Tau06, 9 th Workshop on Tau Lepton Physics Pisa, Italy September 2006 Reconstruction and Identification of hadronic  -decays in ATLAS Fabien Tarrade LAPP, Annecy (on behalf of the ATLAS Collaboration)

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade2 Motivation Characteristic of  leptons The ATLAS detector  -jets identification Algorithms TauRec Tau1P3P Summary Outlook

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade3 Physics processes with τ ’s Higgs Processes : Higgs Processes : Exotic Processes : Exotic Processes : Standard Model : Standard Model : Standard Model Higgs (VBF,ttH) qqH → qqττ, ttH → ttττ MSSM Higgs (A/H, H + ) A/H → ττ, H + → τν SUSY signature with τ ’s in final state Extra dimensions … new theories (?) Z → ττ W→ τν τ m Higgs (GeV/c 2 ) signal significance important for the commissioning 5σ5σ

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade4  decays Leptonic decay modes     e  e (17.4%)       (17.8%) Hadronic decay mode 1 prong     (11.0%)       (25.4%)         (10.8%)           (1.4%)      n   (1.6%)   3 prong      n   (15.2%) ~35 % ~77 % ~23 % How to identify them ? 1 track, impact parameter shower shape, energy sharing 3 tracks, impact parameter secondary vertex shower shape, energy sharing τ decay modes : τ decay modes :  jets

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade5 Solenoid Forward Calorimeters Muon DetectorsElectromagnetic Calorimeters EndCap Toroid Barrel ToroidInner DetectorHadronic CalorimetersShielding ATLAS layout

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade6 ATLAS tracking Resolution : σ(P T )/P T = 0.05% P T (GeV)  % Tracking in range |η|< 2.5 ID inside 2 Tesla solenoid field Precision Tracking : Pixel detector, Semiconductor Tracker (SCT) Continuous Tracking for pattern recognition and e id Transition Radiation Tracker (TRT) Inner Detectors ( ID) : Inner Detectors ( ID) : Magnetic Field : Magnetic Field : Inner Detector Pixel Detectors Transition Radiation Tracker Barrel Silicon Strip Detector Forward Silicon SripsDetector

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade7 Electromagnetic : (in  η  3.2) σ E /E = 10%/√E(GeV)  0.245/E(GeV)  0.7% (low luminosity) Hadronic : ( in  η  3) σ E /E = 50%/√E(GeV)  3.0 % Hadronic Tile Calorimeter EM Accordion Calorimeters Hadronic LAr EndCap Calorimeters Forward LAr Calorimeters η = η = 1.8 η = 3.2 η = 2.5 Calorimeter : Calorimeter : η- Strips Layer Layer Granularity Granularity (  x  ) Tile0 Tile1 Tile2 0.1 x x 0.1 Layer Layer Granularity Granularity (  x  ) Pre-sampler Strips Middle Back x x x x ATLAS calorimetry Back Middle η φ η- Strips

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade8  -jets reconstruction τ decay π0π0 π+π+ π-π- π+π+  Jets Candidate Reconstruction :  Jets Candidate Reconstruction : Backgrounds misidentified as  jets: Backgrounds misidentified as  jets:  jet reconstruction algorithms in ATLAS :  jet reconstruction algorithms in ATLAS : characteristics well-collimated calorimeter cluster with a small number of associated charged tracks acceptance |η|<2.5 acceptance of the inner detector QCD jets electrons that shower late or with strong Bremsstrahlung muons interacting in the calorimeter TauRec and Tau1P3P τ jet

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade9 Reconstruction TauRec (default algorithm) : TauRec (default algorithm) : Start from different objects : clusters or isolated track Associate tracks to the τ jet candidate Calibrate τ jet candidate energy (calorimeters) Start from a good leading hadronic track Create single-prong or three-prong τ jet candidate Calibrate candidate energy (tracker+calorimeters) Determination of the discriminant variables (calculate likelihood, discriminant multi- variate) Apply set of basic cuts for τ -Identification Tau1P3P (new algorithm): Tau1P3P (new algorithm): p T (GeV) resolution (%) inner detector hadronic calorimeters For TauRec and Tau1P3P : For TauRec and Tau1P3P : pions

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade10 TauRec : preselection Default  jets reconstruction and Default  jets reconstruction and identification in ATLAS : Cluster (E T >15 GeV), or track (p T > 2 GeV) Associate tracks pointing to the objet if ΔR=√(Δη 2 +Δφ 2 )< 0.3 Select candidate with 1, 2 or 3 tracks TauRec  jet candidate η number of tracks efficiency of reconstruction  eff reconstruction  cut ΔR<0.3

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade11 TauRec : variables R EM ΔE T 12 N strip Strip WidthE T /p T (1 st track) Signal Bkg Z→ ττ QCD jets Build a set of discriminant variables for  jets reconstruction and identification and for the rejection of QCD jets Charge

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade12 calculate likelihood using : R EM, ΔE T 12, N track, Strip Width, N strip, Charge, Impact parameter, E T /p T (1 st track) calibrate  jets candidates energy weights (Monte Carlo) applied directly to cell energies depending on their E/V content (cell energy density), η and layer (à la H1) Apply set of basic cuts for τ -Identification ε=50% J2 : R  40 J3 : R  100 J5 : R  200  jet identified with TauRec Possibility to start with different objects Good reconstruction efficiency Good energy resolution likelihood  jets QCD jets efficiency reconstruction and identification rejection factor For ε(τ)=30%, 15< p T < Rej(QCD jets) = TauRec σ = 10.4%  = -1.8% TauRec : identification (E T reconstructed τ – E T true τ )/ E T true τ

