Measurement of the Top Mass from the Leptons P T in the Dilepton Channel at CDF

1. Measurement of the Top Mass from the Leptons PT in the Dilepton Channel at CDF Victoria Giakoumopoulou 30 March 2007 XXV Workshop on Recent Developments in High Energy Physics & Cosmology National Technical University, Athens, Greece

2. Outline • Why measure the top quark • Motivation • Present Status • Methodology • Dilepton Event Selection • PT spectra • Top Mass with the Maximum Likelihood Method • Systematic errors • Conclusions & prospects

3. Why study the top quark • Currently the heaviest particle of the SM • Accurate measurement of the top quark mass better localization of SM Higgs mass ΔΜW α Mt2 ΔΜW α lnMH

4. Fermilab Main Injector Tevatron

5. CDF detector

6. QCD Production (~6pb)dominates at Tevatron: 85%: 15%: e-e(1/81) mu-mu (1/81) tau-tau (1/81) e -mu (2/81) e -tau(2/81) mu-tau (2/81) e+jets (12/81) mu+jets(12/81) tau+jets(12/81) jets (36/81) Top Pair Production & Decay • W decays define channel: • Dilepton: 11.12% • Lepton+jets: 44.44% • All-hadronic: 44.44%

7. Measurements of the Top Mass CDF +D0 March 07 (170.9±1.1(stat) ±1.5(syst))GeV/c2 CDF: (170.5±1.3(stat) ±1.8(syst))GeV/c2 • Moderate (CDF RUN II) or very high (LHC) statistics of top production are expected soon • The statistical error will decrease • The systematic error willdominate

8. Sensitivity to the Top Mass The main contribution in the systematic uncertainty is associated with jets Proposal (University of Athens CDF/ATLAS Group)  Seek a variable that: • doesnot depend on the jet energy scale • doesnot depend on b-tagging • it is the same for both the Dilepton and the Lepton+jets channels Such a variable could be the leptons (μ/e) PT/ET This can be calibrated against Z→ll to within ~50 MeV

9. Dilepton Signal • Expect to observe: • two high PT leptons of opposite sign • large missing ET from the two v’s • two or more jets Signal • WW 16.13% • WZ  4.1% • ZZ  1% • Zττ  11.48% • DY  28.04 % • Fakes  38.26% tW+bl+v tW-bl-v Background Drell–Yan: Zμμ, Ζee Fakes Diboson WW/WZ/ZZ Zττ We expect @ 1200 pb-1 23.11 background events 55.95 signal events S/B=2.42 CDF note 8741

10. Methodology Outline • Estimation of the Top Mass using the Lepton PT information • Create lepton PT templates for the signal for several top masses • PT is linearly dependent to the Top Mass • Create lepton PT templates for backgrounds • Fit the PT templates with Gamma x Fermi function • Implement Maximum Likelihood method to estimate the Top Mass

11. PT sensitivity to Top Mass PT sensitiveto the top quark mass Linear dependency <PT> = κMT+λ SLOPE λ=13.52%

12. Shape of Leptons PT • Parameterization of PT • Fit 30 PT histograms for MT=155-192 GeV/c2 • Find the optimum mass dependent parameters p=a1MT+a2 and q=a3MT+a4 • Fit PT of combined background • Find the optimum p and q parameters

13. Likelihood • N: number of data events • nbexp: expected number of background events • σnb: expected background uncertainty • ns: number of estimated signal events • nb: number of estimated background events

14. Example of mass estimationMC@1200pb-1 Input Mass = 175 GeV 79 signal & bg events

15. Sanity tests - only Signal MC@1200pb-1 200PE <Pull>=p1Min+p0 <Pull_RMS>=p1Min+p0 <MF>=p1Min+p0 p0=-0.19±0.25 p1=0.001±0.001 p0=-0.96±0.22 p1=0.000±0.001 p0=-1.9±4.5 p1=1.02±0.03

16. MC@1200pb-1 200PE Fitted Mass – Signal + Background p0=0.017±0.255 p1=-0.0004±0.001 p0=0.95±5.7 p1=0.998±0.033 p0=0.91±0.23 p1=0.0003±0.001

17. Sources of systematics • Gluon radiation in the initial state (ISR) • Estimated by using the official CDF Pythia samples with “more” and • “less” ISR • Choice of Parton Distribution Functions (PDF) • Estimated using the sets CTEQ5L and MRST75 • Choice of Monte Carlo generator • Estimated by comparing the results of Pythia and Herwig with the • same input top mass • Uncertainty associated with the measurement of leptons’ PT • Uncertainty in the expected background shape

18. Measurement of lepton PT • Possible pT scale uncertainty and non-linearity • Tune using Z → dilepton data (CDF note 8632) • Bremsstrahlung from the detected electrons • Found to be negligible Preliminary estimate of the PT scale uncertainty on the Mtop is < 1 GeV Adapted from CDF Joint Physics Group

19. Systematic errors

20. Projected statistical errors - Tevatron

21. Lepton+Jets(LJ) Blessed analysis by CDF @ 340pb-1 Signal • Expect to observe • high PT lepton • large MET • ≥ 4 jets tWb lvb tWbqq’b Background • W+jets: qq’ → W → lν (~80%) • Jets faking leptons (~20%) Composition @ 340pb-1 • Signal:70 expected events • Background:125 expected events • (100 W + 15 fake e + 10 fake μ) • Data: 197 events

22. LJ – Blessed result @ 340pb-1 Mtop=(220 ± 47.4(stat) ± 9.3 (syst) ) GeV/c2

23. Summary - Prospects • New method to measure the Mtop from the lepton(s) PT has been proposed and developed by the UoA group • Method blessed (approved) by CDF • Present systematic error ~4 GeV • Projected combined L+jets &Dilepton uncertainties on MT for ∫Ldt~10fb-1 (~Tevatron end of RUN II) ±5 GeV statistical ±1-2 GeV systematic • Bright prospect for Mtop at LHC

24. CDF Notes • CDF/DOC/TOP/PUBLIC/8741 • CDF/PHYS/TOP/PUBLIC/8632 • CDF/PHYS/TOP/PUBLIC/8617 • CDF/PHYS/TOP/PUBLIC/8616 • CDF/PUB/TOP/PUBLIC/7888 • JINR/E1-2005-104 “Particles and Nuclei, Letters” • CDF/PHYS/TOP/CDFR/7685 • CDF/PHYS/TOP/CDFR/7684 UoA CDF group • Victoria Giakoumopoulou • Athanasios Staveris-Polykalas • Constantinos Vellidis • Arkadios Manousakis-Katsikakis • Nikolaos Giokaris • Work partly supported by: • EPEAEK II program in the framework of the projects • Heraklitos • Pythagoras • GSRT • ELKE - UoA

25. BACKUP

26. Consistency of Fit • <PT> vsMtop from <PT> = κMT+λ, where κ=0.1327 and λ=32.56 • <PT> from Γ x Fermi model Perfect agreement !! Model works fine

27. Luminosity

28. Combined top masses @ 1.2fb-1

29. PE example

30. Statistical Error @Tevatron/LHC (LJ)