Search for the SM Higgs Boson in H->ZZ* and H->WW* at the LHC

1. Search for the SM Higgs Boson in H->ZZ* and H->WW* at the LHC Sinjini Sengupta University of Minnesota CMS Collaboration The 16th International conference on Supersymmetry and the Unification of Fundamental Interactions.

2. Outline • SM Higgs limits, production and decay modes • The CMS detector • About the H->WW* analysis • About the H->ZZ* analysis • SM Higgs Discovery Potential SUSY08, Seoul, June 17th 2008

3. SM Limits on the Higgs Mass Theoretical limits: finite and positive Higgs coupling Experimental limits: Direct (from LEP): mH > 114.4 GeV @ 95% CL Indirect (from EW data): mH < 144 GeV Ref: Phys.Lett.B 565(2003) SUSY08, Seoul, June 17th 2008

4. SM Higgs Production Gluon-gluon fusion (dominant mode) Vector Boson Fusion (forward jets in final state) Associated production (additional leptons or jets in the final state) SUSY08, Seoul, June 17th 2008

5. SM Higgs Decay For mH < 140 GeV/c2 • bb dominant decay mode but is hard to see because of large QCD background. • γγ main discovery channel due to ECAL resolution For 160 < mH < 180 GeV/c2 • H->WW* dominates For 140 <mH ~ 600 GeV/c2 • H->ZZ*->4l is important at higher mass SUSY08, Seoul, June 17th 2008

6. CMS experiment Superconducting Solenoid Muon Detectors Electromagnetic Calorimeter Forward HCAL Hadronic Calorimeter Tracker SUSY08, Seoul, June 17th 2008

7. The Muon Detector • Drift Tubes (DT) in the barrel region • Cathode Strip Chambers (CSC) in the endcap region • Resistive Plate Chambers (RPC) as dedicated trigger detectors in both barrel and endcap. 5 wheels in the Barrel 30° (Φ) sectors 4 layers of muon chambers, |η|=2.4 SUSY08, Seoul, June 17th 2008

8. Higgs―›WW*―›lνlν (where l=e,μ) SUSY08, Seoul, June 17th 2008

9. Signal • Main discovery channel for the Higgs Boson in the mass range 2MW < mH < 2MZ • 3 Signal topologies: e+e-, μ+μ-, e±μ± • Geared for ∫L=1032cm-2s-1, 100 pb-1 of data • Pythia is re-weighted to follow NLO PT distribution. SUSY08, Seoul, June 17th 2008

10. Background • Primary backgrounds • Continuum WW : uncertainty 17% at 5 fb-1 • tt->2μ : uncertainty 16% at 5 fb-1 • γ*/Z->2l • Other backgrounds: ZW->3l, tWb->2l, ZZ->2l • Most samples generated with Pythia SUSY08, Seoul, June 17th 2008

11. Analysis features • Analysis uses full detector simulation • Single and di-lepton (e,μ) triggers at L1 and HLT • 2 charged leptons (e or μ). Leptons are required to be well identified, well reconstructed and isolated • 30 GeV < PTmax < 55 GeV • PTmin > 25 GeV • 2 neutrinos in the final state. Require ETmiss > 50 GeV } mH = 160 GeV/c2 SUSY08, Seoul, June 17th 2008

12. Analysis features • Due to presence of 2 neutrinos, there is no mass peak. • Counting experiments • Accurate background estimates from data are needed. • Good reconstruction tools needed. • Well identified lepton reduces W+jet bkg • To reduce tt and tWb bkg all central jets (|η| < 2.5) with PT > 15 GeV are rejected. (this gets rid of 90% tt but keeps 50% signal) • Backgrounds are the dominant source of systematics (20% for 1 fb-1) SUSY08, Seoul, June 17th 2008

13. Jet veto and Acoplanarity ∆Фll < 45° 12 < mll < 40 GeV Invariant mass before and after central jet veto cut. Azimuthal angular separation between The di-lepton pair after all other cuts. (effective in reducing WW, ZZ and WZ backgrounds) SUSY08, Seoul, June 17th 2008

14. Looking ahead… • Currently cut vs multi-variate analysis is being studied. • First results are very promising • Shows an excess in signal events. 5σ discovery potential can be achieved very rapidly. Need to understand detector and backgrounds well. SUSY08, Seoul, June 17th 2008

