignment• noisy channels
Pat Rec: Triplet Sagitta
x1
x2
x3s
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.200312
s1
s2
HERMES recoil measurement:
E < 1 GeV:
model dE/dx by decreasing sagitta
si+1 < si < s i-1
heavy background:
ask for samecircle origin
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.200313
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, 27.03.200314
Use all constraints :• vertex:
• L2 : 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 ?
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.200315
Improve momentum by dE / dx ?
Th.Naumann, DESY Zeuthen, HERMES Tracking meeting, 27.03.200316
• 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