impact parameter tag
DESCRIPTION
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:. - PowerPoint PPT PresentationTRANSCRIPT
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 1
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:
vertex
Jet direction
Track direction
dca
Decay length
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 2
Steps to tag
1. Reconstruct jets, tracks, primary vertices2. Select best primary vertex for each jet3. Select tracks:4. Calculate PV probability for each track,
based on decay length significance distribution
5. Combine tracks in jet to form discriminant
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 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,
in
1i
1n
0i
i
PΠΠ
!i/ΠlnΠPtracks
tracks
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 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
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 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
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 6
Jet eta
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 7
Track pT cut
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 8
Track dca and nHits cuts
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 9
Track significance
L/dL (red: tracks with MCL > 0;black: tracks with MCL = 0)
|pT| < 1 Gev 1<|pT|<2 GeV
2<|pT|<5 GeV |pT| > 5 GeV
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 10
MC decL - Reco’d decL
|pT| < 1 Gev 1<|pT|<2 GeV
2<|pT|<5 GeV |pT| > 5 GeV
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 11
(MCL-RecoL)/dL
|pT| < 1 Gev 1<|pT|<2 GeV
2<|pT|<5 GeV |pT| > 5 GeV
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 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
April 2001 Collaboration Meeting, 04-25-2001, Frank Filthaut & Bram Wijngaarden 13
<dump pics>