The Tevatron s Search for High Mass Higgs Bosons Konstantinos A. Petridis University of Manchester On behalf of the CDF and DØ Collaborations K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 1 / 27
High mass Higgs searches at the Tevatron Higgs production cross sections for p p collisions at s = 1.96 TeV Gluon fusion (ggh) σ 0.2 1 pb Associated production (VH) σ 0.01 0.3 pb Vector Boson Fusion (qqh) σ 0.01 0.1 pb Precision ewk data yields 114 <M H < 186 GeV @95 C.L High Mass definition: Searches most sensitive for M H 135 GeV Main Decay mode is WW K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 2 / 27
H WW Final States Use of all feasible final states Hadron collider environment requires at least one leptonic W decay Dilepton (e, µ) - BR 6% Most sensitive final state Lowest Background Rate W Branching Fractions Lepton (e, µ)+τ h - BR 4% Consider hadronic τ decays (τ h ) Provides additional sensitivity Larger Background Rate e, µ+hadrons - BR 30% Larger BR gives 5 more signal compared to Dilepton Large Background Rate K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 3 / 27
High Masss Higgs Search Strategy Very low S/B makes a cut based analysis impossible (0.1 1.)% for m H = 165 GeV @ final selection stage Not a counting experiment Employ use of Multivariate techniques (MVA) to extract the signal Maximise power of discriminating variables Input parameters: Kinematic and Event topology variables MVA outputs used as inputs for limit setting (Neural Networks, Decision Trees) Technique validated measuring SM processes Create as many sub-channels as possible Optimise our Signal/Background discriminants for different mixes of signal and background contributions K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 4 / 27
Status in Summer 20 Combining low mass and high mass Using 5.6-6.1 fb 1 of analyzed data DØ almost achieved observed exclusion at M H = 165 GeV CDF achieved excpected exclusion at M H = 165 GeV Work even harder to improve sensitivity! K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 5 / 27
What is new in March 2011 CDF and DØ updated High Mass program using up to 7.1 fb 1 and 8.2 fb 1 respectively Channel CDF DØ H WW l νl + ν l = e, µ, 0/1/2+ jet Add data New l = e, µ, 1 jet low M ll Add data - l = τ h, µ(e) Add data New l = τ h, µ(e), 2+ jet - New (4.3 fb 1 ) H WW lνqq l = e, µ, 2+ jet - (5.4 fb 1 ) VH VWW SS Dilepton Add data (5.4 fb 1 ) Trileptons Add data - K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 6 / 27
H WW l νl + ν Event Selection 2 Opposite Sign high p T isolated leptons distinguishes from multijet and W+jets Missing Energy from neutrinos distinguishes from Z/γ Final state topology due to spin 0 Higgs distinguishes from WW Small opening angle between leptons in Higgs decays K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 7 / 27
H WW l νl + ν (l = e, µ) Splitting into sub-channels I Lepton Flavour DØ: eµ,ee,µµ CDF: Lepton flavour or quality Separation gives high and low S/B regions Entries 5 4 3 2 1 DØ Preliminary 1 L = 8.1 fb ee + MET data Z+jets Diboson W+jets Multijet ttbar Different efficiency, kinematics and resolution 1 0 20 40 60 80 0 120 140 160 180 200 M ee (GeV) Signal (M = 165 GeV) H Entries 4 data 1 3 DØ Preliminary L = 8.1 fb eµ + MET Z+jets Entries 5 4 DØ Preliminary 1 L = 8.1 fb µµ + MET data Z+jets Diboson 3 Diboson 2 W+jets 2 W+jets Multijet Multijet 1 0 0.5 1 1.5 2 2.5 3 φ eµ ttbar Signal (M = 165 GeV) H 1 1 0 20 40 60 80 0 120 140 160 180 200 M µµ (GeV) ttbar Signal (M = 165 GeV) H K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 8 / 27
H WW l νl + ν (l = e, µ) Splitting into sub-channels II Jet Multiplicity: 0jet, 1jet, 2jets Optimise on different signal/background compositions 0jet: WW 1jet: Z/γ 2jet: t t K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 9 / 27
e H WW l νl + ν (l = e, µ) Final Event Selection Reduce large Z/γ using E miss T DØ: Train DT against Z/γ for ee,µµ Each jet bin and mass hypothesis E miss T related variables as inputs Select events in high DT region CDF: Select events with high E miss T 0 signal evts at Final Selection (CDF+DØ) @M H = 165 GeV Jet bin splitting and Z/γ DT improves DØ s expected sensitivity 30% @M H =130GeV 15% @M H =165GeV Entries Entries 5 4 3 2 1 1 DØ Preliminary 1 L = 8.1 fb ee + MET 2 0 20 40 60 80 0 120 140 160 180 200 5 4 3 2 1 1 H WW µµ, 0 jets E T (GeV) Preliminary 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1 RF_Dy 0jets data Z+jets Diboson W+jets Multijet ttbar 6 data DØ Preliminary µµ+met+2jets M H =165 GeV Signal (M = 165 GeV) H KS Prob=8.993000e 01 Z+jets Diboson W+jets Multijet ttbar Sig Tot 1 Sig gghww Sig WH Sig ZH 1 1 Sig VbfH 1 Sig gghzz 1 1 K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 / 27
