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

Transcription

1 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 214

2 Physics with Taus Higgs à ττ Charged Higgs search Z à ττ search ln(1+s/b) w. Events / GeV w. Data-Bkg H VBF+Boosted L dt = 2.3 fb H(125) (µ=1) H(1) (µ=1) H(15) (µ=1) Data H(125) (µ=1) Z Others Fakes Uncert m MMC [GeV] Events / 2 GeV Ldt = 19.5 fb Data 212 True Jet misid Uncertainty m + H = 25 GeV ( x ) tan( ) = 5, MSSM m + Heavy H Selection m T max h [GeV] (pp Z ) BR(Z ) [pb] ATLAS Preliminary L dt = 19.5 fb had had channel Expected limit Expected ± 1 Expected ± 2 Observed limit Z SSM Z SSM th. uncert [GeV] m Z SM physics: Zà ττ, Rbar, tau polariza3on in Wà τν, Beyond SM: SUSY searches, charged Higgs, Z, See backup for documenta3on of performance and physics results 3 July 214 Almut Pingel (NBI) - ICHEP214 2

3 Hadronic Tau Decays in ATLAS o of s Discrimina3on against QCD jets Discrimina3on against electrons jets Discrimina3on against muons Reconstruc3on Trigger ap tag&probe tests and mea T&P measurements Energy calibra3on 3 July 214 Almut Pingel (NBI) - ICHEP214 3

4 m τ = GeV Tau Lepton 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 <.4) Tracks: p T > 1 GeV, dr <.2 3 July 214 Almut Pingel (NBI) - ICHEP214 4

5 Hadronic Tau Decay Characteris3cs Isola3on Lateral shape Narrow energy deposi3on Small track to jet axis distance Leading track momentum frac3on Secondary vertex Invariant mass π informa3on Longitudinal shower shape Transi3on radia3on in TRT Sample Fraction /.2.16 Z,Z τ τ, W τν τ Centrality frac3on Data 212 (jets) L dt = 74 pb, 1-prong, p > 15 GeV T corr fcore 3 July 214 Almut Pingel (NBI) - ICHEP214 5

6 Tau Iden3fica3on 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 Signal eff. vs number of ver3ces 1 Prong p > 15 GeV, < 2.5 T Simulation 212, s = 8TeV TauBDT loose TauBDT medium TauBDT tight Inverse Background Efficiency Background rejec3on vs signal eff. 1 Prong p > 15 GeV, < 2.5 T Data+Simulation 212, TauBDT Summer 212 TauBDT Winter N Vtx Signal Efficiency 3 July 214 Almut Pingel (NBI) - ICHEP214 6

7 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 Energy response Momentum resolu3on 3 July 214 Almut Pingel (NBI) - ICHEP214 7

8 Performance Measurements Z à τ e/μ τ had tag- and- probe analysis on 212 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 3 July 214 Almut Pingel (NBI) - ICHEP214 8

9 Performance Measurements Z à τ e/μ τ had tag- and- probe analysis on 212 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 Events Events c+c N track No tau ID L dt = 8.5 fb, L dt = 8.5 fb, channel, Before ID Z µ had Data 212 Fit (Z ) jets electrons Medium tau ID channel, BDT Medium ID Z µ had Data 212 Fit 1-prong multi-prong jets electrons c+c N track 3 July 214 Almut Pingel (NBI) - ICHEP214 9

10 Performance Measurement: tau ID 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 Scale Factor Events 7 2 Data/MC L dt = fb, Data 212 BDT ID, Inclusive Loose Medium Tight L dt = 2 fb Data 212 Z (OS-SS) W+jets (Data driven) Z/ * ll (OS-SS) Z µ had channel Z e had channel W had channel tt had +jets channel Z lep had combination Top (OS-SS) Other (OS-SS) Same Sign Stat. Unc. Z (full sim.) Tau Tau ID ID BDT BDT Score 3 July 214 Almut Pingel (NBI) - ICHEP214

11 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 212 data Uncertain3es on total TES (a), Data/MC differences (a,b) Uncertain3es: (2 4)%, depending on η, E T, number of tracks Events / 3 / 3 GeV 6 Ldt = 2.3 fb Data 212 Z (OS-SS) Z/ * ll(os-ss) W+jets (OS-SS) Data/MC TES Uncertainty Invariant mass Z (full sim.) Top (OS-SS) Other (OS-SS) Same Sign Stat. Unc m vis vis [GeV] 3 July 214 Almut Pingel (NBI) - ICHEP214 11

12 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! 3 July 214 Almut Pingel (NBI) - ICHEP214 12

13 Summary 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! Thank you J 3 July 214 Almut Pingel (NBI) - ICHEP214 13

