The CMS all silicon tracker simulation Maurizio Biasini - University and INFN Perugia, Italy

The CMS all silicon tracker simulationMaurizio Biasini - University and INFN Perugia, Italy

On behalf of the CMS Collaboration

TEC=Tracker End-Caps

TOB=Tracker Outer Barrel

TIB=Tracker Inner Barrel

TID=Tracker Inner DisksPixel

Z [mm]

R[m

m]

Pseudorapidity η

Detailed simulation of active and passive volumes (95% of the total number)

The CMS Tracker is made of a Silicon Pixel vertex detector and a Silicon Microstrip Tracker• (100 x 150) m2 pixels• 320 – 500 m thick microstrip sensors• Surface: 200m2 and 1m2

• 10 million Strips and 66 million pixels

Simulation based on Geant4 and CMS OO framework.Geometry description using Detector Description Language (DDL)

5%

The Compact Muon Solenoid

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 All Silicon Tracker

Silicon Microstrip and Pixels

Tracker Inner Barrel Pixel Barrel

The Tracker Simulation

The detector simulation is fundamental in optimizing reconstruction algorithms and in understanding the detector and the first LHC collinding beam data

Description of Geometry

Material Budget

Simulated Detector Response

Validation of Simulation using Cosmics

Charge release in Silicon288 eV/µm, 3.6 eV/pair25000 e- in t=320 µmδ-ray cutE> 30 keV (pixel) 120 keV (strip)Lorentz AnglePixel: 23° (120 µm drift)Strip: 7° (36-61 µm drift)Charge diffusionσ≈√Ldrift

(Pixel: 7 µm, Strip: 2 µm)

Electronics SimulationElectrical chain gain factorConversion of the released charge into 6/8-bits ADC countsStrip: 250 e- = 1 ADC, Pixel: 135 e- = 1 ADCElectrical NoiseGaussian noise is added(Pixel: σD=350 e-, Strip: σD=1200 e-)Noise increase with radiation damage (even at operation temperature T=-20°C): conservative +50%AC couplingsInter-strip coupling: 3%-1% (11%-7%) of the charge fraction assigned to the neighbours strips for TOB-TIB in peak (deconvolution) mode

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

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

SubdetectorActive Volumes

PassiveVolumes

Pixel Barrel (PXB) 768 10201Pixel Forward (PXF) 672 23670PIXEL 1440 33871Inner Tracker (TIB+TID) 3540 56488Outer Barrel (TOB) 5208 145419Outer End-Caps (TEC) 6400 113158Outer Structures 0 346STRIP 15148 315411TRACKER 16588 349283

Tracker Inner Barrel Pixel Forward

The average density is 0.17 g/cm3: a MIP loses 35 MeV/mBarrel region x/X0=0.4: 40% of the photons converts

Comparison with lab measurement

Subsystem Simulation (kg) Laboratory (kg)

Outer End-Caps (TEC) 691.70 702.22Inner Tracker (TIB+TID) 427.2 452Pixel Barrel 2.455 2.598

Ratio Data/Simulation

1.0151.0581.058

Validation of Simulation using Cosmics

First full Tracker commissioning Cosmic Run At Four Tesla CRAFT 08270 M cosmic events selected – 6.5 M with track in Tracker – 3.2M/110K high quality tracks for Strip/PixelsPossibility to check and validate Tracker Simulation

Charge Distribution for Pixel Barrel (left) and Endcap (right)

MC Simulated and measured cluster charge for the Silicon StripTracker corrected for the track incident angle.

Track Reconstruction Efficiency estimated with three methods (Tracker Barrel)

Tracking resolution estimated after alignmentBased on independent track reconstruction for upper and lower part of cosmic track

RMS of Residuals as a function of transverse momentum for impact parameter (left) and transverse momentum (right)

Efficiency as a function of transverse momentum for the Combinatorial Track Finder