15. Higgs―›ZZ*―›4l (4l = 4e, 4μ or 2e2μ) SUSY08, Seoul, June 17th 2008

16. H->ZZ->4μ H->ZZ->2e2μ The Golden Channel Cleanest discovery channel for mH > 140 GeV/c2 SUSY08, Seoul, June 17th 2008

17. Signal and Background • Signal: • Potential for discovery over a wide mass range • Possible topologies: 4e, 4μ, 2e2μ • 2e2μ has twice the rate as 4e an 4μ channels • Backgrounds: • qq -> ZZ*/γ* • Irreducible, dominant background • gg -> tt -> WWbb • Zbb • Reducible backgrounds • non-isolated leptons from b decays SUSY08, Seoul, June 17th 2008

18. Event Selection 2e2μ 2e2μ before selection • Require 2 pairs of leptons • Flavor must be conserved • Charge must be conserved • Leptons must be isolated • Originate at primary vertex • Reconstruct to dilepton invariant mass ~ mZ • Analysis requires lepton identification with high efficiency and resolution down to low PT (~ 5 GeV/c) mH = 200 GeV mH = 140 GeV after selection Selection cuts were optimized as a function of mH but mass independent cuts are being developed. SUSY08, Seoul, June 17th 2008

19. Event Selection 4μ • High muon efficiency • Underlying event is calibrated with data. Largest systematic uncertainties are from background. Vary with mH SUSY08, Seoul, June 17th 2008

20. mZ Resolution • For mH < 180 GeV/c2, one Z is on shell, other is off shell • For the on shell Z • Z -> 2μ has 1.14% mass resolution • Z -> 2e has 1.8% mass resolution (worse resolution due to Bremsstrahlung) CMS note 2006/136 mH = 130 GeV/c2 Ratio of the measured to the true invariant mass for μ+μ- pairs SUSY08, Seoul, June 17th 2008

21. Isolation and Impact Parameter • Isolation is important for reducing contamination from b-decay leptons • Isolation is in the tracker only • A cut is applied on the sum of the PT of the tracks in a cone of radius ∆R around the signal lepton • Signal efficiency ~ 90% • Impact Parameter • Leptons from b quarks dont come from the primary vertex • Apply cuts on the transverse and the 3D distance of fitted tracks from the vertex as well as on the impact parameter significance. SUSY08, Seoul, June 17th 2008

22. Significance • Expected events for signal and background for an integrated luminosity corresponding to a discovery significance of 5σ. • Systematic uncertainties (5-30% from backgrounds) have little impact on the discovery potential. mH = 200 GeV mH = 140 GeV SUSY08, Seoul, June 17th 2008

23. Discovery Potential for the Higgs • Luminosity requirements: • ~ 100 pb-1 will exclude certain regions with a 95% CL • ~ 1-10 fb-1 has a discovery potential for mH ~ mWW at 5σ • ~ 30 fb-1 has a discovery potential of upto mH ~ 600 GeV SUSY08, Seoul, June 17th 2008

24. Conclusions • The H -> WW* and H ->ZZ* analyses are already well developed at CMS • Studies are being updated and new results are expected shortly • Multivariate approach over the counting strategy in the case of H -> WW* shows significant early promise • 5σ discovery potential for the Higgs Boson over a large mass range at the LHC with 5 fb-1 of data. • H -> ZZ* has the cleanest signal and has the best discovery potential for a heavier Higgs Boson. SUSY08, Seoul, June 17th 2008

25. Backup Slides SUSY08, Seoul, June 17th 2008

26. Cut Flow Table for H-> ZZ* -> 2e2μ mH = 140 GeV/c2. Errors are statistical only. All values (except number of events) are in fb SUSY08, Seoul, June 17th 2008

27. Cut Flow Table for H -> ZZ* -> 2e2μ mH = 200 GeV/c2. Errors are statistical only. All values (except number of events) are in fb SUSY08, Seoul, June 17th 2008

28. Results for H -> ZZ* -> 2e2μ Expected number of events from signal and background processes for an integrated luminosity corresponding to a 5σ significance. SUSY08, Seoul, June 17th 2008

29. Results for H-> WW* -> 2e Expected number of events for a luminosity of 10 fb-1 Selection cuts optimized for mH = 150 GeV/c2. SUSY08, Seoul, June 17th 2008