GAUSS - GEANT4 based simulation for LHCb GEANT4 Delta Review 9 October 2002 W. Pokorski / CERN

Contents Introduction to LHCb Overview of Gauss project GiGa – Gaudi interface to GEANT4 Physics validation: RICH1 and HCAL results Summary 09/10/2002 LHCb Simulation

LHCb Experiment Precision Measurements of CP violation in the B Meson System Large Sample of Events with Bd and Bs Mesons. Most of the b hadrons are produced at small polar angles. LHCb: Single Forward Arm Spectrometer with Open Geometry. From the CP asymmetries in the final states of B-meson decays, Measure CKM Angles. This design is being modified to optimize the performance of LHCb. 09/10/2002 LHCb Simulation

GAUDI – LHCb software framework all of the LHCb event processing software is built within a framework – Gaudi framework separation between data and algorithms data store-centred architectural style separation between transient and persistent data isolation of user codes/algorithms from underlying persistency technologies components interact through their abstract interfaces 09/10/2002 LHCb Simulation

GAUDI - Object Diagram Converter Interactive Service Application Manager Converter Converter Event Selector Transient Event Store Data Files Message Service Persistency Service Event Data Service JobOptions Service Algorithm Algorithm Algorithm Data Files Transient Detector Store Particle Prop. Service Persistency Service Detec. Data Service Other Services Data Files Transient Histogram Store Persistency Service Histogram Service 09/10/2002 LHCb Simulation

Gauss application Int.face GiGa Digi Alg Geant4 (GiGa) Pythia etc JobOpts JobOpts JobOpts Int.face GiGa Digi Alg Geant4 (GiGa) Pythia etc Geant4 MCParticle MCVertex MCHit Digit MCDigit HepMC Cnv Cnv Cnv Geometry Generator Detector Simulation Digitization 09/10/2002 LHCb Simulation

GiGa overview GEANT4 Interface for Gaudi Applications or Gaudi Interface to GEANT4 Applications GEANT4 callable and controllable from within GAUDI environment common detector geometry source used by other applications (reconstruction, visualisation) communication via Transient Stores (Event, Detector Data) as any other service or algorithm in Gaudi use of common services (ParticlePropertySvc, RandomNumberSvc, MagneticFieldSvc, etc.) 09/10/2002 LHCb Simulation

GiGa structure Data Files Persistency Service Application Manager GiGaKine Conversion Service G4 Kine Transient Event Store Event Service Geant4 GiGaHits Conversion Service G4 Hits Algorithm Converter Algorithm Cnv GiGa Service Algorithm Cnv Transient Detector Store GiGaGeom Conversion Service G4 Geom Action Detec. Service Action we can see two parts of GiGa GiGaCnv – converts data (geometry, events) from and to transient stores (and loads it/extracts it to/from G4) GiGa – configures, triggers and control the actual simulation Other Services Data Files Persistency Service 09/10/2002 LHCb Simulation

GiGa features it’s a Gaudi service provides access to internal G4 event loop via GiGaRunManager all interactions with Geant4 only through abstract interfaces of GiGa Service minimizes the couplings to Geant4 allows loading external physics lists instantiates (using Abstract Factory pattern) different “actions” (makes them to be plugable components) 09/10/2002 LHCb Simulation

GiGa - Geometry Conversion Xml description Materials Volumes Xml Cnv Geo Conversion Service Converter Converter Gaudi transient store Geant4 Materials Geant4 Volumes 09/10/2002 LHCb Simulation

Geometry conversion ex. (RICH 1) XmlGiGa G4OpenGL 09/10/2002 LHCb Simulation

GiGa - Kinematics Conversion HepMC Event LHCb Vertices LHCb Particles Kine Conversion Service Converter Converter Converter Geant4 Trajectories Geant4 Primary Vertices 09/10/2002 LHCb Simulation

Hits Conversion Service GiGa – Hits Conversion LHCb Ecal Hits LHCb Muon Hits LHCb Velo Hits Converter Hits Conversion Service Converter Converter Geant4 Hits Geant4 Hits Geant4 Hits 09/10/2002 LHCb Simulation

Detector Simulation – “physics lists” crucial part of the whole simulation program – will certainly require several tuning iterations most of the stuff already implemented in Geant4 some specific processes needed implementation for RICH: photoelectric process (creation of photoelectrons in HPDs), energy loss: in the silicon of HPDs new feature recently added to GiGa : modular physics lists allows dynamic loading (via jobOptions) of particular physics “sublists” expected to increase flexibility and to make validation easier 09/10/2002 LHCb Simulation

