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The Central Jet Veto in Vector Boson Fusion Analysis

The Central Jet Veto in Vector Boson Fusion Analysis. Markus Schumacher. LHC-D Higgs Workshop, Freiburg October 8/9th 2007. Outline. The importance of the VBF production mode Characteristics and Challenges of the VBF topology Issues for the Central Jet Veto (CJV)

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The Central Jet Veto in Vector Boson Fusion Analysis

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  1. The Central Jet Vetoin Vector Boson Fusion Analysis Markus Schumacher LHC-D Higgs Workshop, Freiburg October 8/9th 2007

  2. Outline • The importance of the VBF production mode • Characteristics and Challenges of the VBF topology • Issues for the Central Jet Veto (CJV) • Overview of CJV Applications at LHC • Track Veto versus Calorimeter Jets • Comparison of MC Generators • Ideas about Efficiency Determination from Data • Conclusions and Outlook Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 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 Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  4. Entdeckungspotenzial im Standardmodell • CMS: Httl had 3n HWW lnqq and llnn new • ATLAS: Httl had 3n + ll 4n HWW lnqq and llnn • VBF dominates discovery potential at LO in ATLAS • VBF provides the only channel to see Htt Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  5. Properties of the Higgs Boson Ratio of Partial Width CP Quantum Numbers ATLAS • dominated by VBF channels (only assumed 30fb-1) • HWW used as reference as measured most precisely Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  6. 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 The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  7. SM or Extended Higgs Sector e.g. Minimal SUSY ? 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. uncerainties D=|RMSSM-RSM|/sexp • similar study by M. Dührssen et al. incl. 13 channels  VBF dominates Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  8. VBF: Event Topology Tagging Jets W/Z f W/Z h Higgs-Zerfall =-ln tan(q/2) 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 The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  9. 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 proton proton collisions / second • ~1600 charged particles in detector per event + effects from „pile up“: readout time > Dt btw. bunch Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  10. 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 The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  11. Basic selection cuts (a) 2 tagging jets: ET(1,2)>x(y) up to |hmax| with h1xh2<0 (b) rapidity difference Dh (c) invariant dijet mass CMS ATLAS Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  12. Central Jet Veto (CJV) EW QCD EW: color singlet exchange QCD: color octet exchange  different radiation pattern expected  born level distribution for Z + 3 jets D. Zeppenfeld et al., Phys.Rev.D54:6680-6689,1996 Challenge: calculation of CJV efficiencies - „matching“ of Z+2j and Z+3j calculations - correct QCD scales - validity of approx. for phase space region Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  13. Central Jet veto • two approaches: - truncated shower approximation (dotted and dashed dotted) • - exponentiation model (solid and dashed) • (for details see, e.g.: • Phys.Rev.D54:6680-6689,1996 • and PhD thesis by D. Rainwater) • or talks by Terrance Figy and • Christoph Hackstein this afternoon CJV survival probabilities : no jet with ET>20GeV btw. tagging jets PhD thesis D. Rainwater, hep-ph 9908378 Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  14. Issues for the Central Jet Veto • Towards Discovery - optimise CJV for significance - robust against pileup, underlying event detector noise, MC modelling, … - if modelling wrong: kill (partially) our signal  need more data for observation - knowledge of CJV efficiency not needed • Investigation of properties • couplings: (pollution from gluon fusion) NOBS – NBG = (effVBF sVBF + eff.GGFVBF sGGF) x lumi  need knowledge of CJV eff. for VBF and GGF • HVV coupling structure from Dfjj  need efficiencies and correlation with observable for VBF, GGF (and background) Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  15. VBF: H tt Httem 30 fb-1 ATLAS • comparable sensitivity in tt lep had channel • caveat: different x-sections, MC generators, BG uncertainty, stat. tool • Zjj dominant background QCD to EW ~ 3:1 Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  16. CMS: CJV in Httlep had • No jet with: ETraw>10 GeV in hmin+0.5 < h3 < hmax-0.5 • and a3= S ptrack /ETraw>0.1 • (sum over tracks in cone of 0.5 around jet axis) • motivation: distiniguish „signal“ from „pileup“ jets CMS CMS Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  17. Comparison of CJV: CMS and ATLAS CMS 45 GeV dependence of CJV efficiency on ET of MC jet (10,15,20,..,45GeV) 10 GeV raw ~ 20 GeV MC Jet 10 GeV ATLAS: lep lep: no jet with ET>20 GeV |h|<3.2 lep had: ‘‘ btw. tagging jets Comparison of CJV survival probabilities Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  18. HWW ATLAS: HWWem CMS: HWWlqq Comparison of significance: • ll: ATLAS more powerful • lq: CMS more powerful • But: different x-sections, MC generators, etc. • Now: investigation of differences Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  19. Central Jet Veto in HWWlnln CMS:PT-Balance: <40 GeV CJV: no jet with ET>20 GeV in |h3* |< 2.0 ATLAS:PT-Balance: <30 GeV CJV: no jet with ET>20 in |h3|<3.2 Rainwater no jet with ET>20 GeV btw. tagging jets Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  20. Summary of Current „Officical“ Experimental Status • no coherent picture of CJV performance (my feeling) • - different applications in channels and both collaborations • is the optimal that different for different channels? • - different MC generators • which gives most correct description? • how do they compare with the theo. calculations (TSA, Exp Mod.)