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Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 1/25
Data Challenge IIData Challenge IIKickoff WorkshopKickoff Workshop
Simulation and Reconstruction
Overview
Tracy Usher
(representing a lot of people – mis-statements are mine, credit is all theirs…)
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 2/25
Goals of this TalkGoals of this Talk
• Overview of Simulation/Reconstruction: – Introduce the simulation and reconstruction to those unfamiliar
with it
• Highlight changes/improvements since DC-1– Attempting to focus on those simulation and reconstruction
features which are new for DC-2 • Though most recent changes are foremost in memory…
• Provide background for next talk:– Hopefully, this serves as a useful introduction to Bill Atwood’s
talk which will describe the performance of the reconstruction, again highlighting what is new from DC-1
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 3/25
OutlineOutline
• Framework– Gaudi environment
• Simulation– Overview of the flow of
simulation
– A look at the LAT Geometry as used in simulation and reconstruction
– Simulating events with Geant4
– Digitization
• Reconstruction– Overview and flow of the
reconstruction
– Calorimeter Reconstruction• Clustering/Moments Analysis• Energy correction methods• MIP Finder
– Tracker Reconstruction• The basic steps
– ACD Recon
– “Analysis” and Output
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 4/25
Sim/Recon Framework: GaudiSim/Recon Framework: Gaudi
• Gaudi– An experiment independent framework providing the necessary interfaces and
services for HEP event data processing applications– Used by several LHC experiments
• Sim/Recon interacts with Gaudi through:– Gaudi Algorithms
• Algorithms define the reconstruction tasks and control the sequence in which they are performed
– Gaudi Services• Provide “global” information across events (e.g. geometry)
– Gaudi Tools• Implementation of specific reconstruction tasks• Interact with Algorithms through abstract interfaces to allow interchangeability
– Gaudi Transient Data Store (TDS)• Globally accessible repository containing the results of each reconstruction
task• Provides communication between the stages of reconstruction
• Gaudi allows us to configure event processing “on the fly” – Job Options files define event processing and Input/Output for a given job
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 5/25
Simulation OverviewSimulation Overview
• Goal of simulation is to produce “raw data”, representing the response of the LAT to a given event, which can be fed to the reconstruction
• Logically breaks into four steps:– Event generation – “source particle”
– Simulation of LAT response to the generated event
– Digitization: the conversion of simulated LAT response to “raw data”
– Simulation of Trigger
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 6/25
Flow of SimulationFlow of SimulationGaudi Algorithm Sructure for DC-2Gaudi Algorithm Sructure for DC-2
New Event
EventGenerator(FluxAlg)
(PointingAlg)
Event Simulation(G4Generator)
Output Datato TDS
(or PDS)
LAT Geometry(G4GeometrySv
c)(also accessed by
the reconstruction)
Sources, Orbit Orientation, Etc.
(Many improvements and additions from DC1 - See Toby’s
Talk later)
Digitization(ACDDigiAlg)(CalDigiAlg)(TkrDigiAlg)
Trigger / Filter(TriggerAlg)
(OnboardFilter)
Geant4Event/Detector
Simulation
Convert simulated detector response
to “raw data”(calibration effects
enter here)
Output of digis given to Trigger
and Onboard FilterEvents MUST pass
Trigger in order to get reconstructed
Onboard Filter results recorded, events not
rejected
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 7/25
LAT GeometryLAT GeometrySimulation and ReconstructionSimulation and Reconstruction
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 8/25
LAT GeometryLAT GeometrySimulation and ReconstructionSimulation and Reconstruction
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 9/25
LAT GeometryLAT GeometrySimulation and ReconstructionSimulation and Reconstruction
• Main Point:– Most detailed LAT geometry to date including all features which
would significantly impact DC-2 results• From active devices • To surrounding support structures• Including electronics, wrapping, …• etc.
