1. STS Simulations Anna Kotynia 15 th CBM Collaboration Meeting April 12 - 16, 2010, GSI 1

2. 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 -  ρ 0 → e + e -  D 0 → π + K -  D + → π + π + K - ▫Channel inefficiencies ▫ADC resolution Next Steps Outline 2

3. 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 magnet Target MVD & STS 3

4. Total area, 8 stations: 3.2 m 2 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 4

5. „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 5

6. 6 Complete chain of physical processes caused by charged particle traversing the detector Magnetic field influences collection of the charge on the strips |B| = 1T Holes:  = 1.5°  x = 8  m Electrons  = 7.5°  x = 40  m STS Digitizer An algorithm for calculating the Lorentz angle in silicon detectors, Nuc. Instr. Meth. A497 (2003) 389-396

7. 7 Particle position in the sensor is obtained by using Center Of Gravity algorithm: 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

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9. Incident angle in STS 25 AGeV 2 AGeV Station 1 Station 5 9

10. Hit Finding Efficiency 10

11. Hit Finding Efficiency 11

12. Pluto simulation10k J/Psi → µ + µ - -3% Hit Finding Efficiency in STS 88% of muons from J/Psi have incident angle in STS<20◦ 12

13. Pluto simulation10k ρ 0 → e + e - -5% Hit Finding Efficiency in STS 77% of electrons from ρ 0 have incident angle in STS<20◦ 13

14. ASCII Generator 10k D0 → π+K-D0 → π+K- -3% Hit Finding Efficiency in STS 77% of particles from D 0 decay have incident angle in STS<20◦ 14

15. ASCII Generator 10k D+ → π+π+K-D+ → π+π+K- -4% Hit Finding Efficiency in STS 85% of particles from D + decay have incident angle in STS<20◦ 15

16. 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 16

17. Channel dead time simulations For minimum bias Au+Au collision at 25AGeV channel occcupancy: 17 Station12345678 min occ0.1 0.30.20.1 max occ4.74.23.63.02.42.01.31.2 Channel dead time Channel occupancy Hit finding efficiency occ>3.0 % (<1% of all chips) 1.0 % 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 ns91.17 % 17

18. 18 ADC resolution Parameters set in simulation ke - per ADC channel Hit finding efficiency Th: 4ke- Nof bitsStep 4-bits2.00 90.35% 5-bits1.50 6-bits1.00 90.44% 7-bits0.50 8-bits0.25 91.05% 20-bits0.01 91.17% 18

19. 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 19