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

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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

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Physics with Taus

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

[GeV]

mT

0 100 200 300 400 500 600

Events / 20 GeV

1 10 102

103

104

105

Selection H+

Heavy Data 2012 True

misID Jet

Uncertainty

= 250 GeV ( x 10)

H+

m

max

) = 50, MSSM mh

tan(

Ldt = 19.5 fb-1

= 8 TeV s

ATLASPreliminary

ln(1+S/B) w. Events / 10 GeV

0 10 20 30 40 50 60 70

[GeV]

mMMC

60 80 100 120 140 160 180 200

w. Data-Bkg.

0 10

µ=1) ( (125) H

µ=1) ( (110) H

=1) µ ( (150) H

Data

=1) µ ( (125) H Z Others Fakes Uncert.

ATLAS Preliminary VBF+Boosted H

L dt = 20.3 fb-1

= 8 TeV s

[GeV]

mZ’

500 1000 1500 2000

) [pb]Z’(BR×) Z’pp(

10-3

10-2

10-1

1

ATLAS Preliminary

L dt = 19.5 fb-1 s = 8 TeV channel

had had

Expected limit

± 1 Expected

± 2 Expected Observed limit Z’SSM

th. uncert.

Z’SSM

Higgs ^à ττ Charged Higgs search Z’ ^à ττ search

SM physics: Z^àττ , Rbar, tau polariza3on in W^àτν, … Beyond SM: SUSY searches, charged Higgs, Z’, …

See backup for documenta3on of performance and physics results

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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 Veto

suppression of muon fakes additional to muon overlap removal Electron Veto

suppression of electron fakes

additional to electron overlap

removal

Tau Energy Scale (TES)

calibration of energy, eta

tag&probe analyses

tests and measurements of efficiencies and TES, using Wtaunu, Ztautau and ttbar

events from data Tau Reconstruction

seeded 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

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Tau Lepton

•  m_τ = 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-‐k_T jets (R < 0.4) –  Tracks: p_T> 1 GeV, dR < 0.2

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Hadronic Tau Decay Characteris3cs

core

fcorr

0 0.2 0.4 0.6 0.8 1 1.2

Sample Fraction / 0.02

0.02 0.04 0.06 0.08 0.1 0.12 0.14

0.16 ^Z,Z’^→^τ^τ^{, W}^→^τ^ν Data 2012 (jets)

= 8 TeV s

-1, L dt = 740 pb

∫ > 15 GeV

pT

1-prong,

ATLASPreliminary

•  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

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Tau Iden3ﬁca3on

NVtx

0 5 10 15 20 25 30

Signal Efficiency

0 0.2 0.4 0.6 0.8 1 1.2

TauBDT loose TauBDT medium TauBDT tight 1 Prong

| < 2.5 > 15 GeV, |

pT

= 8TeV s

Simulation 2012, ATLASPreliminary

•  Boosted Decision Trees (BDTs)

•  Separately for jets (tau ID) and electrons (e-‐veto)

•  Separately for 1-‐prong and 3-‐prong taus

•  Minimum tau p_T : 15 GeV

•  Pile-‐up corrected input variables ^à pile-‐up robust

Signal Efficiency

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Inverse Background Efficiency

1 10 102

103

104

TauBDT Summer 2012 TauBDT Winter 2013

1 Prong

| < 2.5 > 15 GeV, |

pT

= 8 TeV s

Data+Simulation 2012, Preliminary ATLAS

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

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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

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Performance Measurements

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

•  Z ^à τ_e/μ τ_had tag-‐and-‐probe analysis on 2012 data

•  Requirements on

–  visible mass m_vis(e/μ, τ_had-‐vis) –  missing E_T (direc3on,

transverse mass)

to suppress Z ^à ll, W ^à lν

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Performance Measurements

track

Nc+c

0 1 2 3 4 5 6 7 8 9

Events

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 22000 24000

ATLAS Preliminary = 8 TeV s

-1, L dt = 8.5 fb

channel, BDT Medium ID

µ had

Z

Data 2012 Fit 1-prong multi-prong electrons jets

9

track

Nc+c

0 2 4 6 8 10 12 14 16

Events

0 5000 10000 15000 20000 25000 30000

35000 ATLAS Preliminary

= 8 TeV s

-1, L dt = 8.5 fb

channel, Before ID

µ had

Z

Data 2012 Fit

) (Z electrons jets

Medium tau ID

No tau ID

•  Z ^à τ_e/μ τ_had tag-‐and-‐probe analysis on 2012 data

•  Requirements on

–  visible mass m_vis(e/μ, τ_had-‐vis) –  missing E_T (direc3on,

transverse mass)

to suppress Z ^à ll, W ^à lν

•  Data-‐driven background

es3ma3on for jet background:

Template ﬁt of extended track mul3plicity

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Performance Measurement: tau ID

Tau ID BDT Score 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Events

0 1000 2000 3000 4000 5000 6000 7000

Events

0 2000 4000 6000 8000 10000 12000 14000 16000 18000

20000 _{Data 2012}

(OS-SS) Z

W+jets (Data driven) ll (OS-SS)

* Z/

Top (OS-SS) Other (OS-SS) Same Sign Stat. Unc.

