1. H → ZZ →  A promising new channel for high Higgs mass Sara Bolognesi – Torino INFN and University Higgs meeting 23 Sept. 2008 – CMS Week

2. Introduction ≈10×BR(H→ZZ→4  ), same final state of H→WW→   Analysis code/workflow similar to H→VV re-use the code (MET corrections) use the skimmed sample of H→WW (CMSSW_1_6_9)  Results up to preselection already shown in Higgs meeting on 9th May: resolution and efficiency on signal signal and background kinematic definition of preselection cuts  High background: inclusive ZZ  ≈ 15 pb (Pythia) inclusive WW  ≈ 114 pb (Pythia) ttbar  ≈ 840 pb (MC@NLO) Z→   ≈ 830 pb (Pythia) Z+jets  ≈ 5777 pb (Alpgen Chowder) ttbar+jets  ≈ 836.5 pb (Alpgen Chowder) W+jets  ≈ 58155 pb (Alpgen Chowder) compared also with  New channel (  × BR ≈ 50 fb) along the line of H→VV: http://indico.cern.ch/materialDisplay.py?contribId=3&materialId=slides&confId=32886 S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 2

3. Analysis workflow  HLT: 1 or 2 muons isolated or not  Skimming: at least 2 global muons with p T > 20, 10 GeV and |  |<2.4  Preselection: exactly two muons with opposite charge 80 GeV < M(  ) < 100 GeV MET > 25 GeV after Type 1 and 2 corrections (i.e. Jet Energy Scale and muons corrections)  Selection cuts studied: Central Jet Veto or Track Counting Veto muon isolation and impact parameter cut kinematic selection  Final distributions to search signal excess S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 3 (no Higgs mass peak → alternative variable like  (ll) in H→WW→l l )

4. Event yields after preselection (9.54 ± 0.03)% (0.203 ± 0.004)% (1.40 ± 0.03)% (0.071 ± 0.003)% (49.7 ± 0.3)% S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 4

5. Track counting veto  Similar results from Central Jet Veto with calorimetric jets  VBF events in signal (20% for mh500) have 2 jets  sign > √  back gain in significance supposed to be at high  but in highly boosted events (43% of events has p Z H >200GeV) one jet can be central (only  is boost invariant) No CUT on TCV S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 5  UE activity increases with hard scattering energy scale bigger for high mass signal

6. Muon isolation  Good rejection against W+jets and tt+jets in cone (  R=0.3) around the second muon (with lower p T )  Very low signal rejection: VBF jets far away from muons (high  (jet-  )) UE recoils with respect to Higgs S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 6

7. Muon tranverse impact parameter no gain in significance  Same efficiency on signal and Z+jets (which is 97% of the background after preselection) S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 7 i.e. |d 0 /  (d 0 )| < cut

8. Kinematic Signal kinematic dependent on Higgs mass: low mass similar to background No samples available for optimization of the cuts as a function of the Higgs mass (however premature at this stage) S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 8 All these variables are correlated → not so powerful!

9. Kinematic: p T (  )/MET scalar Higgs (isotropic H→ZZ decay) → p T (  )/MET ≈ p T Z1 /p T Z2 ≈ 1 for any mass  Strong rejection (47%) of Z+jets: high Z p T (Z recoling w.r.t. jets and UE) low MET because no neutrinos difference between mh200 and mh500 due to MET measurement error → related with hard scattering scale (i.e. Higgs mass) → related with UE  Good behaviour on signal: S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 9

10. Results (1 fb -1 ) 150-250 GeV signal 200 signal 500 Z+jets tt+jets W+jets WW ZZ significance  MH200: likelihood from kinematic variables → significance 0.2  MH500: 12.5 fb -1 (35 fb -1 ) for Higgs evidence (discovery) events (1 fb -1 )  Higgs transverse mass includes all the previous kinematic variables simple dependence on the Higgs mass to be used as final reference distribution to search for signal excess > 400 GeV 22.4 ± 0.2 24003 ± 165 202 ± 7 33 ± 7 51 ± 3 78 ± 3 ---4.96 ± 0.08 31 ± 5 0.6 ± 0.4 0 0.4 ± 0.2 2.6 ± 0.5 --- 0.143 ± 0.0010.85 ± 0.06 S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 10

