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Kaluza-Klein gluon production at the LHC

Kaluza-Klein gluon production at the LHC

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Kaluza-Klein gluon production at the LHC

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  1. Kaluza-Klein gluon production at the LHC Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Farvah Nazila Mahmoudi (Uppsala University - Sweden) in collaboration with M. Guchait and K. Sridhar From Strings to LHC II – Bangalore – Dec. 20, 2007

  2. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Contents • Randall-Sundrum Model RS1 • Modified RS1 • Collider search • Kaluza-Klein gluon • Tevatron constraints • LHC constraints • Conclusion

  3. SM fields graviton Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Brane world scenarios • Idea: • We are confined on 3-brane • Graviton lives in the bulk • Typical scenarios: • Large (flat) Extra Dimensions (Arkani-Hamed-Dimopoulos-Dvali,’98) • Warped (small) Extra Dimensions (Randall-Sundrum,’99)

  4. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Randall-Sundrum Model (RS1) • Setup: • Five-dimensional theory • Warped extra dimension • A slice of anti-de Sitter spacetime in five dimensions (AdS5) • Fifth dimension  compactified on a S1/Z2 orbifold • The compactification radius Rc is of the order of • Two branes: at orbifold fixed points  = 0 and  = 

  5. Planck Planck bulk bulk  =0  =0 SM particle UV/Planck brane UV/Planck brane IR/TeV brane  = Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Randall-Sundrum Model (RS1) Two D3-branes:  = extra-dimension coordinate Rc = (modest-sized) radius 5 dimensional metric: Warp factor K = mass scale

  6. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Randall-Sundrum Model (RS1) The warp factor acts as a conformal factor for the fields localized on the brane Mass factors get rescaled by this factor Solve the hierarchy!

  7. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Randall-Sundrum Model (RS1) Brane separation stabilized by a bulk scalar field Discrete KK-spectrum with masses given by a common mass factor multiplied by the zeroes of the Bessel function.  Interesting collider phenomenology

  8. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Deformation of the original scenario • AdS/CFT correspondence  RS model is dual to a 4-d effective theory incorporating gravity • The dual theory is conformally invariant from the Planck scale down to the TeV scale • The KK excitations as well as the fields localized on the TeV brane are TeV-scale composites • The original RS theory is dual to a theory of TeV-scale compositeness of the entire SM unviable

  9. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Bulk Randall-Sundrum • Modifying the model: • Simplest possibility: modify the model so that only the Higgs field is localized on the TeV brane while the rest of the SM fields are in the bulk •  only the Higgs is composite • makes sense because only the scalar sector is natural • guiding principles: • flavour hierarchy, • consistency with electroweak precision tests • avoidance of flavour-changing neutral currents

  10. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Bulk Randall-Sundrum The location of the fermions in the bulk:  To get a large Yukawa coupling (overlap with the Higgs) one needs to localize the fermion close to the TeV brane The fermions close to the Planck brane will have small Yukawa couplings top sector: Large Yukawa of the top  proximity to the TeV brane (t, b)L cannot be close to the TeV brane tR needs to be localized close to the TeV brane

  11. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Bulk Randall-Sundrum • To avoid huge effects of FCNCs, •  To be consistent with precision tests of the electroweak • sector: • the masses of the KK modes of the gauge bosons have • to be strongly constrained • bosons are found to be in the region of 2-3TeV

  12. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Production of Kaluza-Klein gluons • The best signal for this scenario is probably: • production of KK gluons  • gluon KK modes near the TeV brane • Orthonormality of profiles of gluons and KK gluons • suppressed coupling •  gg at a hadron collider cannot produce the KK gluon at leading order •  KK gluon can, therefore, be produced by annihilation of light quarks

  13. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Kaluza-Klein gluon Non universal couplings to the SM particles • Large BR into right-handed top/anti-top pairs g = gauge coupling

  14. KK gluon with a mass just a little above the threshold: large branching into top pairs: about 92.5% To this: add the central value of the SM production cross-section: for mt= 175GeV Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Constraint from Tevatron • What is the direct, model-independent bound that existing collider data can provide ?

  15. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Constraint from Tevatron • Tevatron Run II • 1.96 TeV in the center of mass • Experimental value:

  16. CTEQ4M PDFLIB 95 C.L. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Constraint from Tevatron • Direct bound! Direct bound! M. Guchait, F.M. and K. Sridhar, JHEP 0705, 103

  17. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 KK gluon at the LHC Production mechanism: and annihilation Agashe et al., hep-ph/0612015

  18. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 KK gluon at the LHC For 100 fb-1 : Discovery of the KK Gluon with M < 4 TeV Agashe et al., hep-ph/0612015

  19. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Associate production with ttbar • : produced from both gg and initial states • through the usual QCD processes • KK gluon: radiated from one of the heavy-quark legs • Interesting: • gg initial state contributes to the associated production process • the process directly probes the coupling of the gKK to the tops which is an important feature of the new dynamics. •  The produced gKK decays into a pair

  20. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Associate production at the LHC

  21. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Associate production at the LHC • Background: • two non-resonant pairs coming from QCD processes •  computed using ALPGEN • from gKK : large momenta • other : more moderate momenta • enhanced (signal / QCD background)

  22. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Associate production at the LHC • 14 TeV in the center of mass • Assuming 100 fb-1 integrated luminosity Signal kinematics: standard three-jet production  all three final-state particles in our case are massive lower cut of 300 GeV on the pT of the t and the tbar coming from the decay of the gKK and  a cut of 50 GeV on the each of the other pair

  23. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 KK Gluon at the LHC Cuts from gKK : pT > 300 GeV other : pT > 50 GeV significance = 5 M = 2790 GeV background cross section: 0.33 fb M. Guchait, F.M. and K. Sridhar, arXiv:0710.2234

  24. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 KK Gluon at the LHC Mass obtained for a significance of 5 in function of pT M. Guchait, F.M. and K. Sridhar, arXiv:0710.2234

  25. Farvah Nazila MAHMOUDI From Strings to LHC II – Bangalore – Dec. 20, 2007 Conclusions • Interesting phenomenology from the Bulk Randall-Sundrum model • Striking prediction: existence of KK gluons • with large decay to top/anti-top pair • 2 GMS1 results: • GMS1: • Using Tevatron data: • First direct constraints on the KK gluon mass • The lower bound is obtained to be about 770 GeV • GMS2: • Associate production process at the LHC: promising results • LHC will probe masses in the range 2.8-2.9 TeV • next steps: hadron level MC, study of polarizations,… 1Guchait, Mahmoudi, Sridhar