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

On behalf of the CMS Collaboration

TEC=TrackerEnd‐Caps

TOB=TrackerOuterBarrel

TIB=TrackerInnerBarrel

TID=TrackerInnerDisksPixel

Z[mm]

R[mm] Pseudorapidityη

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) µm2 pixels •  320 – 500 µm 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 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

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

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 0 346 STRIP 15148 315411 TRACKER 16588 349283

Tracker Inner Barrel Pixel Forward

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

Comparison with lab measurement

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 1.058

Validation of Simulation using Cosmics

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

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

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

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

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