The CBM sensor digitizer C.Dritsa IKF-Frankfurt, IPHC-Strasbourg (now at JLU Giessen) C.Dritsa, St.Odile, 08 September 2011 1
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 2
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 3
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 4
Challenge: Spirit of the model 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 5
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 6
The digitizer C.Dritsa, St.Odile, 08 September 2011 7
MPV Important definitions (1) Q 25 24 i 0 Q i Landau Lorentz C.Dritsa, St.Odile, 08 September 2011 8
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 9
The model: Input Landau: Accumulated charge on 25 pixels The charge of the cluster is taken by random sampling of the experimental distribution for 25 pixels 0 degrees incident angle 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 10
The model: charge generation Q 0,l 0 Q incl, l incl Q incl Q 0 l incl l 0 Q 0, l 0 : known l incl : provided by GEANT C.Dritsa, St.Odile, 08 September 2011 11
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 12
The model Charge on pixel i x,y-coordinates of segment k L(x k,i,y k,i ) Lorentz Amplitude Lorentz width Sum over segments (k) x,y-coordinates of pixel i Pixel pitch C.Dritsa, St.Odile, 08 September 2011 13
Evaluation C.Dritsa, St.Odile, 08 September 2011 14
Accumulated charge (MPV) Important definitions (2) Q1>Q2>Q3 Accumulated charge plot Q1 Qi<0 (i~n) Q1 Q2 Q3 Qi Q1+Q2 Q1+Q2+Q3 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 15
Evaluation: MPV of Landau C.Dritsa, St.Odile, 08 September 2011 16
Evaluation: sigma of Landau C.Dritsa, St.Odile, 08 September 2011 17
Evaluation Average number of pixels/cluster C.Dritsa, St.Odile, 08 September 2011 18
Evaluation: shape Simulation Experimental data C.Dritsa, St.Odile, 08 September 2011 19
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 20
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 21
Backup C.Dritsa, St.Odile, 08 September 2011 22
Accumulated charge [e - ] High-Res MAPS: Measurement vs. simulation 900 800 700 600 500 400 300 200 100 0 Melissa Domachowski 0 5 10 15 20 25 Number of pixels Measurement Simulation Simulation of HR-MAPS with the MVD-digitiser: OK Simulation of irradiated MAPS: OK C.Dritsa, St.Odile, 08 September 2011 23 Simulation of irradiated MAPS in CBM-Root Melissa Domachowski - CBM Collaboration Meeting, Dresden 2011
Particle yields C.Dritsa, St.Odile, 08 September 2011 24