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STS Simulations
Anna Kotynia
15th CBM Collaboration Meeting April 12 - 16, 2010, GSI
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• STS layout
• New STS geometries
• STS realistic digitizer▫ Noise and threshold
▫ Hit finding efficiencies for : URQMD simulation: 100 Au+Au central collisions at
25AGeV
J/Psi → µ+µ-
ρ0 → e+e-
D0 → π+K-
D+ → π+π+K-
▫ Channel inefficiencies
▫ ADC resolution
• Next Steps
Outline
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Silicon Tracking System
• The CBM experiment at FAIR will investigate the QCD phase diagram at high baryon densities
• The Silicon Tracking System is the central detector for track and momentum determination
Dipol magnetTargetMVD & STS
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• Total area, 8 stations: 3.2 m2
• Number of sensors: >1000
• Number of r/o channels: 1.5M
• Number of FE chips: >12k
Sensors: 6 cm wide; 2-6 cm high;
1024 strips per sensor;
15° stereo angle; 60 µm strip pitch ;
STS Layout
Stations have a modular structure and are constructed from 300 µm thick double-sided silicon microstrip sensors.
Groups of sensors (sectors) are individually read out with electronics located at the perimeter of the stations.
Signals from the sectors are sent through thin aluminum-polyimide micro-cables to the front-end electronics
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• „Standard” : 8 stations
• 9 stations to reduce influence of detector inefficiencies on particles
tracking
• 8 stations, first station at 20cm to achieve better track parameters
• 8 stations with short strips (1-6cm) to reduce number of fake hits in STS
• 8 stations with different thickness of cables from 200 to 700 µm
• 8 stations with and without cables with equal distances between stations
• 8 stations equally spaced with not more than ten sensors in one vertical
module – requirement from detector developers to place one module on
one thin carbon support structure
• 8 stations, larger hole inside stations to avoid overlap with new beam
pipe
STS Geometries
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• Complete chain of physical processes caused by charged particle traversing the detector
• Magnetic field influences collection of the charge on the strips
|B| = 1THoles: = 1.5°x = 8m
Electrons = 7.5°x = 40m
STS Digitizer
An algorithm for calculating the Lorentz angle in silicon detectors, Nuc. Instr. Meth. A497 (2003) 389-396
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• Particle position in the sensor is obtained by using Center Of Gravity algorithm:
n
ii
n
iii
S
xSx
1
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Random noise is added to the charge signal, according to a Gaussian distribution with standard deviation as an equivalent noise charge of the detector system
STS Digitizer
STS Digitizer
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Incident angle in STS
25 AGeV25 AGeV
2 AGeV2 AGeV
Station Station 11
Station Station 55
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Hit Finding Efficiency
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Hit Finding Efficiency
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Pluto simulation10k
J/Psi → µ+µ-
-3%
Hit Finding Efficiency in STS
88% of muons from J/Psi have incident angle in STS<20◦
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Pluto simulation10k
ρ0 → e+e-
-5%
Hit Finding Efficiency in STS
77% of electrons from ρ0 have incident angle in STS<20◦
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ASCII Generator 10k
D0 → π+K-
-3%
Hit Finding Efficiency in STS
77% of particles from D0 decay have incident angle in STS<20◦
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ASCII Generator 10k
D+ → π+π+K-
-4%
Hit Finding Efficiency in STS
85% of particles from D+ decay have incident angle in STS<20◦
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STS simulations’ results• Some of the strips fire 14 times per 100 mbias events • significant part of strips fire 8~9 times per 100 mbias
events • -> less then 1,25 µs time distance between hits in one
channel
Channel dead time simulations• Single channel inefficiencies as a result of the readout electronic’s dead time• Dependence of channel dead time on pulse amplitude
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Channel dead time simulations
For minimum bias Au+Au collision at 25AGeV channel
occcupancy:
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Station 1 2 3 4 5 6 7 8
min occ 0.1 0.1 0.1 0.3 0.2 0.1 0.1 0.1
max occ 4.7 4.2 3.6 3.0 2.4 2.0 1.3 1.2
Channel dead time
Channel occupancy
Hit finding efficiency
occ>3.0 %(<1% of all
chips)
1.0 %<occ>3.0 %(12% of all chips)
occ<1.0 %(88% of all
chips)
Probability of channel inefficiency
100 ns >3 % 1-3% < 1% 89.94 %
500 ns >15 % 5-15 % < 5 % 83.37 %
1000 ns >30 % 10-30 % <10 % 78.25 %
0 ns 91.17 %
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ADC resolution
Parameters set in
simulation ke- per ADC
channel
Hit finding efficiency
Th: 4ke-
Nof bits Step
4-bits 2.00 2.00 90.35%90.35%
5-bits 1.50 1.50
6-bits 1.00 1.00 90.44%90.44%
7-bits 0.50 0.50
8-bits 0.25 0.25 91.05%91.05%20-bits 0.01 0.01 91.17%
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• Tilting outer parts of all STS stations by 20◦ around the
vertical axis
• Testing influence of cables thickness on momentum
resolution
• Adding carbon support structure to STS geometry
• Implementation of dependence of channel dead time on
the signal amplitude and the noise level
• Systematic study of hit losses in STS for all reconstructed
reaction products
• Working on hit finder: testing different methods for finding
particle position in STS
Outlook
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