Study of the to Dilepton Channel with the Total Transverse Energy Kinematic Variable

1. University of Athens, Physics Department Section of Nuclear and Particle Physics Study of the to Dilepton Channel with the Total Transverse Energy Kinematic Variable Athens, April 17th 2003 Victoria Giakoumopoulou Workshop on RECENT DEVELOPMENTS IN HIGH ENERGY PHYSICS AND COSMOLOGY

2. OUTLINE • Introduction • Top Quark Production and Decay • Physics Motivation • H Analysis for the Dilepton Channel • Results from HERWIG simulation study • Conclusions and Future Work

3. Introduction on top quark • Top quark was predicted by the SM as the I3=+1/2 member of a weak SU(2) isodoublet that also contains the b quark • It was discovered both by CDF end D0 at the Femilab Tevatron in 1995

4. b + w b q - w Top Production and Decay At high energy collisions and for Mtop > 100 GeV/c2 fusion to a gluon is the main production mechanism. PROTON q GLUON ANTIPROTON

5. All Hadronic BR=44.4% 6 or more jets Lepton + jets BR=44.4% or W+jets Decay Modes Dilepton BR=11.2% two leptons of opposite sign

6. What about the Dilepton Signal? tW+b jet l+vl • Expect to observe: • two leptons with high PT • large missing ET from the two v’s • two or more jets tW- jet l-

7. Why study the to Dilepton channel • another measurement of the top quark mass with smallest systematic error (?)  better ‘localization’ of SM Higgs mass • i t can provide many checks on the SM

8. Top quark mass from Fermilab Tevatron RUN I All above numbers are in GeV/c2 The first uncertainty is statistical and the second is systematic.

9. Direct checks on the Standard Model ... From Standard Model : N(e-e+και μ-μ+) = Ν (e-μ+ και e+μ-) FromCDF RUN I data : N(e-e+και μ-μ+) = 2 Ν (e-μ+ και e+μ-) =7

10. Central calorimeters Solenoid Central muon New Old Partially new Front end Trigger DAQ Offline TOF Endplug calorimeter Silicon and drift chamber trackers Forward muon CDFDetector atFermilab Tevatron

11. H Analysis • H variable for the study of top in the Dilepton Channel. • Motivation for the use of H variable • the decay products have higher ET’s than the decay products in the background processes.

12. PROTON g JET g q q g JET JET ¢ q q w ANTIPROTON Main background in theW+jets channel QCD W + jets production The W boson recoils against a significant jet activity

13. H distribution for the Signal and the Backgrounds in the W+jets channel • Solid line:CDF RUN I data • Double dotted line:top eventsfromHERWIG 180 • Dottedline :top eventsfromHERWIG and background fromVECBOS • Yellow histogram :events selected withb-tagging F. Abe et al, ‘Study of Production in Collisions Using Total Transverse Energy.’ Phys. Rev.Lett. 75 (1995) 3997

14. l p p q τ- γ*, Ζ* q p p gluon p p p p τ+ gluon jet jet Dilepton Channel Signal : electronsandmuons nottauleptons Two main backgrounds from Run II Drell-Yan Zτ+τ- Total number of background events: 0.103±0.056 events Observe5events

15. Selection criteria CDF cuts Reduced CDF cuts Leptons ΡT >20 GeV >20 GeV |η| 1.0 1.0 Jets ΕΤ >10 GeV >10 GeV |η| 2.0 2.0 Number of jets >2 >2 >25 GeV >25 GeV Δφ( ,jets) >200 Invariant Mass Minv<75 or Minv> 105 GeV Data analysis • For event selection we impose • ‘CDF cuts’και • ‘Reduced CDF cuts’

16. 9 eventsfromCDF Run I e+e-+ ή μ+μ- eμ HERWIG Μt=175 GeV background events top + background data H distribution for the Signal and the backgrounds in the Dilepton Channel in RUN I J. Cassada, M. Kruse, P. Tipton, ‘Top Dilepton Events with the Top Quark Hypothesis. CDF –note 4278.

17. 5eventsfromCDF Run II e+e-+ eμ μ+μ- MC x 10 H distribution for the Signal and the backgrounds in the Dilepton Channel in RUN II

18. Motivated by these last plots we decided to examine the possibility to : • relax or eliminate completely the Δφ and MZ cuts • impose a cut on H • TO : • get higher efficiency • better signal/background ratio (S/B) • Our analysis, so far, has been performed by theHERWIGMC at generation level

19. Simulation of Signal and Background Events • HERWIG59is used for the generation production of and background events

20. Hdistribution for events with HERWIG Production of 20000 events 995 events in Dilepton 5% ofevents decay in the Dilepton Channel

21. Hdistribution of withHERWIG, CDF cuts CDF cuts 306 dilepton events 31% of alldilepton events 187 eμ 119 ee ή μμ Mtop=175 GeV

22. Hfor background events withHERWIG, CDF cuts CDF cuts Drell-Yan 5 events 49 events

23. Hsignal and background withHERWIG, CDF cuts CDF cuts signal Drell-Yan 306 signal events 49 Drell-Yan events 5 events S/B=5.7±1.1

24. Hdistribution for withHERWIG, reduced CDF cuts Reduced CDF cuts 350 dilepton events 35% of all dilepton events

25. Hdistribution for signal and background withHERWIG, reduced CDF cuts Drell-Yan 6events 471 events Reduced CDF cuts

26. Hdistribution for signal and background withHERWIG, reduced CDF cuts signal Drell-Yan 350 signal events 471 Drell-Yan events 6events Reduced CDF cuts

27. Introduction ofH cut in events selected with reduced CDF cuts

28. H cut=275GeV H cut Reduced CDF cuts H cut= 275 GeV 308events 37background events S/B=8.3±1.4

29. Application of H variablein the analysis of Dilepton channelwe have a goodseparationof signal and background • Selecting events withH variablewe have betterefficiency for the signaland much bettersignal/background ratiorelative to the analysis used in CDF RUN I. • Present Work • Use the CDF full simulation package to study the to dilepton signal and all of the backgrounds • Analysis of CDF RUN II data. Conclusions and Future Work

30. Decay Channels

31. Cut on the Invariant Mass of the two leptons • Mll<75 GeV/c2 or Mll>105 GeV/c2 , if leptons are of thesame type • to reduce events from Ζee(or μμ) decays • For events with Total Transverse Energy < 50 GeV we require • Δφ(ΜΕΤ, jet) > 200 and Δφ(ΜΕΤ,lepton) > 200 • This reduces theDrell-Yan background, because in this process there are not real neutrinos and comes from energy mismeasurement in the hadronic calorimeter. Therefore we expect strong correlation between and the jets Beyond ‘Standard’ Cuts

32. 9 eventsfromCDF Run I