r.dubois 9 feb 2000chep 2000 padova, italy north american linear collider detector simulations full...

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


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

Parameter Files (JAS)Geometry Description FilesParameter Files (Root)

fastMC (Root)

ASCII recon

Root files

.lcd files

Root Analysis

JAS parser Root parser

Generator(s)


R.DuboisGismo: Full Simulation• Reasonably full-featured full

simulation package - C++– complex geometries– EGS & GHEISHA

• cutoffs set at 1 MeV

– multiple scattering, dE/dx, etc

• Generator input from /HEPEVT/ via FNAL STDHEP I/O package

• Digitization supplied by ‘user’– tracking

• hit points at tracking/VXD layers

– calorimeters• total energy per channel

– muon strips– all digi’s have full MC record

• Output to ascii file (current)– allows parsers to translate to

JAS & Root for further analysis/processing

e+e- -~~


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Sample 5 GeV +


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Full Sim: Geometry Elements

• Most detector types are cylinders

– input by ascii detector file

– trackers and calorimeters can have inner/outer skins and endplates

– tracker/VXD layers can be individually positioned and sized

– user sets longitudinal cell composition (multi-materials allowed) and ‘sensitivity’ for calorimeters

– special shapes added in with parameters to describe their variations• conical masks configurable

• compound beampipe


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Two Detector Designs

• Large (v. L1, L2)– large!

– Large tracker• optimal tracking resolution

– Large calorimeter• optimal separation of clusters

– size limits B field• may limit vertex detector inner

radius due to e+e- pairs

• Small (v. S1, S2)– small!

– Small detector• larger B field possible

– Small calorimeter• allows high granularity (Si/W)

– Small tracker• Si strips/drift

– large B field• better containment of pairs,

closer-in vertex detector


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B=3TB=6T

Pixel VXDPixel VXD144 lyr TPC144 lyr TPC

CoilCoil

Fe Muon SysFe Muon Sys

Pb-scint EM+HAD calPb-scint EM+HAD cal

CoilCoil

Pixel VXDPixel VXD6-lyr Si drift6-lyr Si drift

W-Si EM calW-Si EM cal

Fe Muon SysFe Muon Sys

Cu-scint HAD calCu-scint HAD cal


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Small Detector: Central Detector

3 Tracker Doublets1.1 mm G10, 600 m Sir = 14, 42, 71 cm

5 EC Tracker disksz = 31, 61, 91, 121, 149 cminner r follows cos=0.99

Luminosity monitor (Si/W)active from 30-116 mrad


R.DuboisBarrel/Endcap Region

Small

• <E> 15% lower than barrel• /<E> 15% higher

B/EC

Barrel

(note different scales on plots)


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Small

Si Tracker hits

EM Cale+e- ZZ


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Large

TPC hits EM Cal

e+e- ZZ


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What You Get from FullSim

• Tracking– hit ID

– (x,y,z) of trajectory crossing layer

– layer E

– ptr to MC parent

– hit smearing held off until recon

• Calorimeters– hit ID (contains location)

– total energy deposited

– list of (MC parents, E)

• MU Strips– hit ID (contains location)

– list of MC parents

• Full MC Truth Table– (x,y,z) at termination point

– initial (px, py, pz)

– type & charge

– pointer to parent

– position & momentum at Cal front face


R.DuboisLCD Event Class Structure

Event

TObjArray

EM CALValue: CalHit

HAD CALValue: CalHit

MU CALValue: CalHit

LUM CALValue: CalHit

MU StripsValue: stripHit

MC ParticlesValue: McPart

CAL ClustersValue: Cluster

Value: McPart

TrackValue: Tracks

Tracker HitsValue: Tracker_Hits

VXD HitsValue: VXD_Hits

EDeposit

Key: McPartValue: Energy

LUM ClustersValue: Cluster

Note: all hits, tracks & clusters have pointers back to parent MC. Clusters have pointers to constituent hits.


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MC Farms & Platforms• MC Farms

– SLAC, Michigan, Colorado, Penn

– Code installed but yet to run production at Vanderbilt (DEC) & FNAL (Linux)

• data repository at Penn

• ‘push’ scripts for file transfer from farms

• server access via JAS

• ftp access for Root

• Timing– ~2 mins/event for udscb 500

GeV on 400 MHz Solaris

• Platforms

– AIX

– Solaris

– DEC Unix

– Linux• call stack corruption: compiler

bug

• cannot optimize code

– Windows


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• The Objective– Provide an alternative to ASCII

files which are by nature• Information lossy • Non dense

– Enforce data versioning

– Easily readable from C++ and Java

• Not Part Of The Objective– A full object oriented

serialization engine (a la Root or Objectivity)

Serial Input Output (SIO)

• Provides– Architecture independent binary format

(uses the xdr standard)

– High integrity, self checking data layout

– Multiple simultaneously open input and output streams

– Heterogeneous record types on each stream

– Pointer relocation (at record level)

– Data compression/decompression (per record).

• Does not provide– Abstract data descriptions

– Pointer chasing

T.Waite

Input: Why Use XML?

• For 1st pass LCD used ad hoc file format, one-of-a-kind code for serial-only parsing of detector geom.

• XML is a standard meta-language for defining markup languages. Good free parsers exist, more tools coming.

• XML languages are plain-text, self-documenting.

• Appl. interface to data (XML document) may be serial or random-access.

• Avoid growing private file formats or, worse, hard-coding parameters.

• Make it easy (well, easier) for several programs to use same input.

J.Bogart

Detector Description in XML

<lcdparm> <global file=“largeParms2.xml” /> <physical_detector topology=“large” id = “L2” > <volume id=“EM_BARREL” > <tube> <barrel_dimensions inner_r = “196.0” outer_z = “322.0” /> <layering n=“40”> <slice material = “Pb” width = “0.4” /> <slice material = “Tyvek” width = “0.05” /> <slice material = “Polystyrene” width = “0.1” sensitive = “yes” /> </layering>

<segmentation cos_theta = “300” phi = “300” /> </tube> <calorimeter type = “em” /> </volume> ...

Start subdetector description

Geometry,materials

function

End subdectectordescription

J.Bogart

So far...

• 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


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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


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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


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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.

r.dubois 9 feb 2000chep 2000 padova, italy north american linear collider detector simulations full...

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