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L’étiquetage des jets b dans ATLAS

L’étiquetage des jets b dans ATLAS. Introduction Performances Préparation aux premières données. Laurent Vacavant / CPPM Marseille,. Atelier Physique Atlas France 2007 – Seignosse - 11/09/2007. Motivation. b-tagging crucial to extract signal from backgrounds in a large

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L’étiquetage des jets b dans ATLAS

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  1. L’étiquetage des jets bdans ATLAS Introduction Performances Préparation aux premières données Laurent Vacavant / CPPM Marseille, Atelier Physique Atlas France 2007 – Seignosse - 11/09/2007

  2. Motivation b-tagging crucial to extract signal from backgrounds in a large variety of channels of interest at LHC: • top physics (pair or single top) • Higgs physics (Hbb) for discovery and/or property measurements • SUSY (hbb, bbH/A) • Exotics (little Higgs, hidden valley models,….) • unexpected… Requirements vary from channel to channel: • ttbar: emphasis on background rejection for clean measurements, efficiency not a problem (prochaines présentations) • ttH(bb): large background as well, requires 4 btags, high efficiency given low signal Xsection (session Higgs demain) Atelier Physique Atlas France 2007 - Seignosse

  3. Soft lepton Jet axis a0>0 a0<0 B Primary vertex Secondary Vertex y x B-tagging basics Lifetime of B hadrons: c ~ 470 m (mixture B+/B0/Bs), ~ 390 m (b) for E(B) ~ 50 GeV, flight length ~ 5 mm, d0 ~ 500 m •  Spatial tagging: • Signed impact parameter • of tracks (or significance) • Secondary vertex • (see note ATL-PHYS-2004-06: • S.Corréard, V.Kostioukhine, • J. Lévêque, A. Rozanov, • J.B. de Vivie) •  Soft-lepton tagging: • Low pT electron from B (D) • Low pT muon from B (D) Atelier Physique Atlas France 2007 - Seignosse

  4. 1-2 GeV/c 2-5 GeV/c 5-10 GeV/c >50 GeV/c Key ingredients CSC-01-00-00 • tracking • newTracking/ iPatRec algo. • impact parameter resolution • σ(d0) ~ 10 (+) 150/pT√sinθm • tracking in (dense) jets • specific quality requirements • esp. N(B-layer) > 0 • ~ - 3% absolute eff. • partionning track coll. • primary vertex • mostly needed along Z • @ high-luminosity • lepton ID (soft leptons) • jets (axis) DC3-02 Atelier Physique Atlas France 2007 - Seignosse

  5. Likelihood Ratio & IP2D Tagger • Smoothed & normalized distributions of significances for the two • b | u hypotheses: b(S), u(S) • For each track: ratio b(S)/u(S) • Advantages: • more powerful • allows to combine non-correlated • variables just by adding the weights • Drawbacks: • requires p.d.f. for b and u • hypotheses: may be difficult to • measure in data Atelier Physique Atlas France 2007 - Seignosse

  6. Secondary Vertex Search • Track selection • Search for all 2-track vertices in the jet (VKalVrt) • Remove V0s, identified interaction with material,… • Common (inclusive) vertex for remaining tracks (NB: reconstruction of all vertices also being studied) beam-pipe, pixel layers  conv. Ks Λ Atelier Physique Atlas France 2007 - Seignosse

  7. Secondary Vertex (SV) Tagger • Variables used: low correlation with IP (Lxy not used) • Use multiD distributions  correlations light jets light jets SVX mass b-jets b-jets E(SVX)/E(jet) M=SVX mass F=E(SVX)/E(jet) N=# 2-track v. Combined with IP: Atelier Physique Atlas France 2007 - Seignosse

  8. List of Main Taggers Atelier Physique Atlas France 2007 - Seignosse

  9. Performances

  10. G.Aad, JB de Vivie Generic performances with release 12 • CSC samples • CSC-01-02-00 geo. • NewTracking • old (CSC11) calib. • noise, 3% pixel ineff. • no pile-up • cone 0.4 jets • standard purification (b) = 60% • careful w/ (pT,η) shape (right plot) • ttbar events: R ~ 200 for (b) = 60% R ~ 800 for (b) = 50% •  ttbar events w/o purification: • R ~ 150 for (b) = 60% • R ~ 400 for (b) = 50% Atelier Physique Atlas France 2007 - Seignosse

