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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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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
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
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
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
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
Jet eta 6
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
MC decL - Reco’d decL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 10
(MCL-RecoL)/dL |pT| < 1 Gev 1<|pT|<2 GeV |pT| > 5 GeV 2<|pT|<5 GeV 11
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
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