idenﬁcaonandenergycalibraonof ......wtaunu, ztautau and ttbar events from data tau reconstruction...

Iden%fica%on and energy calibra%on of hadronically decaying tau leptons with the

ATLAS experiment.

Almut Pingel Niels Bohr Ins3tute

on behalf of the ALTAS collabora3on

ICHEP, Valencia (Spain) 3 July 2014

Physics with Taus

3 July 2014 Almut Pingel (NBI) -‐ ICHEP2014 2

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Expected limitm 1±Expected m 2±Expected

Observed limitSSMZ’

th. uncert.SSMZ’

Higgs à ττ Charged Higgs search Z’ à ττ search

SM physics: Zàττ , Rbar, tau polariza3on in Wàτν, … Beyond SM: SUSY searches, charged Higgs, Z’, …

See backup for documenta3on of performance and physics results

Hadronic Tau Decays in ATLAS

29 May 2012 Almut Pingel (NBI) - Atlas Weekly 2

Tau Object

Tau Identification (tau ID)

discrimination against QCD

jets

Muon Vetosuppression of muon

fakes additional to muon overlap removal

Electron Vetosuppression of electron fakes additional to

electron overlap removal

Tau Energy Scale (TES)

calibration of energy, eta

tag&probe analysestests and measurements of efficiencies and TES, using Wtaunu, Ztautau and ttbar

events from data

Tau Reconstructionseeded by jets, track

and vertex association, calculation of

identification variables


Trigger

Reconstruc3on

Discrimina3on against electrons

Discrimina3on against muons

Energy calibra3on

T&P measurements

Discrimina3on against QCD jets

Tau Lepton

•  mτ = 1.777 GeV •  Most taus decay inside beam pipe •  Hadronic decays: 65% – Mainly charged + neutral pions –  1 or 3 tracks –  Energy deposits in EM and HAD calorimeters

•  Main background: QCD jets •  Reconstruc3on: –  Seeded by an3-‐kT jets (R < 0.4) –  Tracks: pT > 1 GeV, dR < 0.2


Hadronic Tau Decay Characteris3cs

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Tp1-prong,

ATLAS Preliminary


•  Isola3on •  Lateral shape – Narrow energy deposi3on –  Small track to jet axis distance

•  Leading track momentum frac3on •  Secondary vertex •  Invariant mass •  π0 informa3on •  Longitudinal shower shape •  Transi3on radia3on in TRT

Centrality frac3on

τ

Tau Iden3fica3on

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•  Boosted Decision Trees (BDTs) •  Separately for jets (tau ID) and electrons (e-‐veto) •  Separately for 1-‐prong and 3-‐prong taus •  Minimum tau pT : 15 GeV •  Pile-‐up corrected input variables à pile-‐up robust

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Preliminary ATLAS

Signal eff. vs number of ver3ces Background rejec3on vs signal eff.

Tau Energy Scale (TES)


•  Energy scales for taus: EM scale à LC scale à TES

•  TES: compensate differences of reconstructed and true visible energy (MC based) –  Specific hadron mix –  Energy loss on the way –  Pile-‐up contribu3ons

•  Specific for number of tracks =1 and >1, different η-‐regions

Momentum resolu3on

Energy response

Performance Measurements

3 July 2014 Almut Pingel (NBI) -‐ ICHEP2014 8 8

•  Z à τe/μ τhad tag-‐and-‐probe analysis on 2012 data

•  Requirements on –  visible mass mvis(e/μ, τhad-‐vis) – missing ET (direc3on, transverse mass)

to suppress Z à ll, W à lν

Performance Measurements


trackc+cN

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Data 2012Fit

)ooA (Zo

electronsjets

Medium tau ID

No tau ID •  Z à τe/μ τhad tag-‐and-‐probe

analysis on 2012 data •  Requirements on –  visible mass mvis(e/μ, τhad-‐vis) – missing ET (direc3on, transverse mass)

to suppress Z à ll, W à lν •  Data-‐driven background

es3ma3on for jet background: Template fit of extended track mul3plicity

Performance Measurement: tau ID

Tau ID BDT Score0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

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(full sim.)ooAZ

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Data 2012BDT ID, Inclusive

channelhadoµoAZ channelhadoeoAZ channelihadoAW

+jets channelhadoAtt combinationhadolepoAZ

•  Data/MC correc3on factors: –  Combina3on of Z à τμ τhad and Z à τe τhad results

