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Higgs- Fermion SSeeaarrcchh ffoorr h→γγ aatt DØ Alex Melnitchouk University of Mississippi for the DØ collaboration TeV4LHC workshop Fermilab, September 16, 2004 h→γγ Decay Mode in the SM and Beyond. • no tree-level Hγγ coupling (Higgs boson is neutral) • Di-photon decays happen via W loop γ (top-quark loop reduces h W H→γγ width by 20-30% due to destructive interference) γ • H→γγ branching fraction is small: ~ 10-3-10-4 Higgs decays mostly to b-quark and W pairs • However many extensions of the SM predict enhanced γγ decay rate of the Higgs boson How Can h→γγ Decays be Enhanced • One possibility: suppress fermion decay rates (then the full decay width would only be shared with h→WW and H→ZZ decays) • In the Standard Model Higgs is responsible for both Electroweak symmetry breaking (EWSB) and fermion masses • Higgs-W,Z/fermion interaction terms in the SM Lagrangian are: 2 + - (1/v) 2m WW W H 2 (1/v) m ZZZH ψψ (1/v) mf H • Relative strength of Higgs-W,Z and Higgs- fermion couplings is fixed by v (Higgs field vacuum expectation value) • In a more general situation different sectors of theory (or different mechanisms) could be responsible for EWSB and (some of) fermion masses => Higgs couplings to fermions and those to weak gauge bosons can vary independently Some Examples of h→γγ Enhancement • Strong dynamics [1] : EWSB = via technicolor condensation, fermion masses = via “extended techncolor” • Generic two Higgs doublet model [2]: v1 – W,Z masses, v2 – fermion masses • Top-condensation model + Higgs [3] top and bottom quarks get their masses from the topcolor interaction while Higgs gives mass to remaining fermions and gauge bosons • Topcolor Higgs=(top,vector-like quark )[4] Top quark mass from Higgs, other fermion and W/Z masses -- from other interactions present in the theory • Still another possiblity of h→γγ enhancement arises when the Higgs field extends into large extra dimensions (while fermion and gauge boson fields remain confined to 3D) [5] [1] E.Farhi (CERN), L. Susskind Phys,.Rept.74, 277 (1981) [2] H.E.Haber et al, Nucl. Phys. B161, 493 (1979) [3] J.D. Wells, Phys. Rev. D56, 1504 (1997) [4] B.Dobrescu, Phys. Rev. D63, 015004 (2001) [5] L. Hall, C.Kolda, Phys. Lett. B459, 213 (1999) Major Backgrounds : Drell-Yan and QCD q e+ • Z/γ∗→e+e- with Z*, γ* e+e- misidentified e . g . as photons q e- (lost tracks) • QCD processes that in the final state contain : 1. two 2. a photon and a hadronic jet photons misidentified as photon γ q γ q q e.g. q q q γ g 3. two hadronic jets misidentified as photons e.g. q q q g g g q g q q q g q g g Analysis Outline • Select 2 Energetic Photon Objects • Estimate SM backgrounds: - QCD (jj and γj) from data with absolute - Z/γ∗→ee normalization - direct di-photons (PYTHIA MC with k factor of 1.4) • Optimize the analysis kinematically • Look for a bump in the diphoton invariant mass spectrum Selection of γγ Candidate Events • Trigger: di-EM* high pT trigger • Offline: (on both objects) • Kinematic cuts: pT > 25GeV • Acceptance cuts: Central or End Cap Calorimeter up to |η|=2.4 • Photon ID: -- shower shape consistent with EM* shape (EMfraction, Isolation, H-matrix