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

2. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 2 Outline oSM Higgs limits, production and decay modes oThe CMS detector oAbout the H->WW* analysis oAbout the H->ZZ* analysis oSM Higgs Discovery Potential

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

4. S.Sengupta, UMN SUSY08, Seoul, June 17 th 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)

5. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 5 SM Higgs Decay For m H < 140 GeV/c 2 obb dominant decay mode but is hard to see because of large QCD background. oγγ main discovery channel due to ECAL resolution For 160 < m H < 180 GeV/c 2 oH->WW* dominates For 140 < m H ~ 600 GeV/c 2 oH->ZZ*->4l is important at higher mass

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

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

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

9. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 9 Signal oMain discovery channel for the Higgs Boson in the mass range 2M W < m H < 2M Z o3 Signal topologies: e+e-, μ+μ-, e±μ± oGeared for ∫L=10 32 cm -2 s -1, 100 pb -1 of data oPythia is re-weighted to follow NLO P T distribution.

10. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 10 Background oPrimary backgrounds  Continuum WW : uncertainty 17% at 5 fb -1  tt->2μ : uncertainty 16% at 5 fb -1  γ*/Z->2l oOther backgrounds: ZW->3l, tWb->2l, ZZ->2l oMost samples generated with Pythia

11. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 11 Analysis features oAnalysis uses full detector simulation oSingle and di-lepton (e,μ) triggers at L1 and HLT o2 charged leptons (e or μ). Leptons are required to be well identified, well reconstructed and isolated  30 GeV < P T max < 55 GeV  P T min > 25 GeV o2 neutrinos in the final state. Require E T miss > 50 GeV } m H = 160 GeV/c 2

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

13. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 13 Jet veto and Acoplanarity 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) ∆Ф ll < 45° 12 < m ll < 40 GeV

14. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 14 Looking ahead… oCurrently 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.

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

16. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 16 The Golden Channel Cleanest discovery channel for m H > 140 GeV/c 2 H->ZZ->2e2μH->ZZ->4μ

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

18. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 18 Event Selection 2e2μ oRequire 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 ~ m Z oAnalysis requires lepton identification with high efficiency and resolution down to low P T (~ 5 GeV/c) 2e2μ before selection after selection m H = 200 GeV Selection cuts were optimized as a function of m H but mass independent cuts are being developed. m H = 140 GeV

19. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 19 Event Selection 4μ oHigh muon efficiency oUnderlying event is calibrated with data. Largest systematic uncertainties are from background. Vary with m H

20. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 20 m Z Resolution oFor m H < 180 GeV/c 2, one Z is on shell, other is off shell oFor 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 m H = 130 GeV/c 2 Ratio of the measured to the true invariant mass for μ+μ- pairs

21. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 21 Isolation and Impact Parameter oIsolation is important for reducing contamination from b-decay leptons  Isolation is in the tracker only  A cut is applied on the sum of the P T of the tracks in a cone of radius ∆R around the signal lepton  Signal efficiency ~ 90% oImpact 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.

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

23. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 23 Discovery Potential for the Higgs oLuminosity requirements:  ~ 100 pb -1 will exclude certain regions with a 95% CL  ~ 1-10 fb -1 has a discovery potential for m H ~ m WW at 5σ  ~ 30 fb -1 has a discovery potential of upto m H ~ 600 GeV

24. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 24 Conclusions oThe 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 o5σ discovery potential for the Higgs Boson over a large mass range at the LHC with 5 fb -1 of data. oH -> ZZ* has the cleanest signal and has the best discovery potential for a heavier Higgs Boson.

25. S.Sengupta, UMN SUSY08, Seoul, June 17 th 2008 25 Backup Slides

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

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

28. S.Sengupta, UMN SUSY08, Seoul, June 17 th 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.

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