1. 25 sep 2008michele.pioppi@cern.ch1/18 Reconstruction and Identification of Hadronic Decays of Taus using the CMS Detector Michele Pioppi – CERN On behalf of the CMS collaboration TAU 08 Novosibirsk – Russian Federation 25 September 2008

2. 25 sep 2008michele.pioppi@cern.ch2/18 Outline The CMS detector Physics with hadronic  at CMS Hadronic  reconstruction Hadronic  identification  trigger Conclusions

3. 25 sep 2008michele.pioppi@cern.ch3/18 The CMS detector |  |<2.4 Muon |  |<3.0 barrel |  |< 5.0 forward HCAL |  |<3.0 ECAL |  |<2.4 Tracker CoverageResolution

4. 25 sep 2008michele.pioppi@cern.ch4/18 Physics with  SM Higgs qq  qqH(  ) VBF Forward jet tagging Central Higgs decay products to trigger

5. 25 sep 2008michele.pioppi@cern.ch5/18 Physics with  MSSM Higgs Neutral Higgs (A.H,h)Charged Higgs (H ± ) 5  discovery potential Production mechanism

6. 25 sep 2008michele.pioppi@cern.ch6/18 Physics with  SUSY 5  discovery potential In mSUGRA models, light mass SUSY can be discovered soon in di-  final states through the decay chain

7. 25 sep 2008michele.pioppi@cern.ch7/18  reconstruction strategy 1.Particle Flow reconstruction High efficiency, low fake rate and optimal resolution for each kind of particle 2.Common  selection used as a basis for all the final states Robustness wrt unexpected detector effects, high  reconstruction efficiency and sufficient QCD background rejection 3.Sophisticated  identification Suitable and tunable  reco and id algorithms for each individual analysis

8. 25 sep 2008michele.pioppi@cern.ch8/18 The particle flow algorithm ParticleSubdetectors MuonsTK-Ecal-Hcal-Mu system ElectronsTK-Ecal-Hcal PhotonsTK-Ecal Charged hadronsTK-Ecal-Hcal Neutral hadronsTK-Ecal-Hcal Particle Flow consists in identifying and reconstructing each particle in an event followed by the best possible determination of the energy and direction, by including the information of all CMS subdetectors. Jet, tau and missing transverse energy reconstruction is then made from these reconstructed and calibrated particles directly.

9. 25 sep 2008michele.pioppi@cern.ch9/18  Pre-selection Sample Entries Signal Z   250K Background QCD(2  2) 750K Jet P T >15 GeV/c Lead track P T >5 GeV/c Lead track cone  R<0.1 An iterative tracking approach (allows to have good tracks with only 3hits) is significantly improving the leading track finding

10. 25 sep 2008michele.pioppi@cern.ch10/18 Isolation algorithm All the  decay products are expected to be in a narrow signal cone around the leading track. If the  is isolated an isolation annulus, expected to contain little activity, is defined.  candidates with charged particles (Pt>1GeV/c) and neutrals (Pt>1.5GeV/c) in the isolation cone are rejected

11. 25 sep 2008michele.pioppi@cern.ch11/18 Shrinking vs fixed cone In both the cases the Isolation cone = 0.5 CDF implements a 3D signal cone that shrinks as a function of jet E -1,while historically CMS uses a fixed signal cone (  R=0.07) The shrinking cone is defined in  -  plane and scales as E -1 to be extended in the forward region.

12. 25 sep 2008michele.pioppi@cern.ch12/18 Common selection performance The shrinking cone algorithm improves signal efficiency at the cost of increasing QCD fake rate. The range affected by the cone algorithm is between 20 and 60 GeV/c

13. 25 sep 2008michele.pioppi@cern.ch13/18 Secondary background sources The common selection is aimed to fight the main source of background (QCD jets) Secondary sources are in order of importance: –Electrons Due to the high material budget in the tracker, several electrons often emit a significant fraction of energy by radiation. A special treatment is needed to reduce electron contamination –Photons P hotons convert frequently, and the isolation is much more difficult for such photons (under study). –Muons Very high identification efficiency

14. 25 sep 2008michele.pioppi@cern.ch14/18 Electron rejection A veto is applied to all the tracks pre-identified as electrons in the particle-flow The electron pre-identification is aimed to identify electrons (isolated and within jets) in a wide range of transverse momentum, pseudo-rapidity and physics case The algorithm uses a multi-variate analysis of information from calorimeters and tracker(more efficient for electrons emitting high-energy Bremmstrahlung photons) Eff(e)>95% Eff(  )=5%

15. 25 sep 2008michele.pioppi@cern.ch15/18 Electron rejection The main electron source of background for isolated  are isolated electrons. For such electrons the rejection can be improved by using inclusive calorimetric information. E Ecal = sum of the cluster energy in a window (around the extrapolated impact point of the leading track) |  |<0.04 and  <0.5 in the direction of the expected brem photon deposition E Hcal = sum of the cluster energy in a window (around the extrapolated impact point of the leading track) in a window  R <0.184

16. 25 sep 2008michele.pioppi@cern.ch16/18  trigger The hadronic  trigger is crucial for final states with a single  (e.g H ±   ) Level1 trigger relies on pure calorimetric information Three different paths dedicated to  have been designed

17. 25 sep 2008michele.pioppi@cern.ch17/18  trigger HLT is composed by 3 steps(Lvl2, Lvl2.5,Lvl3) of increasing complexity –Lvl2 is based on jet reconstruction and isolation –Lvl 2.5/3 is based on tracking seeded by the jet direction Efficiency for SingleTau path

18. 25 sep 2008michele.pioppi@cern.ch18/18 Summary  physics program in CMS is ambitious A common and robust selection for hadronic  has been developed –  (Pt>40 GeV/c) eff > 50% –QCD (Pt>40 GeV/c) eff<3% Sophisticated identification to reduce secondary source of background – Z   eff 92% – Z  ee eff 1% Dedicated trigger for hadronic  in place to achieve the physics goal