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Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion

INDIA – CMS, 5-6 April 2007. Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion. Ashok Kumar and Suman Beri Panjab University – Chandigarh Ritva Kinnunen Helsinki Institute of Physics. Cross-sections and Branching Fractions.

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Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion

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  1. INDIA – CMS, 5-6 April 2007 Search for the Standard Model Higgs Boson Decaying to Muons via Weak Gauge Boson Fusion Ashok Kumar andSuman Beri Panjab University – Chandigarh Ritva Kinnunen Helsinki Institute of Physics Ashok Kumar PU & GNDU

  2. Cross-sections and Branching Fractions Though the H → m+m-branching fraction is tiny and the backgrounds from Z→m+m- and ttbar production are large, but it is an interesting channel because it provides information on the Hmm coupling s[pb] Two search methods possible: - Inclusive search profiting from the larger cross section, fast simulation study in CMS IN 2005/013 - Search in the weak gauge boson fusion, exploits an efficient background reduction with forward jet tagging Ashok Kumar PU & GNDU

  3. Event Generation and Reconstruction • Z+jet generation with qq’ -> gZ and gq -> qZ, • preselection: 10 < pT < 100 GeV, Z-> mm, ee, tt • 2) preselection cuts: W-> mn, pTm1 > 20 GeV, pTm2 > 10 GeV ,|hm|<2.5, Mmm > 10 GeV • preselection cuts: pTq > 20 GeV, |hq|<5, |hq1 –hq2| > 4.2, hq1 * hq2 < 0, • Mq1,q2 > 900 GeV, Mmm > 70 GeV Standard ORCA packages for reconstruction: - Muons:GlobalMuonReconstructor - Hadronic jets: TransientJetAlgorithm with Jet reconstruction cone = 0.5, Corrections: MCJet with SplittedEcalPlusHcalTowerInput, Ettower > 0.5 GeV, Etower > 0.8 GeV and with ET(raw jet) > 20 GeV - MET from EcalPlusHcalTowers with Type1 jet corrections Ashok Kumar PU & GNDU

  4. Event Selection Higgs boson mass reconstruction Select events with exactly two isolated muons with pTm > 20 GeV,passing the L1 and HLT di-muon or single muon triggers Muon isolation:no tracks with pT>1 GeV in a cone ofDR = 0.4around the muon New values due to the potential bb+jets background, pTm >15 GeV and DR = 0.3 were used in the first version Reconstructed muons MC muons Results from a gaussian fit: s = 1.42 GeV (1.18%), <mmm> = 120.1 GeV Ashok Kumar PU & GNDU

  5. Central variables for event selection 1. No neutrinos in the signal event: an upper bound on ETmisscan be used to suppress the ttbar background 2. Expect more boosted di-muon system in the signal than in the Z+jet background: cut in pTmm Rejection of tt ~4 forETmiss< 50 GeV Rejection of Z+jets ~12 forpTmm>60 GeV Ashok Kumar PU & GNDU

  6. Number of signal and background events and cut efficiencies after central event cuts and mass window No signal visibility possible even with large integrated luminosity, assume that Higgs boson mass is known from other processes to select the mass window Ashok Kumar PU & GNDU

  7. Forward jet tagging in the mass window1) Selection of forward jets: two hardest jets anywhere in rapidity withhj1*hj2 < 0 Select lowest possible value, ET > 20 GeV, due to PYTHIA generation of Z+jet background No optimization of this variable Signal vs qqZ differences due to generator level cuts on qqZ Differences may arise also due to the possibility of the Z originating from a final state quark • Due to the small mass window, statistics low for Z+jets: • - need to open the mass window and • - assume decoupling of pTmm and tagging cuts Ashok Kumar PU & GNDU

  8. Rapidity gap between the tagging jets Expect large rapidity gap for the q jets in qq -> qqH |hq1 –hq2| > 4.2 at the generator level for qqZ |hj1 - hj2| >4.5 Ashok Kumar PU & GNDU

  9. Di-jet invariant mass With all (previous) event selection cuts, including |hj1 - hj2| >4.5 Optimal cut value:Mtaggingjets > 1 TeV Ashok Kumar PU & GNDU

  10. Central jet veto • Selection of central jets: • All corrected jets between the two tagging jets within • hmin + 0.5 < hjet < hmax – 0.5 and with ET > 20 GeV Statistics too low for Z+jet to obtain the efficiency curve ETjet = 20 GeV taken as the threshold Ashok Kumar PU & GNDU

