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. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 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  2  1e +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

3. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 3 Data Set Data Sample GeneratorNumber of events Cross section (fb) ZZ (5931)MC@NLO20k67 Zb (6540)AcerMC20k SIM. in 12.0.6 RECO. In 13.0.40 14000 Zbb (5176)AcerMC25k SIM. in 12.0.6 RECO. In 13.0.40 12663 WZ (6359)Jimmy15k800 ttbar (5211)MC@NLO400k6064

4. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 4 Initial selection Pt of the 3 leptons P T 3e > 10 GeV and P T 2  1e > 10 GeV (helps with Zbb and Zb) Medium electrons, STACO for muons Impact parameter significance do/  o < 5.5 for electrons, do/  o < 3 for muons This should help reduce the Zbb, Zb and ttbar. Isolation etcone20/et < 0.14 for all the three selected leptons Missing ET E T miss < 25 GeV (This is useful for WZ and ttbar BG)

5. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 5 Use Z mass as a cut in the case of ZZ  3e +X 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 bb e1 e2 Z Z e1 e3 e2 e4 ZZ Zbb Zb arbitrary units

6. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 6 The 4th Electron might be seen as a jet In the event of 3 Medium electrons are reconstructed With Pt > 10 GeV Remove jets within dR < 0.2 From any Medium electron “Jet Candidate” (i.e. a potential electron reconstructed with Jet Algorithm C4) Does the jet candidate match the “unfound truth electron” ZZ sample Most reconstructed jets are actually electrons in this sample.

7. 10/30/2008Azeddine 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  R < 0.2  = 1209/1318= 92% Eta of jet candidate matched to the unfound Z electron. Leading jet usually matches unfound electron Truth unfound Z electron Matched Jet candidate Similar P T spectra Wide range in eta coverage Minimum  R between a jet candidate and the unfound truth electron in ZZ

8. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 8 Pt Resolution in two Pt ranges Pt Resolution if Pt truth > 20 GeV Pt _resolution = 0.24 Pt Resolution if Pt truth < 20 GeV Pt _resolution = 0.41

9. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 9 The CaloTopoCluster algorithm Minimum  R between a topocluster candidate and the unfound truth electron in ZZ M 3e GeV Most of jet candidate match the unfound truth electron There are 1693 matches in  R < 0.2  = 98% Wide range in eta coverage

10. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 10 Pt resolution for Topo Cluster RMS = 0.26 RMS = 0.39 Truth unfound electron Matched cluster candidate Similar P T spectra P T > 20GeV P T < 20GeV

11. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 11 Particle Identification on the jet candidates EM fraction Zbb Jet candidate with a truth match in ZZ No match in ZZ Plots are not Normalized The EM fraction was used. EMF_Barrel > 0.8 EMF_Barrel > 0.85 Zbb Jet candidate with a truth match in ZZ No match In ZZ End Cap Barrel

12. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 12 There are more Cluster moments to consider. EMF does not exist on AOD A possibility to build a likelihood. the normalized second longitudinal moment is the distance of the cell from the shower center along the shower axis, with = 0 for the two most energetic cells, with  = 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 Particle Identification on the calo Topo cluster candidate ZZ with truth matching Zbb Zb Not normalized

13. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 13 M Z_Best vs. M Z_second in ZZ  3e + X ZZ MZ_Best GeV MZ_Second 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): 4 th lepton makes the second Z peak Basic particle ID cuts: EM fraction: EMF_B > 0.8 EMF_EC > 0.85 The EMF reduces the Zbb by a factor of 4 and Zb by a factor of 3. ZZ Zbb Zb arbitrary units Finding the second Z peak with the Jet C4 algorithm

14. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 14 Secondary vertex of the jet candidates The are 80 entries that have and an SV2> 0 5% The are 99 entries that have and an SV2 > 0 99/192 = 51 % ZZZbb

15. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 15 Finding the second Z peak with the CaloTopoCluster Algorithm The first leading calo topocluster is taken from the ones passed the longitudinal moment cut. A 2D cut on MZ Best and MZ Second should be within the interval 80GeV -100 GeV MZ_Best GeV MZ_Second GeV ZZ  3e MZ_Best (2  ) GeV MZ_Second GeV ZZ  2  1e

16. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 16 Final Selection cuts while using the jet algorithm and the calo Topocluster Pt of the 3 leptonsP T 3e > 10 GeV and P T 2  1e > 10 GeV Medium electrons, STACO for muons Impact parameter significance do/  o < 5.5 for electrons do/  o < 5 for electrons do/  o < 3 for muons Isolation : etcone20/et < 0.14 Missing ET : E T miss < 25 GeV ( to deal with WZ) SV2 -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

17. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 17 Results (1fb^-1) for the Jet Algorithm and TopoCluster The 3e+X channel ZZ Zbb Zb WZ tt Event selection efficiency 2.5 % 0.003 % 0.028% 0.0025 % 0.005% 0.02 % 0.027% 0.025 10 -2 % Number of event for 1fb -1 ~2 0.3 3.5 0.3 0.7 0.1 0.2 0.0015 The 2mu1e+X channel ZZ Zbb ZbWZ tt Event selection efficiency 4 % 0.001 % 0.008 % 0.0025 % 0.005 % 0.02 % 0.006% 0.025 10 -2 % Number of event for 1fb -1 ~3 0.1 1 0.3 0.7 0.1 0.5 0.0015 Signal: ~ 5 events Background:~ 1 event Signal: ~ 5 events Background:~ 6.6 event

18. 10/30/2008Azeddine 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

19. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 19 BACK UP SLIDES

20. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 20 Jets vs Jet candidates in ZZ, Zbb and Zb (not scaled) Jets “Jet candidate” Higher number of jets per events is due to the electrons seen as jets ZZ Zb Zbb Most ZZ events have at least 1 jet not matching a medium electron

21. 10/30/2008Azeddine Kasmi SM ElectroWeak group meeting 21 Secondary vertex cut SV2 algorithm 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% Zb tt

22. 10/30/2008Azeddine 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]