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					Experimental Top Status
              Gordon Watts
             Brown University
        (soon to be at University of Washington)

    For the DØ & CDF Collaborations

        D
              July 25-29, 1999
                                                       Outline
              Standard Model Top
                       New cross-section results (NN, CDF)
                       Mass status
                       Introduction to Fermilab Tevatron Run 2
              Top (decay) Properties
                       Single Top Limits
                       Spin Correlations
                       pT distributions
                       W Helicity
                       Mtt
              Extended Top
                       Higgs Disappear


Gordon Watts (Brown University)   Top Status 7/28/99              D   2
                                                  The Tevatron

                                            Tevatron
                                                        D




                                     Main Injector
                                       (Run 2)
                                                             Located just west of Chicago




Gordon Watts (Brown University)   Top Status 7/28/99                    D                   3
                         The CDF And DØ Detectors




Gordon Watts (Brown University)   Top Status 7/28/99   D   4
                                  Typical (!) Event (CDF)




Gordon Watts (Brown University)    Top Status 7/28/99   D   5
                                  Top Quark Discovery
              Before Run I
                       One of three unobserved particles (H, t, nt)                                       u        1.5-5 MeV
                       The lightest 5 quarks had been observed.                                           d          3-9 MeV
                       It was known that the top quark was much heavier than any                          c      1.1-1.4 MeV
                        of the other quarks.                                                               s      60-170 MeV
                       Top decay and search are classified by the W decay mode.                           b      4.1-4.4 GeV
                                                                                                           t        > 91 GeV
                                                       W Decay Mode
                                           W           ln    jj       ln   jj
                                                                                                     Run I started in Sept ‘92
                p                           b           b    b        b    b                         and Top discovery was
                                           W            ln   ln       jj   jj                        announced in March ‘95
                p                           b           b    b        b    b
                                                                                All Jets Huge QCD Background
                                                                                Lepton + Jets Good cross section and manageable
                                                                                    backgrounds
                                                                                Dilepton Very small backgrounds, but very small
                                                                                    cross section


Gordon Watts (Brown University)   Top Status 7/28/99                                                  D                           6
                                       Top Cross-Section
       CDF has updated the b-tagging
                 Affects both Lepton + Jets and All-Hadronic cross sections.
                 Both experiments use a B-tagging algorithm to require a b-jet
                          Softlepton detection (from B decay) - CDF & D
                          Displaced vertex reconstruction - CDF
                 Efficiency and fake rates must be calculated for the tagging methods
                          Mistags determined by counting
                           negative decay lengths in the data
                          gbb is a physics source of negative
                           decay lengths



          Mistag rate goes down by 20-55%
          Associated error goes from 40% to 10%
Gordon Watts (Brown University)    Top Status 7/28/99                         D          7
                                          Top Cross-Section
        Other s(tt) changes since                         Preliminary
         publication:
                 All of CDF’s results reflect an
                  updated Luminosity.
                 CDF’s SLT changed a small
                  amount (selection cuts made
                  uniform)
                 DØ’s results are unchanged

            CDF          s (t t)  6.5 -1.4 pb
                                          1.7



           DØ            s (t t)  5.9  1.7 pb
                              No Excess
             CDF’s old value: s (t t)  7.6 -1.5
                                               1.8

Gordon Watts (Brown University)       Top Status 7/28/99                 D   8
                     Neural Net Analysis of ttem
              em is a golden channel
                       Low Backgrounds
                       But, low BR (2.5%)
                                     tt  enmn bb
              Long standing standard analysis
                       Can multivariate techniques do better?
                       Standard Analysis
                                   Cuts on ET of electron,      Feed forward NN trained on simulated signal
                                    muon, missing ET, jets,       and background
                                    and total energy in event
                                    (HT).                            QCD, Zttem, and WWem
                       NN Analysis:                                 Variables:
                                   Release the jet ET and               ETe
                                                                                  ETjet1/ 2   ET
                                    missing ET cuts
                                   Remove the HT                        ETjet   M (e, m )  (e, m )
                                    requirement


Gordon Watts (Brown University)          Top Status 7/28/99                               D                     9
                       Neural Net Analysis of tem




