Randall-Sundrum KK Gluon & Energetic Tops at the LHC

1. Randall-Sundrum KK Gluon & Energetic Tops at the LHC K. Agashe, A. Belyaev, T. Krupovnickas, G. Perez and JV / hep-ph/612015 Work in Progress with K.Agashe, T.Han, G.Perez Joseph Virzi, LBL

2. Outline • Brief Introduction to Randall-Sundrum (RS) Model • Focus on detection of KKG using top quark pair production • Top reconstruction @ high PT • discuss associated challenges • propose approaches to address these challenges • Polarization asymmetry measurement • Background Analysis & Discussion • Conclusions Joseph Virzi UC Berkeley

3. Randall-Sundrum Modelwith SM fields propagating in the bulk solves the hierarchy problem for • motivation for model is hierarchy problem – vast difference between the weak and Planck scales 4D metric Joseph Virzi UC Berkeley

4. Warp Factor • SM phenomenology constrains profiles in 5th dimension • Yukawa couplings are given by overlap with Higgs on TeV brane Joseph Virzi UC Berkeley

5. Particle Profiles LIGHT HEAVY • Couplings to tops are enhanced and parity violating • Dominant coupling to tR because of pheno’ constraints Joseph Virzi UC Berkeley

6. Analysis • The formalism of the RS1 model leads to KK excitations • We consider here the first excitation of the gluon, G(1) • Experimental constraints favor masses of G(1) > 2TeV • Case study: 3 TeV KK gluon • Will use 100 fb-1 of data (3 years at high luminosity @ LHC) Joseph Virzi UC Berkeley

7. RS1 KK Gluon Branching Ratio of KKG vs MKKG • Prefers decay into heavier quarks, especially to tops. • BR > 0.95 • Heavy quark couplings to G(1) are enhanced relative to the SM. • For tR ~5 • For tL & bL ~1. • Light quarks & bR couplings are suppressed by factor ~5. • SM gluon couplings vanish due to orthogonality conditions Joseph Virzi UC Berkeley

8. Feynman Diagrams • Relevant Tree Level Diagrams for our discussion • The gg→KKG vertex does not exist because of orthogonality arguments • Primary production mechanism for top quark pairs + Joseph Virzi UC Berkeley

9. Signatures of KK Gluon • The RS1 KK Gluon provides a resonance structure • Width ~0.2 MKKG ( 600 GeV ) • total cross section 850 pb • ΔσRS = O(100 fb) σvs Invariant Mass

10. Signatures of KK Gluon (cont’d) • The excess production will have more tR than tL • Strategy • G(1) contribution to PLR is large & opposite sign than SM • Correlate large L/R polarization asymmetry to the mass peak L/R Polarization vs Invariant Mass RS prediction SM prediction

11. L/R Polarization Asymmetry Introduction to PLR • Look at the direction of the lepton in the top quark rest frame θ N+ & N- are the number of events where the lepton is forward (cos(θ) > 0.0) and where the lepton is backward, respectively in the top rest frame Joseph Virzi UC Berkeley

12. Dileptonic channel → 2 neutrinos • Difficulty resolving neutrino • 10% BR • Fully hadronic decay • Background more difficult • 60% BR • Semileptonic (ttbar→bbjjℓν) channel most promising for this analysis. • BR(ttbar →{μ,e}) = 30% Joseph Virzi UC Berkeley

13. Monte Carlo Simulation Strategy • Used a customized version of the Sherpa MC • Full spin correlations in top decays • 100 fb-1 of signal ( SM/RS ) with MKKG = 3 TeV • Invariant Mass > 1 TeV • σ(M>1TeV) x 0.3 semileptonic BR = 8.8 pb • 100 fb-1 of W+jets sample • Invariant Mass > 1 TeV & PT > 300 GeV • σ (M>1TeV) = 6.5 pb • 100 fb-1 of single top production sample • Invariant Mass > 1 TeV & PT > 50 GeV • σ (M>1TeV)= 5 pb Joseph Virzi UC Berkeley

