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Soft Lepton Tagging for B-meson Decays: Preliminary Results and Methodology

This presentation discusses a study on soft lepton tagging, specifically focused on identifying soft leptons from semi-leptonic B-meson decays. The study reports preliminary findings from ORCA reconstruction, with the efficiency of soft lepton tagging constrained by the fraction of B-meson decays that yield leptons, approximately 20%. We explore various test samples, Monte Carlo truth associations, and improved methodologies for jet flavor identification. Results indicate good performance in reconstructing muons and highlights issues with background separation in sample datasets.

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Soft Lepton Tagging for B-meson Decays: Preliminary Results and Methodology

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  1. Catania Lepton Tag Andrea Bocci Vitaliano Ciulli Riccardo Ranieri INFN and Università di Firenze Alessia Tricomi INFN and Università di Catania CMS CPT Week - b Meeting 3rd November 2004

  2. Soft Lepton Tag • Based on identification of the soft leptons from semileptonic B-meson decays • we studied only leptons=muons case • Efficiency of soft lepton tagging limited by the fraction of B-meson decays containing leptons (20%) • Provide a valuable complement with respect to the impact parameter tagging • Some very very preliminary results with ORCA reconstruction already presented at bτ meeting during July Tracker Week • http://agenda.cern.ch/askArchive.php?base=agenda&categ=a042955&id=a042955s1t7%2Fmoreinfo%2FCataniaLeptonTag.ppt Catania Lepton Tag II

  3. The test samples • QCD jets from Christian’s test samples • 2500 “b”, 4750 “c”, 5000 “udsg” • 80<pT[GeV/c]<120 • no pileup • some problems related to the samples: • Not well defined separation between signal and background • “udsg” means no requests: this sample contains also c or b jets depending on c/b quark production probability • “c”(“b”) means at least one c(b) quark in the final state: this sample is pure QCD enriched in c(b) quark content • Variable number of jets • we have not under control the number and flavour of jets we expect to see • problems in debugging algorithms • if jets are separated in ET bins too few jets per bin ^ Catania Lepton Tag II

  4. Monte Carlo Truth • Muons • information on the origin of the muon (i.e. “mother” particle of the generated muon) • information on the origin of the decay chain (i.e. the particle which originates the decay chain) • to separate b→μ and c→μ from b→c→μ • Jets • we used Christian’s BReco/BTagMCTools package • associates to the reconstructed jet the main parton within ΔR(η,φ)<0.3 and assigns jet flavour • some modifications inside JetIdentifier and MCParton/LundCode classes Catania Lepton Tag II

  5. Modified BTagMCTools • JetIdentifier.h • added methods to return not only the HepLorentzVector (Energy-Momentum) of the three partons, but also the partons themselves to access all the MCParton’s methods too MCParton mainParton (){return m_MainParton;} MCParton heaviestParton (){return m_HeaviestParton;} MCParton closestParton (){return m_ClosestParton;} Catania Lepton Tag II

  6. Modified BTagMCTools • JetIdentifier.cc • inside the loop to assign the most suitable MCParton to the jet, partons with PYTHIA status = 3 are excluded • example: Gluon Fusion gg→bb event: - E X C L U D E D Catania Lepton Tag II

  7. Modified BTagMCTools • MCParton • mother and grandmother HEP-PID and top quark decay int getMotherLundCode() const{returnmotherLundCode;} int getGrandMotherLundCode()const{returngrandmotherLundCode;} bool getIsFromT()const{return isFromT;} • Gluon Splitting Finder • loop on PYTHIA lines to find qq pairs from gluon common mother • at least a gluon in PYTHIA event (lines 3 or 4 or 5 or 6 or 7 or 8) • search for parton-antiparton with PYTHIA status≠3 “daughters” of the previous gluon • both q and q are labelled as coming “fromGluonSplitting” • too much PYTHIA-dependent • already passed to Pisa people… waiting for feedback… - - Catania Lepton Tag II

  8. Reconstruction • Studies done with ORCA_8_2_0 • Reconstruction of RecMuon objects • L3 Muon Reconstructor • RecQuery query ("L3MuonReconstructor"); • no further thresholds applied • Reconstruction of JetWithTracks objects • L2 Kt jet algorithm • RecQuery jetFinder ("PersistentJetFinder"); • jetFinder.setParameter ("JetAlgorithm", 4); // Kt=4 • Tracks in cone ∆R<0.3 around jet axis • RecQuery query ("BTagJetWithTracksAlgo"); • query.setComponent ("JetFinder", jetFinder); • query.setComponent ("TrackFinder", RecQuery(“CombinatorialTrackFinder”)); • query.setParameter ("deltaRCut", 0.3); Catania Lepton Tag II

  9. Reconstructed Muons Entries/bin • Association between RecMuon’s and TkSimTrack’s • 93% of the times we are able to say what is the simulated particle reconstructed as a muon Catania Lepton Tag II

  10. Reconstructed Muons Entries/bin • We can study the “life” of the RecMuon associated to a SimTrack • PYHTIA list navigation, decay chains… • for the moment we are not able to reconstruct the story of PYTHIA “stable particles” (GEANT decays) here there are both b→c→μ and c→μ Catania Lepton Tag II

  11. L2 Jets corrected ET Entries/bin • Reconstructed L2 Jets with ET>40 GeV • jet flavour from MC association • more than 80% of b/c jets are selected • jet η and φ recalculated with tracks • improved resolution from 0.05 to 0.03 Catania Lepton Tag II

  12. Gluon Splitting • Fraction of jets coming from Gluon Splitting (GS) • sample: selected L2 jets ET>40 GeV • 50% of b/c jets come from GS Catania Lepton Tag II

  13. Number of L2 Jets • 4 bins in jet ET • light-flavoured jets have lower ET than b/c Low Statistics Catania Lepton Tag II

  14. L3 Muons inside L2 Jets • A L3 Muon is associated to the L3 jet if ΔR(η,φ)<0.5 • 691/924=75% of L3 Muons are inside L2 Jets • Fraction of 40<ET[GeV]<120 jets with muons: • b 12.9%c 6.2% • uds 0.88%g 1.2% Statistical Error: ±0.01 Low Statistics Catania Lepton Tag II

  15. Where are generated b muons? • 494 MC generated b Muons are inside L2 Jets [ET>40 GeV] • Fraction of 40<ET[GeV]<120 jets with generated muons (pT>0.5 GeV/c, |η|<2.5) coming from b mesons/baryons decay: • b 18.6%c <0.1% • uds 0.26%g 0.2% Statistical Error: ±0.01 Low Statistics Catania Lepton Tag II

  16. Conclusions • We have a lot of work to do and problems to solve • A simpler di-jet event sample (DAQ-TDR like) would help to debug our code Catania Lepton Tag II

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