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Spectrometer Reconstruction : Pattern recognition and Efficiency

This presentation by Giuseppe Ruggiero discusses the reconstruction efficiency of a spectrometer used in particle physics experiments. Key topics include the layout of the spectrometer using straw chambers, pattern recognition algorithms, and the challenges associated with multi-track events and L-R ambiguity resolution. The talk outlines the importance of achieving high resolution and efficiency in tracking particles, especially in complex environments. The use of Kalman filtering techniques for cluster detection and reconstruction is also explored, offering insights into the instrumentation and data analysis processes at CERN.

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Spectrometer Reconstruction : Pattern recognition and Efficiency

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  1. SpectrometerReconstruction: Pattern recognition and Efficiency Giuseppe Ruggiero CERN StrawChamber WG meeting 07/02/2011 G.Ruggiero - Spectrometer Efficiency

  2. Introduction • SpectrometerLayout (MC) • Reconstruction • L-R ambiguityresolution • Pattern Recognitionalgorithm • Strawtubesperformances vs 1 trackreconstruction • Full set-up • Minimal set-up (2012) • Conclusions G.Ruggiero - Spectrometer Efficiency

  3. Full SpectrometerSimulation • Layout: • 4 Chambers • 4 Views / Chamber (UVXY) • 4 Single tube planes / View • Geometryfrom TD • Chamber and tube positionsfromBeatch file 11/06/2010. • Physical/instrumentaleffect: • drays, effectiveradius, uniforminefficiency, gaussiansmearingof R measurement, phadronicinteractions, p decays. • Reconstructionalgorithmbuiltusingp+p+p-events. • Analysisperformedusing a sample ofpnnevents • Generatedbetween 104000 and 170000 m G.Ruggiero - Spectrometer Efficiency

  4. SpectrometerReconstruction • Requiremets: • High resolution (againstbackgroundsconstrainedbykinematics) also in case ofmulti-trackevents • High efficiency(signalacceptance and rejectionofmulti-track background π+π+π-, Ke4) also in case ofmulti-trackevents • As muchaspossibleindependentfromthe sourcesofinefficiencyof the straws (effectiveradius, smoothinefficiency…) • Whymulti-trackenvironment ? • s(t) straw ≈ 7 ns • Dt ≈ 3s(t) ≈ 20 ns • Rate per chamber ≈ 10 MHz • Prob(> 1 hit/view) ≈ 0.18 ≈ Prob(> 1 track) G.Ruggiero - Spectrometer Efficiency

  5. L – R ambiguityresolution • 4 hit fired: notallowedbygeometry. • 3 hitsfired: 1 tube hit closeto the wire, the other 2 tubes are hit closeto the edges. LR solutionalwayspossible. • 2 hitsfired: bothtubes are hit in the central part. LR solutionalwayspossible. • 1 hit fired: onlycloseto the beamhole and in case ofstraw tube inefficiency. LR solutionneverpossible. • Steps: • Look forcontiguoustubesfired. • Sum or subtract the measured R in one tube to the position of the tube accordingto the pattern ofcontiguoustubes. G.Ruggiero - Spectrometer Efficiency

  6. Hits and Clusters • Definitions • Hit:onestraw tube fired. • Measuredinfos: • 1-D coordinate of the impact pointof the track on the tube (or the position of the tube if the LR ambiguityisnotsolved). • Time (Notused in the present work). • Cluster:groupofHits in oneviewusedto solve their LR ambiguity. • Types:1-Hit, 2-Hits, 3-Hits accordingto the impact pointof the track on the viewplanes. • Measuredinfos (extractedbylinearinterpolationof the hitsforming the cluster): • 1-D coordinate of the impact pointof the trackextrapolated at anaverage Z • Slopeof the track. Eachclusterisdefinedbya coordinate AND by a slope (trackslope) G.Ruggiero - Spectrometer Efficiency

  7. Single hit reconstruction Idealconfiguration Realconfiguration • Effectiveradius 4.7 mm • drayspileupallowed • 3% smoothinefficiency • R smearing (40-200 mm) • phadronicinteractions • pdecays • Effectiveradius 5 mm • No drayspileup • No smoothinefficiency • No R smearing • phadronicinteractions • pdecays G.Ruggiero - Spectrometer Efficiency

  8. Single hit reconstruction (cont’d) Idealconfiguration Realconfiguration 17mm 100 mm G.Ruggiero - Spectrometer Efficiency

  9. 1 hit clustersregions Idealconfiguration Realconfiguration 199 954 5 more G.Ruggiero - Spectrometer Efficiency