11. Systematics MET: 5% from Z/W comparison* → propagated into analysis 2% Muon efficiency (trigger, reconstruction, isolation): measured from single Z data* with negligible uncertainty Muon momentum scale measured and calibrated from single Z data* → residual systematics due to magnetic field and misalignement is negligible (<1% on Z xsec) Jet energy scale and jet reconstruction efficiency no impact (no CJV used)  Systematics on background yield (luminosity, PDF, NLO) can be avoided with background normalization from data  Experimental systematics * Towards a measurements of the inclusive W→  and Z→  cross sections in pp collisions at √s = 14 TeV CMS AN 2007/031, PAS 2007/002 S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 11

12. Z+jets normalization Control region: all analysis cuts but MET<25 GeV has negligible uncertainty: pollution from other processes 0.02% statistical uncertainty 0.2% with 1fb -1  MC extrapolation dominated by MET uncertainty → 3% final uncertainty on Z+jets yield in signal region 2% in each region  S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 12

13. ZZ normalization  No region where ZZ dominates because Z always overwhelming → use single Z process as reference control region: all analysis cuts on muons, MET not considered  Extrapolation to signal region (= control region + MET related cuts)  dominated by MET uncertainty → 4% on  uncertainty negligible: main effects (muon trigger, reco, iso efficiency), which are however small, mostly cancel out main effect (PDF) mostly cancel out  uncertainty negligible:  uncertainty very small: 0.2% pollution from other processes 0.15% statistical uncertainty with 1fb -1 S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 13

14. Conclusion 15.5 fb -1 (43 fb -1 ) needed for Higgs evidence (discovery) with mass 500 GeV. S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 14 Sourcessignal MH500background luminosity PDF MET modeling normalization MC statistics Total 10% 0.3% --- 1.6% 14.2%15.4% 2% --- 15% --- 3% CL B 22.34% 0.76 

15. Open issues  Too small MC background samples available: background MC statistics is the main systematics  Samples with different Higgs mass needed to assess the discovery power for different masses (possibly optimizing cut VS mass)  Z inclusive p T (and MET in Z+jets events) must be measured from data to tune MC!! MC level Z p T (after HLT+skimming) reco Higgs transverse mass (after full analysis selection) S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 15

16. Back-up

17. Higgs transverse mass S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 17 Two possible definitions: using only muon info using also MET ≈ p T ( ) (energy and direction: p x,p y ) mh200mh500

18. MH200 likelihood S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 18

19. Signal reconstruction resolution  Z →  :  p T resolution M(  ) resolution mean = 0.12% std.dev. = 1.6% mean = 0.19% std.dev. = 1.3% resolution: gaussian with underestimated mean (recoMET < genMET) + not gaussian queue with recoMET > genMET importance of the JES and muon corrections  Z → (MET): MET MET resolution  = -10%  = 33% S. Bolognesi (INFN To)Higgs meeting - 23 September 2008 19

20. Signal VS backgrounds After HLT (all muon paths) and skimming (at least 2 mu with p T > 20, 10 GeV and |  |<2.4) M(  ) signal Z →  ttbar inclusive ZZ inclusive WW inclusive All histograms normalized to 1 biggest muon p T 2° muon p T MET (i.e. Z p T ) number of muons charge of muons important for Zbb e ZW

21. HLT, skimming, preselection efficiency on signal  HLT: all muon paths  Skimming:  at least muons with  p T > 20, 10 GeV and |  |<2.4  exactly two muons with opposite charge  muon p T > 20, 40 GeV  80 GeV < M(  ) < 100 GeV  corrected MET > 25 GeV  Preselection: acceptance and reco eff. for each  86.0 ± 0.1 % HLT91.5 ± 0.2 % HLT + skimming71.5 ± 0.3 % HLT+skim accept×accept () 96.7 ± 0.3 % HLT + skimming + preselection 40.1 ± 0.3 % HLT+skim+presel HLT+skim ( ) 56.1 ± 0.3 %  Signal efficiencies: S. Bolognesi (INFN To)Higgs meeting - 23 September 2008 21

22. Background yield 0.05 0.1 (only poissonian error = √N)  Additional cuts needed to increase the significance S. Bolognesi (INFN To)Higgs meeting - 23 September 2008 22 (CJV, mu isolation and IP, kinematic cuts)  Main backgrounds Z→  and ttbar preselection cuts efficiency (after HLT+skim) Significance: signal Z →  ttbar inclusive ZZ inclusive WW inclusive 0.06

23. isolation efficiency reconstruction efficiency trigger (L1×HLT) efficiency Muon efficiencies from tag & probe S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 23

24. MET systematics Muon scale calibration S. Bolognesi (INFN To)Higgs meeting – 23 September 2008 24