14 BACKUP 3 July 214 Almut Pingel (NBI) - ICHEP214 14

15 Tau Performance Tau Iden3fica3on: ATLAS- CONF , hrps://cds.cern.ch/record/ Tau energy scale: ATLAS- CONF , hrps://cds.cern.ch/record/ Tau trigger: ATLAS- CONF , hrps://cds.cern.ch/record/15157 hrps://twiki.cern.ch/twiki/bin/view/atlaspublic/ TauPublicCollisionPlots 3 July 214 Almut Pingel (NBI) - ICHEP214 15

16 Physics with Taus (CONF notes) Higgs à ττ: ATLAS- CONF , hrps://cds.cern.ch/record/ Charged Higgs: ATLAS- CONF , hrps://cds.cern.ch/record/ Z prime: ATLAS- CONF , hrps://cds.cern.ch/record/ SUSY with taus: ATLAS- CONF , hrps://cds.cern.ch/record/ Rbar: ATLAS- CONF , hrps://cds.cern.ch/record/ Tau polariza3on in W à τν events, ATLAS- CONF , hrps://cds.cern.ch/record/ Z à ττ: ATLAS- CONF , hrps://cds.cern.ch/record/ Complete list: hrps://twiki.cern.ch/twiki/bin/view/atlaspublic/confnotes 3 July 214 Almut Pingel (NBI) - ICHEP214 16

17 Physics with Taus (published) SUSY with taus: Phys.LeR. B723 (213) 15-32, hrp://arxiv.org/abs/ ttbar: Eur. Phys. J. C, 73 3 (213) 2328, hrp://arxiv.org/pdf/ v2.pdf Z prime: Phys. LeR. B 719 (213) , hrp://arxiv.org/abs/ More SUSY with taus: Eur.Phys.J. C72 (212) 2215, hrp://arxiv.org/abs/ SM Higgs: JHEP (212) 7, hrp://arxiv.org/abs/ More Rbar with taus: Phys. LeR. B 717 (212) 89-8, hrp://arxiv.org/abs/ Complete list: hrps://twiki.cern.ch/twiki/bin/view/atlaspublic/publica3ons 3 July 214 Almut Pingel (NBI) - ICHEP214 17

18 Electron Veto Signal eff. (taus) vs background efficiency (electrons) Candidates pass loose BDT tau ID and are not overlapping with 3ght electrons Background efficiency <.8.8 < < < < 2.47 TauID electron veto Winter Simulation Signal efficiency 3 July 214 Almut Pingel (NBI) - ICHEP214 18

19 Cut- based veto Muon 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 Fraction of reconstructed taus Fraction of reconstructed taus Simulation True muons True taus 212 Simulation True muons True taus f EM 3 July 214 Almut Pingel (NBI) - ICHEP214 19

20 Performance Measurement: Trigger Z à τ μ τ had events Efficiency wrt. offline iden3fied taus (BDT medium) 2 GeV tau trigger Plateau: p T > 35 GeV Uncertainty: (2 8)% Efficiency Trigger efficiency vs nvtx and p T 1 L dt = 2.3 fb L1 L1 + L2 L1 + L2 + EF Z µ had all-prong 2 GeV tau trigger Number of primary vertices Combined triggers to achieve low p T thresholds Higgs à ττ : Di- tau trigger Charged Higgs: tau + E T miss Efficiency Data / MC L dt = 2.3 fb Stat. (Data) Stat. (MC) Sys. Z µ had 2 GeV tau trigger Data 212 Data stat. error Data sys. error all-prong MC Z MC stat. error Offline tau p [GeV] T 3 July 214 Almut Pingel (NBI) - ICHEP214 2

21 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 ) >.15 OS charge (lep, tau) m T < 5 GeV φ(tau, lep) > 2.4 Scale Factor L dt = fb, Data 212 BDT Medium ID, Inclusive Z µ had channel Z e had channel Combination (binned) Combination (overall) July 214 Almut Pingel (NBI) - ICHEP214 21

22 Extended Track Mul3plicity Tracks are added to the core tracks if they sa3sfy:.2 < dr(track, tau axis) <.6 p T (track) > 5 MeV p T (core track) / p T (track) dr(core track, track) <.4 for at least one of the core tracks Core tracks sa3sfy: p T (track) > 1 GeV, dr(track, tau axis) <.2 General track requirements (distances wrt tau vertex): # pixel hits 2, # pixel + SCT hits 7 d 1. mm (transverse distance of closest approach) z sin θ 1.5 mm (longitudinal distance of closest appr.) 3 July 214 Almut Pingel (NBI) - ICHEP214 22

23 ATLAS detector ATLAS Collabora3on, The ATLAS Experiment at the CERN Large Hadron Collider, JINST 3 (28) S83 3 July 214 Almut Pingel (NBI) - ICHEP214 23

24 Many studies ongoing: Outlook 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) 3 July 214 Almut Pingel (NBI) - ICHEP214 24