        Standard analysis was optimized using RGS
                 RGS is a selection-cut phase-space optimizer
        NN is about 10% better than the standard analysis
                 Broad range of top masses tested

                   NN Analysis                           Conventional Analysis
             s (tt )  8.8  5.1pb                       s (tt )  7.1  4.8pb
        Relative Uncertainly: 60%                      Relative Uncertainly: 68%

Gordon Watts (Brown University)   Top Status 7/28/99                               D   10
                                                         Mt
              Recent Updates (~1 year)
                       CDF Dilepton Result
                       CDF all-hadronic error re-evaluation
                       Official Tevatron Combined Result

                 The top quark has the best
                measured mass of any quark

                                                                        CDF

          CDF Mt=176.0 ± 6.5 GeV/c2
                                                               DØ
            DØ Mt=172.1 ± 7.1 GeV/c2


Gordon Watts (Brown University)   Top Status 7/28/99                D         11
                                                                  Tevatron Mt
               Systematic errors are divided into six
                components with six subparts
                           All correlations are taken into account.

                          mt = 174.3 ± 5.1 GeV/c2
                                        CDF all-
                                        hadronic
                                          10%
                                                           Contribution to
                                                            Central Value
   D0 le pton+je ts
         34%




                                                     CDF le pton+je ts
                                                          34%




           D0 dile pton
              12%
                             CDF dile pton
                                10%            If you believe SuperKamiokande   12 orders of magnitude range in mass
                                                       0 < Mn < 10-12 Mt         for the fundamental SM fermions!
Gordon Watts (Brown University)              Top Status 7/28/99                                D                       12
                                                       MW

                 DØ Average
                80.474  0.093


                 CDF Average
                80.433  0.079




Gordon Watts (Brown University)   Top Status 7/28/99        D   13
                                                       MH
              Light Higgs Favored
                       Good news for LEP and
                        future collider searches

                                                             LEPEWWG
                                                            [summer ‘99 plots]




Gordon Watts (Brown University)   Top Status 7/28/99                             D   14
                                                 Tevatron Run 2
              What is Run II?                                  Top at Fermilab
                                                                                         Run I     Run II
                       Start Slow: 3 fb-1 in first couple of     Expected dilepton             17      300
                        years per detector                        Expected lepton+jets B Tags 45      2000
                                                                  Expected lepton+jets dbl B Tags9      600
                       Finish Fast: 5 fb-1 per year till LHC
                                                                  Mass Sample                  45     1500
                       2 TeV center of mass energy               Mass Sample Double Tags       5      500
                               40% increase in s(tt)             Luminostity           ~200 pb-1   ~4 fb-1
              Concentrate on bread & butter at start
                                                                   Better Detectors in Run II
               of Run II
                                                                          Improved Tracking
                       Top!
                                                                          Better B-tagging efficiency
                                                                                 Large double tag sample
                                                                          Better lepton detection efficiency
                                                                   Better top efficiency
                                  Top Factory

Gordon Watts (Brown University)       Top Status 7/28/99                                      D                 15
                                                         Top In Run 2
              Limiting Systematics for the Cross Section in Run 1
                       Backgrounds Wbb, Wcc, etc. are based on MC and have large cross-section
                        uncertainties
                       Tagging
                       Luminosity
              Limiting Systematics for the Mass
                       Jet Energy Scale Detector effects and soft gluon effects
                       Gluon Radiation How well is the QCD radiative process modeled?



                      dMt  3 GeV/c2
                                                                  dMHiggs  40%
                   dMW  40                MeV/c2
                                       Run 1 Results:
                                                                (per experiment!)
                                   dMt  6.7 GeV/c2 (each)
                                  dMW  110 MeV/c2 (each)
Gordon Watts (Brown University)          Top Status 7/28/99                         D             16
                                     Systematic Errors in Mt
                                                              CDF l+jets D0 l+jets CDF diltpon D0 dilepton

                                  Statistical Error                  4.8       5.6         10.3        12.3

                                  Jet Energy Scale                   4.4         4          3.8         2.4
                                  Signal Model (MC)                  2.6       1.9          2.8         1.7
                                  Total Systematic                   5.3       5.5          4.8         3.6

                                  Measured Mass                    175.9     173.3        167.4       168.4

                                  % Stat Error                       2.7       3.2          6.1         7.3
                                  % Sys Error                          3       3.1          2.8         2.1




                                     Dilepton systematic errors are the smallest!


