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B-tagging, leptons and missing energy in ATLAS after first data Ivo van Vulpen (Nikhef) on behalf of the ATLAS collaboration.

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Presentation on theme: "B-tagging, leptons and missing energy in ATLAS after first data Ivo van Vulpen (Nikhef) on behalf of the ATLAS collaboration."— Presentation transcript:

1 B-tagging, leptons and missing energy in ATLAS after first data Ivo van Vulpen (Nikhef) on behalf of the ATLAS collaboration

2 Studying top quarks pairs – the building blocks Jets are discussed in a separate talk 2/40

3 ATLAS data-sets 2009: √s = 900 GeV Lumi = 12 μ b -1 (stable beams)  538,000 collision candidates Main focus of this talk is on this data-set 2010: √s = 7 TeV 3/40 Public ATLAS results: https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults Integrated luminosity

4 You are here Upcoming ATLAS results

5 B-tagging

6 B-tagging in top analyses - Reduce W+jets & QCD bckg. - Reduce jet-combinatorics Complications: - JES b-jet difficult (vital for M top ) - multi-jet environment B-tagging in top analyses 6/40

7 Inner detector Pixel detector Transition Radiation Tracker SemiConductor Tracker ATLAS inner detector 3 systems in 2 T solenoid |η|< 2.5 7/40 barrel: 4 layers (x2) barrel: 3 layers barrel: ≥ 30 straws

8 Tracking performance SCT - number of hits Events with: - Minimum bias trigger, primary vertex ≥ 3 tracks - Tracks with:P T > 0.5 GeV, N pixel ≥ 1, N SCT ≥ 6, |d 0 |<1.5 mm, |z 0 sinθ|<1.5 mm - Simulation: reweighted beamspot and corrections for disabled modules in data Minimum bias events at √s=900 GeV Track reconstruction efficiency Monte Carlo 8/40 Excellent agreement: simulation reproduces track properties

9 Alignment tracking detectors residual Pixel –x residuals 9/40 Radius in ATLAS [mm] MC: 38 μ m SCT –x residuals Data: 43 μ m MC: 23 μ m Data: 28 μ m Tracks with: P T > 2 GeV, N silicon ≥ 6, |d 0 |<10 mm barrel

10 Primary vertices Pile-up event Vertex resolution ~75 μ m Luminous region: σ X =45 μ m, σ Y =70 μ m Vertexing 10/40 ~2.5 cm

11 Secondary vertices K s invariant mass 11/40 Λ invariant mass

12 Impact parameter significance d0d0 primary vertex secondary vertex jet 12/40 Flight length significance: L/σ L B-tagging algorithms: - jet tracks (combined) incompatibility with originating from primary vertex - soft lepton tagging - secondary vertices & their properties d 0 significance: d 0 /σ d0

13 ‘Typical’ b-jet candidate primary vertex secondary vertex √s=7 TeV B-jet details: - P T = 19 GeV (EM scale) - 4 b-tag quality tracks Prob(PV compatibility) 9∙ Secondary vertex: o 50 sigma in 3d away from PV o Mass sec. vertex = 3.9 GeV 13/40

14 electrons

15 Electrons in top analyses isolated & high-P T - dominant trigger stream - reduce QCD multi-jet bckg. - handle on leptonic W-boson Complications: - extrapolation from Z  e + e - to top multi-jet environment - fake and non-prompt electrons o e/jet ~ at P T =40 GeV o identify b/c-decays: isolation Electrons in top analyses 15/40

16 Electromagnetic calorimeter & particle identification Transition Radiation Tracker Electromagnetic calorimeter e/ π separation Liquid Argon / Lead |η|< X 0 16/40

17 L1 rates: normalised to L=10 27 cm -2 s -1 L1 efficiency w.r.t. offline (~3 GeV) EM calorimeter trigger - level /40 SignatureRate (1x10 31 ) L1: e10 5 kHz EF: e10 21 Hz Nominal settings / rates ATLAS detector paper

18 EM & e/ γ trigger - level 2 and event filter - Shower shapes at L2 L2 rate versus E T Note: - Already at Level 2 fairly good agreement on e/ γ specifics - Highest level (Event Filter) trigger offline - more refined 900 GeV 7 TeV 18/40

19 879 electron candidates:  electrons from photon conversions and fake electrons (hadrons) Electrons in 900 GeV data Eta Transverse energy γ/π 0 – separation bulk energy leakage-estimate 19/40

20 Photon conversions Pixel layers SCT layer 1 beampipe Conversion radius Eta of candidate 20/40 - Clean electron sample - Good material description in MC

