1. The CBM sensor digitizer
C.Dritsa
IKF-Frankfurt, IPHC-Strasbourg
(now at JLU Giessen)
C.Dritsa, St.Odile, 08 September 2011

2. C.Dritsa, St.Odile, 08 September 2011
Outline
Motivation
Model requirements
Description of the model
Important definitions (1)
charge generation
charge sharing
Evaluation
Important definitions (2)
Comparison with experimental data
Outlook
C.Dritsa, St.Odile, 08 September 2011
C.Dritsa, Workshop on system integration of highly granular and thin vertex detectors, St.Odile, France

3. C.Dritsa, St.Odile, 08 September 2011
Motivation
Digitizer model developed in order to allow simulating the CBM-MVD.
In collaboration with the IPHC-PICSEL group in Strasbourg and the IKF-MVD group in Frankfurt.
It was inspired by a detector response model developed for the ILC vertex tracker
M. Battaglia, “Response simulation of CMOS pixel sensors for the ILC vertex tracker” , Nuclear Instruments and Methods in Physics Research A 572 (2007) 274–276
C.Dritsa, St.Odile, 08 September 2011

4. CBM-MVD response model requirements
Realistic simulations allowing to simulate:
Cluster properties: size, shape
pixel size
vary number of ADC channels of the readout
particles impinging with high incident angles
noise, fake hits
Rapid simulation features
simulate collision pile up
delta electrons (of concern in CBM)
fast, allowing high statistics simulations
C.Dritsa, St.Odile, 08 September 2011

5. C.Dritsa, St.Odile, 08 September 2011
Spirit of the model
Challenge:
Charge carrier transport process too complex and slow for simulation
Solution:
Parameterization of the sensor response
Use experimental data
GEANT provides only entry and exit coordinates of the particle in the volume
no dE/dx from GEANT
C.Dritsa, St.Odile, 08 September 2011

6. C.Dritsa, St.Odile, 08 September 2011
Reference data
Data acquired at CERN/SPS with pions 120 GeV/c
Sensor under test: MIMOSA17
AMS 0.35
standard low resistivity epitaxial layer
analogue output (12 bit charge resolution)
30 µm pixel pitch
Particle incident angles 0-75 degrees
(90 degrees is parallel to the sensor plane)
C.Dritsa, St.Odile, 08 September 2011

7. C.Dritsa, St.Odile, 08 September 2011
The digitizer
C.Dritsa, St.Odile, 08 September 2011

8. Important definitions (1)
08-Sep-2011
Important definitions (1)
Landau
Lorentz
MPV
C.Dritsa, St.Odile, 08 September 2011
C.Dritsa, Workshop on system integration of highly granular and thin vertex detectors, St.Odile, France

9. C.Dritsa, St.Odile, 08 September 2011
Other features
Simulated by random sampling of a distribution following a Gauss law with adjustable µ, σ
mean=0
σ =15 electrons
Number of ADC bits adjustable
12 bits
Pixel pitch adjustable
30 µm
C.Dritsa, St.Odile, 08 September 2011

10. C.Dritsa, St.Odile, 08 September 2011
The model: Input
The charge of the cluster is taken by random sampling of the experimental distribution for 25 pixels
0 degrees incident angle
Landau:
Accumulated charge on 25 pixels
The simulation of inclined particles is derived by this initial parameterization.
The charge distribution among the pixels in the cluster is based on a 2D Lorentz distribution (derived from the 1D)
0 degrees incident angle
C.Dritsa, St.Odile, 08 September 2011

11. The model: charge generation
Q0, l0 : known
lincl: provided by GEANT
C.Dritsa, St.Odile, 08 September 2011

12. The model: charge distribution
Illustration for inclined track
Charge provided by Landau (25 pixels)
The trajectory is divided in segments
A Lorentz function corresponds to each segment
C.Dritsa, St.Odile, 08 September 2011

13. C.Dritsa, St.Odile, 08 September 2011
The model
Charge on pixel i
x,y-coordinates
of segment k
Lorentz
Amplitude
Lorentz
width
L(xk,i,yk,i)
Sum over segments (k)
x,y-coordinates
of pixel i
Pixel pitch
C.Dritsa, St.Odile, 08 September 2011

14. C.Dritsa, St.Odile, 08 September 2011
Evaluation
C.Dritsa, St.Odile, 08 September 2011

15. Important definitions (2)
08-Sep-2011
Important definitions (2)
Accumulated charge plot
Q1>Q2>Q3… Q1
Qi<0
(i~N) Q1 Q2 Q3
Q1+Q2
Accumulated charge (MPV) Q1 Q2
Q1+Q2+Q3 Q3 Qi
Q1+Q2+…+Qi 1 2 3 … N
Number of Pixels
The accumulated charge plot describes the charge sharing
among the pixels of the cluster:
e.g. the seed pixel collects ~30% of the total cluster charge.
C.Dritsa, St.Odile, 08 September 2011
C.Dritsa, Workshop on system integration of highly granular and thin vertex detectors, St.Odile, France

16. Evaluation: MPV of Landau
C.Dritsa, St.Odile, 08 September 2011

17. Evaluation: sigma of Landau
C.Dritsa, St.Odile, 08 September 2011

18. C.Dritsa, St.Odile, 08 September 2011
Evaluation
Average number of pixels/cluster
C.Dritsa, St.Odile, 08 September 2011

19. C.Dritsa, St.Odile, 08 September 2011
Evaluation: shape
Simulation
Experimental data
C.Dritsa, St.Odile, 08 September 2011

20. C.Dritsa, St.Odile, 08 September 2011
Summary and outlook
Digitizer model developed for the CBM-MVD and successfully tested with experimental data.
Model was successfully tested on High-Resistivity sensors (M.Domachowski)
Successfully tested on neutron irradiated sensors (M.Domachowski)
Simulation of MIMOSA-26 data sparcification in process (Q.Li)
C.Dritsa, St.Odile, 08 September 2011

21. C.Dritsa, St.Odile, 08 September 2011
Acknowledgments
Thanks to:
the IPHC-PICSEL group and the IKF-MVD group.
In particular:
IPHC: J.Baudot, M.Goffe, R.DeMasi, M.Winter
IKF: M.Deveaux, M.Domachowski, Q.Li, J.Stroth
C.Dritsa, St.Odile, 08 September 2011

22. C.Dritsa, St.Odile, 08 September 2011
Backup
C.Dritsa, St.Odile, 08 September 2011

23. C.Dritsa, St.Odile, 08 September 2011
High-Res MAPS: Measurement vs. simulation
Melissa Domachowski
Simulation of HR-MAPS with the MVD-digitiser: OK
Simulation of irradiated MAPS: OK
C.Dritsa, St.Odile, 08 September 2011
Simulation of irradiated MAPS in CBM-Root Melissa Domachowski CBM Collaboration Meeting, Dresden 2011
C.Dritsa, Workshop on system integration of highly granular and thin vertex detectors, St.Odile, France 23

24. C.Dritsa, St.Odile, 08 September 2011
Particle yields
C.Dritsa, St.Odile, 08 September 2011