Gordon Watts (Brown University)          Top Status 7/28/99                                        D          17
                                    Search for Single Top
              Measure top properties in isolation                                 q            q
              Signal
                       One or two hard b-jets                                                               Stelzer 1998
                                                                                                W
                       W decay products
                                                                                                         t
              Backgrounds are Wbb, Wcc, Wc, mistags,                                  b
               and tt production.                                                                    Signal is W+b+q
                 W-g                                                                                 b
                           After detector efficiency/acceptance
                                  Expect only 1.2 ± 0.3 events!                            s  1.70  0.09pb
                                      Expected total background: 12.9 ± 2.1
                                      Observe 15 events


                                  s W glu  15 .4pb @ 95% CL                 Preliminary
Gordon Watts (Brown University)       Top Status 7/28/99                                        D                           18
                                  Search for Single Top

                                                         q                             t
                                                                    W*
                                                                                 s  0.73  0.04pb
                                                                                           Smith 1996
                                                         q    Signal is W+b+b         b



                                                        s-W   After detector efficiency/acceptance
                                                              Expect only 1.0 ± 0.3 events!

                                                                  Expected total background: 29.7± 2.1
                                                                  Observe 42 events

                                                              s s W  15 .8pb @ 95% CL
Gordon Watts (Brown University)   Top Status 7/28/99   Preliminary      D                                19
                                          Single Top in Run 2
              Run 2
                       100-200 events per experiment
                       Increased data set size allows for better selection cuts
                                   Better Signal-to-background ratio
              Measurements
                           Partial Widths G(tWX)
                           Vtb (12% error)
                           s (10% error)
                           Top Quark Polarization




Gordon Watts (Brown University)          Top Status 7/28/99                        D   20
                                           Spin Correlation
     The top quark decays before it can hadronize
               Mt = 175 GeV/c2                         Typical lifetime ~ 410-25 seconds

                       Decay products will have spin information of top quark
                                                  Strong interaction has no time to affect spins

        Can measure spin of top quark by looking at its decay products
                                                                              Particle              
           1 dG            1  i cosi                                         l, d                1
                                                                               n,u
           G d (cos i )
                                                                                                   -0.31
                                2
                                                                                W+                  0.41
                                                                                b                  -0.41
                      Use top dilepton events
Gordon Watts (Brown University)   Top Status 7/28/99                                        D              21
                                           Spin Correlation
              Top spin is not polarized at Tevatron
                       But spins of the two top quarks are correlated!

                   Spin has a quantization axis
                         Off diagonal basis
                                  [Mahlon and Parke, PLB411, 173 (1997)]


                     , 


                                                 1        d 2s              1   cos  cos 
                                                                          
                                                 s d (cos  )d (cos  )            4

                                                                      Correlation information is in .
                                                           SM Prediction for TeV ~ 0.9


Gordon Watts (Brown University)   Top Status 7/28/99                                              D      22
                                           Spin Correlation
              Events are reconstructed using the      =-1        =+1
               same method as for the dilepton
               mass reconstruction
                       Events are underconstrained                       MC

              6 Dilepton Candidates
              Binned 2D likelihood fit




                  >-0.25 @ 68% CL


                                                        Data
Gordon Watts (Brown University)   Top Status 7/28/99           D               23
                                  Spin Correlation in Run 2


   150 Events
 per Experiment




Gordon Watts (Brown University)     Top Status 7/28/99   D    24
                             Top Quark PT Distribution
              Look for deviations in the top quark
               production variable pT
                       Extended Technicolor predicts these
                        deviations
                       R4 is where most difference is expected
              Use standard Lepton + Jets sample
                       Hadronic Top only (the two are correlated)
              Unfold reconstruction smearing
                       Bin in true top pT
              Excellent agreement with the SM
                       Work in progress to establish quantitative
                        limits on various models.