21 Electron classifications and data Loose Medium Tight ECAL: shower shapes Track: loose track Loose 94.3 % ~ 1 Medium: 90.0 % ~ 7 Tight: 71.5 % ~ 140 Efficiency (Z  e + e - ) Expectations, √s=10 TeV (MC) Jet rejection (x 10 3 ) ECAL: strip layer info Track: tighter quality + matching Track: B-layer hit + tight match TRT: high-threshold hits 21/40

22 Calorimeter information Fraction of energy in strip layer electrons hadrons Fraction of energy in strip layer Loose Medium Tight ECAL: shower shapes Track: loose track ECAL: strip layer info Track: tighter quality + matching Track: B-layer hit + tight match TRT: high-threshold hits 22/40 Strip layer info

23 Tight electrons Loose Medium Tight ECAL: shower shapes Track: loose track ECAL: strip layer info Track: tighter quality + matching Track: B-layer hit + tight match TRT: high-threshold hits 23/40 Number of pixel hits Fraction TRT high-threshold hits

24 Transition Radiation Tracker (e/ π separation) Note: also tested using high-energy muons in the cosmic runs 24/40 TRT: high-threshold probability

25 Z  e + e - candidate at √s=7 TeV E T (e - ) = 45 GeVE T (e + ) = 40 GeV Invariant mass = 89 GeV 25/40

26 Muons

27 Muons in top analyses isolated & high-P T - dominant trigger stream - reduce QCD multi-jet bckg. - handle on leptonic W-boson Complications: - extrapolation from Z  μ + μ - to top multi-jet environment - fake and non-prompt muons mainly from b-decays:  identify using isolation Muons in top analyses 27/40

28 Muon Spectrometer Muon trigger and momentum resolution < 10% up to 1 TeV standalone or combined with inner detector information Barrel/endcap toroid B=0.5/1.0 T Coverage: |η| < /40

29 Cosmic runs Millions and millions of cosmics Transverse momentum resolution Resolution close to nominal Ongoing effort on alignment and calibration 29/40

30 Muon trigger L2 eff. (combined) w.r.t. offline L2 eff. (standalone) w.r.t. offline P T track: EF versus offline Level 2 plots from events with: - L1 muon trigger - offline muon (P T > 2 GeV, P > 4 GeV) - N silicon ≥ 6, match L1 ROI in dR<0.5 |η|< /40

31 Toroids are off transverse plane 31/40

32 Muons in √s=900 GeV data phi eta Monte Carlo expectation: Mainly π/ K decays (~25% b/c decays) Momentum 32/40

33 Muons in √s=7 TeV data J/ Ψ peak in di-muon mass (opposite charge with p>3 GeV) Mean = 3.06 ± 0.02 GeV Resolution = 0.08 ± 0.02 GeV Mean = 3.06 ± 0.02 GeV Resolution = 0.08 ± 0.02 GeV 33/40

34 Muons in W- and Z-boson candidates in 7 TeV data W  μν candidateZ  μμ candidate M( μ + μ - ) = 87 GeV 34/40

35 Missing transverse energy

36 E T -miss in top analyses - reduce QCD multi-jet bckg. E T >20 GeV: ε (tt) ~ 90% QCD rejec. ~ 10 - handle on leptonic W-boson - tails important for new physics Complications: - multi-jet topology (2 b-jets) - high-p T muons E T -miss in top analyses 36/40

37 Calorimeter response E cell : EM Endcap E cell : Tile Calorimeter E T -miss= Calorimeter (+cryo+muons) Electromagnetic calorimeter Hadronic calorimeter 37/40

38 Missing transverse energy and resolution (E x,E y )-miss resolution Minimum bias events at 900 GeV and 2.36 TeV RMS ~ 1.8 GeV 38/40 E x -miss E y -miss

39 Missing transverse energy: 7 TeV data Note: - tails under control - cells from topo-clusters (EM-scale) Collision data at √s = 7 TeV Missing transverse energy E x -miss E y -miss 39/40

40 Summary: - ATLAS collecting data at 7 TeV - Good performance on reconstructing building-blocks for a top analysis. shown here: leptons, E T -miss, b-tag - Much more data & results available (at PLHC conference … next week) Reconstruct many top quarks in 2010

41 Backup slides

42 Alignment tracking detectors Pixel –x residuals MC: 38 μ m SCT –x residuals Data: 43 μ m MC: 23 μ m Data: 28 μ m Tracks with: P T > 2 GeV, N silicon ≥ 6, |d 0 |<10 mm Barrel Endcap Pixel –x residuals SCT –x residuals MC: 20 μ m Data: 23 μ m MC: 40 μ m Data: 45 μ m

43 B-tag distributions in √s=7 TeV data Flight length significance: L/σ L Jet probabillity


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