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Probing RS scenarios of flavour at LHC via leptonic final states

This presentation explores the discovery potential of the Randall-Sundrum model with matter in the bulk in the search for a Z' particle at the LHC. It discusses parameters, di-lepton invariant mass, interference resonance, and the ATLAS detector efficiency.

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Probing RS scenarios of flavour at LHC via leptonic final states

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  1. Probing RS scenarios of flavour at LHC via leptonic final states Julien MOREL Fabienne LEDROIT Gregory MOREAU ATLAS Exotics group LPSC - Grenoble 28 march 2007 – GDR Susy – X-Dim

  2. Outline • Short presentation of the bulk RS model • Parameters space points • The ATLAS Z’ discovery potential • Conclusions and outlook

  3. Introduction • We already studied Z’ coming from Grand Unified Theories : • Using the CDDT parametrisation • Discovery potential in TeV4LHC note (ATL-PHYS-PUB-2006-024) • We are now interested in an extra dimension model : • Randall Sundrum model with matter in the bulk • Z’ excluded up to 3 TeV • We study Z’ in the e+e- channel

  4. X-dim theory - Randall-Sundrum with bulk matter [ G.Moreau, J. I. Silva-Marcos, hep-ph/0602155 ] • Gauge fields are in the bulk. • Higgs field remains on the TeV brane. • Fermions are in the bulk with different localizations along the extra-dimension. • Z’ mass < 10 TeV in order to adress the gauge hierarchy problem. TeV Brane (our 4D space) Planck Brane H t u fermions G W g Z • 3 important features : • New interpretation of the fermion mass hierarchy. • Compatible with a Grand Unified Theory [hep-th/0108115] . • KK excitation provides WIMP candidate. γ

  5. Parameters space points We are interested in 3 points in agreement with the EW constraint : Di-lepton invariant mass in the RS model Interference Resonance • We can see 2 effects • An excess of cross section due to a resonance • A lower cross section due to a destructive interference

  6. Parameters space points Z’ = first Z/g KK- excitation but we take into account the other excitations in the calculation Di-lepon invariant mass in the RS model Z’ = 1rst KK 2nd KK

  7. Parameters space points Integrated cross section for Z’ only (No DY) in fb-1 as a function of the Z’ mass

  8. ATLAS Discovery potential for a Z’ To compute the Z’ ATLAS Discovery potential we need : • A significance convention (S12) (this slide) • The signal acceptance (e) (2 next slides) • The cross section (sZ’) signal • The DY cross section (sDY)main background • Definition of the signal integrating windows We use the same strategy as for the TeV4LHC note. Using an event counting method with the realistic significance S12 propose in hep-ph/0204326 : Asking S12 > 5 with S > 10 events for a discovery

  9. The signal acceptance … 1/2 Selection criteria for a Z’  e+e- • 2 e± with |h|<2.5 (geometrical acceptance) • 2 identified e± • Opposite charges • back to back in the transverse plane • To compute detector efficiency : • We use Z’ samples coming from a full simulation of the ATLAS detector. (DC1) • As the efficiency depends only on the partonflavour, we can compute the discovery potential of Z’RS with the efficiencies coming from different Z’ samples

  10. The signal acceptance … 2/2 Acc Acc We plug these efficiencies in our Pythia user process for Z’RS to compute the ATLAS discovery potential

  11. Definition of the signal integrating window Z’ width and mass threshold Z’ Width @ MZ’=4 TeV Γ = 800 GeV for point A (0.2 MZ’) Γ = 200 GeV for point B (0.05 MZ’) Γ = 170 GeV for point C (0.04 MZ’) • For the widest point, 3Γ correspond to 0.6 MZ’ • To compute the discovery potential as a function of the Z’ mass : • We look for signal above 0.6 MZ’ .

  12. Conclusion • The ATLAS detector can discover such a Z’ up to few TeV within the first running years of the LHC. • The discovery potential is being approved by the ATLAS collaboration and will be found in an ATLAS note • ATL-COM-PHYS-2007-018

  13. The ATLAS detector efficiency … Selection criteria : • 2 identified e± • 2 e± with |h|<2.5 • Opposite charges • back to back in the transverse plane The efficiency of the event selection depends on : • The di-lepton mass • The angle between the electron and the beam in the lab frame

  14. The ATLAS detector efficiency … The efficiency depend on the model due to the Z’ boost : dileptons coming from are more boosted than di-leptons coming from because of different pdfs. Y Z ' SSM This angular dependence is related to the Z’ boost : 1 model-dependent combination (different couplings) Z’ rapidity: model-independent shapes

  15. The ATLAS detector efficiency … Selection efficiency vs di-electron mass For and events separately (low masses): • All models compatiblefor a given parton flavour • Efficiency only depends on initial parton flavour (for a given mass) • Efficiency for events lower than efficiency for

  16. A model-independent method to take into account the efficiency … Selection efficiency vs di-electron mass For , , events separately (all masses and all models) In the effective cross section calculation We assign the right efficiency depending on the initial parton flavour and the invariant mass, event by event.

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