• Large number of updates to geometry since DC-1– Primarily CAL and ACD– For complete list see the xmlGeoDbs change log at:
http://www-glast.stanford.edu/cgi-bin/viewcvs/xmlGeoDbs/ChangeLog?rev=1.413&view=markup
• Still working on improvements for DC-3:– e.g. Curved ACD tiles
• One other important point:– The reconstruction, through the propagator, uses the same
geometry as the simulation
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 10/25
Overview of Geant4 SimulationOverview of Geant4 Simulation
• Geant4 determines the evolution of the event
– G4 given “source” which is propagated through the LAT
– G4 output to TDS:• McParticles – particles produced during
trackinig• McPositionHits – positions and energy
deposited in Silicon and ACD• McIntegratingHits – energy deposited in
“sub-cubes” of CsI crystals
• Passed on to Digitization stage
• For DC-2 we are using G4 v6.2.2– “Vanilla” G4 for everything…– However, we continue to experience
“problems” with the multiple scattering• Native G4 v6.2.2 Multiple Scattering
“too small” • Continue to use formalism circa G4 v3
– Have recently upgraded to G4 v7 where this problem is claimed to be fixed (finally)…
Incident Gamma
Conversion Point
Incident Gamma
Conversion Point
Propagation of primarye+ and e- through LAT
McPositionHits in Active Silicon
of Tracker
Incident Gamma
Conversion Point
Propagation of primarye+ and e- through LAT
McPositionHits in Active Silicon
of Tracker
Production and Trackingof Secondaries
McIntegratngHitsproduced in the
Calorimeter Crystals
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 11/25
DigitizationDigitization
• Digitization: Convert Monte Carlo information to detector response– Simulates the response of the detector to the simulated event
• TKR– Input: McPositionHits – position/energy in active silicon– Output: hit strips and ToT (Time over Threshold)– New for DC-2:
• Implementation of “bad” (hot/dead) strips• Implementation of cable controller buffer limit
– Truncation of data in “big” events (64 strips/plane end, 128 strips/cable)• Improved ToT response
• CAL– Input: McIntegratingHits – Energy deposited in cubes subdividing the Calorimeter
crystals– Output: ADC counts for both diodes at both ends– New for DC-2 (but mostly in well over 1 year ago, past time horizon…):
• New code throughout– Improved/updated xTal response– Calibrations (DC-2 uses “ideal” though)
• ACD– Input: McPositionHits – position/energy in ACD Tiles/ribbons– Output: PMT ADC counts per end
• Many updates / improvements from DC-1
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 12/25
Reconstruction OverviewReconstruction Overview
• Goal of the reconstruction:– Determine the incident gamma direction and energy– Provide tools for suppressing background
• Follow a two pass approach for Cal and Tracker– Best energy from Calorimeter needs tracking information– Best tracks from Tracker needs best energy reconstruction– Solve by breaking into two passes
• Background suppression– ACD Recon– MIP Finder
• Analysis step at end of reconstruction– Create output ntuple for detailed performance studies– Event Classification– Create FT1 output for analysis
• NOTE:– Will not discuss Calibrations
• Critical piece of “real” reconstruction• But (mostly) not using calibrations for DC2
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 13/25
Flow of ReconstructionFlow of ReconstructionGaudi Algorithm Sructure: Envisioned for DC-2Gaudi Algorithm Sructure: Envisioned for DC-2
“Raw data” from
TDS
CalReconPass I
TkrReconPass I
CalReconPass II
TkrReconPass II
AcdReconEvent
“Analysis”
Root tree/ntupleoutput to PDS
CalXtalRecAlg
CalClusterAlg
CalMipFinderAlg
CalEventEnergyAlg(parametric only)
TkrClusterAlg
TkrFilterAlg(inactive for DC2)
TkrFindAlg
TkrTrackFitAlg
TkrVertexAlg
CalEventEnergyAlg
TkrTrackFitAlg
TkrVertexAlg
AcdReconAlg
meritAlg(output ntuple)
Key
Existing Algorithms
New Algorithms
Not “Recon”
ClassifyAlg(Classification
Analysis)
FT1Alg(FT1 tuple)
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 14/25
Calorimeter ReconCalorimeter Recon
• CalRecon extensively restructured for DC-2 – Break into logical pieces– Follow TkrRecon organization paradigm
• Consists of a number of tasks handled by Gaudi Algorithms:– CalXtalRecAlg (Recon First Pass Only)
• Takes in raw data (CalDigis – diode readouts) and produces calibrated output data (CalXtalRecData – energy, position) for input to rest of CalRecon.
– CalClusterAlg (Recon First Pass Only)
• Associates CalXtalRecData objects into a “Cal Cluster”• Performs a “Moments Analysis” to determine principal axis,
etc.– CalMipFinderAlg (Recon First Pass Only)
• Search for MIP signature(s) in CalXtalRecData– CalEventEnergyAlg (Recon First and Second Pass)
• Run various energy correction algorithms
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 15/25
Calorimeter ReconCalorimeter ReconClustering and Moments AnalysisClustering and Moments Analysis
CalXtalRecAlg:• Convert diode ADC counts to energy, position in crystals: - Select range/diode - Pedestal subtraction - Correct for Light attenuation - etc.• Use “ideal” response – no calibrations• Much work here – all “new” code from DC-1 (but nearly 2 years ago now!)