– No pT dependence, small η dependence (barrel/end-‐cap)

– Uncertain3es: (2 – 6)% •  Cross check: W à τν and Rbar:

Consistent results in all channels •  Outlook: “Con3nuous” Data/MC

correc3on factors à explore full BDT score in physics analysis

Performance Measurement: TES


•  (a): Deconvolu3on method –  Single par3cle response –  Low pileup data taking, MC

•  (b): Z à τμ τhad tag-‐and-‐probe –  Invariant mass distribu3on –  2012 data

•  Uncertain3es on total TES (a), Data/MC differences (a,b)

•  Uncertain3es: (2 – 4)%, depending on η, ET, number of tracks

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PreliminaryATLAS

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Invariant mass

TES Uncertainty

Summary

•  BDTs for discrimina3on of hadronic tau decays from jets and electrons

•  Tau energy scale to restore the true visible energy •  Performance measurements on data for valida3on – MC/Data scale factors around 1 – Uncertain3es < 6% (ID) and < 4% (TES)

•  All algorithms / measurements are stable with changing pile-‐up condi3ons!


Summary


Thank you J

à Visit also the poster on “Iden3fica3on of hadronically decaying tau leptons with the ATLAS experiment” by Dirk Duschinger!

•  BDTs for discrimina3on of hadronic tau decays from jets and electrons

•  Tau energy scale to restore the true visible energy •  Performance measurements on data for valida3on – Data/MC correc3on factors around 1 – Uncertain3es < 6% (ID) and < 4% (TES)

•  All algorithms / measurements are stable with changing pile-‐up condi3ons!

BACKUP


Tau Performance

•  Tau Iden3fica3on: ATLAS-‐CONF-‐2013-‐064, hRps://cds.cern.ch/record/1562839

•  Tau energy scale: ATLAS-‐CONF-‐2013-‐044, hRps://cds.cern.ch/record/1544036

•  Tau trigger: ATLAS-‐CONF-‐2013-‐006, hRps://cds.cern.ch/record/1510157

•  hRps://twiki.cern.ch/twiki/bin/view/AtlasPublic/TauPublicCollisionPlots


Physics with Taus (CONF notes) •  Higgs à ττ: ATLAS-‐CONF-‐2013-‐108,

hRps://cds.cern.ch/record/1632191 •  Charged Higgs: ATLAS-‐CONF-‐2013-‐090,

hRps://cds.cern.ch/record/1595533 •  Z prime: ATLAS-‐CONF-‐2013-‐066, hRps://cds.cern.ch/record/1562841 •  SUSY with taus: ATLAS-‐CONF-‐2013-‐026,

hRps://cds.cern.ch/record/1525882 •  Rbar: ATLAS-‐CONF-‐2012-‐032,

hRps://cds.cern.ch/record/1432198 •  Tau polariza3on in W à τν events, ATLAS-‐CONF-‐2012-‐009,

hRps://cds.cern.ch/record/1428549 •  Z à ττ: ATLAS-‐CONF-‐2012-‐006, hRps://cds.cern.ch/record/1426991

