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Impact Parameter Tag

Jet direction. Track direction. Decay length. vertex. dca. Impact Parameter Tag. Use b-hadron long lifetime without reconstructing secondary vertex (to gain efficiency) Consider compatability of “collection of tracks” (jet) with primary vertex Use decay length significance of tracks:.

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Impact Parameter Tag

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  1. Jet direction Track direction Decay length vertex dca Impact Parameter Tag • Use b-hadron long lifetime without reconstructing secondary vertex (to gain efficiency) • Consider compatability of “collection of tracks” (jet) with primary vertex • Use decay length significance of tracks: 1

  2. Steps to tag • Reconstruct jets, tracks, primary vertices • Select best primary vertex for each jet • Select tracks: • (Quality of track fit) • Number of track hits (total / SMT) • Track pT • |2D Impact Parameter| • (V0 Rejection) • (Study further cuts) • Calculate PV probability for each track, based on decay length significance distribution • Combine tracks in jet to form discriminant 2

  3. Jet discriminant • Simplest approach: tag jet with a minimum number of tracks that have significance exceeding a certain value • Simple product of probabilities: • D = -ln,  = (Pi) • …will yield larger values as #tracks increases • Default, independent of #tracks: • D = -lnP, 3

  4. Samples / definitions • 500 z->bb and 500 z->ud samples • Efficiency: (tagged b-jets) / (selected b-jets) Selected jets are jets with |eta| < some cut (1.5) and Ntracks > some cut (2); Need to study this selection in more detail! (“Tagable” jets?) • Rejection: 1- (tagged light) / (selected light jets) 4

  5. Jet eta 5

  6. Track pT cut 6

  7. Track dca and nHits cuts 7

  8. Track significance L/dL (red: tracks with MCL > 0; black: tracks with MCL = 0) |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 8

  9. MC decL - Reco’d decL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 9

  10. (MCL-RecoL)/dL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 10

  11. Status • Not yet fully developed (hence many RCP parameters…) • Need to study performance for various jet properties (E, pT, eta) • Investigate proper resolution functions (standard Gaussian currently used to calculate track PV probability) • Study impact of 3D decay length (need estimates on jet and track direction uncertanties) • Further study of track cuts 11

  12. <dump pics> 12

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