1. Geant4 in the BaBar Simulation
Geant4 Delta Review
9 October 2002
Dennis Wright

2. Outline BaBar Overview Comparison projects Performance
EM process validation
Hadronic process validation
Performance

3. The BaBar Detector

4. Overview of the BaBar Simulation
Event
Generator
Detector Response
And Background
Mixing
(SimApp)
Reconstruction
And Analysis
(Bear)
Tracking, Physics,
Hit Scoring
(Bogus, GEANT4)
Objectivity
Database

5. Use of Geant4 in BaBar BaBar uses: BaBar does not use: Geometry
Hit-scoring
Decay processes
EM physics processes (< 10 GeV)
Low energy hadronic processes (< 10 GeV)
BaBar does not use:
Standard tracking/navigation
Detector response
Persistence

6. BaBar/Geant4 Validation (1)
1 million events generated by October 2000
B0B0bar, Bhabha, dimuons
Use to test gross features of simulation:
Material model validation
Tracking/resolution tests
G3/G4/Data comparison of EM processes
Rough check of hadronic processes
Tests of performance/robustness

7. BaBar/Geant4 Validation (2)
Detailed comparisons of MC and data
11 million event sample completed July 2002
> 25 different event types simulated
Goals:
fine tuning of EM processes (check recent improvements)
Take a serious look at hadronic processes
Examine calorimetry, tracking, PID

8. EM processes/calorimetry

9. EM processes/calorimetry

10. EM processes/calorimetry

11. Tracking

12. Tracking

13. Hadronic Validation Currently using low energy parameterized model
Not especially appropriate for BaBar energies
only model available in this range
decided to use and fix where needed
Several fixes reported by LCD group at SLAC – passed to G4
Some included in toolkit, some to be included soon
Use latest MC data set and BaBar “thin target” tests to search for and fix other problems
Very recent results from tests –hadronic group hasn’t seen them yet

14. BaBar “Thin Target” Hadronic Testsp
Drift Chamber Be
CF support tube
Vertex Tracker

17. Performance
Simulation stage of generic B0-B0bar event includes event generator, tracking, hit-scoring
On 866 MHz PIII takes 5.0 s/evt
Used Geant4 4.0
Currently running MC production at 19 sites (1 billion events so far)
BaBar recently decided to double the MC/data ratio (to 3)
Speed is now more an issue than before

18. Conclusions EM validation well in hand
A little tweaking remains
Hadronic validation beginning in earnest
Results will be passed to hadronics group
Huge amount of MC data to be produced using Geant4 over life of experiment
Seeking ways to speed up simulation