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Light Higgs search in SUSY cascades First Results

Light Higgs search in SUSY cascades First Results. Introduction Simulated events Reconstruction framework Part I : trigger Part II : b tagging efficiency Part III : invariant mass reconstruction Part IV : jet calibration Conclusion . Alain Romeyer (Mons - Belgium)

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Light Higgs search in SUSY cascades First Results

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  1. Light Higgs search in SUSY cascadesFirst Results • Introduction • Simulated events • Reconstruction framework • Part I : trigger • Part II : b tagging efficiency • Part III : invariant mass reconstruction • Part IV : jet calibration • Conclusion Alain Romeyer (Mons - Belgium) Filip Moortgat (CERN) Alain Romeyer - Nov. 2004

  2. LSP MET Introduction B tagging h0 b Signature : • It has been shown in CMS-note 1997/070 : • signal can be seen with • only few months of data • main bkg : SUSY • SM bkg very low • discrimination betweenSUSY signal and SUSY bkg is difficult Alain Romeyer - Nov. 2004

  3. LSP MET Introduction… B tagging Benchmark point LM5 Tan b = 10 AO = 0 µ > 0 M1/2 = 360 GeV M0 = 230 GeV h0 b MSUGRA 5 parameters : m0, m1/2,A, tan b, sign(µ) S. Abdullin – L. Pape Update II of the new MSUGRA test points proposal Signature : Alain Romeyer - Nov. 2004

  4. Simulated events Isajet 7.69 + Pythia 6220 + CMKIN • Production of signal events and pile-up • Signal events : all SUSY channel (easier for later event reweighting) • Private production of 10 000 evts @ Mons(~25 days) • ~20% contains our decay chain • Digitisation : merge pile-up and signal • Start to use the 100 000 evts production generator FULL SIMULATION CHAIN simulation OSCAR2_4_6 digitisation ORCA7_6_1 Low statistic -> only a first try Alain Romeyer - Nov. 2004

  5. « Reconstruction » strategy • ORCA_8_1_3 + patch for muon reconstruction Reconstruction Simulatedevents • II - Jet Reconstruction : • Iterative Cone Algo. • cone size : 0.4 • tower Et thr. : 0.5 GeV • seed Et thr. : 1 GeV I – L1 +HLT • Signal • + Background : • SUSY • SM : top, QCD… Efficiency ? Jet sel. Pt > 10 GeV • III - B tagging : • By Secondary Vertex • Regional reconstruction • cone size : 0.4 • Vertex algo. : principal • Min. tracks from sec. vertex : 3 • Analysis • event selection • IV - b ̅b inv mass reco. • MET : • MET from EcalHcalTower Alain Romeyer - Nov. 2004

  6. Part I : trigger • L1 : 99.9 % - HLT : 94 % Low Lumi. Non cumulative Trigger !!! Caveat : ~ same efficiency for SUSY bkg. ~ all events !!! Alain Romeyer - Nov. 2004

  7. Part II : b tagging efficiency By S.V. - Cone size : 0.4 <> ~ 51,7 % <> ~ 9,3 % h Alain Romeyer - Nov. 2004

  8. Part III: inv. mass reco. • Look for the h0 peak in the b -b invariant mass distribution • Jet pairing : crucial point Evts with 6 b jets 2 from higgs decay No simple « a priori »kinematic constrainsts I.P. • Select most probable b jets (biased  high energy jets ~ better proba ) • Select closest b jets (higgs boost not so high… ) • try all the possible combinations of reconstructed b tagged jets Alain Romeyer - Nov. 2004

  9. Jet pairing strategy Reco jet + B tagging MC jet Energy and momentum Try all combinations seems the best Bkg due to combinatorial S/√B Alain Romeyer - Nov. 2004

  10. Likelihood fit • Follow the Z’  µµ strategy (CMS AN 2004/018) • Unbinned method NormalisedGaussian Extract from fit out of peak Fraction of signal 3 parameters : mh, s and No constraints on the absolute background level  only the shape Alain Romeyer - Nov. 2004

  11. Likelihood fit… mh = 116 GeV Reco jet + B tagging True jet Energy and momentum SUSY bg + signal Alain Romeyer - Nov. 2004

  12. Inv. mass reco with Rec. Info. mh = 116 GeV Reco jet + B tagging Reco. jet Energy and momentum No calibration • no peak • jet energy calibration -> hand made Alain Romeyer - Nov. 2004

  13. Part IV : jet calibration • Jet calibration method following CMS-note 1999/066 • Association between rec. Jets and generated partons before hadro. (cone < 0.3) • 2 types of jets : b jets and other • Etruejet = sum(Equarks,gluons) • Correction Factor C = Etruejets / Erecjets • Fit of the correction factor surface in the E vs || plane : Alain Romeyer - Nov. 2004

  14. Correction factor Emc / Erec Non B jets B jets C(, E) C(, E) || || Ejet Ejet Alain Romeyer - Nov. 2004

  15. Inv. mass reco with Hand made Jet calibration mh = 116 GeV Reco jet + B tagging Reco. jet Energy and momentum Hand made calibration (CMS-note 1999/066) No peak !!! Alain Romeyer - Nov. 2004

  16. Test with Z  bb • Iterative Cone Algorithm not adapted ? • Test jet reconstruction and calibration with a Zbb sample (production of 50 000 events)Very usefull in order to check : • Position of the peak • Jet Energy calibration • Energy resolution Important Validation Sample MidPoint ? Alain Romeyer - Nov. 2004

  17. Conclusion • First results with 10k events : • Trigger efficiency 94 % • Higgs peak visible if using the MC information • Fit strategy already working • Jet energy reconstruction is not working • Try other algorithms • Optimize B tagging • Move to more recent ORCA version • Future results with 100k event production • In addition, now we will start : • Study the background : SUSY and SM (Z, top…) • Define several selection criteria Alain Romeyer - Nov. 2004

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