χ2) -- sum of pT of all tracks in a hollow cone of 0.05<R<0.4 around photon candidate must be < 2.0 GeV -- track veto • *EM = Electromagnetic Object (Photon or Electron) Event Displays of γγ Candidate Run 148830 Event 3510187 Tue May 21 21:28:31 2002 Run 148830 Event 3510187 Tue May 21 21:28:43 2002 • 14 ET scale: 44 GeV y 35 ET GeV x 2PI -3.7 -1.2 phi 0.0 eta 1.2 0.0 3.7 -2.3 2.3 Run 148830 Event 3510187 Tue May 21 21:28:37 2002 E scale: 42 GeV Mass = 125.8 GeV +z 180 0 Definitions of Analysis Objects LooseEM = reconstructed cluster that passes minimal EMID cuts based on calorimeter info (EM fraction>0.9 && Isolation<0.15) Electron/Photon (e/γ) = LooseEM object that passes shower shape cuts and has/NO associated track Approximation: Photon = Electron = EM object as far as calorimeter info (more on this a few slides later) Deriving Z/γ∗→ee and QCD jj+ γj backgrounds from data • Use two orthogonal samples: Di-LooseEM (Exactly One) Loose EM >85% -- misidentified jets for M >100 GeV <15% -- real photons jj • And four measurements : EMID efficiency Tracking efficiency Electron (e) misID rate Photon (γ) misID rate Z/γ∗→ee and QCD jj+ γj backgrounds (cont’d) di-LooseEM Data SAMPLE EMID Z/γ∗→ee bkgd efficiency QCD (jj+γj) bkgd select ee tracking subtract efficiency subtract Z/γ∗ fake ee di-LooseEM e misID rate derive γγ derive γγ from ee from di-LooseEM γ misID rate LooseEM+X Data SAMPLE Estimating QCD (jj+γj) Background γγ NQCD( ) = × 2 γ = {N(di-LooseEM) - NDY(di-LooseEM)} f ( ) NDY(di-LooseEM) = NDY(ee) ε2(EM) × ε2(track) = [N(ee) - N(di-LooseEM) × f 2(e)] ε2(EM) × ε2(track) γγ NQCD( ) = = {N(di-LooseEM) - [N(ee) - N(di-LooseEM) × f 2(e)] } × f 2(γ) ε2(EM) × ε2(track) EMID/tracking efficiencies Electron/Photon misID rates Estimating Zγ∗→ee Background σ → γ∗ × × × × ε NDY(ee) = (pp Z/ +X) Br(ee) Lint A (trigger) × ε2(EM) × ε2(track) γ γ σ → γ∗ × × × × ε NDY( )= (pp Z/ +X) Br(ee) Lint A (trigger) × ε2(EM) × [1- ε(track)] 2 γ γ × ε 2 NDY( ) = NDY(ee) [1- (track)] = ε2(track) = {N(ee) - N(misidentified ee)} × [1- ε(track)] 2 ε2(track) = {N(ee) - N(di-LooseEM)×f 2(e)} × [1- ε(track)] 2 ε2(track) Electron misidentification rate Tracking efficiency Relying on Electrons for Photon ID • Ideally we would use high PT photon sample from diphoton decays of a ~>100 GeV scalar (if there were one available) for Photon ID efficiency for the Higgs search • In reality we rely on • Z→ee electrons from data • Z→ee and H→γγ Monte Carlo to correct for the difference between electron and photon efficiency • Assumption: MC e/γ difference = e/γ difference in real data DØ Calorimeter Central Calorimeter (CC) and 2 End Calorimeters (EC) DO LIQUID ARGON CALORIMETER END CALORIMETER Outer Hadronic (Coarse) Middle Hadronic (Fine & Coarse) CENTRAL End-View of CC CALORIMETER Electromagnetic Inner Hadronic Fine Hadronic (F ine & Coarse) Coarse Hadronic 1m Electromagnetic (one quarter) rz-view of the D0 calorimeter EM calorimeter 0.2 0.4 0.6 0.8 1.0 EM4: 10X0 1.2 EM3: 7X0 1.4 EM2: 2X 1.6 0 1.8 2.0 EM1: 2X0 2.2 2.4 2.6 2.8 3.0 look at some shower 3.2 3.7 properties in EM3 4.5 Photon and Electron Shower Properties iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC MC γ 12000 MC γ MC γ MC