Iterative Tracking in LCSim

July 20, 2010

Christian GrefeCERN, Bonn University

Page 2Christian Grefe – July 15, 2010

Motivation

• Currently tracking in LCSim is steered by a list of strategies

• Each strategy defines the roles of each layer• 3 seed layers + 1 confirm layers + several extension layers (usually all other)• χ2 cut for the helix fit

• A strategy list should cover the minimum number of layer combinations needed to find all tracks (above certain pt and minimum nHits req)• This is automatically done using a training sample• Weighting layers is possible to favor certain strategies (i.e. inside-out)

• All Strategies are equal• All are tried and a list of candidates is formed• If candidates share hits the “best” is chosen (based on χ2 of fit)

Page 3Christian Grefe – July 15, 2010

Motivation (cont.)

• Iteration allows another level of steering• Each strategy list is used to form tracks and all used hits are removed• Following strategy lists suffer from less confusion

• Possible scenario to increase performance• Start with well defined tracks (many hits, moderate χ2-cut)• Find low pt tracks (less hits, tighter χ2-cut)

Page 4Christian Grefe – July 15, 2010

Status

• Implemented IterativeSeedTracker as derived class from SeedTracker• Small changes to HitManager (does not break SeedTracker)• No other changes needed• Compatible with existing SeedTrackerDiagnostics drivers

• First tests done

Page 5Christian Grefe – July 15, 2010

XML Steering Example

<lcsim xmlns:lcsim="http://www.lcsim.org/schemas/lcsim/1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema-instance" xs:noNamespaceSchemaLocation="http://www.lcsim.org/schemas/lcsim/1.0/lcsim.xsd"> <inputFiles> <file>/afs/cern.ch/eng/clic/work/events/clic01_sid/uds91_09_.slcio</file> </inputFiles> <control> <numberOfEvents>-1</numberOfEvents> <verbose>false</verbose> <printDriverStatistics>true</printDriverStatistics> <printDriversDetailed>true</printDriversDetailed> </control> <execute> <driver name="hitMaker" /> <driver name="iterativeSeedTracker" /></execute> <driver name="hitMaker" type="org.lcsim.recon.tracking.seedtracker.steeringwrappers.SiD02HybridHitMakerNoCCD" > </driver> <driver name="iterativeSeedTracker" type="org.lcsim.recon.tracking.seedtracker.IterativeSeedTracker" > <inputCollection type="String">HelicalTrackHits</inputCollection> <trkCollectionName type=“String”>Tracks</trkCollectionName> <strategyFile type="String">StrategyList1.xml</strategyFile> <strategyFile type="String">StrategyList2.xml</strategyFile> <timingPlots type="boolean">true</timingPlots> </driver></drivers></lcsim>

• Usage almost identical to SeedTracker

digitization driver

Use as many as you want,order is important!

Page 6Christian Grefe – July 15, 2010

First Tests

• 1000 uds @ 3 TeV, first use 7Hit strategies and 6Hit strategies later

• The 6 hit strategy picks up some extra tracks

Page 7Christian Grefe – July 15, 2010

First Tests (cont.)

• No notable impact on track reconstruction time

Page 8Christian Grefe – July 15, 2010

Outlook

• Extend StrategyBuilder to allow for “iterative training”• Give several prototype strategies with individual definition of findability (nHits,

pT, d0, z0, χ2-cut)• Train strategy lists successively• Remove tracks that are findable by this strategy list before training the next• (This is only iterative training on different phase spaces, can not simulate gain

by removing confusion because it is on MC level)

• Extensive testing!• Impact on tracking efficiency / purity