  11. Number of signal and background events and cut efficiencies for forward jet tagging and central jet veto cuts Ashok Kumar PU & GNDU

  12. Comparison of PYTHIA and ALPGEN generation for the Z+jets background Data samples: - existing ALPGEN production samples for exclusive 2-5 jet final states, generated with Z-> ee, mm,tt, mll > 40 GeV - generation of PYTHIA events with the data cards used for the ORCA production samples but with mll > 40 GeV Comparison method: Jet reconstruction within |h | < 5 with the PYTHIA jet reconstruction package in CMKIN Main event selection cuts: - two leptons (electrons or muons) with pT > 15 GeV/c - cut in the di-lepton pT, pTll > 60 GeV/c - two tagging jets with the method used for the ORCA analysis - central jet veto - No MET cut, no mass window cut Ashok Kumar PU & GNDU

  13. ALPGEN generation Ashok Kumar PU & GNDU

  14. Conclusion from ALPGEN/PYTHIA comparison Differencies due to harder jets in ALPGEN - Higher efficiency from forward jet tagging cuts from ALPGEN, - higher efficiency for central jet veto from PYTHIA + normalization in PYTHIA (pT > 10 GeV/c) -> level of Z+jets background in ORCA simulation not underestimated Ashok Kumar PU & GNDU

  15. Estimate of WW+jets, W->mn background • Exploit the ALPGEN samples: • s(WW+2jets) = 1.22 pb • PYTHIA jet reconstruction • Main event relection (as for Z+2jet events) • Result: s(selected) = 6.5x10-5 pb, 0.8% of Z+2jet cross section Estimate of bb+jets background • Estimate based on the study of bb background on bbH/A->em+XPTDR2, page 346, Table 11.1: • Leptonic triggers, lepton pT cuts (pTm>19 GeV, pTe>29 GeV) and isolation (pT > 1 GeV, DR = 0.4): 37.4 pb, rejection factor ~106 • Assume that for the remaining selection the efficiency is similar to that of Z+jets • Result: ~ 4x10-3 events in the mass window Ashok Kumar PU & GNDU

  16. Signal superimposed on the total background With all selection cuts, for 60 fb-1 Ashok Kumar PU & GNDU

  17. JES uncertainty in the background determination Signal visibility not obtained with 60 fb-1 , background could be estimated around the already known Higgs mass (from H->gg) Main uncertainty expected from JES uncertainty Uncertainty on the backgrounds from JES uncertainty, 10% MET uncertainty included tt most sensitive to the increase of JES uncertainty due to large jet multiplicity • 30% uncertainty in this estimate due to MC statistics Ashok Kumar PU & GNDU

  18. Estimate of statistical significance Total background in the mass bin 3.74 events Systematic uncertainties: JES uncertainty dominates for this channel tt 20% Z+jets 16% qqZ 8% Assume 5% uncertainty for all production cross sections Total background with systematics 3.74 ± 0.73 events Significance (Poisson stat., ScPf program): 0.75 with systematic uncertainty 0.80 without systematic uncertainty Ashok Kumar PU & GNDU

  19. Conclusions Full simulation study on qq → qqH, H → mm with forward jet tagging and central jet veto yields S/B ~ 0.5 in a mass window assuming mH to be known from H → gg for 60 fb-1 Statistical significance = 0.75 and upper bound for sxBR = 12.7 fb at 95% CL, including systematic uncertainty • Main backgrounds from Z+jets, ttbar and qqZ were simulated • For better optimization of jet tagging and veto cuts, generation of the Z+jets background with a NLO generator needed • For high luminosity, Lt > 100 fb-1, inclusive H->mm channel more profitable: • background can be extracted with high precision around the known mass value • (0.5% from fast simulation for 60 fb-1) Ashok Kumar PU & GNDU

  20. The analysis note was presented in the Physics meeting on December 8, 2006 by Suman Beri Minutes of the Physics Meeting of 08/12/06: AN2006/105 Search for the Standard Model Higgs Boson Decaying into Muons -  Comments from room: approach of the analysis is not the right one.presently this is approached like a discovery analysis, while there is no chance in this analysis. Instead one should take into account thealready measured mass of the Higgs, select on a mass window in the di-muon system  and then optimize the cuts against background. In any case it will remain a difficult channel for the LHC. -  Z+jets ALPGEN files are now available so these files can be used tomake the background analysis of that channel, or at least cross checkexplicitely against PYTHIA -  Concerns from the referees are to be taken to be taken into account STATUS: Not approved. Sent back to the Higgs group to re-discuss the analysis strategy Ashok Kumar PU & GNDU

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