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Reconstruction of SUSY with tau's in the final state at CMS

Reconstruction of SUSY with tau's in the final state at CMS. GDR SUSY "Probing SUSY Models at Colliders" 23 rd of October, LPNHE, Paris. Motivations Tau reconstruction and event selection Inclusive search for SUSY in di-tau final states Reconstruction of the SUSY mass spectrum.

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Reconstruction of SUSY with tau's in the final state at CMS

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  1. Reconstruction of SUSY with tau's in the final state at CMS GDR SUSY "Probing SUSY Models at Colliders" 23rd of October, LPNHE, Paris Motivations Tau reconstruction and event selection Inclusive search for SUSY in di-tau final states Reconstruction of the SUSY mass spectrum Dominique J. Mangeol IPHC, Strasbourg

  2. Cascade decay at LM2 BF for :96% At large tanb, suppressed ___ tanb=10 ___tanb=35 hep-ph/0306219 LM2 compatible with WMAP result Cascade decays LM2 Point m0 = 185 GeV m1/2 = 350 GeV tan β = 35 A0 = 0; μ > 0 Probing this sector of SUSY essential BUT… GDR SUSY

  3. Always one very soft tau per event To reconstruct a full cascade we need to tag both tau's produced by neutralino2 and stau Experimentally difficult !!!! GDR SUSY

  4. Reconstructing Tau's decaying hadronically Discrimination between tau decays (1-prong) achieved by comparing the energy deposited in both Ecal and Hcal to the leading track momentum Use main Tau decay property: narrow jet-like structure with 1 or 3 charged particles produced within a small opening angle Works well as long as Et>>Mt Problematic with low energy tau Allow to remove Tau leptonic decays (Even though) Tau selection used here optimized for low energy hadronic Tau's GDR SUSY

  5. Event selection Selection: • Large Etmiss ( 2 LSP's) • 2 energetic jets (one for each cascade) • at least two hadronic tau's with DR(t,t)<2 2 t, DR(t,t)<2 Cut Etmiss>150GeV Main backgrounds: • QCD multi-jet events (50%) • ttbar (39%) • W+jets (11%) Cut 2 jets avec Et>150GeV GDR SUSY

  6. Selection table All Tau Candidates Hadronic Tau Candidates If the nature favors a scenario such as LM2 a 5s discovery is possible with only 125pb-1 GDR SUSY

  7. Discovery potential of SUSY in di-tau final states Generalizing LM2 results to any m0,m1/2 values and for tanb=10 and 35 5s discovery contours systematics on background accounted for SUSY with di-tau final states could be discovered very early in LHC running GDR SUSY

  8. SUSY Mass Spectrum Measurement with end-point technique End-Point technique: with successive 2-body decays can build relations between sparticle masses and endpoint of invariant mass obtained with the observables (tau's and jets). With this cascade: 3 observables Hence: Fully resolved system of equations Problem: The tau (again) and neutrino produced in its decay Position of end-point not changed by loss of neutrinos but much more difficult to extract !!! GDR SUSY

  9. End-Point extraction (di-tau's) 95±5 GeV Large Combinatorial background due to multiple candidates Need to understand this background to extract end-points: • Fit the background distribution • Fit the distribution sum signal+background For di-tau invariant mass: • Di-tau from have always opposite charge • Di-tau from combinatorics estimated with same charge di-tau Extract end-points from the fits Measure invariant masses at 40fb-1 GDR SUSY

  10. Invariant mass distribution with tau's and jets For invariant mass with tau's and jets: • for : one of the 2 most energetic jets + tau's of opposite sign • Combinatorics: any tau + random jet from already used events GDR SUSY

  11. Invariant mass distribution with tau's and jets end-points extractions 559±11 GeV 596±12 GeV 780±20 GeV 298±7 GeV GDR SUSY

  12. From end-points to masses aFor a same set of end-points several mass spectra are possible depending on sparticle mass hierarchy hypothesis In this analysis, 2 hypotheses returns a physical solution: Used for mass calculation GDR SUSY

  13. From End-point to masses E5 end-point is used to choose between the 2 solutions: E5 calculated using the 2 mass solution gives 765GeV in case (1) and 815 GeV in case (2) E5 extracted from the mass invariant gives 780±20GeV aIn agreement with case 1 (LM2) GDR SUSY

  14. Summary • The use of tau constitutes a highly competitive way to probe SUSY Discovery potential possible with low luminosities • Offer possibilities to extend SUSY reaches at large tanb • Mass reconstructions challenging but achievable SUSY mass spectrum are measured with tau's (for the first time) Details in CMS Note 2006/096 GDR SUSY

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