? • is the use of current MC generators meaningful at all? • - disentangle effects from underlying event, pileup, noise, … ? • does the inclusion of track information really help? • - different basic VBF cuts (correlation not studied in great detail) • what is correlation with method and threshold of CJV? • better understanding by cooperation from theory+CMS+ATLAS  maybe good candidate for Analyis Group in Helmholtz Alliance Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  21. Track Jet Veto versus Calorimeter Jet Veto in HWWllnn S. Horvat, S. Kaiser, O.Kortner MPI Munich • Idea: • disentangle jets from pileup pp collision and signal pp collision via tracks • for now: signal vertex = vertex with largest ptsum of tracks • jet finding via cone of 0.4 on tracks and calorimeter objects Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  22. Multiplicities without and with pile-up Calo jets: increased multiplicity at low ET and large eta Track jets: multiplicity distribution stable Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  23. Multiplicities above Threshold without and with pile-up Calo Jets Track Jets |h|<2.5 tracking detector acceptance Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  24. Survival Probabilities • pT of track jets ~ 0.5 of calo jets •  compare jet veto for • - track jets above 10 GeV • - calo jets above 20 GeV • both within |h| < 2.5 • jet veto survival probabilities • track jet veto seems more robust • ongoing study and optimisation Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  25. idea:count charged particles in rapidity gap: hJmin+0.5<htrk<hJmax-0.5 Track Veto versus Central Jet veto (S. Nikitenko) hadron level study with PYTHIA • without • underlying event • with • underlying event Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  26. Track veto vs CJV: Survival probabilities for Httl had Jet veto Track veto * Numbers in parenthesis from CMS PTDR with full simulation Next steps:- check with full simulation - compare results without and with pileup Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  27. Comparison of MC Event Generators (M. Röder, BN) • Rapidity of non tagging jets with PT>20 GeV Cuts applied:pt1(2) >50(30)GeV, |h1,2|<4.9, h1xh2< 0, mj1j2 > 700 GeV, Dhj1j2> 4.4, Dfj1j2 < 2.2 Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  28. Comparison of Different MC Generators • Survival probability depending on pt of 3rd jet in |h|<3.2 • significant dependence on event generator • mainly caused by different parton shower, not by underlying event Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  29. Determination of CJV Efficiency from Data • needed for investigation of Higgs boson properties • useful for optimising selection w.r.t. discovery • general interest to understand radiation pattern goal: • find and select samples with similar topology as VBF signal with reasonable rate and signal-to-background ratio • determine radiation pattern • transfer to Higgs signal process (directly or via MC) • tune MC generators to reproduce data two candidates: • „the obvious“: jjZee+mm competing QCD and EW contribution • „the obscure“: single top (t-channel) purely EW process Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  30. The obvious jjZeemm (D. Zeppenfeld et al. Phys.Rev.D54:6680-6689,1996) EW QCD Z • disentangle jjZ EW from QCD by VBF like selection problem: QCD rate large compared to EW rate, still factor 7 after above cuts Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  31. The obvious jjZeemm s in fb • good S/B only • - with hard cuts • on Mjj and Dhjl • - at (too) small rate • small S/B  discrimination om statisticsl basis QCD EW Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  32. The obvious jjZeemm • CJV: no jet with ETr>10GeV in hmin+0.7 < h3 < hmax-0.7 • average vetos per event n calculated in exponentiation model - CJV thresholds > 10 GeV > 20 GeV > 40 GeV > 80 GeV • negligible correlation between veto prbabilty and Dhjl (for <2.2) • maybe unfolding in Dhjl may be usful • detailed experimental study needed Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  33. The obscure: single top (t-channel) production (MS, Si) Single top: qbqt VBF Htt q 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%  250 evts/fb Signal-to-BG(tt): 2 to 3 s(LO,120GeV)~0.4 pb Efficiency: ~0.4% • similar colour structure  similar radiation pattern after selection? • is it possible to prepare sample with similar topology? • what is influence of differences? - initial b from gluon splitting - different polarisations of Ws - tbW decay Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  34. The obscure: single top (t-channel) production • samples produced with: Herwig+Jimmy+ ATLAS fast detector simulation • select tagging jets in opposite hemispheres • for single top: require b-tag (|hb|<2.5 due to tracker acceptance) rapidity difference of tag jets invariant tag jet mass Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  35. Characteristics of the third jet transverse momentum h3*=h3 - ½(h1+h2) • with small statistics no definite conclusion possible! • at 1st glance: no significant discrepancy btw. single top and VBF • next steps: - use ME calculations for 3rd jets - determine amount of tt background after „VBF“ selection - use TSA or Exponentiation Model to get CJV efficiencies Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

  36. Conclusions and Outlook None yet. This is supposed to be a workshop ! Hope for lively and interesting discussions during this meeting. Hope for close, good and fruitful cooperation between theory, CMS and ATLAS people here and in the future. Markus Schumacher The Central Jet Veto in VBF Analysis LHC-D Higgs WS Freiburg, Oct. 2007

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