H WW l νl + ν (l = e, µ) Extract Signal Train MVA using Final Selection events in each jet bin and mass Input discriminating variables: Likelihood ratio of Matrix Element calculation (0jet CDF) Topological+kinematic combos Transverse mass of vector sum of lepton p and E miss T Use b-tagging information as input variable or veto in 1 or 2jet bin against t t K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 11 / 27
H WW l νl + ν (l = e, µ) MVA distributions CDF: NN DØ: DT Events 2 H WW eµ, 0 jets DØ Preliminary eµ+met+0jets M H =165 GeV Preliminary data Z+jets Events 3 data 2 H WW ee, 1 jets Preliminary DØ Preliminary ee+met+1jets M H =165 GeV Z+jets Diboson Diboson W+jets W+jets Multijet 1 Multijet 1 ttbar ttbar 1 m H =165 GeV 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Final Discriminant Sig Tot 2 1 0.8 0.6 0.4 0.2 0 0.2 0.4 0.6 0.8 1 Final Discriminant Tot. Sig K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 12 / 27
H WW l νl + ν (l 1 = τ h l 2 = µ,e) Including τ leptons decaying to hadrons. New channels for DØ! CDF updated e + τ h and µ + τ h as well µ and hadronically decaying τ (τ h ) + 1jet 3 subchannels based on τ h track/calo structure MVA based on NN µτ h and eτ h + 2jet For M H < 135 sensitive to H ττ final state K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 13 / 27
H WW lνq q (l = e, µ) Including hadronic W decays 1 lepton 2jets+E miss T 52 expected signal events @M H =160 GeV! Main background W+jets Reconstruct p z of neutrino using W mass constraint Possible to extract Higgs mass for M H >160 GeV K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 14 / 27
VH VWW (V=W or Z) Multi-lepton and jet final states from W/Z decays Suppress SM backgrounds Same Sign Dilepton + E miss T WH WWW Lepton charge measurement important Trilepton OS same flavour pair in/out Z mass window ZH ZWW/WH WWW K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 15 / 27
Systematic Uncertainties Events/0.13 Affecting Normalization or Shape of signal and background in the final discriminant Correlated luminosity (Total:6% Correlated:4%) and x-section between CDF and DØ Lepton ID 2 4%, Jet 3 25%(process dependent) 50 40 30 20 Tevatron Run II Preliminary L 8.2 fb -1 Data-Background SM Higgs Signal ±1 s.d. on Background 0 - -20-30 -40 March 7, 2011 m H =165 GeV -50-1.8-1.6-1.4-1.2-1 -0.8-0.6-0.4-0.2 0 log (s/b) σ NNLO+NNLL ggh scale variation 7 33% jet bin dependent JHEP 0908, 099 (2009), Phys Rev D 81, 074023 (20) σ NNLO+NNLL ggh PDF uncertainty 8 30% jet bin dependent Treatment recommended by PDF4LHC group Shape systematic for resummation scale by varying NNLO+NNLL p H T spectrum Expected signal lies above background uncertainty! K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 16 / 27
Limits No significant excess of signal like events is observed MVA outputs used to set exclusion limits at 95% C.L DØ: Single Experiment Exclusion!! 163<M H <168 @95% C.L (160<M H < 168 expected) CDF: Single Experiment Exclusion!! 158<M H <168 @95% C.L (160<M H < 167 expected) K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 17 / 27
Conclusions and Outlook Presented an overview of the latest Tevatron High mass Higgs searches A great milestone achieved by both experiments reaching exclusion sensitivity individually Explore all available avenues Large Data Samples All feasible final states considered All feasible channel splittings considered Sophisticated signal/background discriminants Still room for improvement fb 1 by the end of RunII Improvements in object IDs Additional channels such as H ZZ And now for the Combined Results! (see Bo s talk coming soon) Many thanks to CDF and DØ collaborators K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 18 / 27
Backup K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 19 / 27
Expected limits per channel Exp Limit x SM @165 Channel CDF DØ H WW l νl + ν l = e, µ, 0/1/2+ jet 0.93 (incl. low M ll,ss dilep,trilep) 0.97 l = τ h, µ(e) 13.1 7.5 (µτ h ) l = τ h, µ(e), 2+ jet - 12.3 H WW lνqq l = e, µ, 2+ jet - 5.1 VH VWW SS Dilepton - 7.0 K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 20 / 27
Matrix Element Discriminant K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 21 / 27
MVA cross check K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 22 / 27
Responses I K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 23 / 27
Responses II K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 24 / 27
Responses III K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 25 / 27
Responses IV K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 26 / 27
Responses V K.A. Petridis (University of Manchester) Tevatron High Mass Higgs Searches Moriond EW March 2011 27 / 27