Multivariate Analysis for Zeμ

Kyoko Yamamoto Iowa State University

8TeV eμ/eτ/μτ

LFV resonance search meeting January 22, 2013

MC12 Zeμ Sample Request• Job option file:

MC12.180333.Pythia8_AU2MSTW2008LO_Zemu_LeptonFilter.py • Generator: Pythia 8.165 • Filter efficiency: 0.62291

– Lepton filter: pT(l) > 5GeV, |η(l)| < 2.8, and N(l) = 2

• Number of events: 50K (10 files)

• Full simulation• Zeμ validation wiki page including validation plots: https://

twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/LFVinZemu• Savannah request URL: https://savannah.cern.ch/task/?38680

– Request has been approved, and simulation will be running soon

• Using my private full simulated Zeμ sample (50K events) without the lepton filter until the official sample is available

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Event Selection• Trigger (unprescaled for all periods)

– Electron: EF_e24vhi_medium1 || EF_e60_medium1

• Good Run Lists for data only• Vertex: primary vertices associated with more than 3 tracks • Data quality: veto LAr noise burst, Tile corrupted, or incomplete events• Jet cleaning (cleaning should be applied to AntiKt4TopoEM jets)

– Use only jets that survive the lepton overlap removal (remove jets with ΔR < 0.3 to SELECTED electrons/muons)

– Remove events with at least one LOOSE bad or ugly jet with pT (calibrated jet) 20GeV for ≧both data and MC (jet_isBadLooseMinus, jet_isUgly)

– Hot tile calorimeter cleaning for data only– FCal cleaning for both data and MC

• Exactly one high pT isolated tight e and one high pT isolated combined μ

• Veto events with 2nd high pT “no isolation required” loose electron or combined muon

• Trigger matching• Opposite charge of electron-muon pair

• Invariant mass: 66 < Meμ < 116 GeV

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Not applied |Δφ(e,μ)| > 2.7 at this time

Dilepton Mass Distribution

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• Signal (Zeμ) corresponding to the LEP1 BR limit (BR < 1.7×10-6) is overlaid with the stuck background histogram

• Our MVA analysis does not include QCD background, but QCD is small• NOS(QCD) ~ NSS(QCD)

• W+jet sample shows statistical fluctuations

Opposite charge pair Same charge pair

MET and Jet Distributions in 86 < M(eμ) < 96 GeV (Z-mass Pole)

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More plots: http://hep-int1.physics.iastate.edu/~kyoko/IowaState/Zemu/

Missing transverse energy Transverse momentum for leading jet

Multivariate Analysis (MVA)

• TMVA (Toolkit for MVA) – ROOT-integrated machine learning

environment for the processing and parallel evaluation of multivariate classification and regression techniques

– Including many multivariate methods

• Boosted Decision Trees (BDT)– Sequential application of cuts splits

the data into nodes, where the final nodes classify an event as signal or background

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Ref: Helge Voss, “Decision Trees and Boosting,” TMVA Workshop , CERN, 21 Jan 2011

Variables for MVA

• Picking up some variables to test MVA although some variables are correlated– Missing transverse energy

• Using MET_RefFinal_STVF after the MET correction

– Leading jet pT (if no jets, pT(1st jet) = 0)• Using AntiKt4LCTopo jets after the jet calibration

– AntiKt4LCTopo improves the resolution and is recommended by the Jet/EtMiss group and Arantxa (SM Jet convener)

– Number of jets for pT(jet) > 20GeV and |y| < 4.5

– Azimuth angle between electron and muon: Δφ(e,μ)

– Dilepton pT(eμ)

– pT(e) (after pT(e) > 25GeV cut)

– pT(μ) (after pT(μ) > 25GeV cut)

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Correlation MatrixBackground Data

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data

• Some variables are highly correlated as we expected• pT(jet) and N(jet), Δφ(e,μ) and pT(eμ)

MVA Response: BDT

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Background shape for BDT response agrees with data well

Tested signal and backgroundTested background and applied the

BDT result to data

Signal and Background Efficiencies

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High background rejection at high signal efficiency It looks good!