Z tau tau (mu+ tau→Z tau tau (mu+ tau→ hadhad) with 7 TeV data) with 7 TeV data

M.Bachtis, A.Savin

University of Wisconsin

EWK Tau meeting, Aug 27th 2010

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Samples usedSamples used• Simulation

– /Ztautau/Summer10-START36_V9_S09-v1/AODSIM

– /WplusToMuNu-CTEQ66-powheg/Summer10-START36_V9_S09-v1/AODSIM

– /WminusToMuNu-CTEQ66-powheg/Summer10-START36_V9_S09-v1/AODSIM

– /Zmumu_M20_CTEQ66-powheg/Summer10-START36_V9_S09-v2/AODSIM

– /WplusToTauNu-CTEQ66-powheg/Summer10-START36_V9_S09-v1/AODSIM

– /WminusToTauNu-CTEQ66-powheg/Summer10-START36_V9_S09-v2/AODSIM

– /WminusToTauNu-CTEQ66-powheg/Summer10-START36_V9_S09-v2/AODSIM

– /QCD_Pt-20_MuEnrichedPt10_7TeV-pythia6/Spring10-START3X_V26_AODSIM-v1/AODSIM

– /InclusiveMu15/Summer10-START36_V9_S09-v1/AODSIM

• Note 1: QCD Pt 10 is 35X sample (not ReRECOed in36X)

– We have requested it for 38X

– Inclusive Mu 15 can be used instead but we have to restrict the muon PT threshold > 15 GeV/c(Results are similar)

• Note 2 : POWHEG Z tau tau not used due to Z->ee contamination→

• Data

– Official recipe and JSONs for 1.1 /pb .

– Private JSON + PromptReco for latest runs (total 1.7 /pb)

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Preselection (as ICHEP)Preselection (as ICHEP)• HLT Mu 9

– Normalization factor 0.975 applied to the MC

• One muon with Pt > 10 GeV/c |eta|<2.1 and tight Muon ID – Absolutely the same with VBTF W mu nu Analysis→– Require matching to the HLT object

• One HPS Tau with Pt > 15 GeV/c ans |eta|<2.4– Decay mode reconstructed

• There is a tau decay in a jet

– Discrimination Against Muon• No muon segments for the leading charged hadrons

• Muon non overlapping with the Tau – Delta R > 0.3

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Muon and Tau PtMuon and Tau Pt

• Essentially monitoring QCD background

• Good agreement with MC– Normalization within luminosity error

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Transverse mass of muon +METTransverse mass of muon +MET• Used to reject W mu →

nu events

• Without isolation shows good DATA/MC agreement also for the EWK contributions

• Useful to control EWK contribution

• PF MET used for this plot– Very similar results

with TC MET as shown for ICHEP

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Muon IsolationMuon Isolation

• Trying both Particle based and detector based isolation

– Particle Based at cone=0.4 Sum ET/mu PT<0.1

– Detector based at cone=0.5 (Sum Track +Calo ET)/pt<0.1

• Particle based isolation improves discrimination power (PFT-10-003)

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Tau DiscriminatorsTau Discriminators

• Good agreement with MC

• Isolation calculated in solid cone of 0.5 after subtracting Tau constituents

• Most of the WPs are using Loose Isolation– Veto PF hadrons > 1 GeV . PF gammas > 1.5 GeV

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Hadrons and Photons in TausHadrons and Photons in Taus

• Good agreement for the Tau constituents

• Loose Isolation is applied for this plot

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Rejecting Z mumu + jets→Rejecting Z mumu + jets→

• We used Mu+OS Track mass before

• Proposal from S.Nikitenko– Veto Mu + Isolated OS Mu

– Works + it reduces also DY

• Kept old definition for the following results for consistency

No mumu veto

mumu veto

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Results WP50 , WP65Results WP50 , WP65

• WP 50%

• Mu Pt>10 GeV/c,Tau Pt>15/c GeV

• Loose Isolation

• WP 65%

• Mu Pt>15 GeV/c,Tau Pt>15/c GeV

• Loose Isolation

29 signalevts expected

21 signalevts expected

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WP75% (ICHEP)WP75% (ICHEP)

• Mu Pt>15 GeV/c

• Tau Pt>20 GeV/c

• Loose Isolation16 signalevts expected

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Naïve cross section calculationNaïve cross section calculation• Taking everything from MC• Assume WP 65%• Sigma = N_events x P /(ExAxLint)

• N_events = 53 +-7

• P = 0.50 (Purity)• ExA = 1.0%• Lint=1.7 /pb

• Sigma = 1.6 +- 0.2(stat) + 0.2(lumi) (+ systs) nb– Agreement with NNLO

• As the data size increases we will apply the data driven methods and compare

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Extrapolation: Prospects for measurementExtrapolation: Prospects for measurement• At 25 /pb• WP50 gives S/SQRT(S+B) ~15

– Expected 432 Z tau tau events→

• WP65 gives S/SQRT(S+B) ~14– Expected 307 Z tau tau events →

• In both cases statistical error is < 8 %– After data driven background estimation

• Assuming that the goal is to show that we can do Z →tau tau a result can come faster than we expect

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OS/LS StudiesOS/LS Studies

• Two approaches to measure OSLS ratio– OSLS1 :No isolation on mu+tau applied – OSLS2 :Apply Tau Isolation but anti-isolate the muon

OSLS1 OSLS2

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OS/LS results in DATAOS/LS results in DATAOS/LS 1 OS/LS 2

• OS/LS 1 = 1.03 +- 0.01

• OSLS 2 = 1.05 +- 0.04

• Results in agreement within statistical errors

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One prong + 0 pi0 eventOne prong + 0 pi0 event

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Three Prong EventThree Prong Event

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ConclusionsConclusions• Z tau tau is observed in the mu+tau final state• The results are encouraging for a fast cross section

measurement

• As the luminosity increases we can start looking seriously at bckground estimation and systematic uncertainties.