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Weak Vector Boson Fusion --- a Tool to Explore the Higgs Sector at LHC

Weak Vector Boson Fusion --- a Tool to Explore the Higgs Sector at LHC. Markus Schumacher. SFB WS on „Massive Particle Production at LHC“ Berlin, 31 October 2007. Outline. Characteristics and challenges of the VBF topology Discovery potential in H  tt and WW in the SM

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Weak Vector Boson Fusion --- a Tool to Explore the Higgs Sector at LHC

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  1. Weak Vector Boson Fusion---a Tool to Explore the Higgs Sector at LHC Markus Schumacher SFB WS on „Massive Particle Production at LHC“ Berlin, 31 October 2007

  2. Outline • Characteristics and challenges of the VBF topology • Discovery potential in H tt and WW in the SM • Discovery potential in extended models • Investigation of Higgs boson properties • Central jet veto efficiency from data? • Conclusions and Outlook • only discuss experimental aspects • for theoretical issues see talks by e.g. Ansgar and Malgorzata Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  3. Production of a SM Higgs Boson at LHC • dominant process: gluon fusion • factor 10 suppressed: Vector Boson Fusion (VBF) but:additional signature in the detector • theoretical knowledge of key features at ~5 to 10%  see talks by Ansgar and Malgorzata Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  4. Towards Discovery • channels investigated: • ATLAS:H  tt  lep had 3n and  lep lep 4n • H  WW 2lep 2n and  qq lep n • (SN-ATL-2003-68 Eur.Phys.JC32(2003)19) • CMS:H  tt  lep had 3n and  em 4n • H  WW  qq lep n and  2 lep 2 n • H  gg (not discussed today) • (CMS TDR and CMS-2007/011 and CMS-2006/081) for discovery: - need knowledge of expected background  daten driven approaches under study - signal efficiencies not needed wrong modelling  not optimal selection strategy  more data needed Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  5. VBF: Event Topology W/Z W/Z signature: 2 tagging jets at large rapidities  challenge: jet reconstruction no color flow between jets, rapidity gap  challenge: central jet veto Higgs decay products in central region  challenge: mass reconstruction for Htt and HWWlnqq dominated by ETmiss resolution ATLAS degree 1 2 15 90 15 2 1 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  6. An Event at the LHC „low lumi“  10 to20 fb-1/year „high lumi“  100 fb-1/year hard collision + ISR,FSR + „underlying event“ + ~23 overlapping pp-interactions per bunch crossing at high lumi.  ~109 pp collisions /s  ~1600 charged particles/evt. in detector + effects from „pile up“: readout time > Dt btw. Bunches up to now: VBF studies only perfomed for low lumi. scenario Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  7. Jet Reconstruction ATLAS reconstruction efficiency - approximately confirmed by new preliminary ATLAS studies - optimisation w.r.t. jet algo ongoing low lumi pT>20GeV 90 15 2 1o fake rate = probability to find jet from pileup in central part of detector ATLAS low lumi CMS both experiments: fake rate ~ 2% for ET>20 GeV Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  8. Basic Selection Cuts (a) trigger provided by high pt leptons (b) 2 tagging jets: ET(1,2)>x(y) up to |hmax| with h1xh2<0 (c) rapidity difference Dh (d) invariant dijet mass CMS ATLAS (d) lepton/jet ID for Higgs decay products + some angular cuts Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  9. Central Jet Veto (CJV) EW: color singlet exchange QCD: color octet exchange  different radiation pattern expected EW QCD  born level distribution for Z + 3 jets D. Zeppenfeld et al., Phys.Rev.D54:6680-6689,1996 CMS 45 GeV • no agreement among channels and two collaborations yet •  need support from our theoretical friends for modelling especially of QCD background 10 GeV Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  10. Weak Boson Fusion: HWW HWW • HWWlnln • - no mass peak only transverse mass • + spin • correlations • HWWqq lep n • - only 1 n  mass peak • - mass resolution: ~ 9% CMS 60fb-1 ATLAS HWWe MH=160 GeV 10 fb-1 GeV dominant background: top pair (+ Wt) production estimated background uncertainty ~ 10 % Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  11. Comparison of Sensitivity • ll: ATLAS more powerful • lq: CMS more powerful • but: different x-sections, MC generators, etc. • now: investigation of differences • Background from data: • build control samples using loose/reversed cuts in observables • ideally not (weakly) correlated to MT e.g. Dfll, Dhll, etc. • signal enhanced and background enhanced = signal free samples • + in addition b-tagged samples for tt background • extrapolate from signal in BG region (MC prediction) • or simultaneous fit to signal and background regions •  full validation of data driven methods under study Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  12. H tau tau mass reconstruction despite 4 n in collinear approximation mass resolution ~ 9 to 11 % dominated by ETmiss resolution Httem 30 fb-1 ATLAS dominant background Zjj (QCD to EW 3 to 1) estimated background uncertainty ~ 7 to 10% Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  13. Comparison of Sensitivity • comparable sensitivity • caveat: different x-sections, MC generators, BG uncertainty statistical tools • background from data: • shape: - Zjj: using jjZmm and replacing decay products to look like tt • - tt: select b-tagged tt-sample • normalisation: - from sidebands • - free parameter in fit of data to signal + BG • (already done in CMS analysis) •  full validation of data driven methods under study Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  14. Discovery Potential in Standard Model VBF dominates discovery potential at LO in ATLAS VBF provides the only channel to see Htt Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  15. Discovery Potential in Extensions of the SM Invisible Higgs MSSM 30 fb-1 ATLAS 30 fb-1 ATLAS preliminary MSSM: VBF, esp. Htt dominates discovery potential at LO invisible Higgs: VBF cleary most sensitive channel Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  16. Investigation of Properties • mass: no detailed study in VBF yet • my estimate ~ few GeV for 30fb-1 • couplings / partial widths •  signal rate measurements • spin and CP quantum numbers •  angular distributions rates: NOBS – NBG = (effVBF sVBF + eff.GGFVBF sGGF) x lumi. need estimate of signal efficiencies for VBF and gluon fusion „pollution“ angular distributions: need estimate of efficiencies and correlations with selection variables (gluon fusion is background at 5 to 10% level with diff. kin. distributions) Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  17. Determination of „Couplings“ Signal rates Ratio of Partial Width 13 analysis (incl. „cross talk“) with various systematic uncertainties dominated by VBF channels (only assumed 30fb-1) assumes 5% uncertainty for efficiency on tagging jets and CJV Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  18. SM or Extended Higgs Sector e.g. MSSM ? discrimination via VBF compare expected measurement of R in MSSM with SM prediction for same MH BR(h WW) BR(h tt) R = 300 fb-1 ATLAS prel. assume: Mh precisely known no sys. uncertainties D=|RMSSM-RSM|/sexp • similar study by M. Dührssen et al. incl. 13 channels  VBF dominates Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  19. HVV Vertex Coupling Structure Higgs electroweak gauge boson vertex + new terms in effective Lagrangian: Jet 1 • most sensitive observable: • azimuthal angle difference btw. tagging jets Dfjj • (Plehn, Rainwater, Zeppenfeld Phys.Rev.Lett. 88(2002)05180) Dfjj Jet 2 investigation performed in 2 steps 1) dominant coupling term ? pure SM or CP even or CP odd 2) SM + small anomalous new contribution? Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  20. Dominant Coupling Term if SM shape dominant: scalar field has a vev (“Higgs”) if CP conserved: CP of coupling = scalar particle CP quantum number Signal after all cuts HWW: Signal + BG 10fb-1 ATLAS ATLAS • Sensitivity to exclude non SM contribution from CPE/CPO: • HWW (160 GeV):~ 5 s with 10 fb-1 • Htt (120GeV): ~ 2.5 s with 30 fb-1 • (MC-Generator VBFNLO D. Zeppenfeld et al.) (Eur.Phys.J.C51(2007)385 SN-ATLAS-2007-060) Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  21. Additional small coupling: „SM + g5E CPE“ (i) different total cross section and (ii) distorsion of Dfjj distribution - SM+CPE: interference significant in Dfjj distribution - SM+CPO: no interference effects in the Dfjj distribution (with signed Df you regain sensitivity, see V. Hankele et al. Phys.Rev.D74(2006)095001)  only SM+ g5E CPE contribution studied here Excl. by L3 D g5E = 0.11 at mH = 160 GeV in H  WW for 30 fb-1 D g5E= 0.24 at mH = 120 GeV in H tt for 30 fb-1 systematic uncertainty from BG normalisation < 0.02 caveats: LO MC generators, gluon fusion from PYTHIA Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  22. Estimating the CJV Efficiency from Data • knowledge of central jet veto efficiency needed for investigation of properties and optimisation of selection strategy • find and select samples with similar topology as VBF signal with reasonable rate and signal-to-background ratio • determine radiation pattern and transfer to Higgs signal process directly or via tuning of MC generators • the obvious candidate: jjZee+mm after basic VBf cuts competing QCD and EW contribution QCD loose cuts: EW/QCD = 1:7.2 sEW = 87 fb tight cuts: EW/QCD= 1.6 (2.9) sEW = 11(5) fb EW D. Zeppenfeld et al., Phys.Rev.D54:6680-6689,1996 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  23. The obscure: single top (t-channel) production q Single top VBF Htt q q q t n W W H t W t b W e,m q q b • s(NLO)~50 pb (incl. BR tbWbln) • efficiency: ~ 0.5%  sacc=250 fb • signal: BG (mainly tt)~ 2(3):1 • similar radiation pattern ? • similar topology selectable? • what is influence of differences? Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

  24. Conclusion and Outlook • VBF is the tool to explore the Higgs sector at LHC • VBF dominates the discovery potential at LHC (at LO) • in SM, MSSM and for Hinvivible • VBF dominates determination of couplings • and allows determination of HVV coupling structure • Current and open issues: • optimisation of jet, ETMiss, mass reconstruction • background determination from data and signal extraction • optimising CJV (tracks vs. calo, robustness against pileup, …) • determination of CJV efficiency from data • here a strong and fruitful cooperation between • theory and experiment is needed Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007

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