Z0+- Method to determine hadronic tau efficiencyiktp.tu-dresden.de/bndschool/student/fischer.pdf ·...
Transcript of Z0+- Method to determine hadronic tau efficiencyiktp.tu-dresden.de/bndschool/student/fischer.pdf ·...
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Z0 → τ+τ− → Method to determinehadronic tau efficiency
Gordon Fischer
Deutsches Elektronen Synchrotron - DESY
Summer school Rathen 2009
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 1 / 22
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Schedule
What do I have to do?
Efficiency determination
Embedding method
Summary and Outlook
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 2 / 22
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What do I have to do?
What do I have to do?
"....determine the hadronic tau selection efficiencyfrom channel Z0 → τ+τ− → had ` in first data atATLAS...."
I Why?
I How?
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 3 / 22
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What do I have to do?
Why Tau Leptons?
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 4 / 22
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What do I have to do?
Why Tau Leptons? Higgs search!
I Higgs boson couples tomass favouring thedecay to the heaviertau-leptons
I for light Higgs masses→ τ τ final statebecomes important
I bb̄ is difficult to measure
I third generation is veryuseful for new physics! Figure: BR for different possible Higgs
masses
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 5 / 22
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What do I have to do?
Why Tau Leptons? SUSY search!
I τ leptons often finalstate in SUSY models
I τ̃L , τ̃R mixing → τ̃1 , τ̃2→ τ̃1 and τ productionenhanced
I BR for χ̃02 → τ̃1 τ largerthan for e or µ decays
I τ final states provideinformation for e.g. τ̃masses
I tau decay offersopportunity to measuretau polarization →χ̃01,χ̃02, τ̃1 coupling
Figure: typical SUSY chain with τ ’s in thefinal state
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 6 / 22
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What do I have to do?
Motivation for the channel Z0 → τ+τ− → had `
I in first data Z0 → τ+τ− → had ` is useful (τ ) channel for (τ )trigger studies, with hadronic channel trigger studies notpossible
I most important control channel (together with W → τνand t → τνb) to control the tau reconstruction
I Comparison with Z0 → µ+µ− or Z0 → e+e− allowsefficiency determination using Z-Resonance
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 7 / 22
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What do I have to do?
different τ decay channels → what does that mean?
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 8 / 22
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What do I have to do?
important detector moduls for hadronic τ identification
I to select 1 prong and3 prong decays →good tracking system
I τ Jets have a smallerEM-radius than QCDDi-Jets→ for τ Jets and QCDDi-Jets separationgood calorimetersystem required
I QCD background is abig challenge!
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 9 / 22
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What do I have to do?
Selection cutsI Event cuts:
- Missing ET and Sum ET(QCD BG reduction)
I Particle cuts:- trigger e10, mu10i- PT for Tau-Jet or Leptoncandidate- |Charge| and η- mT- different identification cuts
I for τ ,` combinations:- |∆ΦTauJet,Lepton|- invariant Mass window
- opposite minus samesign charge (OS-SS)Assumption: forBackground OS-SS ≈ 0 (forstatistical reasons)⇒ good backgroundrejection
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Electron mT distribution
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Muon mT distribution
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Ztautau
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Figure: mT distribution for final state leptons
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 10 / 22
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Efficiency determination
τ -efficiencyhadronic τ efficiency is defined as:
�τ→had =NselZ0→τ+τ−
N iniZ0→τ+τ− ·BRτ→had ·BRτ→lep · �kinZ0→τ+τ− · �τ→lep
(1)
possible to substitute N iniZ0→τ+τ−
with
NselZ0→µ+µ− ·BRZ0→µ+µ−
BRZ0→τ+τ−
�kinZ0→µ+µ− · �2µ(2)
Finally for efficiency calculation:
�τ→had=�kinZ0→µ+µ−
�kinZ0→τ+τ−·
NselZ0→τ+τ− ·BRZ0→µ+µ− · �µNselZ0→µ+µ− ·BRτ→lep ·BRτ→had ·BRZ0→τ+τ−
(3)
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 11 / 22
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Efficiency determination
Parameter for L = 100 pb−1I all BR available from PDG
I kinematic efficiencies (systematic studies for uncertainties of kin.efficiencies upcoming! Assume error O(10 %) just in order to checkwhether this would lead to acceptable order of magnitude of overallerror)
�kinZ0→µ+µ− = 0.26 ± 0.026
�kinZ0→τ+τ− = 0.0230 ± 0.002I selected number of events
NselZ0→τ+τ− = 219 ± 14NselZ0→µ+µ− = 21517 ± 147
I Muon efficiency (uncertainty from ATLAS Note)
�µ =
√√√√ NselZ0→µ+µ−σZ0→µ+µ−·100pb
−1
�kinZ0→µ+µ−
= 0.85 ± 0.05
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 12 / 22
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Efficiency determination
Current values for hadronic efficiency
I Tau-Jet,Tau-Lepton combinations for L = 100 pb−1
Signal OS SS OS-SSselected taus 208 11 197
selected taus truthmatched 201 2 199Background OS SS OS-SSselected taus 96 91 5
I hadronic efficiency �had for (OS-SS) (uncertainty with errorpropagation)�had (Signal) = 0.537 ± 0.0642�had (Signal (truth)) = 0.542 ± 0.0654�had (Signal + BG) = 0.550 ± 0.073
I effects from selection uncertainties have to be studied in detail
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 13 / 22
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Embedding method
Challenge: determine kinematic efficiency for Z0 → τ+τ− and
Z0 → µ+µ−
I don’t know all detector (and trigger) effects in detail → challenge todetermine
�kinZ0→µ+µ−
�kinZ0→τ+τ−
I Idea 1: select µ pairs from Z decay (in real data)
I kinematic behaviour of µ and τ (before decaying) is the same →allowed
I replace µ with τ
I let τ decay and run full reconstruction chain again
I compare number of (kinematic) selected τ and µ → no more initialinformation needed
1Markus Schumacher, Nicolas Möser (Uni Bonn), Martin Schmitz (UniBonn) et al.