1 GeV Gamma
Energy Flow
Monte Carlo Version of event
“McIntegratingHits”
“McPositionHits”
1 GeV Gamma
Energy Flow
CalXtalRecAlg Version of event
“McPositionHits”
“hit” crystals
1 GeV Gamma
Energy Flow
CalXtalRecAlg Version of event
“hit” crystals
Red Box size proportionalto total energy deposited, longitudinal position fromreadout asymmetry at eachend of crystal
1 GeV Gamma
Energy Flow
CalClusterAlg Version of event
Energy centroid foreach layer
Cluster Centroidfrom
Moments Analysis
Cluster Axisfrom
Moments Analysis
CalClusterAlg:•Associate hit crystals to form a single cluster •Determine cluster centroid and axis via a Moments Analysis• Provide “raw” calorimeter energy - simple sum of crystal energies• New “code” from DC-1• New “TDS” output from DC-1• Much work here as well
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 16/25
Calorimeter ReconstructionCalorimeter ReconstructionEnergy Correction AlgorithmsEnergy Correction Algorithms
• The Problem:– Large phase space of Glast
• Energy range from 20 MeV to 300 GeV
• Large FoV: ~2.5 str
– Tracker above
• Up to 1.5 radiation lengths BEFORE the Cal
– Gaps between towers
• Crystals ~187 mm, gaps ~35 mm
– Cal is “only” 8.6 radiation lengths deep
– etc.
• Corrections:– Energy Deposit in the Calorimeter
• e.g. Wallet Card Shower Profile correction– a and b are parameters
» b scales the radiation length» a sets the location of the energy centroid t
– Detector / Geometry (see next slide)
• Huge Amount of Effort in this area– Cannot do justice to this work in these few slides…
)(
1
0 a
ebtbE
dt
dE bta
b
at
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 17/25
2 GeV PhotonCal E = 950 MeV
Conversion
Bottom of Cal
Calorimeter ReconstructionCalorimeter ReconstructionEnergy Correction AlgorithmsEnergy Correction Algorithms
• Correct for:– Leakage out the back
• Cal is 8.6 rl deep
• Correct for:– Leakage out the back
• Cal is 8.6 rl deep
– Gaps between towers
2 GeV photonCal E = 980 GeV
conversion
Bottom of Cal
2 GeV PhotonCal E = 200 MeV
Conversion
Gap between towers
• Correct for:– Leakage out the back
• Cal is 8.6 rl deep
– Gaps between towers
– Edge of Calorimeter
2 GeV PhotonCal E = 200 MeV
Edge of Cal
100 MeV PhotonCal E = 60 MeV
Conversion
Positron stopsin Tracker
Electron rangesin Calorimeter
• Correct for:– Leakage out the back
• Cal is 8.6 rl deep
– Gaps between towers
– Edge of Calorimeter
– Loss in the Tracker
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 18/25
Calorimeter ReconstructionCalorimeter ReconstructionEnergy Correction Algorithms - continuedEnergy Correction Algorithms - continued
• Maximum Likelihood Estimator – Replaces the previous (DC-1) Last Layer Leakage method with Maximum
Likelihood estimator – In addition, method extended to the low energy range to correct energy
taking into account energy lost in tracker• Extends method to provide correction in range from 50 MeV to 300 GeV
– Also, angular acceptance extended from around 30o to 50o
– See Pol D’Avezac’s note: http://polywww.in2p3.fr/glast/CalLikelihood.pdf
• Full Profile Shower Fit– Extension of previous 1D method (not used in DC-1) to a full 3D shower
profile fit– Finds energy correction for events above ~1 GeV – Angular acceptance extended to 90o – See Philippe Bruel’s note: http://polywww.in2p3.fr/~bruel/CalFullProfile.ps
• Parametric Method– Parameterized shower profile model – Provides corrected energy in range 20 MeV to 300 GeV and over the full
field of view– See Bill Atwood’s talk: http://www-glast.slac.stanford.edu/software/AnaGroup/Atwood-EnergyRecon-2May2005.ppt
• The following talk will compare these methods
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 19/25
Calorimeter ReconCalorimeter ReconMIP FinderMIP Finder
• The MIP finder analyzes the calorimeter data looking for a Minimum Ionizing Particle signature
– Goal is to eliminate a large source of charged particle backgrounds which enter from the sides and bottom of the Calorimeter
• The Method in two bullets or less:– Select CalXtalRecData objects in Calorimeter
• Take those crystals with energy deposits consistent with a MIP energy deposit• Look for a straight line trajectory through these crystals• Does Full fit of MIP track – returns a number of powerful background rejection variables
– Can then reject as background those events with clear MIP tracks
• Completely new for DC-2
See: http://www-glast.slac.stanford.edu/software/AnaGroup/Piron_ana2005-08-08.pdf
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 20/25
• Current Status:– Blue Lines - Protons– Red Lines - Gammas– Selection Cuts:
• Bottom right shows efficiency to identify MIPs (or misidentify Gammas)