14. Signal Reconstruction Overview • Conventional methods of top reconstruction at the LHC involve reconstruction of whole top decay chain • beats down background • Requires ≥4 jets, of which ≥2 are b-jets • The approach breaks down at energies ~ TeV • Jets collimate. We will discuss later • We overhauled the methods to address deficiencies Joseph Virzi UC Berkeley

15. Conventional Signal Reconstruction • Reconstruction of top pairs • ≥4 jets, 2 are b-tagged • Isolated lepton - ΔR • Missing energy → neutrino • Top mass (174 GeV ) is an input • 1 b-jet + W reconstructs leptonic top • 2 light jets reconstruct hadronic side W • Other b-jet + W reconstructs hadronic top Joseph Virzi UC Berkeley

16. Problem with Conventional Method • As the invariant mass of the ttbar event ↑ the jet multiplicity ↓ • Conventional approach works well here • Reconstruction efficiency is adversely affected @ high invariant mass • Very few 4 jet events Number of Events Number of Jets Joseph Virzi UC Berkeley

17. TopJet Reconstruction • Hadronic side – giving up • Use the events where the decay products of the top are observed as a single jet • Impose a top-jet hypothesis on the hadronic side jet • remove b-tagging constraint on hadronic side • Stiff ( >600 GeV ) PT cut on the leptonic side top decimates background • Modify leptonic top reconstruction • Lepton isolation difficult (next) Joseph Virzi UC Berkeley

18. Removing B Decay Leptons - MBL • MBL – the invariant mass between b-jet and lepton • B decay leptons have MBL ~ 5 GeV • Signal leptons have MBL ~ 50 GeV • 20% of b-jets contain leptons • descriminate against B decay leptons • Keep leptons from t → bW →bℓν Joseph Virzi UC Berkeley

19. Invariant Mass Plots TopJet Method • TopJet approach is vastly more statistically significant over the mass window • The conventional method is more appropriate for lower energies • Shape of the background Conventional Method Where’s the peak? Joseph Virzi UC Berkeley

20. Efficiency Plot Huge increase in reconstruction efficiency The efficiency & mass curves are shaped by the physics The mass curve is not shaped by the efficiency curve Reconstruction Efficiency vs Invariant Mass Joseph Virzi UC Berkeley

21. Boost profile for com is central for large invariant mass • Primary production is through qqbar Motivates stiff PT cut

22. JETS Joseph Virzi UC Berkeley

23. Jet PT over mass peak • Distributions are normalized to unit area • <PT> of b-jets = 555 GeV • 50% of b-jets have PT > 300 GeV Joseph Virzi UC Berkeley

24. B-tagging @ high PT • Important Issue but still relatively uncertain • Best estimates at low energies place ε = b-tag efficiency = 60% • Best estimates are approximately 20% at upper end of the PT spectrum • March, Ros, Salvachua ATL-PHYS-PUB-2006-002 • Remain conservative & use 20% throughout • Conventional reconstruction methods depend on 2 b-tags. Quadratic dependence on ε • New approach described here only requires 1 b-tag. Linear dependence on ε Joseph Virzi UC Berkeley

25. Light Jet Rejection • Ensuring that we do not label jets from lighter partons as b-jets • especially important for W+jets background • Current estimates • March, Ros & Salvachua ATL-PHYS-PUB-2006-002 • Rc = 30. Ru = 130 • This analysis is performed with a uniform rejection ratio Rq=30 Joseph Virzi UC Berkeley

26. L/R Polarization Asymmetry Challenges • Jet Energy Corrections • Jet Energy ≠ Parton Energy • Vital to reconstructing quark cm frame for PLR • Adds uncertainty to reconstruction of cms kinematics. Jet Energy Scale for b & light jets Taken from ATL-SOFT-2003-010 Joseph Virzi UC Berkeley

27. L/R Polarization Asymmetry Cont’dLepton PT Distribution The L/R polarization asymmetry will manifest itself in the lepton <PT> (A.T.Holloway) Lepton PT vs Invariant Mass Joseph Virzi UC Berkeley

28. Background Analysis Joseph Virzi UC Berkeley

29. Efficiency of CutsOn Signal & Background RED survives all cuts Signal (RS+SM) W+JETS SINGLE TOP Joseph Virzi UC Berkeley