γ 16000 MC e MC e 14000 MC e 14000 MC e 10000 14000 DATA e DATA e 12000 DATA e DATA e DATA fake rϕ-width in EMDATA3 fake DATA fake 12000 DATA fake 12000 8000 10000 10000 10000 8000 6000 8000 8000 6000 6000 6000 4000 4000 4000 4000 2000 2000 2000 2000 0 0 0 0 0 10 20 30 40 50 0 10 20 30 40 50 0 10 20 30 40 50 0 20 40 60 80 100 rφ-width in EM1, cm rφ-width in EM2, cm rφ-width in EM3, cm rφ-width in EM4, cm iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC iso<0.15 CC object from CCEC γ γ γ γ 3500 MC 14000 MC 4500 MC MC MC e MC e MC e 7000 MC e 4000 3000 DATA e 12000 Energy(EM3)DATA e DATA e DATA e 6000 DATA fake DATA fake 3500 DATA fake DATA fake 2500 10000 Total Energy 3000 5000 8000 2000 2500 4000 2000 1500 6000 3000 1500 1000 4000 2000 1000 500 2000 500 1000 0 0 0 0 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 0 0.2 0.4 0.6 0.8 1 EEM1 / Etotal EEM2 / Etotal EEM3 / Etotal EEM4 / Etotal Leading SM Higgs Production Processes at Tevatron g gluon fusion: cross-section ~ m2 h the top-quark loop is dominant t Cross-Section, pb g 10.0 s = 2 TeV W/Z associated q W ((Z)Z) 1.0 W* ((Z*)Z*) 0.1 q h 0.01 W/Z fusion 80 100 120 140 160 q q Higgs Mass, GeV W* (Z*) h quark-antiquark fusion cross-section is small : q q • Higgs-fermion coupling ~ mf • Masses of u,d quarks are small Topcolor and Fermiophobic Scenarios Topcolor Higgs (all major production mechanisms) g q W (Z) q q h W* (Z*) t W* (Z*) h g q h q q Fermiophobic Higgs (no gluon fusion) expect large transverse boost of the Higgs g q W (Z) q q h W* (Z*) t W* (Z*) h g q h q q M=60 h_bgd_060 M=70 h_bgd_070 Entries 1661 Entries 1792 Mean 0.1225 200 Mean 0.1159 RMS 0.3677 RMS 0.3657 120 anjet30 (good runs) bkgd 180 160 100 anjet30 FHiggs 140 80 120 100 60 80 40 60 40 20 20 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 M=80 h_bgd_080 M=90 h_bgd_090 Entries 2060 Entries 2195 Mean 0.1215 Mean 0.1311 RMS 0.3751 220 RMS 0.3925 M=60180 h_bgd_060 M=70 h_bgd_070 Entries 1982 200 Entries 2141 16070 Mean 10.3 Mean 11.91 RMS 11.47 180 RMS 10.86 140 70 160 60 120 14060 γγ 10050 Jet multiplic120 ity and p 50 100 T 80 40 4080 60 30 60 40 30 40 2020 2020 0 0 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 10 Jet multiplicity and 10 0 0 0 20 γγ40 60 80 100 120 140 0 20 40 60 80 100 120 140 M=100 h_bgd_100 MM==M=120112200 GGeeVV h_bgd_120 pT are correlatedEntries 1071 Entries 333 Mean 0.1754 Mean 0.2216 RMS 0.4561 300 RMS 0.5004 M=80 h_bgd_080 M=90 background h_bgd_090 250 Entries 2548 Entries 2643 70 Mean 13.29 Mean 14.07 Signal : 25090 signal γγ RMS 11.22 RMS 12.83 20060 80 Higgs p (pT ) 200 T 70 50 150 is balanced 15060 40 100 50 by the p of the jets 100 30 T 40 50 q W (Z) 3050 20 20 0 1 2 3 0 0 10 0 0.5 1 1.5W* (Z*)2 2.5 3 3.5 4 0 0.5 1 1.5 2 2.5 3 3.5 4 10 jet multiplicity 0 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140 q h M=100 h_bgd_100 M=120 h_bgd_120 Entries 1274 Mh=120 GeV Entries 413 Mean 16.89 Mean 19.57 RMS 14.32 90 RMS 16.8 80 background 80 70 signal 70 60 Background : 60 50 50 40 p of misidentified T 40 30 diphotons is balanced 30 20 by ISR jet p 20 10 T 10 q 0 g 0 0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 140
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