Sensitive Detectors & Hits GiGaSensDetTracker G4TrackerHits (Geant4) creates GiGaTrackerHitsCnv ProcessHit() Geant4 world converts to: invoked when particle passed through the sensitive volume MCHits (/Event/MC/OT/Hits) lvVolume (XmlDDDB) Gaudi world <logvol name="lvU_ActiveLayer" … sensdet="GiGaSensDetTracker/myDet"> 09/10/2002 LHCb Simulation

Physics Validation - RICH - HCAL

RICH detectors in LHCb To identify charged particles in the momentum range 1-150 GeV/c. Two detectors: RICH1, RICH2. Momentum range RICH1: Aerogel 210 GeV/c C4F10 < 70 GeV/c RICH2: CF4 <150 GeV/c. Photo Detectors: Baseline solution- HybridPhotodiodes (HPD). RICH test beam presented: To test the performance of the Aerogel radiator. S. Easo 09/10/2002 LHCb Simulation

Test beam Set-up at CERN S. Easo Beam from CERN-PS: πˉ and p/π in the range 6 – 10 GeV/c (Δp/p = 1%) 09/10/2002 LHCb Simulation

Simulation of the Testbeam Setup. Mirror Rad. of Curvature=1185 mm. Four Pad Hpds are used. Hpd Mirror Vessel Filter S. Easo Aerogel 09/10/2002 LHCb Simulation

A Typical event in the Testbeam Red lines: Charged particle Green lines : Photons. Transmission in Aerogel, Cherenkov radiation, Rayleigh scattering, etc, simulated properly S. Easo 09/10/2002 LHCb Simulation

Photoelectric Effect at the HPD Standard Geant4 processes not applicable in this case (tabularized quantum efficiency data available from the manufacturer) A Special class created to generate the photoelectrons, which is derived from a GEANT4 base class. This process uses the quantum efficiency data and the results of Fountain focussing tests. Electron Energy: High Voltage applied. Direction: From Fountain focussing. The quantum efficieny data includes the loss of photons by reflection at the Hpd quartz window surface. S. Easo 09/10/2002 LHCb Simulation

Hit Creation in the Si Detector Implemented using a special process class since the standard Geant4 procedure too complex for this purpose the only important point: photoelectrons loose all their energy in the Si The backscattering causes a loss of efficiency in creating hits Parameterized efficiency = 1.0 - B* N/S where N = threshold cut in terms of width of the pedestal = 4 S= Signal to noise ratio=10 B= backscattering probability=0.18. S. Easo 09/10/2002 LHCb Simulation

RICH1 with SingleParticleGun RICH1 Event Pion with 7 GeV/c. Cherenkov Photons In Aerogel and C4F10. Rayleigh scattering Switched off for Illustration. S. Easo 09/10/2002 LHCb Simulation

RICH1 Hits 09/10/2002 LHCb Simulation

HCAL Test beam HCAL is a sampling device made out of steel as absorber and scintillating tiles are active material. The scintillating tiles run parallel to the beam axis. It will provide data for the LHCb hadron trigger. Testbeam studies of the response to particles incident at various angles is studied comparison to simulation I. Belyaev + A. Berdiouguine et al. 09/10/2002 LHCb Simulation

Energy Response in HCAL Response to 50 GeV/c Pions Histogram : Real Data Dots: Simulation Testbeam (1) Data , GEANT3 (MICAP +FLUKA). HCAL TDR. Testbeam (2) Data, GEANT4. I. Belyaev + A. Berdiouguine et al. 09/10/2002 LHCb Simulation

Energy Resolution of HCAL Data and G3 Energy Resolution of HCAL Testbeam Data, GEANT3 GEANT3 with GEISHA, FLUKA,MICAP Testbeam Data , GEANT4 G4+GEISHA agrees with G3+GEISHA. Need help to understand and use G4 with QGS+CHIPS Data G4 (QGS+CHIPS) G4(GEISHA) Data and G4 I. Belyaev + A. Berdiouguine et al. 09/10/2002 LHCb Simulation

Panoramix view of MCHits 09/10/2002 LHCb Simulation

Panoramix view of MCHits (2) 09/10/2002 LHCb Simulation

Summary Current Status: we can run GEANT4 simulation with all the subdetectors included we are testing/validating subdetector specific code and physics processes RICH test beam data comparison – well advanced HCAL test beam data comparison – well advanced other subdetectors participation increasing 09/10/2002 LHCb Simulation

Summary (2) Planning: by end of the year: to have a complete GEANT4 based simulation application by the summer: to perform some “test productions” by … : to definitely move from the old GEANT3 based simulation program to the new one, GEANT4 based 09/10/2002 LHCb Simulation