Search for the Higgs via Vector Boson Fusion in H → WW → e ν jj with m H = 160 GeV

1. Search for the Higgs via Vector Boson Fusion inH→WW→eνjjwith mH = 160 GeV Kira Grogg UW-Madison May 14, 2007 Kira Grogg, UW-Madison

2. Outline • Importance of finding the Higgs particle • Vector Boson fusion • Higgs & W decays • Compact Muon Solenoid (CMS) • Signal qqH→qqW+W-→qqeνjj attributes • Simulated events • Finding electrons -- overview of cuts • Reconstructed electrons • Comparison between reconstructed and generated electrons • Dijet mass and comparison between reconstructed and generated jets • Missing Et • Backgrounds and selection cuts Kira Grogg, UW-Madison

3. Importance of Higgs Particle • Cannot simply add a mass term to the weak lagrangian • Introducing a scalar field (higgs) with hidden symmetry breaking allows a mass term to appear • The coupling strength of a particle to the higgs determines its mass • The Higgs particle is essential to the standard model Kira Grogg, UW-Madison

4. Search for the Higgs • The mass of the Higgs cannot be determined from the current theory: • The scale factor λ is unknown, v = 246 GeV (measured) • Experiments so far (at LEP) have put a mass limit on the higgs particle of about 115 GeV • The LHC, with 14 TeV center of mass energy, will search at higher ranges • At a mass starting at 160 GeV the higgs can be found from the fusion of two real Ws (Vector Boson Fusion) Kira Grogg, UW-Madison

5. Vector Boson Fusion (VBF) • Forward, “tag”, jets help identify signal Kira Grogg, UW-Madison

6. Higgs & W Decays where Kira Grogg, UW-Madison

7. Compact Muon Solenoid (CMS) CMS is a large general purpose detector for proton-proton collisions LHC Kira Grogg, UW-Madison

8. CMS Detector Kira Grogg, UW-Madison

9. Event Simulation Kira Grogg, UW-Madison

10. Generation of SignalH→WW→eνjj Pythia Parameters Pythia generates Higgs from VBF, forces decay into WW and the Ws into electron, neutrino and two jets Kira Grogg, UW-Madison

11. Signal Identification Cuts • Require: • One lepton, 30< pt < 120 GeV (no near jets) • Njets  4, Et > 25 GeV • Missing Et > 30 GeV • Forward tag jets • Et > 30 • 1·2 < 0 • | 1·2 | > 3.8 • mjj > 800 GeV • Hadronic W mass • ∆mw < 25 GeV • Leptonic W -- reconstruct mass using lepton and missEt • Choose L-W which is closest to H-W • Pseudorapidity’, where theta is angle from beam path Kira Grogg, UW-Madison

12. Electron Selection • Look at energy in clusters of EM calorimeter towers • Number of events with generated electrons: 4600 • Require minimum energy (97% efficiency) • Require no nearby jets of significant energy (90% efficiency) • Require a nearby track of sufficient energy (75% efficiency) • “Nearby” is defined by a cone: • Phi is around detector, eta is a function of angle form the beam path Kira Grogg, UW-Madison

13. Plots to determine jet cuts Δr must be < 0.15 and sc Et < 85% jet Pt to eliminate a supercluster as an electron r between jets and superclusters supercluster Et / jet pt Kira Grogg, UW-Madison

14. Plots to determine track cuts Δr must be < 0.15 and supercluster Et / track Pt > 0.75 Minimum r supercluster Et / track pt Kira Grogg, UW-Madison

15. Gen and Reco Electron Et (~76% efficiency) Generated and reconstructed electrons from events with reconstructed electrons All generated and reconstructed electrons Kira Grogg, UW-Madison

16. Phi and Eta of Gen and Reco Electrons Detector simulation only goes to eta = 3 Kira Grogg, UW-Madison

17. Comparison of Reco and Gen Electrons Δr for ET of Reconstructed and Generated Electrons -- very close Kira Grogg, UW-Madison

18. Electron gen v. reco Et and Pt Much of the mismatched Pt comes from the endcap region Kira Grogg, UW-Madison

19. Electron gen v. reco Eta & Phi Kira Grogg, UW-Madison

20. Gen and Reco DiJet Mass (only jets) Kira Grogg, UW-Madison

21. Missing Et & Neutrino Et Miss Et from Reco::METCollection Kira Grogg, UW-Madison

22. QCD events tt + jets W + t +jets W + tb t decays to W +b W + jets Z + jets – decays into two leptons but often one is in the forward region WW + jets ZZ + jets ZW + jets tt + jets and W +jets have the largest cross-sections Will need hard cuts to see signal over the backgrounds which all have much larger cross-sections Backgrounds Kira Grogg, UW-Madison

23. Background Reduction Cuts • No, or limited, extra jets • Stricter ∆ and mjj cuts on tag jets • Optimize ∆r between hardronic and leptonic Ws • Require ∆mw < 20 • Optimize jet Et thresholds Kira Grogg, UW-Madison

24. Comparison with Backgrounds – Electrons Kira Grogg, UW-Madison

25. Backgrounds--Dijets Kira Grogg, UW-Madison

26. Backgrounds – Missing Et Kira Grogg, UW-Madison

27. Conclusions • It should be possible to find the Higgs particle via H→WW→eνjj given hard selection cuts • Signal will be hard to identify given the high backgrounds • The tag jets and a reconstructed higgs mass will help • For the simulation, the reconstructed electrons match well the energy and location of generated electrons • Efficiency ~ 76% • Additional plots and documentation of procedure can be found at http://www.hep.wisc.edu/~grogg Kira Grogg, UW-Madison

28. Kira Grogg, UW-Madison

29. Backup slides Kira Grogg, UW-Madison

30. Proton-Proton interaction at the LHC Luminosity L = particle flux/time Interaction rate Cross section  = “effective” area of interacting particles Kira Grogg, UW-Madison

31. Higgs production Kira Grogg, UW-Madison