Gordon Watts (Brown University)   Top Status 7/28/99                 D   25
                                                       W Helicity
      SM top decays only to longitudinally
       polarized or left-handed W
                hW = 0 or -1
                                                2
            BR (t  bWlong )  1 m               0.70
                               t             
             BR (t  bWleft ) 2  mW
                                
                                              
                                                 0.30

      Lepton pT distributions in tbln
       distinguish the two helicity states.
                hW=0: perpendicular to W
                hW=-1: Opposite to W
      Lepton pT discriminates
                Better measured than angular correlations
                Unaffected by combinatorics or n
                 reconstruction


Gordon Watts (Brown University)   Top Status 7/28/99                D   26
                                                          W Helicity
              Backgrounds include W+jets, fake
               leptons, HF production, Ztt, and
               WW.                                                         Signal
              Unbinned maximum likelihood fit to                          Background
               the MC predicted expectations for
               longitudinal and left and background
              Fright determined by repeating fit with
               Flong constrained to the SM value of
               0.7

    Flong=0.91  0.37 (stat)  0.12 (sys)
    Fright=0.11  0.15 (stat)  0.06 (sys)

                                  Run 2: d ~ 6%

Gordon Watts (Brown University)      Top Status 7/28/99                D                27
                                                          Mtt
              Some Technicolor theories predict
               existence of heavy objects that
               decay to tt pairs.
                       top gluons and a Z’ in topcolor
                        assisted Technicolor.




Gordon Watts (Brown University)   Top Status 7/28/99            D   28
                                                            Mtt
              Perform binned likelihood fit using Mtt
               templates.
                       Z’ tt
                       SM tt
                       QCD W+Jets
              In the region less than 650 GeV/c2
                       Existence of a narrow width topcolor Z’
                        which maximizes the predicted Z’
                        production cross-section is excluded.




                                  In Run 2 we will have a
                                  large sample of top in
                                  which to do this study

Gordon Watts (Brown University)       Top Status 7/28/99          D   29
                                  Higgs Disappearance
              SM has single Higgs doublet
                       One physical Higgs: H0
              Many theories call for two doublets
                       SUSY
                       Other non-SUSY extensions

          Five physical states: H0, h0, A0, H+, H-
                EW interactions specified by:
                      mW, MH+, tan b




                                            If mH+ is light enough, then tH+b is open
Gordon Watts (Brown University)   Top Status 7/28/99                               D     30
                                  Higgs Disappearance
              tH+b will compete with tW+b
                       Can do a disappearance search         s (tt )  4.5
                        based on the Lepton + Jets analysis   s (tt )  5.0
                       For each bin in (mH+, tan b) space    s (tt )  5.5
                        simulate many Monte Carlo
                        experiments
                       Compare number of expected
                        events with tt lepton + jets data




Gordon Watts (Brown University)   Top Status 7/28/99                    D     31
                          Run 2 Higgs Disappearance
              Assume:


                         s (tt )  7.0pb
                         n obs  600
                         background  50  5
                          SM  4.0  0.4%




Gordon Watts (Brown University)    Top Status 7/28/99   D   32
                                                          Other Results
              Vtb measurement
                       Unitarity (with 3 generation SM) means Vtb ~ 1
                       CDF analyzes lepton + jets and dilepton samples
                                   Ratios of events with 0, 1, and 2 b-tags
                       |Vtb| > 0.76 @ 95% C.L.
              CDF Rare Decay Searches
                       BR(tZq) < 33% @ 95% CL
                       BR(tgq) < 3.2% @ 95% CL
              Branching fraction BR(t  e,m)
                       SM predicts 1/9
                       CDF measures 0.094  0.024




Gordon Watts (Brown University)           Top Status 7/28/99                   D   33
                                                          Conclusions
              The Top Quark is the best measured of any of the known quarks
                       s(tt)CDF = 6.5+1.7-1.4 pb
                       s(tt)DØ = 5.9±1.7 pb
                       mt = 174.3±5.1 GeV/c2
              We have moved beyond the discovery phase
                       Are already able to characterize properties of the Top Quark & its decay
                       Mtt, pt, spin, W decay, etc.
              Run 2 Outlook is bright for top physics at the Tevetron
                       dM, dW, dH
                               New techniques (Neural Nets)
                       Rare Decays
                       Top Properties (Vtb, etc)




Gordon Watts (Brown University)      Top Status 7/28/99                                 D          34

				
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