Performance studies of the CBM Silicon Tracking System

Anna Kotynia - Silicon Tracking System in CBM experiment

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Performance studies of the CBM Silicon Tracking System

Anna KotyniaHic for Fair, Frankfurt University

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Silicon Tracking System in CBM experiment

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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Silicon Tracking System


Chellanges: 10 MHz interaction rate Up to 1000 charged particles per one

Au+Au central collision at 25 A GeV Track densities up to 30 per cm2

Conditions: Highly granular , low-mass and

radiation hard detector system Fast data acquisition system for

online event selection Efficient charged particle tracking

and high momentum resolution

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STS layout


Total area, 8 stations: 3.2 m2

Number of sensors: >1000 Number of r/o channels: 1.5M Number of FE chips: >12k

Sensors: 300 µm thick; 6 cm wide; 2-6 cm high.

Outer regions covered by larger sensors, or even chained sensors (1-3 sensors in one module), to minimize number of channels

1024 strips per sensor; 15° stereo angle; 60 µm pitch strip.

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STS Digitizer


Complete chain of physical processes caused by charged particle traversing the detector

Magnetic field influances collection of the charge on the strips

|B| = 1THoles:Q = 1.5°Dx = 8mm

ElectronsQ = 7.5°Dx = 40mm

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STS Digitizer


Particle position in the sensor is obtain by using Center Of Gravity algorithm:

n

ii

n

iii

S

xSx

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1

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

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Hit Finding Efficiency


Center Of Gravity method results in a strong dependence of the hit finding efficiency on the particle crossing angle

Hit finding efficiency:54-99% ~92%

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Channel inefficiencies

Single channel inefficiencies as a result of the readout electronic’s dead time

Dependence of channel dead time on pulse amplitude


Pulse amplitude [V]

Pulse amplitude [fC]

Pulse length [ns]

0,57 1,70 8100,97 2,58 11001,17 3,47 12201,5 4,45 13802,3 6,80 17302,6 7,70 18403,0 8,91 19803,4 10,10 21304,2 12,47 24105,0 14,85 2670

0 2 4 6 8 10 12 14 160

500

1000

1500

2000

2500

3000

pulse length [ns]

Pulse amplitude [fC]

Pul

se le

nth

[ns]

Preliminary STS simulations results

• Max channel occupancy is 14 times per 100 mbias events • Mostly it is 9~8 times per 100 mbias events

• -> less then 1,25 us time distance between hits in one channel

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Channel inefficiencies

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 %

For minimum bias Au+Au collision at 25AGeV channel occupancy:

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Summary


• CBM requirements for the Silicon Tracking System call for a highly granular, low-mass and radiation hard detector system;

• The performance of the Silicon Tracking System has been evaluated with realistic detector responce functions inplemented;

• As a result of implementation of all realistic functions, hit finding efficiency drops down by 2% for particles with incident angle below 20°.

Next Steps Detailed studies of influence of noise level, ADC resolution and channel inefficiencies on

full particles reconstruction; Improvement of STS geometry in order to achieve more then 90% of particles with

incident angle below 20°; Comparision of simulations results with real date obtain from test experiments.

Performance studies of the CBM Silicon Tracking System

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