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Track based tau calibration

Track based tau calibration. R. Kinnunen, S. Lehti and A. Nikitenko. Motivation for this study. - Calorimeter reconstruction of the t jet smears the distribution of p p /E t -jet used to exploit the t helicity correlations

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Track based tau calibration

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  1. Track based tau calibration R. Kinnunen, S. Lehti and A. Nikitenko R. Kinnunen, S. Lehti and A. Nikitenko

  2. Motivation for this study • - Calorimeter reconstruction of the t jet smears the distribution of pp/Et-jet used to exploit the t helicity correlations • - In this range t jet is collimated and separation of energy depositions from p0’s and interacting charged pions in ECAL in difficult • - The correction originally developed for one-prong t jets, ET > 100 GeV, from gg->tbH+, H+ • - Now extending to lower energies and H • - Calorimeter measurement is replaced with the tracker measurement when possible, keeping the calorimeter jet in the configuration of overlapping p0’s and interacting charged pions R. Kinnunen, S. Lehti and A. Nikitenko

  3. Software and data samples • Event sample used:/Ztautau/Summer09-MC_31X_V3-v1 • Development with CMSSW_3_1_4 • t-jet candidates: reco::CaloTaus • corrected taus also reco::CaloTaus • Definition of energy resolution: ETjet / ETvisible MC t -1 • where matching is required with the MC t jet • visible MC tau = MC tau – MC neutrinos from the tau • tau ID: Rm=0.1,Rs=0.07,Ri=0.4,pT(ltrack)>6GeV,pT(tracks)>1GeV R. Kinnunen, S. Lehti and A. Nikitenko

  4. Algorithm of reconstructing one-prong t’s • for good geometrical ECAL-HCAL-track matching : • 1. If |ETHCAL+ECAL - pTtrack| < 2 sCALO: use t ~ track p, corresponds to t -> p± + n • If ETHCAL+ECAL – pTtrack > 2 sCALO • 2.1 if |ETHCAL - pTtrack| < 2 sHCAL : uset ~ track p + ECAL cluster, • corresponds to t -> p± + np0 + n with charged pion not interacting in ECAL 2.2 if pTtrack - ETHCAL > 2 sHCAL , p±interaction in ECAL, take the calo jet • 2.3 if ETHCAL - pTtrack > 2 sHCAL, hadronic jet, reject • 3. IfETHCAL+ECAL – pTtrack < 2 sCALO: track reconstruction problem,reject 2.1) 2.2) - Optimization of the cones for energy collection in ECAL and HCAL needed HCAL ECAL p0 p0 p± p± R. Kinnunen, S. Lehti and A. Nikitenko

  5. I. Testing of Calo cluster/track matching • Use the variable: ETcalo cluster / pTtrack – 1 • Calo cluster reconstruction from CaloRecHits: • Sum of cell ET within DR around the leading • track impact point in ECAL • Minimize the HCAL fluctuations by taking a • small window with • DR(ECAL impact point, cell) < 0.2 in ECAL • DR(ECAL impact point, cell) < 0.2 in HCAL Photons (ECAL energy) added in cone 0.2-0.5 The effect is small Distribution of DR for ET(ECAL cell)>1 GeV Effect of HLT ECAL isolation Algorithm optimised separating t -> p±n andt -> p+ +n p0 + n R. Kinnunen, S. Lehti and A. Nikitenko

  6. Calo cluster/track matching t -> p+ +n p0 + n t -> p+ + n II II I II III I III III I Bad track ? reject pt jet ~ ptrack Test here the HCAL cluster/track matching R. Kinnunen, S. Lehti and A. Nikitenko

  7. Optimization ofCalo Cluster/track matching window Quality of the reconstruction tested with |ETjet / ETvisible MC t -1| < 0.1 including both decay modes • Cluster energy underestimated, • an asymmetric cut is taken: • 0.9 < ETcalo cluster / pTtrack – 1 < 0.0 • Lower bound selected to keep as • many t candidates as possible • Optimal upper bound around zero If the upper bound is too high, underestimating the energy since the jet is replaced too often with a track R. Kinnunen, S. Lehti and A. Nikitenko

  8. Optimization of HCAL cluster/track window for t -> p+ +n p0 + n Region III Select upper bound ETHCAL cluster / pTtrack – 1 < 0.5 to keep as much as possible of the t candidates HCAL cluster/track matching: add the ECAL cluster to include p0’s Optimal value for lower bound ETHCAL cluster / pTtrack – 1 > -0.3 present results with ETHCAL cluster / pTtrack – 1 > -0.5 Hadronic jet: reject p±interaction in ECAL, take the calo jet R. Kinnunen, S. Lehti and A. Nikitenko

  9. Energy resolution LOG scale R. Kinnunen, S. Lehti and A. Nikitenko

  10. Eta and Phi resolution R. Kinnunen, S. Lehti and A. Nikitenko

  11. Summary • Calorimeter tau jet energy can be corrected combining tracker, ECAL and HCAL information • This algorithm is originally designed for energetic 1-prong taus • The idea is to replace, when possible, the ECAL+HCAL, or HCAL energy with the track momentum • Very good improvement in the energy resolution is achieved • The code is in cvs, tested with CMSSW_3_1_4: • JetMETCorrections/TauJet • Analysis note about the algorithm: CMS AN-2008/022 • Reoptimizing the algorithm for soft taus • Aiming for a JPT+TCTau corrected CaloTau collection to be added in PAT R. Kinnunen, S. Lehti and A. Nikitenko

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