  10. Pattern recognitionalgorithm Identificationof the clusters in the differentviews and chambersbelongingto the sametrack • Kalmanfilterapproachstartingto the last chamber and adding the clusters down to the first chamber: • Initializationstepprofitsfrom the a-priori knowledgeof the trackslope. • Complications: at least 2 viewsneededfor the initializationof the X-Y angle of the track.The numberof the viewsfired in onechamberdependson the track impact point on the chambers. • Momentuminitializationpossibleat the levelof the secondchamberonly. • Step 0: all the possible cluster combinations in chambers4 are considered. And eachcombinationispropagated back in chamber 3 down to a viewwith at least 1 cluster. • Step 1: A cluster in thisviewischosenaccordingto the differencebetween the measured position and the position expected on the basisof the estimatedtrackparameters, dividedby the correspondingerrors. • Step 2: a “good” cluster isadded, the trackparametersrecomputed, some modelof MS addedto the correlationmatrixof the trackparameters and trackpropagated back again (step 1). • Processendswhen no more viewswithclusters are found INIT FILTER G.Ruggiero - Spectrometer Efficiency

  11. Pattern recognitionalgorithm • Furthercomplications (short examples): • Onetrackwith a cluster in only 1 view in chamber 4. A notparallaelview in chamber 3 neededfor a suitableinitialization. • No clusters in chamber 4. Clusters in chamber 3 usedforinitialization. • Onetrackwithclusters in chamber 4 and anothertrackwithoutchamber 4… • No cluster in chamber 2, or 1 cluster in chamber 2 in Y direction. A cluster in chamber 1 isneededtoinitialize the trackmomentum. • … • Output: setsofcombinations. • Trackcandidateschosenamong the combinations on the basisof a suitable2. • Addedfeatures: trackcandidates are indetifiedalso in case ofclusters in 3 chambersonly (the case ofanychambermissingisaddressed). • Algorithmtunedusingp+p+p-events. G.Ruggiero - Spectrometer Efficiency

  12. 1-track eventresults • Resultspresentedasa functionof the effectiveradius • RealConfiguration Clusters per trackvs effectiveradius hit per clustersper track vs effectiveradius G.Ruggiero - Spectrometer Efficiency

  13. 1-track eventresults Realconfiguration 2 hits cluster 1 hit cluster 3 hits cluster G.Ruggiero - Spectrometer Efficiency

  14. Spectrometerefficiency (1-track) Total: 95% 4 Chambers 3 Chambers Effectfromp hadronicinteractions and pdecayincluded G.Ruggiero - Spectrometer Efficiency

  15. Efficiency vs P (1-track) Geometricalacceptance (beamhole) Effectiveradiusbetween 5.0 and 4.5 mm: no visibleeffect vs trackmomentum G.Ruggiero - Spectrometer Efficiency

  16. Minimal Spectrometer Layout (2012) • Layout: • 4 Chambers • 2 Views / Chamber : Chamber 12 XY, Chamber 34 UV • 4 Single tube planes / View • Geometryfrom TD • Chamber and tube positionsfromBeatch file 11/06/2010. • Analysisperformedusing a sample ofpnnevents • Generatedbetween 104000 and 170000 m G.Ruggiero - Spectrometer Efficiency

  17. Minimal Spectrometer Layout • Resultsstudiedas a functionof the effectiveradius • RealConfiguration Clusters per trackvs effectiveradius (hit per clusters ) per track vs effectiveradius G.Ruggiero - Spectrometer Efficiency

  18. Minimal Spectrometer Layout Efficiency vs EffectiveRadius Total: 75% 4 Chambers 3 Chambers G.Ruggiero - Spectrometer Efficiency

  19. Minimal Spectrometer Layout Efficiency vs P G.Ruggiero - Spectrometer Efficiency

  20. Conclusions • Timetobuild a “realistic” reconstructionof the Spectrometer • L-R resolutionalgorithmdeveloped: • Independentfrom the geometryof the planes • Provide position and first trackslopeestimation • Pattern recognitionalgorithmstarted: • Useof a KalmanFiltertechnique • Most part ofpossiblecasesaddressed and solved. • Works in multi-trackenvironments (some refinementstillneeded) G.Ruggiero - Spectrometer Efficiency

  21. Conclusions (cont’d) • Strawperformances vs 1 trackevents: • Reconstructionefficiencyalmostnotdependent on the effectiveradius • Reconstructionqualitydoesdepend on the effectiveradius • Spectrometerefficiency(includinggeometry, pinteractions, pdecays, 3% smoothefficiencyof the straws, 4.7 mm effectiveradius): • 95% (90% fortrackswith 4 chambers) full set-up (16 views) • 75% (70% fortrackswith 4 chambers) minimal set-up (8 views). • Reconstructionqualitytobeaddressed. A furtherstep in the reconstructionneededtoreach the highestlevelofresolution (next talk.) G.Ruggiero - Spectrometer Efficiency

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