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

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 Z→   ≈ 830 pb (Pythia) Z+jets  ≈ 5777 pb (Alpgen Chowder) ttbar+jets  ≈ pb (Alpgen Chowder) W+jets  ≈ pb (Alpgen Chowder) compared also with  New channel (  × BR ≈ 50 fb) along the line of H→VV: S. Bolognesi (INFN To)Higgs meeting – 23 September

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 (no Higgs mass peak → alternative variable like  (ll) in H→WW→l l )

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

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  UE activity increases with hard scattering energy scale bigger for high mass signal

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

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 i.e. |d 0 /  (d 0 )| < cut

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 All these variables are correlated → not so powerful!

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

Results (1 fb -1 ) 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 ± ± ± 7 33 ± 7 51 ± 3 78 ± ± ± ± ± ± ± ± 0.06 S. Bolognesi (INFN To)Higgs meeting – 23 September

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

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

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

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 Sourcessignal MH500background luminosity PDF MET modeling normalization MC statistics Total 10% 0.3% % 14.2%15.4% 2% % --- 3% CL B 22.34% 0.76 

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

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

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

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

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

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

Background yield (only poissonian error = √N)  Additional cuts needed to increase the significance S. Bolognesi (INFN To)Higgs meeting - 23 September (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

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

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