(Plots from Sylvain Guiriec)
Calorimeter ReconCalorimeter ReconMIP FinderMIP Finder
http://www-glast.slac.stanford.edu/software/DataChallenges/DC2/MarchWorkshop/Presentations/Ana05-08-29-1.ppt
Pre-cuts :
TkrNumTracks > 0&& CalCsIRLn > 4&& CalEnergyRaw > 5&& CalTotalCorr < 3.5&& CalDeadTotRat < 0.15&& CalGapFraction < 0.30&& CalTransRms < 60&& CalLRmsAsym > 0
Cuts :
CalMipErm / CalMipArcLen < 1&& CalMipChi2 < 30&& CalMipEcor between 8 and 25 MeV&& CalMipEcorRms < 5&& dirErr < 0.7
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 21/25
1 GeV Gamma
Conversion point
e+ and e- trajectories
1 GeV Gamma
Conversion point
Pattern Track trajectories
1 GeV Gamma
Conversion point
Fit TrackTrajectories
1 GeV Gamma
Conversion point
Vector resultingfrom vertexing offit track pair for
this event
1 GeV Gamma
Conversion point
Vector resultingfrom vertexing offit track pair for
this event
The Illustrated Tracker ReconstructionThe Illustrated Tracker Reconstruction
Tkr Clustering:Associate adjacent hit strips to form strip clusters (corrected for hot and dead strips)
Pattern Recognition:Associate strips to form candidate tracks (Combinatoric pattern recognition using Kalman Filter to accept/reject candidate hits)
Track Fit:Take candidate tracks and track energy estimate and fit using a Kalman Filter
Vertexing:Combine fit tracks to form common vertex point- If one track, vertex is head of track- If two tracks don’t “combine” well, keep as separate vertices
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 22/25
Tracker ReconstructionTracker Reconstruction
• What is new for DC-2? – Pretty much everything…
• Algorithm Structure remains same– Two pass reconstruction format same as for DC-1
• But… Underlying code extensively reworked– Combo Pat Rec
• Combinatoric loops restructed and optimized to improve performance
• Uses same KF as track fit for hit selection
• Much improved performance
– Track Fit
• New Kalman Filter
• Track fit parameters (energy loss, particle type, etc.) controlled from Job Options file
– Vertexing
• New scheme for deciding whether to pair tracks or not
• Completely new TDS structure
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 23/25
ACD ReconstructionACD Reconstruction
“Active Distance”
outside tile boundary
no tile hit
inside tile
boundary
[cm]
1 GeV Muon
Reconstructed Track
Struck ACD TileProjection of Track back to
nearest ACD Tile
•ACD: Primary Background Suppression Tool
•Project Track to plane of struck tile
•Calculate distance to nearest edge 3D calculation if outside tile 2D calculation if inside tile
•Sign Positive if track projection inside the tile Negative if track projection outside the tile
•Reject if inside the tile
For complete details see Eric Charle’s IA Workshop talk on Monday February 27
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 24/25
Post Reconstruction ProcessingPost Reconstruction ProcessingThe Final StepsThe Final Steps
• meritAlg– Controls the creation of the merit output ntuple
• Used, for example, in various event classification analyses
• ClassifyAlg– Runs the classification analysis:
• Energy Selection• PSF Tail suppression• Background Rejection
– For DC-2 this is the Insightful Miner Analysis provided by Bill Atwood (see next talk)
• Future versions will allow alternate analyses as well (e.g. Toby Burnett’s Random Forests analysis)
• FT1Alg– Produce the Fits Level 1 output
• Will be discussed in more detail later
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 25/25
Main Points for DC-2Main Points for DC-2
• Very Detailed LAT Geometry– Really getting to the very fine details at this point
• Most of what is missing is already in the pipeline for DC-3
• Very Detailed Geant4 simulation– Based on G4 v6.2.2
• Multi-pass Reconstruction Algorithms– New algorithms to improve energy resolution and background
suppression– Many improvements to existing algorithms– Resulting in improved energy and psf resolution and background
rejection
• Enhanced post reconstruction processing– Perform Event Classification as part of reconstruction
Science Analysis Software DC-2 Kickoff Workshop March 1-3, 2005
Tracy Usher 26/25
SummarySummary
• Since DC-1 TkrRecon, CalRecon and AcdRecon have undergone extensive restructuring with many improvements…– Substantial updates to existing code
– Major overhaul of the algorithm output
– Implementation of many new tools along full reconstruction chain
• Resulting in major improvements– Background rejection
– PSF Tail suppression
– Energy Resolution
– Reconstruction efficiency
– Event classification
• See next talk for the results!