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A search for the ZZ signal in the 3 lepton channel

A search for the ZZ signal in the 3 lepton channel

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A search for the ZZ signal in the 3 lepton channel

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  1. A search for the ZZ signal in the 3 lepton channel Azeddine Kasmi Robert Kehoe Southern Methodist University Thanks to: H. Ma, M. Aharrouche

  2. Motivation • A measure of the Triple Gauge coupling (TGC) • 3l has higher acceptance than 4l reconstructed • This Analysis is exclusive for 3l+X (4l excluded) • Background for higher mass Higgs • Critical SM test case for 3l+X selection • However, the background is higher • Current analysis includes ZZ3e +X and ZZ2m1e +X • In this talk, the emphasis is on cluster based approach • Use the C4 Jet algorithm to find the missing electron • Use the CaloCalTopocluster algorithm to find the missing electron Azeddine Kasmi SM ElectroWeak group meeting

  3. Data Set Azeddine Kasmi SM ElectroWeak group meeting

  4. Initial selection Azeddine Kasmi SM ElectroWeak group meeting

  5. Use Z mass as a cut in the case of ZZ3e +X e1 e2 • Find which combination of 2 electrons makes a Z for both samples ZZ and Zbb. • Difference in kinematics gives different distribution when the electrons are Pt ordered. • Require opposite sign. • Define a variable M_ZBest. Check the two combination M13 and M23 • The closest of them to the M_ZPDG is the M_ZBest. Consider a cut |M_ZPDG – M_ZBest | < 10 GeV The Zbb and Zb are still too high. There is a need for the 4th lepton Z e2 Z e4 e3 Z b b e1 ZZ Zbb Zb arbitrary units Azeddine Kasmi SM ElectroWeak group meeting

  6. The 4th Electron might be seen as a jet Remove jets within dR < 0.2 From any Medium electron In the event of 3 Medium electrons are reconstructed With Pt > 10 GeV ZZ sample “Jet Candidate” (i.e. a potential electron reconstructed with Jet Algorithm C4) Does the jet candidate match the “unfound truth electron” Most reconstructed jets are actually electrons in this sample. Azeddine Kasmi SM ElectroWeak group meeting

  7. Kinematics of matched jet candidate in ZZ 3e +X Most of jet candidate match the unfound truth electron There are 1209 matches in DR < 0.2 e = 1209/1318= 92% Minimum DR between a jet candidate and the unfound truth electron inZZ Wide range in eta coverage Truth unfound Z electron Matched Jet candidate Similar PT spectra Eta of jet candidate matched to the unfound Z electron. Leading jet usually matches unfound electron Azeddine Kasmi SM ElectroWeak group meeting

  8. Pt Resolution in two Pt ranges Pt Resolution if Pttruth > 20 GeV Pt_resolution = 0.24 Pt Resolution if Pttruth < 20 GeV Pt_resolution = 0.41 Azeddine Kasmi SM ElectroWeak group meeting

  9. The CaloTopoCluster algorithm Wide range in eta coverage Minimum DR between a topocluster candidate and the unfound truth electron inZZ Most of jet candidate match the unfound truth electron There are 1693 matches in DR < 0.2 e = 98% M3e GeV Azeddine Kasmi SM ElectroWeak group meeting

  10. Pt resolution for Topo Cluster RMS = 0.26 Truth unfound electron Matched cluster candidate PT > 20GeV Similar PT spectra RMS = 0.39 PT < 20GeV Azeddine Kasmi SM ElectroWeak group meeting

  11. Particle Identification on the jet candidatesEM fraction Barrel End Cap Jet candidate with a truth match in ZZ Jet candidate with a truth match in ZZ No match In ZZ No match in ZZ Zbb Zbb • The EM fraction was used. • EMF_Barrel > 0.8 • EMF_Barrel > 0.85 Plots are not Normalized Azeddine Kasmi SM ElectroWeak group meeting

  12. Particle Identification on the calo Topo cluster candidate • There are more Cluster moments to consider. • EMF does not exist on AOD • A possibility to build a likelihood. • the normalized second longitudinal moment • l is the distance of the cell from the shower center along the shower axis • , with l = 0 for the two most energetic cells • , with l = 10 cm for the two most energetic cells and for all other cells • 0 means shower more compact in 3D • 1 means shower more spread • For now cut on 0.8 ZZ with truth matching Zbb Zb Not normalized Azeddine Kasmi SM ElectroWeak group meeting

