Spectrometer Reconstruction : Pattern recognition and Efficiency

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