  11. JB de Vivie, R. Zaidan, LV Impact of material with CSC geometries Material increase: d0 resolution: CSC-01-00-00 DC3-02 1-2 GeV/c 2-5 GeV/c 5-10 GeV/c >50 GeV/c • More realistic description of material • Biggest change is from DC3-02 to CSC-01-00-00 • Additional degradation with CSC-01-02-00 (and a bit more to come) G. Gorfine Impact on b-tagging:rejection /~1.5 for fixed ε(b), for R(u)=100 <~5% absolute on ε(b) • Understanding: • rescaling in DC3 of IP • resolution to match CSC • removal of G4 secondaries • Explain 60-70% of losses (more in central region, ~100%) • Need to understand the missing part & address recoverability secondaries ! resolution ! Atelier Physique Atlas France 2007 - Seignosse

  12. LV Track classification: example of shared hits Use dedicated calibration for several track classes e.g. tracks with shared hits (≥1 Pix || ≥2 Sct) (NB: default treatment since release 11) IP3D, 50% sh. rejected sh. calibrated  Good understanding/monitoring of tracking (beyond resol.) is important !  More track categories are being studied (0B-layer,fragmentation, pT, η) Atelier Physique Atlas France 2007 - Seignosse

  13. JetFitter: a whole new algorithm • Main idea:try to constrain all tracks from the • B/D hadron decays to intersect the same flight • axis (instead of the common vertex approach) • Technique: a new dedicated Kalman filter fitting: • Treatment of incomplete/1-prong topologies: • on average 1.9 (1.7) OK track from D (B) decays • recover « 1 track from B + 1 track from D  » (9%) • can improve purity • Based on likelihood: • categories for topology (0,1,2+ vertices) • vertex mass, energy fraction, significances • of {disti} • can also use charm p.d.f for improving • b/c separation •  Available in release 13 Atelier Physique Atlas France 2007 - Seignosse

  14. Towards first data

  15. JB. de Vivie, LV JetProb Tagger • Tagger à la Aleph/Lep: • Compatibility of the tracks with the primary vertex • Fit negative side of Signed impact parameter w/ resolution func (gaus+2exp) • But easier to understand/calibrate in early data  Performances poorer than IP2D: x0.5 (but less optimized)  Should give results early (performances to be quantified) Atelier Physique Atlas France 2007 - Seignosse

  16. H.Bachacou Soft Muons • Br(bX)+Br(bcX) = 11% + 10% • Independent of vertex tagging • Muon reconstruction: currently Staco+Mutag (high-efficiency down to 4 GeV/c pT, low fakes) • 2 steps: • association muon-jet (cone ∆R < 0.5) • Likelihood ratios (1D, 2D) for b/light hypothesis using pT, pTrel. • Rejection of 200 for 10% b-tagging efficiency (incl. Br. & -ID) • Fake muons vs pile-up/cavern bckgd being checked Atelier Physique Atlas France 2007 - Seignosse

  17. @60% e(b) DC3 R(u) = 130 CSC R(u) = 133 R(u) @50% e(b) DC3 R(u) = 165 CSC R(u) = 190 Rejection of u-jets (60% a.e.  ~ 8%) DC1- no pileup R(u) = 151 (166) ± 11 (7.8.0) DC1- low lumi R(u) = 136 (144) ± 9 (7.8.0) DC1-high lumi R(u) = 104 (123) ± 11 (7.8.0) Rome R(u) = 145 ± 6 (11.0.3) DC3 R(u) = 130 (12.0.6) CSC R(u) = 133 (12.0.6) Rejection of c-jets DC1-no pileup R(c) = 35 (35) ± 2 (7.8.0) DC1-low lumi R(c) = 36 (35) ± 2 (7.8.0) DC1-high lumi R(c) = 33 (33) ± 2 (7.8.0) e(alg-b) – efficiency of the b-tagging algorithm F. Derue Soft Electrons • Soft Electron reconstruction: • starts from ID track • associate cluster • Soft Electron ID: likelihood • tracks (TRT, …) • shower shape NB: derniers résultats avec géométrie CSC-01-02: R(u)~80 Atelier Physique Atlas France 2007 - Seignosse

  18. Muon jet   Muon jet SVT tag jet L.Feligioni Measuring b-tagging efficiency with di-jets • pTrel templates • Non-linear system (System8 à la D0): • 2 samples • Muon Jets (n) • MJ + other tag opposite jet Jet (p) • 2 different b/l fractions • 2 non-correlated taggers • Tracks (impact param./SVT) • Soft Muon (pTrel) • system can be solved analytically • Results: (for ~10k MJ)  definition of Muon+Jet trigger in progress Atelier Physique Atlas France 2007 - Seignosse

  19. W jets: ET>40 GeV, 20 b-veto (weight < 3) Hadronic side b-jet: ET>40 GeV b-tag (weight>3) Lepton: ET>20 GeV Leptonic side b-jet: ET>20 GeV No tag requirement ETmiss> 20 GeV Selecting a pure b-jet sample in ttbar events Leptonic top mass:  bkgd shape from mjjb sideband • b-tag on hadronic side • predict (kinematics) b-jet • on leptonic side (unbiased) 100 pb-1 Atelier Physique Atlas France 2007 - Seignosse

