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L2 B Tagging

L2 B Tagging. Bad news: Pre-STT parameters Generator level L2 trigsim Good news: STT parameters Purity vs. Efficiency Correlation Good news: SVM. MC Data – Generator Level. Pythia b b-bar incl. / QCD incl. 2000 events each 0 min bias p08.10. MC Data – L2 “trigsim”. Pythia, Pt > 20

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L2 B Tagging

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  1. L2 B Tagging • Bad news: Pre-STT parameters • Generator level • L2 trigsim • Good news: STT parameters • Purity vs. Efficiency • Correlation • Good news: SVM B ID meeting

  2. MC Data – Generator Level • Pythia • b b-bar incl. / QCD incl. • 2000 events each • 0 min bias • p08.10 B ID meeting

  3. MC Data – L2 “trigsim” • Pythia, Pt > 20 • b b-bar incl. / QCD incl. • 3260 events / 5000 events • 0 min bias / 0.5 min bias • mixture • p10.06.01 • Data dumped by filter as l2 analyze packages broken B ID meeting

  4. Pre-STT parameters • Generator level B ID meeting

  5. Pre-STT parameters • L2 “trigsim” data B ID meeting

  6. Pre-STT Parameters • Not feasible. • Main problems: • small number of tracks / jet • binning of tracks’ phi (160 segments) • Jet’s eta binned into 0.05 eta segments, only Jet Et known, large error on Jet E for high eta jets • Only way out: STT • DCA parameters have much higher suppression power (about 1 OoM) B ID meeting

  7. STT Parameters • Decay length • Axial tracks (within 1.6 cone) projected onto jet theta • Sum over all distances primary vertex - track / jet intersection Purity Efficiency B ID meeting

  8. STT Parameters • Ratio of tracks with high decay length • Number of tracks within 1.6 cone and LD > 10mu (OoM of STT resolution) divided by number of tracks within 1.6 cone B ID meeting

  9. STT Parameters • Decay Length Area: • Areas of the triangle spanned by • Primary vertex • PCA • Intersection of track and jet • Summed over all tracks with positive DL and relative angle < 1.6 Jet DLA Track Primary Vtx B ID meeting

  10. STT Parameters • Decay Length Area: • Track with spatial error + small relative angle can result in huge DL, but small DLA • Track with spacial error + high relative angle results in precise DL, big DLA • Relatively independent of jet axis errors • Phi: no error if as many tracks “left” of jet as “right” • Eta: Projected • Track’s DCA and phi resolution well known, and so is DLA’s. B ID meeting

  11. STT Parameters • Decay Length Area B ID meeting

  12. STT Parameters • Correlations x: DLA y: DLA x: DL y: DLR x: DLA y: DLR B ID meeting

  13. SVM • SVM output for MC Generator pre-STT parameters • 3400 jets in training sample (approx 50% QCD) • 1000 jets in test sample (50% QCD) • Non-standard implementation of SVM: Improvement by using gaussian kernel with parameter dependant width B ID meeting

  14. SVM • SVM output for MC Generator pre-STT parameters B ID meeting

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