L dt = 20 fb-1

= 8 TeV s

Preliminary ATLAS

(full sim.) Z

Tau ID BDT Score

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Data/MC ^0.6

0.81 1.21.4

Loose Medium Tight

Scale Factor

0.8 0.9 1 1.1 1.2

1.3 ^ATLAS Preliminary = 8 TeV s

-1, L dt = 8.5-14.3 fb

Data 2012 BDT ID, Inclusive

channel

µhad

Z

channel

e had

Z

channel W had

+jets channel t had

t

combination

had

Z lep

•  Data/MC correc3on factors:

–  Combina3on of Z ^à τ_μ τ_had and Z ^à τ_e τ_had results

–  No p_T 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

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Performance Measurement: TES

•  (a): Deconvolu3on method –  Single par3cle response

–  Low pileup data taking, MC

•  (b): Z ^à τ_μ τ_had tag-‐and-‐probe –  Invariant mass distribu3on –  2012 data

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

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

[GeV]

mvis

20 40 60 80 100 120

Events / 3 GeV

0 1000 2000 3000 4000 5000 6000

Events / 3 GeV

0 2000 4000 6000 8000

10000 ^{Data 2012}

(OS-SS) Z

(OS-SS) ll

* Z/

+jets (OS-SS) W

Top (OS-SS) Other (OS-SS) Same Sign Stat. Unc.

Ldt = 20.3 fb-1

= 8 TeV s

(full sim.) Z

[GeV]

mvis

20 40 60 80 100 120

Data/MC ^0.6

0.81 1.2 1.4

Invariant mass TES Uncertainty

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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!

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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!

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BACKUP

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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

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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

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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

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Electron Veto

•  Signal eﬀ. (taus) vs background eﬃciency (electrons)

•  Candidates pass loose BDT tau ID and are not overlapping with 3ght electrons

Signal efficiency 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Background efficiency

10-4

10-3

10-2

10-1

| < 0.80 |

0.00

| < 1.37 |

0.80

| < 1.52 |

1.37

| < 2.00 |

1.52

| < 2.47 |

2.00

ATLAS Preliminary Simulation

= 8 TeV s

TauID electron veto Winter 2013

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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

fEM

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Fraction of reconstructed taus

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

True muons True taus ATLASPreliminary 2012 Simulation

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5

Fraction of reconstructed taus

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

True muons True taus ATLASPreliminary

2012 Simulation

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Performance Measurement: Trigger

Efficiency

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Data 2012 MC Z

Data stat. error MC stat. error Data sys. error

L dt = 20.3 fb-1

= 8 TeV s

all-prong µ had

Z

20 GeV tau trigger

[GeV]

Offline tau pT

0 20 40 60 80 100

MC/Data

0.8 0.9 1 1.1 1.2

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

•  Z ^à τ_μ τ_had events

•  Efficiency wrt. offline iden3fied taus (BDT medium)

•  20 GeV tau trigger

–  Plateau: p_T > 35 GeV

•  Uncertainty: (2 – 8)%

•  Combined triggers to achieve low p_T thresholds

–  Higgs ^à ττ : Di-‐tau trigger –  Charged Higgs: tau + E_T^miss

Number of primary vertices

0 5 10 15 20 25

Efficiency

0 0.2 0.4 0.6 0.8 1

L1 L1 + L2 L1 + L2 + EF L dt = 20.3 fb-1

= 8 TeV s

µ had

Z all-prong 20 GeV tau trigger

Trigger eﬃciency vs nVtx and p_T

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Performance Measurement: Tau ID

•  m

_T

= Sqrt( 2 ·∙ p

_T

(lep) ·∙ E

_T^miss

·∙ ( 1 − cos ∆φ(lep, E

_T^miss

) )

•  No addi3onal leptons in event

•  42 GeV < m

_vis

(lep, tau) < 82 GeV

•  cos ∆φ(lep, E

_T^miss

) + cos ∆φ(tau, E

_T^miss

) > −0.15

•  OS charge (lep, tau)

•  m

_T

< 50 GeV

•  ∆φ(tau, lep) > 2.4

|

0 0.5 1 1.5 2 2.5

Scale Factor

0.85 0.9 0.95 1 1.05

1.1 1.15

1.2

ATLAS Preliminary = 8 TeV s

-1, L dt = 8.5-10.5 fb

Data 2012

BDT Medium ID, Inclusive

channel

µ had

Z

channel

e had

Z

Combination (binned) Combination (overall)

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Extended Track Mul3plicity

Tracks are added to the core tracks if they sa3sfy:

•  0.2 < dR(track, tau axis) < 0.6

•  p_T(track) > 500 MeV

•  p_T(core track) / p_T(track) ·∙ dR(core track, track) < 0.4 for at least one of the core tracks

Core tracks sa3sfy:

•  p_T(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.)

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ATLAS detector

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

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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)

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