  20. H. Bachacou Counting method for measuring b-tag efficiency in ttbar events Atelier Physique Atlas France 2007 - Seignosse

  21. Activities and CSC notes for b-tagging CPPM, LAL Algorithms and generic performances: • BT0: performances and parametrization [Ed: L. V.] • BT1: vertexing (primary, secondary, beam-lines) [Ed: V. Kostioukhin] • BT2: alignment and b-tagging [Ed: G. Gorfine] • BT3: soft muons [Ed: H. Bachacou] • BT4: soft electrons [Eds: F. Derue, A. Kaczmarska] • BT5: HLT b-tagging [Ed: C. Schiavi] Specific performance studies: • BT6: SUSY [Ed: J.B. de Vivie] • BT7: ttH [Ed: A. Rozanov] • BT9: bbH/A->tautau [Ed: E. Staneckla] Calibration & performance estimation from data: • BT10: with di-jet events [Ed: G. Watts, F. Rizatdinova] • BT8: with ttbar [Eds: H. Bachacou, R. Hawkings] • BT11: 900 GeV run [Ed: F. Rizatdinova] (now merged with BT10) Saclay LPNHE LAL CPPM CPPM  Saclay  Atelier Physique Atlas France 2007 - Seignosse

  22. Conclusion • High-performances b-taggers have been developped • R>100 for (b)=60% achieved, not so far from (b)=70% • New developments (JetFitter, optimization) allow to maintain performances despite increase of material • Still many developments/studies going on  CSC notes • Now shifting priorities towards first data • Impact of alignment a.s.a.p. • Commissioning b-tagging with simple/robust taggers • Strategies for cross-calibrating taggers and measuring performances/p.d.f. in data • Several methods for extracting b-efficiency: <10 % relative error achievable with 100 pb-1 • Work starting for estimating mistag rates Atelier Physique Atlas France 2007 - Seignosse

  23. Back-up slides

  24. More information • Talks from Marseille workshop (last May): • recent results covering the whole spectrum (~40 talks) • In CDS agenda: Physics/B-tagging/workshop • http://indico.cern.ch/conferenceDisplay.py?confId=14475 • HyperNews forum • WiKi page: https://uimon.cern.ch/twiki/bin/view/Atlas/FlavourTagging • And soon (hopefuly) the CSC notes !!! Atelier Physique Atlas France 2007 - Seignosse

  25. The case of high-pT jets • Performances decrease for moderate/high jet-pT (150-250 GeV): • pattern-recognition becomes more difficult in dense jets • b-tagging track selection even more critical  Optim. of cone size for track-jet assoc.: Fragmentation tracks selected: 15 < pT < 30 GeV/c Light jet rejection improvment w.r.t nominal +:for pT  250 GeV/c ~ 6% of b-jets have only tracks from fragmentation !! 200 < pT < 400 GeV/c • 20% (8%) of B in jets w/ pT>200 GeV decay beyond the beam-pipe (b-layer) • track selection (|d0|<1mm, NBLayer>1) too tight for high boosts • For very high pT (TeV) (e.g. little Higgs, Z’) even worse • requires dedicated tracking, tagging algorithms • but also simulation: propagation of B hadrons in matter in G4 ! Atelier Physique Atlas France 2007 - Seignosse

  26. Impact of (mis)alignment Random misalignments: IP3D tagger , ttH events, realistic conditions improving alignment up to almost perfect in one year, recovery of light jet rejection • will redo the exercise with misaligned detectors from simulation when available (more realistic than random misalignments) Atelier Physique Atlas France 2007 - Seignosse

  27. System8 on di-jet events Measurements system solvable analytically for , r and sample composition ! k: correlation between soft muon & track-based taggers ,: sample dependency Atelier Physique Atlas France 2007 - Seignosse

  28. L2 & HLT b-tagging • Aims:increase acceptance for multi- b-jets events, lower threshold X when used in combination with X, extract b-jet calibration samples • Inputs: L1 jet RoI (pT>15 GeV, ∆x∆=0.4x0.4), tracks from L2 (SiTrack/IDScan) • PV: in Z using histogramming • Taggers: impact parameter significance (LHR), secondary vertex in progress • Performances: • (NB: also an alternative à la CDF/SVT in the works: FTK) • Working on menus:e.g. 4j65/2b + 6j40/3b doubles efficiency for ttH(bb) w.r.t. 4j100+3j165, with 1.3kHz @ L1, 4 Hz @ EF (2.1033) • On-going improvements: • signed IP • speed of SV • PV search w/ multi RoI Atelier Physique Atlas France 2007 - Seignosse

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