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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: • 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. Track selection cuts • pT > 1.5 GeV • DCA < 2cm (transverse and z) • # SMT hits  2, total # hits  4 •  Track – Jet angle •  Track quality •  V0 rejection 4

  5. Performance • 1000 z->bb and 1000 z->ud samples • ~5% fake rate at 50% efficiency for jets within • -2 <  < 2,  3 tracks • Major improvement for vertical review mostly due to bug fix (sign error in decay length for some tracks) • Study track cuts, decay length error, 3D implementation for further improvement 5

  6. Jet eta 6

  7. Track pT cut 7

  8. Track dca and nHits cuts 8

  9. 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 9

  10. MC decL - Reco’d decL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 10

  11. (MCL-RecoL)/dL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 11

  12. Status • Sign bug fixed just before vertical review • More performance improvement expected from • Better handle on error in jet / track angles • Implementation of (pseudo-) 3D decay length • Further study of track cuts (V0 rejection, 2?, track direction) • Other projects: • Jet acceptance • Profiling of algorithm • Higher statistics / certification sample studies 12

  13. <dump pics> 13

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