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. 2 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Outline Characteristics and challenges of the VBF topology Discovery potential in H   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

3. 3 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 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

4. 4 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Towards Discovery 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 channels investigated: ATLAS: H    lep had 3and  lep lep 4 H  WW  2lep 2 and  qq lep (SN-ATL-2003-68 Eur.Phys.JC32(2003)19) CMS: H    lep had 3 and  e 4 H  WW  qq lep and  2 lep 2 H   (not discussed today) (CMS TDR and CMS-2007/011 and CMS-2006/081)

5. 5 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 VBF: Event Topology 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   and H  WW  lqq dominated by ETmiss resolution ATLAS W/Z degree 1 2 15 90 15 2 1

6. 6 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 „low lumi“  10 to20 fb -1 /year „high lumi“  100 fb -1 /year An Event at the LHC + ~23 overlapping pp-interactions per bunch crossing at high lumi.  ~10 9 pp collisions /s  ~1600 charged particles/evt. in detector + effects from „pile up“: readout time > t btw. Bunches up to now: VBF studies only perfomed for low lumi. scenario hard collision + ISR,FSR + „underlying event“

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

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

9. 9 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 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 10 GeV 45 GeV CMS  no agreement among channels and two collaborations yet   need support from our theoretical friends for modelling especially of QCD background

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

11. 11 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 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 M T e.g.  ll,  ll, 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

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

13. 13 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Comparison of Sensitivity  comparable sensitivity  caveat: different x-sections, MC generators, BG uncertainty statistical tools background from data: shape: - Zjj: using jjZ   and replacing decay products to look like  - 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

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

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

16. 16 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Investigation of Properties rates: N OBS – N BG = (eff VBF  VBF + eff. GGF  VBF  GGF ) 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) 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

17. 17 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Signal rates 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 Determination of „Couplings“ Ratio of Partial Width

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

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

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

21. 21 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 Excl. by L3 g 5E = 0.11 at m H = 160 GeV in H  WW for 30 fb -1  g 5E = 0.24 at m H = 120 GeV in H   for 30 fb -1 systematic uncertainty from BG normalisation < 0.02 caveats: LO MC generators, gluon fusion from PYTHIA Additional small coupling: „SM + g 5E CPE“ (i) different total cross section and (ii) distorsion of  jj distribution - SM+CPE: interference significant in  jj distribution - SM+CPO: no interference effects in the  jj distribution (with signed you regain sensitivity, see V. Hankele et al. Phys.Rev.D74(2006)095001)  only SM+ g 5E CPE contribution studied here

22. 22 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 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 QCD EW D. Zeppenfeld et al., Phys.Rev.D54:6680-6689,1996 loose cuts: EW/QCD = 1:7.2  EW = 87 fb tight cuts: EW/QCD= 1.6 (2.9)  EW = 11(5) fb the obvious candidate: jjZ  ee+ after basic VBf cuts competing QCD and EW contribution

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

24. 24 Markus Schumacher VBF: A tool to explore the Higgs sector at LHC Berlin, 31 October 2007 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