  13. MZ_Best vs. MZ_second in ZZ3e + X Finding the second Z peak with the Jet C4 algorithm ZZ MZ_Best GeV • Apply all cuts and take the first leading jet candidate (no truth used here). Using jet candidate can improve S/B in two ways. • Kinematic constraints • (used for now 2D cut): • 4th lepton makes the second Z peak • Basic particle ID cuts: • EM fraction: • EMF_B > 0.8EMF_EC > 0.85 • The EMF reduces the Zbb by a factor of 4 and Zb by a factor of 3. MZ_Second GeV ZZ Zbb Zb arbitrary units Azeddine Kasmi SM ElectroWeak group meeting

  14. Secondary vertex of the jet candidates ZZ Zbb The are 99 entries that have and an SV2 > 0 99/192 = 51 % The are 80 entries that have and an SV2> 0 5% Azeddine Kasmi SM ElectroWeak group meeting

  15. Finding the second Z peak with the CaloTopoCluster Algorithm MZ_Best GeV MZ_Best (2m) GeV ZZ2m1e ZZ3e • The first leading calo topocluster is taken from the ones passed the longitudinal moment cut. • A 2D cut on MZBest and MZSecond should be within the interval 80GeV -100 GeV MZ_Second GeV MZ_Second GeV Azeddine Kasmi SM ElectroWeak group meeting

  16. Final Selection cuts while using the jet algorithm and the calo Topocluster • Pt of the 3 leptons PT3e > 10 GeV and PT2m1e > 10 GeV • Medium electrons, STACO for muons • Impact parameter significance • do/so < 5.5 for electrons • do/so < 5 for electrons • do/so < 3 for muons • Isolation : etcone20/et < 0.14 • Missing ET : ETmiss < 25 GeV ( to deal with WZ) • SV2 < 0 and 3DSV1comb (w_cmb > -2) &&(w_cmb < 3.5)) . • EMF_B > 0.8 and EMF_EC > 0.85 • The second longitudinal moment < 0.8 • Take the first leading jet candidate • Take the first leading TopoCluster candidate • MZ_Best between 75 GeV to 100 GeV • MZ_second between 85 GeV to 110 GeV • MZ_Best between 80 GeV to 100 GeV • MZ_second between 80 GeV to 100 GeV Azeddine Kasmi SM ElectroWeak group meeting

  17. Results (1fb^-1) for the Jet Algorithm and TopoCluster Signal: ~ 5 events Background:~ 1 event Signal: ~ 5 events Background:~ 6.6 event Azeddine Kasmi SM ElectroWeak group meeting

  18. Conclusion • An S/B~5 was achieved for 1fb-1 in the two exclusive channels ZZ3e and ZZ2mu1e using the jet algorithm to find the missing electron. • In the case of the topocluster an S/B~0.75 1fb-1 was achieved but we believe that it can be improved significantly if we make a better use of the cluster moments (likelihood method). • Optimize the cuts • Increase the major background (Zbb and Zb) statistics Azeddine Kasmi SM ElectroWeak group meeting

  19. BACK UP SLIDES Azeddine Kasmi SM ElectroWeak group meeting

  20. Jets vs Jet candidates in ZZ, Zbb and Zb (not scaled) Higher number of jets per events is due to the electrons seen as jets Jets “Jet candidate” Most ZZ events have at least 1 jet not matching a medium electron ZZ Zb Zbb Azeddine Kasmi SM ElectroWeak group meeting

  21. Secondary vertex cut SV2 algorithm tt Zb The are 86 entries that have and an SV2 > 0 86/192 = 44 % The are 70 entries that have and an SV2 > 0 70/87 = 80% Azeddine Kasmi SM ElectroWeak group meeting

  22. Combination of IP3D and SV1 • No Zbb events pass my cuts • Only 2 Zb events pass my cuts ( 2 out of 4 events) • Use the 3DSV as a cut [-2,3.5] Azeddine Kasmi SM ElectroWeak group meeting