B-tagging, leptons and missing energy in ATLAS after first dataB-tagging, leptons and missing energy in ATLAS after first data

Ivo van Vulpen (Nikhef)

on behalf of the ATLAS collaboration

Studying top quarks pairs – the building blocks

Jets are discussed in a separate talk

2/40

ATLAS data-sets

2009: √s = 900 GeV

Lumi = 12 μb-1 (stable beams) 538,000 collision candidates

Main focus of this talk is onthis data-set

2010: √s = 7 TeV

3/40

Public ATLAS results:

https://twiki.cern.ch/twiki/bin/view/Atlas/AtlasResults

Integrated luminosityIntegrated luminosity

You are here

UpcomingATLAS results

B-tagging

B-tagging in top analyses

- Reduce W+jets & QCD bckg.- Reduce jet-combinatorics

Complications: - JESb-jet difficult (vital for Mtop)

- multi-jet environment

B-tagging in top analysesB-tagging in top analyses

6/40

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

Tracking performance

SCT - number of hitsSCT - number of hits

Events with: - Minimum bias trigger, primary vertex ≥ 3 tracks - Tracks with:PT > 0.5 GeV, Npixel ≥ 1, NSCT ≥ 6, |d0|<1.5 mm, |z0 sinθ|<1.5 mm

- Simulation: reweighted beamspot and corrections for disabled modules in data

Minimum bias events at √s=900 GeV

Track reconstruction efficiencyTrack reconstruction efficiency

Monte Carlo

8/40

Excellent agreement:simulation reproduces track properties

Alignment tracking detectors

residual

residual

Pixel –x residualsPixel –x residuals

9/40

Radius inATLAS [mm]

122.588.550.5

371299

443

514

MC: 38 μmMC: 38 μm

SCT –x residualsSCT –x residuals

Data: 43 μmData: 43 μm

MC: 23 μmMC: 23 μm

Data: 28 μmData: 28 μm

Tracks with: PT > 2 GeV, Nsilicon ≥ 6, |d0|<10 mm

barrel

barrel

Primary vertices Pile-up event

Vertex resolution ~75 μm

Luminous region: σX=45 μm, σY=70 μm

Vertexing

10/40

~2.5 cm

Secondary vertices

Ks invariant massKs invariant mass

11/40

Λ invariant massΛ invariant mass

Impact parametersignificance

d0

primary vertex

secondary vertex

jet

12/40

Flight length significance: L/σLFlight length significance: L/σL

B-tagging algorithms:

- jet tracks (combined) incompatibility with originating from primary vertex - soft lepton tagging - secondary vertices & their properties

d0 significance: d0/σd0d0 significance: d0/σd0

‘Typical’ b-jet candidate

primary vertex

secondary vertex

√s=7 TeV

B-jet details: - PT = 19 GeV (EM scale)

- 4 b-tag quality tracks Prob(PV compatibility) 9∙10-6

- Secondary vertex: o 50 sigma in 3d away from PV o Mass sec. vertex = 3.9 GeV

13/40

electrons

Electrons in top analyses

isolated & high-PT

- dominant trigger stream- reduce QCD multi-jet bckg. - handle on leptonic W-boson

Complications: - extrapolation from Ze+e- to top multi-jet environment - fake and non-prompt electrons o e/jet ~ 10-5 at PT=40 GeV

o identify b/c-decays: isolation

Electrons in top analysesElectrons in top analyses

15/40

Electromagnetic calorimeter& particle identification

Transition Radiation Tracker

Electromagnetic calorimeter

e/π separation

Liquid Argon / Lead|η|< 3.220-30 X0

16/40

L1 rates: normalised to L=1027 cm-2s-1

L1 efficiency w.r.t. offline (~3 GeV)L1 efficiency w.r.t. offline (~3 GeV)

EM calorimeter trigger- level 1 -

17/40

Signature Rate (1x1031)

L1: e10 5 kHz

EF: e10 21 Hz

Nominal settings / rates

ATLAS detector paper

EM & e/γ trigger- level 2 and event filter -

Shower shapes at L2Shower shapes at L2L2 rate versus ET L2 rate versus ET

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

879 electron candidates: electrons from photon conversions and fake electrons (hadrons)

Electrons in 900 GeV data

EtaEtaTransverse energyTransverse energy

γ/π0 – separation bulk energy leakage-estimate 19/40

Photon conversions

Pixel layers

SCT layer 1beampipe

Conversion radiusConversion radius

Eta of candidateEta of candidate

20/40

- Clean electron sample- Good material description in MC

Electron classifications and data

Loose

Medium

Tight

ECAL: shower shapes Track: loose track

Loose 94.3 % ~ 1Medium: 90.0 % ~ 7Tight: 71.5 % ~ 140

Efficiency(Z e+e-)

Expectations, √s=10 TeV (MC)

