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

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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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