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 14 / 22
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Embedding method
recipe for kinematic efficiency determination from dataI select µ pairs from Z0 → µ+µ− with pT > 5 GeV, opposite chargeI determine correction factor for lepton pT −→ ξ = E
2−mτ|p|2 and replace µ
with τI let τ decay (TAUOLA) → digitisation → reconstruction → embedding→ Z0 → τ+τ−
I Embedding → ∆R matching of τ to corresponding µI all track segments in muon spectrometer are deleted → track
information from Z → ττ eventsI Track particles and tracks of µ are deleted and replecad by tracks
from Z → ττ eventsI all higher-level objects and missing et will be reconstructed (Offline
reconstruction (e.g. MuTag or STACO)
I run the kinematic selection and ratio�kinZ0→µ+µ−original
�kinZ0→τ+τ−replaced
yields the
required efficiency!
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 15 / 22
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Embedding method
Performance plots
ET for visible τ vs. Full detector energy on:
I case 1: truth level
I case 2: reconstructionlevelwith truth match
I case 3: reconstructionlevel
without truth match
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Energy_NewTaus_10TeVEntries 79681Mean x 259.6Mean y 47.33RMS x 99.95RMS y 25.25
Energy Tau vs. Full Energy
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EnergyReco_NewTaus_10TeVEntries 49479Mean x 268.7Mean y 42.29RMS x 99.93RMS y 26.92
Energy Reco-Tau vs. Full Energy
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EnergyReal_NewTaus_10TeVEntries 78787Mean x 249.7Mean y 87.77RMS x 92.2RMS y 43.33
Energy Reco-Tau vs. Full Energy without Truth Match
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 16 / 22
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Embedding method
case 2: reconstructed (and truth matched) τ ’sI =⇒ τ pair energy contribution relative small
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Energy Reco-Tau vs. Full EnergyEnergyReco_Taus_10TeV
Entries 13153Mean x 268.7Mean y 41.65RMS x 99.74RMS y 26.48
Energy Reco-Tau vs. Full Energy
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 17 / 22
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Embedding method
Performance plots → Embedding
I choose Z0 → µ+µ− →full embedding chain
I compare with regularZ0 → τ+τ− sample(same production)
I plot pT fromreconstructed τ
I compare R = #τ`#µµ fortruth MC andEmbedding:
htempEntries 705Mean 2.064e+04RMS 1.552e+04
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Entries 705Mean 2.064e+04RMS 1.552e+04
Tau_p_T {Tau_p_T>1000 && Tau_p_T
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Summary and Outlook
Summary and Outlook
Summary:
I τ and µ kinematic well understood
I technical problems solved
I embedding method works fine (on this level)
Outlook:
I of course more statistic needed
I disussion of further uncertainties (e.g. µ selection, TAUOLA, effectsfrom underlying events..)
I more detailed studies of embedding tool will be done
I .....
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 19 / 22
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Summary and Outlook
Backup
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 20 / 22
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Summary and Outlook
Embedding method in more detailI µµ declared as ττ → four vectors together with four vector of Z boson
are written in HEPEVT formatI ASCII file read in into TAUOLA (→ lets τ decay) and PHOTOS (→
final state radiation)I fed into ATLAS detector simulation, digitisation, reconstructionI Embedding → ∆R matching of τ to corresponding µI all track segments in muon spectrometer are deleted → track
information from Z → ττ eventsI Track particles and tracks of µ are deleted and replecad by tracks
from Z → ττ events
I all higher-level objects and missing et will be reconstructed (Offline
reconstruction (e.g. MuTag or STACO)
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 21 / 22
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Summary and Outlook
Embedding flow
ATL-COM-PHYS-2009-446.pdf
Gordon Fischer (DESY) Z0 → τ+τ− 21.09.2009 22 / 22
What do I have to do?Efficiency determinationEmbedding methodSummary and Outlook