Jet rejection (x 103)ECAL: strip layer info

Track: tighter quality + matching

Track: B-layer hit + tight matchTRT: high-threshold hits

21/40

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 infoTrack: tighter quality + matching

Track: B-layer hit + tight matchTRT: high-threshold hits

22/40

Strip layer infoStrip layer info

Strip layer infoStrip layer info

Tight electrons

Loose

Medium

Tight

ECAL: shower shapes Track: loose track

ECAL: strip layer infoTrack: tighter quality + matching

Track: B-layer hit + tight matchTRT: high-threshold hits

23/40

Number of pixel hitsNumber of pixel hits

Fraction TRT high-threshold hitsFraction TRT high-threshold hits

Transition Radiation Tracker (e/π separation)

Note: also tested using high-energy muons in the cosmic runs24/40

TRT: high-threshold probabilityTRT: high-threshold probability

Ze+e- candidate at √s=7 TeV

ET (e-) = 45 GeV ET (e+) = 40 GeV

Invariant mass = 89 GeV

25/40

Muons

Muons in top analyses

isolated & high-PT

- dominant trigger stream- reduce QCD multi-jet bckg. - handle on leptonic W-boson

Complications: - extrapolation from Zμ+μ- to top multi-jet environment - fake and non-prompt muons mainly from b-decays: identify using isolation

Muons in top analysesMuons in top analyses

27/40

Muon Spectrometer

Muon trigger and momentum resolution < 10% up to 1 TeVstandalone or combined with inner detector information

Barrel/endcap toroid B=0.5/1.0 T

Coverage: |η| < 2.7

28/40

Cosmic runs

Millions and millions of cosmics Transverse momentum resolution

Transverse momentum resolutionTransverse momentum resolution

Resolution close to nominalOngoing effort on alignmentand calibration

29/40

Muon trigger

L2 eff. (combined) w.r.t. offlineL2 eff. (combined) w.r.t. offlineL2 eff. (standalone) w.r.t. offlineL2 eff. (standalone) w.r.t. offline

PT track: EF versus offline PT track: EF versus offline Level 2 plots from events with: - L1 muon trigger - offline muon (PT > 2 GeV, P > 4 GeV)

- Nsilicon ≥ 6, match L1 ROI in dR<0.5

|η|< 1.05

30/40

Toroids are off

transverse plane

31/40

Muons in √s=900 GeV data

phiphi

etaeta

Monte Carlo expectation:Mainly π/K decays (~25% b/c decays)

MomentumMomentum

32/40

Muons in √s=7 TeV dataJ/Ψ peak in di-muon mass (opposite charge with p>3 GeV)

Mean = 3.06 ± 0.02 GeVResolution = 0.08 ± 0.02 GeV

Mean = 3.06 ± 0.02 GeVResolution = 0.08 ± 0.02 GeV

33/40

Muons in W- and Z-boson candidates in 7 TeV data

Wμν candidate Zμμ candidate

M(μ+μ-) = 87 GeV

34/40

Missing transverse energy

ET-miss in top analyses

- reduce QCD multi-jet bckg. ET>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-pT muons

ET-miss in top analysesET-miss in top analyses

36/40

Calorimeter responseEcell: EM EndcapEcell: EM Endcap

Ecell: Tile CalorimeterEcell: Tile Calorimeter

ET-miss= Calorimeter (+cryo+muons)

Electromagnetic calorimeter

Hadronic calorimeter37/40

Missing transverse energy and resolution

(Ex,Ey)-miss resolution (Ex,Ey)-miss resolution

Minimum bias events at 900 GeV and 2.36 TeV

RMS ~ 1.8 GeV38/40

Ex-missEx-miss

Ey-missEy-miss

Missing transverse energy: 7 TeV data

Note: - tails under control - cells from topo-clusters (EM-scale)

Collision data at √s = 7 TeV

Missing transverse energyMissing transverse energy

Ex-missEx-miss

Ey-missEy-miss

39/40

Summary:

- ATLAS collecting data at 7 TeV

- Good performance on reconstructing building-blocks for a top analysis.

shown here: leptons, ET-miss, b-tag

- Much more data & results available (at PLHC conference … next week)

Reconstruct many top quarks in 2010

Backup slides

Alignment tracking detectors

Pixel –x residualsPixel –x residuals

MC: 38 μmMC: 38 μm

SCT –x residualsSCT –x residuals

Data: 43 μmData: 43 μm

MC: 23 μmMC: 23 μm

Data: 28 μmData: 28 μm

Tracks with: PT > 2 GeV, Nsilicon ≥ 6, |d0|<10 mm

Barrel

Endcap

Pixel –x residualsPixel –x residuals SCT –x residualsSCT –x residuals

MC: 20 μmMC: 20 μm

Data: 23 μmData: 23 μm

MC: 40 μmMC: 40 μm

Data: 45 μmData: 45 μm

B-tag distributions in √s=7 TeV data

Flight length significance: L/σLFlight length significance: L/σL Jet probabillityJet probabillity