# Presentation: 836366

## The CMS Object-Oriented Simulation

*V. Daniel Elvira and Maya Stavrianakou, FNAL*
*On behalf of the CMS collaboration*
*CHEP 2006*
**Outline**
**Overview**
**Interfaces and services**
**CMS detector simulation and validation**
**Parameterized simulations **
**Production**
**Summary and outlook**

- H->eeμμ at 300 GeV
- Luminosity 1034

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Simulation Software in CMS

**Generation –**** MC truth information from particle gun or physics generator about vertices and particles. Stored in HepMC format.**
**Detector Simulation –**** Hit objects with timing, position, energy loss information. Based on the Geant4 tool kit.**
**Digitization –**** Constructs Digi objects which include realistic modeling of electronic signal.**
**Reconstruction –**** Physics Objects: vertices, photons, e, ********, jets,......**

**Simulation Software in CMS**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Simulation Tools and the Framework

_**Geant4**_
**physics processes describing electro-magnetic and hadronic interactions**
**tools for detector**** geometry and sensitive element response**
**interfaces for ****tuning and monitoring**** particle tracking**
_**CMS framework**_
**Manages application control, incl. module scheduling, ****action-on-demand where indicated, non-event data handling, ****data persistency, I/O,...**
**Interfaces to common services and tools such as magnetic field, generators, MC truth handling, infrastructure for hits, event mixing, digitization,...**
**Ensures provenance tracking and event immutability**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Simulation Tools and Framework cont’d

***CMS switched from GEANT3 to GEAN4-based simulation end 2003 ***
***So far the CMS OSCAR simulation package has delivered ******~100 M physics events for CMS 2004 Data Challenge and on-going Physics TDR studies ***
***OSCAR is being adiabatically replaced by a new suite (referred to as here as SimG4), based on the new Event Data Model Software Framework***
**CPU: SimG4 ******** 1.5 x SimG3 - with lower production cuts!**
**Memory: ~110 MB/evt for pp in SimG4 vs. ~100 MB in SimG3**
**Robustness: from ~1/10****4**** crashes in pp events (mostly in hadronic physics) in DC04 to  < 1/10****6**** crashes in latest productions**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Interfaces and services (I) 

**Application control** **using** **customized Event Data Producer module and RunManager interfacing Geant4 to the CMS Event Data Model Framework*****; *****persistency, I/O etc as provided by the Framework **
**Geometry**** provided by the Framework EventSetup, using the Detector Description package to convert the XML input files**
**Sensitive detector construction** **with configurable registration of sensitive elements**
**Hit collection** **and** **formatting, event mixing, and digitization** **based on common SimDataFormats classes and services**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Interfaces and services (II)

**Magnetic field**** provided by the Framework EventSetup with configurable field selection, propagation tuning and optional user-defined local field managers **
**Physics** **with** **configurable physics lists and production cuts, cross section table storage and retrieval options **
**User actions**** for application monitoring and tuning, based on dispatcher-observer pattern (using BOOST signal library) for observable entity (run, event, track, step etc)**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Interfaces and services (III)

**Event generation and Monte Carlo truth**
**Choice of specific generator (Pythia, Herwig, gun etc) and event format (ASCII, Pool, etc) run-time configurable**
**HepMC::GenEvent converted to G4Event**
**Navigable Monte Carlo truth record with decay/interaction history for all generated as well as selected simulated particles**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## The CMS Detector

- 22 m long  & 15 m in diameter

- Solenoid Magnet: 4 Tesla Field

- Electromagnetic Calorimeter (Ecal)

- Hadronic Calorimeter (Hcal)

- Silicon Tracker

- Muon System

- More than 1 Million Geometrical volumes

- SVS modular structure follows the detector sub-systems

**The CMS Detector**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Magnetic Field

**Field Map - TOSCA calculation**

**Designed to optimize simulation and reconstruction **
**Based on dedicated geometry of  “magnetic volumes”**
**Decouple volume finding and interpolation within a volume**

**Time spent in magnetic field query (P4 2.8 GHz) for 10 minimum bias events 13.0 vs 23.6 s for****new field ~1.8-2 times faster than FORTRAN/G3**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Tracker

**Key role in the development and optimization of simulation infrastructure and validation**
**Tracker material budget - estimated with detailed description of all active and passive components - directly affects e/m calorimeter physics; places stringent requirements on detector description and geometry construction accuracy **
**Correct, navigable Monte Carlo truth, for correct decay tree reconstruction and proper treatment of hard electron bremmsstrahlung - crucial for B-t  studies**
**Tracker performance extensively validated in terms of tracking and hit distributions for single particles, minimum bias, and physics events**

**tracker geometry, hits and **
**tracks (green - electrons)**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Electromagnetic Calorimeter (ECAL)

**Electromagnetic Calorimeter (ECAL)**

**G4/test-beam comparisons ********excellent representation of electromagnetic showers by G4**
**Overall ECAL performance, in terms of energy and position resolution dominated by effects not included in shower simulation (electronics noise, photostatistics, longitudinal uniformity of light collection and crystal inter-calibration) ******** only gross errors are identified by energy and position resolution comparisons **
**Largest sensitivity to changes in radiation and showering in tracker material, but not trivial in to validate in test beam**