30. Results of Top Jet Approach • The peak becomes much more statistically significant • We correlate the mass peak to the PLR • Additionally, we can observe the <PT> of the lepton

31. LHC Reach • Our reconstruction efficiency remains relatively flat to 4 TeV • Current estimates place the reach of the LHC for our signal to 4 TeV Joseph Virzi UC Berkeley

32. Conclusions • With new reconstruction technique, the signature(s) of the RS KK gluon becomes much more statistically significant • Combination of Topjet and Conventional techniques spans low to high MTT • The efficiency of reconstruction increases by O(5) • And turns out to stay relatively flat for increasing invariant mass ~4TeV • The W+jets and single top background is small • 100 fb-1 of data is a long time. • Depending on the mass of the KK gluon, efficiencies and fake rates, maybe we can get by with less data • Need to leave some wiggle room ( PDF & other uncertainties ) • Preliminary analysis using more realistic reconstruction techniques shows consistency with the results herein Joseph Virzi UC Berkeley

33. Backup Slides Joseph Virzi UC Berkeley

34. Summary of Cuts Joseph Virzi UC Berkeley

35. Jet PT Distributionsfrom signal sample • B-jet spectrum is harder than for light jets Joseph Virzi UC Berkeley

36. Single TopBackground • Sample used is single top production • Representing 100 fb-1 • MCMS > 1 TeV • PT > 50 GeV • 5 pb cross section • PT cut yields high background rejection • 97% light jet rejection • t-channel production is dominant green is conventional mode Evolution of cuts for single top production

37. PT of leptonic top after cuts

38. W+JETS background • Sample is W+jets • representing 100 fb-1 • MCMS > 1.5 TeV • PT > 300 GeV • cross section 6.5 pb • Light jet rejection → 97% Evolution of cuts for W+jets background

39. Efficiencies of Cuts Conventional Reconstruction Method • TopJet Reconstruction Method • Stiff PT cut provides the coup-de-grace (discuss later) • Has high signal efficiency GREEN is conventional reconstruction RED are events passing all cuts Both plots are drawn to same scale

40. Conventional Reconstruction Joseph Virzi UC Berkeley

41. TopJet Cut Statistics Joseph Virzi UC Berkeley

42. Efficiencies of Reconstructionusing Different Modes Leptonic top PT>600 GeV Joseph Virzi UC Berkeley

43. Efficiencies of Reconstructionusing Different Modes Leptonic top PT>400 GeV Joseph Virzi UC Berkeley

44. W+JETS background • I focus here on background most likely to do damage • Invariant mass > 1.5 TeV • PT > 300 GeV • Cross section 6.5 pb • The background plot looks at all combinations of 2, 3 and 4 jets which pass the indicated cuts on the leptonic side. • Superset of actual background • No b-tagging / light jet rejection assumptions Evolution of cuts for W+jets background Joseph Virzi UC Berkeley

45. Single TopBackground • Sample used is single top production • MCMS > 1.5 TeV. • PT > 100 GeV • 5 pb cross section • The background plot looks at all combinations of 2, 3 and 4 jets which pass the indicated cuts on the leptonic side. • Superset of actual background • No b-tagging / light jet rejection assumptions Evolution of cuts for single top production Joseph Virzi UC Berkeley

46. Spectrum of Hadronic SideReconstruction Modes • 2 light jet + 1 b jet events • b → semileptonic top • 2 light jets summed • 1 light jet + 2 b jet events • b → semileptonic top • hadronic top = b + j • 3 light jets + 1 b jet events • b → semileptonic top • hadronic top = j + j + j • 5+ jet events • In all cases, the jets on the hadronic side are summed to the top • Reconstruction modes are separated for different jet multiplicities • The final reconstruction depends weakly on jet reconstruction algorithm • Allows for weighing contribution from each mode Joseph Virzi UC Berkeley

47. single tops-channel PT(leptonic top) Joseph Virzi UC Berkeley

48. Joseph Virzi UC Berkeley

49. Joseph Virzi UC Berkeley

50. Single top t-channelTruth Level Analysis Joseph Virzi UC Berkeley