5% The CMS all silicon tracker simulation Maurizio Biasini - University and INFN Perugia, Italy On behalf of the CMS Collaboration The Compact Muon Solenoid The CMS All Silicon Tracker TEC=Tracker End-Caps TOB=Tracker Outer Barrel TIB=Tracker Inner Barrel TID=Tracker Inner Disks Pixel Z [mm] R[mm] Pseudorapidity η The Compact Muon Solenoid is a general purpose detector designed to study proton proton and lead lead collisions at the LHC. Silicon Tracker inside the superconducting solenoid for the reconstruction of charged particles, momentum, position and decay verticies. The CMS Tracker is made of a Silicon Pixel vertex detector and a Silicon Microstrip Tracker (100 x 150) mm2 pixels 320 – 500 mm thick microstrip sensors Surface: 200m2 and 1m2 10 million Strips and 66 million pixels Silicon Microstrip and Pixels The Tracker Simulation Description of Geometry Tracker Inner Barrel Pixel Barrel Tracker Inner Barrel Pixel Forward Detailed simulation of active and passive volumes (95% of the total number) Subdetector Active Volumes Passive Volumes Pixel Barrel (PXB) 768 10201 Pixel Forward (PXF) 672 23670 PIXEL 1440 33871 Inner Tracker (TIB+TID) 3540 56488 Outer Barrel (TOB) 5208 145419 Outer End-Caps (TEC) 6400 113158 Outer Structures 346 STRIP 15148 315411 TRACKER 16588 349283 The detector simulation is fundamental in optimizing reconstruction algorithms and in understanding the detector and the first LHC collinding beam data Simulation based on Geant4 and CMS OO framework. Geometry description using Detector Description Language (DDL) Material Budget Comparison with lab measurement Each component has been weighted , from the smallest capacitor (mg) to the whole subdetectors (Tons) Agreement at the 5-10% level found between simulation and measured values 5% Subsystem Simulation (kg) Laboratory (kg) Outer End-Caps (TEC) 691.70 702.22 Inner Tracker (TIB+TID) 427.2 452 Pixel Barrel 2.455 2.598 Ratio Data/Simulation 1.015 1.058 The average density is 0.17 g/cm3: a MIP loses 35 MeV/m Barrel region x/X0=0.4: 40% of the photons converts Simulated Detector Response Validation of Simulation using Cosmics Charge release in Silicon 288 eV/µm, 3.6 eV/pair 25000 e- in t=320 µm δ-ray cut E> 30 keV (pixel) 120 keV (strip) Lorentz Angle Pixel: 23° (120 µm drift) Strip: 7° (36-61 µm drift) Charge diffusion σ≈√Ldrift (Pixel: 7 µm, Strip: 2 µm) Electronics Simulation Electrical chain gain factor Conversion of the released charge into 6/8-bits ADC counts Strip: 250 e- = 1 ADC, Pixel: 135 e- = 1 ADC Electrical Noise Gaussian noise is added (Pixel: σ̄=350 e-, Strip: σ̄=1200 e-) Noise increase with radiation damage (even at operation temperature T=-20°C): conservative +50% AC couplings Inter-strip coupling: 3%-1% (11%-7%) of the charge fraction assigned to the neighbours strips for TOB-TIB in peak (deconvolution) mode First full Tracker commissioning Cosmic Run At Four Tesla CRAFT 08 270 M cosmic events selected – 6.5 M with track in Tracker – 3.2M/110K high quality tracks for Strip/Pixels Possibility to check and validate Tracker Simulation The electronics pile-up is simulated processing the signals of the preceding 5 and fhe ollowing 3 bunch crossings when simulating the actual bunch crossing (25 ns) Strips: two readout modes, signal shape in deconvolution reduces the pile-up Charge Distribution for Pixel Barrel (left) and Endcap (right) Validation of Simulation using Cosmics Track Reconstruction Efficiency estimated with three methods (Tracker Barrel) Tracking resolution estimated after alignment Based on independent track reconstruction for upper and lower part of cosmic track Efficiency as a function of transverse momentum for the Combinatorial Track Finder MC Simulated and measured cluster charge for the Silicon Strip Tracker corrected for the track incident angle. RMS of Residuals as a function of transverse momentum for impact parameter (left) and transverse momentum (right)