Complete list: hRps://twiki.cern.ch/twiki/bin/view/AtlasPublic/CONFnotes


Physics with Taus (published) •  SUSY with taus: Phys.LeR. B723 (2013) 15-‐32,

hRp://arxiv.org/abs/1212.1272 •  ttbar: Eur. Phys. J. C, 73 3 (2013) 2328,

hRp://arxiv.org/pdf/1211.7205v2.pdf •  Z prime: Phys. LeR. B 719 (2013) 242-‐260,

hRp://arxiv.org/abs/1210.6604 •  More SUSY with taus: Eur.Phys.J. C72 (2012) 2215,

hRp://arxiv.org/abs/1210.1314 •  SM Higgs: JHEP (2012) 070, hRp://arxiv.org/abs/1206.5971 •  More Rbar with taus: Phys. LeR. B 717 (2012) 89-‐108,

hRp://arxiv.org/abs/1205.2067

Complete list: hRps://twiki.cern.ch/twiki/bin/view/AtlasPublic/Publica3ons


Electron Veto

•  Signal eff. (taus) vs background efficiency (electrons) •  Candidates pass loose BDT tau ID and are not overlapping with 3ght electrons


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ATLAS PreliminarySimulation

= 8 TeVs

TauID electron vetoWinter 2013

Muon Veto

•  Cut-‐based veto •  Candidates not overlapping with reconstructed muons

•  Muons fake taus by failing muon reconstruc3on –  Inefficient detector regions –  Low momentum muons –  Significant energy loss in HAD calorimeter


EMf0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

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Performance Measurement: Trigger

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Data stat. error MC stat. error

Data sys. error

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PreliminaryATLAS

all-pronghad

oµAooAZ20 GeV tau trigger

[GeV]T

Offline tau p0 20 40 60 80 100

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Stat. (Data)Stat. (MC)Sys.


•  Z à τμ τhad events •  Efficiency wrt. offline iden3fied

taus (BDT medium) •  20 GeV tau trigger –  Plateau: pT > 35 GeV

•  Uncertainty: (2 – 8)%

•  Combined triggers to achieve low pT thresholds – Higgs à ττ : Di-‐tau trigger –  Charged Higgs: tau + ETmiss

Number of primary vertices0 5 10 15 20 25

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Trigger efficiency vs nVtx and pT

Performance Measurement: Tau ID

•  mT = Sqrt( 2 ·∙ pT(lep) ·∙ ETmiss ·∙ ( 1 − cos ∆φ(lep, ETmiss) ) •  No addi3onal leptons in event •  42 GeV < mvis (lep, tau) < 82 GeV •  cos ∆φ(lep, ETmiss) + cos ∆φ(tau, ETmiss) > −0.15 •  OS charge (lep, tau) •  mT < 50 GeV •  ∆φ(tau, lep) > 2.4


|d|0 0.5 1 1.5 2 2.5

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= 8 TeVs, -1 L dt = 8.5-10.5 fb0Data 2012

BDT Medium ID, Inclusive

channelhadoµoAZ channelhadoeoAZ

Combination (binned)Combination (overall)

Extended Track Mul3plicity Tracks are added to the core tracks if they sa3sfy: •  0.2 < dR(track, tau axis) < 0.6 •  pT(track) > 500 MeV •  pT(core track) / pT (track) ·∙ dR(core track, track) < 0.4

for at least one of the core tracks

Core tracks sa3sfy: •  pT(track) > 1 GeV, dR(track, tau axis) < 0.2

General track requirements (distances wrt tau vertex): •  # pixel hits ≥ 2, # pixel + SCT hits ≥ 7 •  |d0| ≤ 1.0 mm (transverse distance of closest approach) •  |z0 ·∙ sin θ| ≤ 1.5 mm (longitudinal distance of closest appr.) 3 July 2014 Almut Pingel (NBI) -‐ ICHEP2014 22

ATLAS detector


ATLAS Collabora3on, The ATLAS Experiment at the CERN Large Hadron Collider, JINST 3 (2008) S08003

Outlook

Many studies ongoing: •  Refine reconstruc3on of decay products (tracks, neutral

pions, tau decay substructure) •  Improve energy and posi3on resolu3on •  BeRer reject jets, electrons, muons •  Update iden3fica3on at trigger level •  Provide “con3nuous” MC/Data correc3on factors

à explore full BDT score in physics analysis (instead of pre-‐defined working points)


idenﬁcaonandenergycalibraonof ......wtaunu, ztautau and ttbar events from data tau reconstruction...

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