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade13 Explores exclusive feature of the  lepton hadronic does not correspond to a typical jet but : 1 track + n π 0 (Tau1P) 3 tracks + n π 0 (Tau3P) Good quality hadronic track (p T > 9 GeV), find nearby good quality track (p T >1 GeV, ΔR< 0.2) 1 track of good quality + no nearby track + 2 nearby tracks new algorithm for  jets reconstruction and identification in ATLAS : new algorithm for  jets reconstruction and identification in ATLAS :  jet candidate of Tau1P dedicated Tau1P3P in searches for the light Higgs or soft SUSY:  's with E T vis = GeV  jet candidate of Tau3P efficiency of reconstruction ETET efficiency of reconstruction for signal limited by good quality tracking efficiency of reconstruction Tau1P3P : preselection ETET Tau1P Tau3P

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade14 Tau1P3P : variables Build a set of discriminant variables for  jets reconstruction and identification and for the rejection of QCD jets Energy scale for  jet candidates using energy flow based on tracks instead of pure calorimeter jet techniques (E T reconstructed τ – E T true τ )/ E T true τ σ = 9.9%  = 0.4% σ = 2.7%  = 0.8% Tau1PTau3P

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade15 Tau1P3P : identification Based on sampling the signal and background densities in a multi-dimensional phase-space using range-searching and probability density estimation. Combine all observables in one discriminant variable Apply set of basic cuts for τ -Identification Start by a good quality track  jets separation with 1 or 3 tracks Good energy resolution  jet identified with Tau1P  jet identified with Tau3P Tau1P efficiency rejection various E T bins rejection efficiency For ε(τ)=30%, 15< p T < 60 Rej(QCD jets) = various  bins

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade16 Summary Efficient  identification is crucial for several physics studies Good sensitivity for identifying τ ’s in many physics channels, from light Higgs to Heavy SUSY TauRec gives good results,possibility to use different seeds : cluster, track … Track based Tau1P3P gives good results, separation of  jet with 1 or 3 tracks is most powerful for low P T The tau-identification achieved will allow the study of physics channels where the jets background is very large two complementary  algorithms have been developped in ATLAS, so a robust  reconstruction and identification should be available to be checked with early data  jets reconstruction algorithms in ATLAS :  jets reconstruction algorithms in ATLAS : Perpectives : Perpectives :

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade17 Trigger Trigger in ATLAS High Level Trigger Level μs ~10 ms ~sec PC farms Level 2 Event Filter  Hz  kHz  kHz LVL1 Calorimeter+Muon Trigger, coarse granularity LVL2 Region of Interest, All detectors, full granularity Event Filter refines the selection, can perform event reconstruction using latest alignment and calibration data (full offline reconstruction)

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade18  triggers Possible way of selecting taus with the ATLAS trigger Lepton Trigger trigger with the electron or the muon Hadronic Tau Trigger - LVL1 Tau Trigger ( Calo) use EM (0.2×0.2) and hadronic (0.2×0.2) towers to define a Region of Interest and also for the isolation in the EM (1.2×1.2) and hadronic (1.2×1.2) calorimeter - LVL2 Tau Trigger ( Calo+Tracking) evaluating offline variables : em radius of the cluster, width in energy deposition, isolation fraction, track … - Event Filter based on the default  -jet reconstruction code  lepton  hadrons PRELIMINARY  trigger efficiency : still under evaluation

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade19 LVL1 Tau-Trigger ‘ Hadronic Cal. EM Cal. 2-Tower EM cluster A 2x2 tower EM cluster + 2 x 2 hadronic cluster used to ID cand. ROIs A 2x1/1x2 tower EM clusters added to the energy in the hadronic inner region (shown in red) is compared to a threshold. There are 4 in the ROI the highest ET is taken. A ring of 12 EM towers surrounding the clusters, which is used for isolation in the EM calorimeters 12 hadronic towers (behind the EM isolation ring) for isolation in the hadronic calo. Tau trigger at LVL1

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade20 Definition : efficiencie and rejection Efficiencie and Rejection eff RECONSTRUCTION = N  (Reco & labeled  ) N  (in acceptance) eff IDENTIFICATION = N  (Reco & labeled  &  Id) N  ( Reco & labeled  ) Rejection = N(Reco & non labeled  ) N(Reco & non labeled  &  Id)

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade21 Variables for TauID Δη=0.1 Δ  =0.1 granularity of the tower Δη ×Δ  η  EM Had tau_EMRadius : R EM =Σ (E T EM ×ΔR) / Σ E T EM tau_IsoFrac : ΔE T 12 =Σ (E T EM +E T Had ) 0.1<ΔR<0.2 / Σ(E T EM +E T Had ) tau_stripWith2 : Δη 2 =Σ (η 2 ×E T )/Σ E T – ( Σ (η×E T )/ Σ E T ) 2

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade22 H1 Method –Weights applied directly to cell energies –Better resolution and residual non linearities Parameter Sampling MethodH1 Method  R=0.4  R=0.7  R=0.4  R=0.7 a (%GeV 1/2 )66.0 ± ± ± ± 1.1 b (%)1.2 ± ± ± ± 0.2  2 prob. (%) Cone Algorithm –Highest E T tower for jet seed + cone –Iteration of cone direction, jet overlap, energy sharing, merging Cluster and Energy scale

Tau06, 9 th Workshop on Tau Lepton PhysicsF.Tarrade23 Energy Flow Z ->  E T eflow = E T emcl +E T neuEM +  p T track +  resE T chrgEM + resE T neuEM   =   = E T eflow /E T truth prong3 prong used only EM cells within  R < 0.2 around tau1P direction