GAUSS GEANT 4 based simulation for LHCb GEANT

GAUSS - GEANT 4 based simulation for LHCb GEANT 4 Delta Review 9 October 2002 W. Pokorski / CERN 09/10/2002 LHCb Simulation

Contents Introduction to LHCb Overview of Gauss project Gi. Ga – Gaudi interface to GEANT 4 Physics validation: RICH 1 and HCAL results Summary 09/10/2002 LHCb Simulation 2

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 3

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 4

GAUDI - Object Diagram Interactive Service Application Manager Message Service Job. Options Service Particle Prop. Service Other Services 09/10/2002 Converter Event Selector Persistency Service Data Files Detec. Data Service Transient Detector Store Persistency Service Data Files Histogram Service Transient Histogram Store Persistency Service Data Files Event Data Service Transient Event Store Algorithm LHCb Simulation 5

Gauss application Job. Opts Int. face Gi. Ga Geant 4 Cnv Hep. MC Cnv Pythia etc Job. Opts MCParticle MCVertex MCHit Digi Geant 4 Alg (Gi. Ga) Digit MCDigit Cnv Geometry Generator 09/10/2002 Detector Simulation LHCb Simulation Digitization 6

Gi. Ga overview GEANT 4 Interface for Gaudi Applications or Gaudi Interface to GEANT 4 Applications GEANT 4 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 (Particle. Property. Svc, Random. Number. Svc, Magnetic. Field. Svc, etc. ) 09/10/2002 LHCb Simulation 7

Gi. Ga structure Persistency Service Application Manager Event Service Transient Event Store Converter Cnv Algorithm Data Files Gi. Ga. Kine Conversion Service G 4 Kine Gi. Ga. Hits Conversion Service G 4 Hits Gi. Ga Service Geant 4 Other Services 09/10/2002 Detec. Service Transient Detector Store Persistency Service Gi. Ga. Geom Conversion Service G 4 Geom Action Data Files LHCb Simulation 8

Gi. Ga features it’s a Gaudi service provides access to internal G 4 event loop via Gi. Ga. Run. Manager all interactions with Geant 4 only through abstract interfaces of Gi. Ga Service minimizes the couplings to Geant 4 allows loading external physics lists instantiates (using Abstract Factory pattern) different “actions” (makes them to be plugable components) 09/10/2002 LHCb Simulation 9

Gi. Ga - Geometry Conversion Xml description Xml Cnv Materials Volumes Geo Conversion Service Gaudi transient store 09/10/2002 Converter Geant 4 Materials LHCb Simulation Converter Geant 4 Volumes 10

Geometry conversion ex. (RICH 1) Xml Gi. Ga G 4 Open. GL 09/10/2002 LHCb Simulation 11

Gi. Ga - Kinematics Conversion Hep. MC Event LHCb Vertices LHCb Particles Kine Conversion Service Converter Geant 4 Primary Vertices 09/10/2002 Converter Geant 4 Trajectories LHCb Simulation 12

Gi. Ga – Hits Conversion LHCb Ecal Hits LHCb Muon Hits LHCb Velo Hits Converter Hits Conversion Service Geant 4 Geant 4 Hits 09/10/2002 LHCb Simulation 13

Detector Simulation – “physics lists” physics lists: crucial part of the whole simulation program – will certainly require several tuning iterations most of the stuff already implemented in Geant 4 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 Gi. Ga : modular physics lists allows dynamic loading (via job. Options) of particular physics “sublists” expected to increase flexibility and to make validation easier 09/10/2002 LHCb Simulation 14

Sensitive Detectors & Hits Gi. Ga. Sens. Det. Tracker Process. Hit() creates G 4 Tracker. Hits invoked when particle passed through the sensitive volume lv. Volume (Xml. DDDB) Gi. Ga. Tracker. Hits. Cnv (Geant 4) Geant 4 world Gaudi world converts to: MCHits (/Event/MC/OT/Hits) <logvol name="lv. U_Active. Layer" … sensdet="Gi. Ga. Sens. Det. Tracker/my. Det"> 09/10/2002 LHCb Simulation 15

Physics Validation - RICH - HCAL 09/10/2002 LHCb Simulation

RICH detectors in LHCb • To identify charged particles in the momentum range 1 -150 Ge. V/c. • Two detectors: RICH 1, RICH 2. Momentum range RICH 1: Aerogel C 4 F 10 2 10 Ge. V/c < 70 Ge. V/c RICH 2: CF 4 <150 Ge. V/c. • Photo Detectors: Baseline solution- Hybrid. Photodiodes (HPD). • RICH test beam presented: To test the performance of the Aerogel radiator. 09/10/2002 LHCb Simulation S. Easo 17

Test beam Set-up at CERN S. Easo Beam 09/10/2002 from CERN-PS: πˉ and p/πLHCb in Simulation the range 6 – 10 Ge. V/c (Δp/p = 1%) 18

Simulation of the Testbeam Setup. Mirror Rad. of Curvature=1185 mm. Four Pad Hpds are used. Hpd Mirror Vessel Filter Aerogel 09/10/2002 LHCb Simulation S. Easo 19

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 20

Photoelectric Effect at the HPD • Standard Geant 4 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 GEANT 4 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 21

Hit Creation in the Si Detector • Implemented using a special process class since the standard Geant 4 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 Ø 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 22

RICH 1 with Single. Particle. Gun RICH 1 Event Pion with 7 Ge. V/c. Cherenkov Photons In Aerogel and C 4 F 10. Rayleigh scattering Switched off for Illustration. S. Easo 09/10/2002 LHCb Simulation 23

RICH 1 Hits 09/10/2002 LHCb Simulation 24

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 09/10/2002 LHCb Simulation I. Belyaev + A. Berdiouguine et al. 25

Energy Response in HCAL Response to 50 Ge. V/c Pions Histogram : Real Data Dots: Simulation • Testbeam (1) Data , GEANT 3 (MICAP +FLUKA). • HCAL TDR. I. Belyaev + A. Berdiouguine et al. • Testbeam (2) Data, GEANT 4. 09/10/2002 LHCb Simulation 26

Data and G 3 Energy Resolution of HCAL • Testbeam Data, GEANT 3 • GEANT 3 with GEISHA, FLUKA, MICAP • Testbeam Data , GEANT 4 • G 4+GEISHA agrees with G 3+GEISHA. • Need help to understand use G 4 with QGS+CHIPS Data and G 4 • Data § G 4 (QGS+CHIPS) I. Belyaev + A. Berdiouguine et al. G 4(GEISHA) 09/10/2002 LHCb Simulation 27

Panoramix view of MCHits 09/10/2002 LHCb Simulation 28

Panoramix view of MCHits (2) 09/10/2002 LHCb Simulation 29

Summary Current Status: we can run GEANT 4 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 30

Summary (2) Planning: by end of the year: to have a complete GEANT 4 based simulation application by the summer: to perform some “test productions” by … : to definitely move from the old GEANT 3 based simulation program to the new one, GEANT 4 based 09/10/2002 LHCb Simulation 31