**Tracks and energy deposition in ECAL**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Hadronic Calorimeter (HCAL)

**Hadronic Calorimeter (HCAL)**

**HCAL studies on energy resolution and linearity, e/********  ratio, and shower profile instrumental in G4 hadronic physics validation**
**Comparisons between single particle measurements  in test beam: 2002-2004, different HCAL modules, preceded by ECAL prototype, to beams of ********, e and ******** over large energy range - G4 hadronic physics parametric (LHEP) and microscopic (QGSP) models**
******  ****energy resolution and response linearity as a function of incident energy in good agreement with the data within the large systematic uncertainties in the latter**
**Transverse and longitudinal shower profiles studied in 1996 and 2004 test beam **
****** ****showers predicted by G4 narrower than those by G3**
**Showers predicted by QGSP (v 2.7) shorter than those by LHEP (v 3.6) list, with LHEP predictions closer to those from G3/Geisha**

**test beam 2004 results**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Muons

**G3/G4 comparisons for single ******** 10 GeV-10 TeV: good agreement for ionization but ******** brem, e+e− production, and in particular, ********-nuclear significantly different, due to newer theoretical developments included in G4**
**Multiple scattering significantly smaller in G4, in agreement with experimental results **
**G4 results also show improvement wrt precision of ******** propagation in detector**
**Test beam setup: two chambers with and without iron slab between, to investigate effect of ******** showers in passive material; ****analysis: ******** with P****T**** 50-300 GeV**
**G4 slightly underestimates soft ********-ray production in cell volumes, while hard ********- rays and e/m showers are correctly modeled; despite this, local track reconstruction efficiency and resolution well reproduced by simulation**

**H********ZZ********4********, M****H**** =150 GeV**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Forward Detectors

**Forward detectors, CASTOR and ZDC calorimeters, Totem telescopes: essential for diffractive and heavy ion programs. **
**ZDC: Cerenkov detector designed to collect any remaining neutral fragments of the colliding nuclei - may be used as a measure of collision centrality**
**Simulation underway to study energy resolution and leakage to be compared with Nov 2005 test beam data**

**3D view of CASTOR**

**ZDC: Zero Degree Calorimeter at 140 m**

**Castor Calorimeter **
**at 14.37 m (5.3 <h< 6.7)**

**Totem Telescopes**
**at 7.5 m < z < 13.5**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Parameterized Simulation (I)

**detailed simulation of e/m showers CPU intensive Þ parameterization of spatial energy distribution of e/m shower, based on probability density functions, allows speed up without compromising simulation accuracy**
**GFlash model**** (G. Grindhammer, S. Peters), based on three probability density  functions (originally developed and used by H1) used to parameterize electrons and positrons in CMS barrel and endcap e/m calorimeter**
_**comparisons between GFlash-based and full simulation**_
**energy depositions in central crystal, 3x3, 5x5 matrices: agreement to ~1%**
**transverse and longitudinal shower profiles: agreement to ~1-3%**
**speed increases by factors 3-10 depending on event type, particle energy and detector region**
_**examples**_
**single e or ******** with E=100 GeV in ECAL barrel: factor ~10 speed-up**
**large extra dimensions full signal event, with single ******** > 1000 GeV: factor ~4**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Parameterized Simulation (II)

**Energy deposition in a 5x5 crystal matrix **
**for 50 GeV electrons**
- Histograms = full geant4 simulation
- Red markers = shower parameterization

**Transverse shower profile for 50 GeV ******

**Longitudinal shower profile for 50 GeV ******

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Production

**11/2003 - 10/2005:**** ****~100 M physics events**** ****simulated by production team**
**Failure rate: ~1/10****4**** - 10****6**** events**
**Performance for typical signal event:**
**~250 MB memory**
**~100-200K Si2K (*) CPU**
**~1 MB output data**
**CMS Computing Model: same amount of simulated as real data, ****~1.5 x 10****9**** events/year ******** mix of full and fast simulation will be used to manage required resources**

- (*) typical 3 GHz CPU is ~1.7 K Si2K, so
- 200K Si2K is 2 minutes on such a CPU;
- Si2K ratings scale more or less linearly
- with CPU speed

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Summary and Outlook

**SUSY **(leptons, missing ET)

***visualization with IGUANACMS***

**In CMS, the Geant4-based OO simulation has successfully replaced its Fortran/Geant3 predecessor. ****It has been validated and adopted by all CMS detector and physics groups. ****It has proven robust and performant, easily extensible and configurable.**
**It has also proven modular and portable to a different software framework without loss of functionality or usability.**
**New features, extending functionality, such as exotics simulation, or improving performance, such as hadron shower parameterization, envisaged for 2006, can be added without disrupting standard operation/ performance.**

**Black Hole Event**
**Model of Landsberg and Dimopoulos**
**Planck scale = 1 TeV**
**Number of extra dimensions = 2**

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006

## Heavy Ion Simulation 

- G3: event in slices of 100 tracks run separately*(ZEBRA limitations)* - _G4: run full HI events_
**55K generated particles, with 97K tracks from 80K vertices...**
**Event in slices of 100 particles**
**G3 230 min**
**G4 180 min**
**Full event ****G4  210 min ***(P4 3.2 GHz* *)*
**hits in tracker and ECAL by particles from central Pb+Pb collision at 5.5 TeV/nucleon**

* *

- D.  Elvira, M. Stavrianakou, FNAL

- CHEP 2006