9 Feb 2000 CHEP 2000 Padova, Italy R.Dubois North American Linear Collider Detector Simulations • Full Simulation – flexible geometry specs within some constraints – Gismo for simulation tool – versatile output – full MC record of digis • platform support & MC Farms • Use New Tools for Analysis – using Root for simulation analysis and FastMC – using JAS for all phases • see Tony Johnson’s JAS talk • Lessons learned LCD
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R.Dubois 9 Feb 2000CHEP 2000 Padova, Italy North American Linear Collider Detector Simulations Full Simulation –flexible geometry specs within some constraints.
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9 Feb 2000 CHEP 2000Padova, Italy
R.DuboisNorth American Linear Collider Detector
Simulations
• Full Simulation
– flexible geometry specs within some constraints
– Gismo for simulation tool
– versatile output
– full MC record of digis
• platform support & MC Farms
• Use New Tools for Analysis
– using Root for simulation analysis and FastMC
– using JAS for all phases• see Tony Johnson’s JAS talk
• Lessons learned
LCD
9 Feb 2000 CHEP 2000Padova, Italy
R.DuboisLCD Road Map
stdHEP files
fastMC (JAS)
JAS analysis
ASCII raw data
Gismo
Full Recon
Root parser
JAS parser
.lcd filesRoot files
Gismo Material FilesGenerator FilesTrack Momentum Resolution Tables
• Parser (XML4C) a good choice but multi-platform headaches. Java version also exists.
• Wrote a thin layer of utilities to provide more appropriate API. So far used by (but separate from) simulation only. Easy to port to Java.
• Benefits of standard format, pre-existing (free!) tools already apparent.
• Bigger, better utility layer
• Support for other forms of input, e.g. analysis cuts
• Evolving specs in the XML family (DOM Level 2, Schemas,...) bear watching.
• Other HEP (e.g. Atlas) and astrophysics (e.g. GLAST) experiments are doing similar things. Should coordinate efforts, aim for common XML DTDs/schema and supporting utilities.
To come...J.Bogart
9 Feb 2000 CHEP 2000Padova, Italy
R.Dubois
Beam Backgrounds Overlays
4000 Beamstrahlung particlesin the Small detector(A normal event will have
88,000/bunch x 95 bunches/train)
• Background particles from Guinea Pig machine simulation
• We plan to create a separate library of background events to overlay on top of the generator events.
• Will have to apply cuts to the GP output to allow a reasonable particle count
– large fraction don’t get to the beampipe because of the B field (by design!)
• Then must overlay beam backgrounds, physics backgrounds and noise on top of true physics event
(white lines are neutrals)
G.Bower
9 Feb 2000 CHEP 2000Padova, Italy
R.Dubois
Gismo?• In ‘96. Gismo was the only OO
C++ simulation package on the market
• GEANT4 only available to public in past year
• Gismo does do full simulation with complex geometries
• so what’s the problem?
• Gismo has bugs/features that need fixing– bug handling loopers
– MC particle chain not optimal for bremms
– no fluctuations on E loss
– and a few others
• Gismo support is down to one person in GLAST– not so much interest in support
as tool for HEP in general
– little or no documentation
Future will need to include GEANT4
9 Feb 2000 CHEP 2000Padova, Italy
R.Dubois
Lessons Learned• e+e- detectors look pretty
similar (except RICH!)– not hard to define user
interface (ascii file) to describe important features
– specialty items can be added as designs start to focus on details
– XML does the job nicely
• Flexible I/O needed– must be easy to read from
different analysis interfaces (eg C++, Java)
– ascii is bad for numeric precision
– ended up with xdr-based binary I/O
• Provide Full MC parentage for understanding algorithms
• Gismo sufficed for startup of project prior to G4, but should switch
• Hard to fully support more than one framework
– tried to support JAS and Root
– could not share code between them
– had to write everything twice
– was divisive
– should have (and will) support one fully and the other only as able to take output from the other.