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H -> 4 m in the low mass region E.Meoni, L.Larotonda, M.Antonelli, F.Cerutti

H -> 4 m in the low mass region E.Meoni, L.Larotonda, M.Antonelli, F.Cerutti. Introduction ATLFAST++ and MOORE/MuID performance Irreducible background rejection Reducible bkg. Rejection Status and prospects. Introduction. Study started more then 1 year ago with twofold goals:

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H -> 4 m in the low mass region E.Meoni, L.Larotonda, M.Antonelli, F.Cerutti

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  1. H -> 4 m in the low mass regionE.Meoni, L.Larotonda, M.Antonelli, F.Cerutti • Introduction • ATLFAST++ and MOORE/MuID performance • Irreducible background rejection • Reducible bkg. Rejection • Status and prospects

  2. Introduction • Study started more then 1 year ago with twofold goals: • Validate ATLFAST++ and ATHENA Moore/MuID • Improve analysis w.r.t. TDR by using multivariate techniques against irreducible (ZZ->4m) and reducible (tt and Zbb) backgrounds • Started with ATHENA release 6.0.3 • Mass region studied: MH[130-180] GeV (low mass is the most challenging because of the off-shell Z and higher bkg) • Here results showed for MH=130 GeV

  3. Introduction • Samples produced with PYTHIA 6.2 with the exception of Zbb (ACERMC ME) • Filter: 4 m with Pt>4 GeV and |h|<2.7

  4. Introduction: Pt and h spectra Pt(GeV) h ATLFAST++, MH=130 GeV

  5. Introduction: analyses chain COMMON PRESELECTION 4 muons, null total charge : 2 with pT > 20 GeV and | | < 2.5 2 with pT > 7 GeV and | | < 2.5 Analysis with Multivariate methods TDR analysis Couples µ+ µ- with invariant mass : M12= Mz ± 15 GeV M34> 20 GeV ( mH= 130GeV ) M12= Mz ± 10 GeV M34>30 GeV ( mH= 150GeV ) M12=Mz ± 6 GeV M34>60 GeV ( mH= 180GeV ) Angular cut likelihood/NN (with angular variables and M12 & M34) cuts Lepton isolation cut likelihood/NN (with isolation variables) cut Mass window cut (mH  2 ) to compute significance Lepton isolation cuts (single variable cuts) Mass window cut (mH  2 ) to compute significance

  6. Introduction: software codes • ATLFAST++ (object oriented version of ALTAS fast simulation implemented in ATHENA framework) • ATHENA: MOORE/MuID with muon spectrometer in standalone and combined • started with version 6.0.3 many bugs found • latest results with 7.0.2 • First step check of general performance • Efficiency • Pt resolution • MH resolution

  7. Selection efficiency • Acceptance after kinematic cuts (4m and M12 and M34 cuts): • ATLFAST++: 33.0% • TDR: 33.5% • MOORE/MuID combined 6.0.3: 9% • Inefficiency concentrated in low Pt region  Muid Combined Athena6.0.3

  8. Selection efficiency • Improved with version 7.0.2 • MOORE/MuID combined 7.0.2: 23% • Inefficiency concentrated eta~2 region  Muid Combined Athena7.0.2

  9. Mass resolution • Performance muon spectrometer: • TDR: 2.7 GeV • MOORE 7.0.2: 3.0 GeV • Combined (including Z mass constraint): • TDR: 1.4 GeV • ATLFAST++: 1.5 GeV • MOORE/MUID comb 7.0.2: 1.7 GeV

  10. Irreducible bkg.: ZZ->4m • Multivariate analyses: in addition to MH, M12 and M34 there are other 9 independent kinematic variables (12 in total) • Try to select variable sensitive to the spin and parity of the signal • Combine all variables with multivariate techniques: likelihood and NN • Likelihood function (and neural network) • with 11 variables: • Angle of the decay planes of the two Z in Higgs rest frame • (see ATL-COM-PHYS-2003-001,Buszello et al.) • Angle between m- in Z rest frame and Z boost in Higgs rest • frame (both for on-shell Z and off-shell Z) • (see ATL-COM-PHYS-2003-001,Buszello et al.) • Angle between Z (both on-shell and off-shell) direction in • Higgs rest frame and the Higgs boost • Angle between the two m+ in Higgs rest frame • Angle between the two m- in Higgs rest frame • Angle between the two m of Z (both on-shell and off-shell) • Invariant masses of the two m+ m- couples (M12 and M34)

  11. Angle between m- in the Z rest frame and Z boost in Higgs rest frame Angle between the decay planes of the two Z in Higgs rest frame Angle between on-shell Z direction in Higgs rest frame and Higgs boost H4 H4 H4 ATLFAST ATLFAST ATLFAST ZZ4 ZZ4 ZZ4 ATLFAST ATLFAST ATLFAST H4 H4 H4 FULL REC. FULL REC. FULL REC. ZZ4 ZZ4 ZZ4 FULL REC. FULL REC. FULL REC.

  12. Results with Fast simulation Improvement: mainly coming from M12 and M34 optimization angles relevant only at higher MH

  13. Reducible background • 2 out of 4 muons not isolated in tt and Zbb background • Likelihood (and neural network) with 6 variables: • the 2 largest normalized impact parameters(IP) in trasverse plane of the 4 IP • the 2 largest pT reconstructed inside a cone of R=0.2 around the 4 µ tracks • the 2 largest total transverse energy depositions in calorimeters (EM+HC) in a cone of R=0.2 around the 4µ tracks We have added in CBNT ntuple block of Moore/Muid the energy deposition in cones of different radii around the “muon track” “muon track” defined in 4 ways: moore trk, muid statandalone trk, muid combined trk, iPat trk Best results with: energy of radius R=0.2 around “iPat” trk

  14. Largest energy loss Around iPat track Signal ttbar Zbb Signal ttbar Zbb Largest IP Signal ttbar Zbb Largest pT After pT &  cuts and m12 & m34 cuts

  15. Neural Network Likelihood After pT &  cuts and m12 & m34 cuts

  16. Final Results: L=30 fb-1

  17. Mass plots • Preselection (as in TDR) : 4 m , total charge =0, pT &  cuts • Angular cut: likelihood- 11 variables • Isolation cut : likelihood– 6 variables After preselection (4m,Qtot=0,pT& h cuts) Signal ZZ 4m ZZ 2m2t ttbar Zbb All channels Signal ZZ 4m ZZ 2m2t ttbar Zbb All channels After overall analysis (preselection+ ang. lik cut+isol lik cut)

  18. Conclusions and Prospects • ATLFAST++ and MOORE/MuID (7.0.2) comb. performance studied on H->4m (low mass): worse performance then TDR, still low efficiency at |h|~2 to be understood Prospects • Add Noise and pileup, relevant for lepton isolation • Control samples to study lepton isolation variables on data: tt-> WWbb: W->l W->jj select b jet with Mbjj=Mtop (b forced to leptonic decay) • Wait for bug fixes ? • Produce documentation: ATLAS note and SN • Participation to DC2 validation very important: • New digitization • New simulation GEANT4 • New output data format • New reconstruction release

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