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

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

Introduction on top quark Top quark was predicted by the SM as the I 3 =+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

Top Production and Decay At high energy collisions and for M top > 100 GeV/c 2 fusion to a gluon is the main production mechanism. PROTON ANTIPROTON q q b b + w - w GLUON

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

What about the Dilepton Signal? t  W + b jet l + v l t  W - jet l - Expect to observe: two leptons with high P T large missing E T from the two v’s two or more jets

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

Top quark mass from Fermilab Tevatron RUN I ChannelCDF All-hadronic186±10 ±5.7 Lepton+MET+jets176±5.1 ±5.3 Dilepton167±10.3 ±4.8 All above numbers are in GeV/c 2 The first uncertainty is statistical and the second is systematic.

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

CDF Detector at Fermilab Tevatron New Old Partially new Forward muon Endplug calorimeter Silicon and drift chamber trackers Central muonCentral calorimeters Solenoid Front end Trigger DAQ Offline TOF

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 E T ’s than the decay products in the background processes.

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

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

Dilepton Channel Signal : electrons and muons not tau leptons Two main backgrounds from Run II Total number of background events: ±0.056 events Observe 5 events p p gluon jet p p q l γ *, Ζ * p p τ-τ- p p τ+τ+ q gluon jet Drell-Yan Zτ+τ-Zτ+τ-

Data analysis For event selection we impose ‘CDF cuts’ και ‘Reduced CDF cuts’ M inv <75 or M inv > 105 GeV Invariant Mass >20 0 Δφ(,jets) >25 GeV >2 Number of jets  2.0 |η| >10 GeV ΕΤΕΤ Jets  1.0 |η| >20 GeV ΡTΡT Leptons Reduced CDF cutsCDF cutsSelection criteria

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 events from CDF Run I e + e -+ ή μ + μ - eμ HERWIG Μ t =175 GeV background events top + background data

H distribution for the Signal and the backgrounds in the Dilepton Channel in RUN II 5 events from CDF Run II e + e -+ eμ μ + μ - MC x 10

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

Simulation of Signal and Background Events HERWIG59 is used for the generation production of and background events

H distribution for events with HERWIG Production of events 995 events in Dilepton 5% of events decay in the Dilepton Channel

H distribution of with HERWIG, CDF cuts M top =175 GeV CDF cuts 306 dilepton events 31% of all dilepton events 187 eμ 119 ee ή μμ

H for background events with HERWIG, CDF cuts CDF cuts Drell-Yan 49 events 5 events

H signal and background with HERWIG, CDF cuts CDF cuts signal Drell-Yan 306 signal events 49 Drell-Yan events 5 events S/B=5.7±1.1

H distribution for with HERWIG, reduced CDF cuts Reduced CDF cuts 350 dilepton events 35% of all dilepton events

H distribution for signal and background with HERWIG, reduced CDF cuts Drell-Yan 471 events 6 events Reduced CDF cuts

H distribution for signal and background with HERWIG, reduced CDF cuts signal Drell-Yan 350 signal events 471 Drell-Yan events 6 events Reduced CDF cuts

Introduction of H cut in events selected with reduced CDF cuts

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

Application of H variable in the analysis of Dilepton channel we have a good separation of signal and background Selecting events with H variable we have better efficiency for the signal and much better signal/background ratio relative to the analysis used in CDF RUN I. Conclusions and Future Work 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.

Decay Channels

Beyond ‘Standard’ Cuts Cut on the Invariant Mass of the two leptons M ll 105 GeV/c 2, if leptons are of the same type to reduce events from Ζ  ee(or μμ) decays For events with Total Transverse Energy < 50 GeV we require Δφ(ΜΕΤ, jet) > 20 0 and Δφ(ΜΕΤ,lepton) > 20 0 This reduces the Drell-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

9 events from CDF Run I