Experimental Top Status Gordon Watts Brown University For the DØ & CDF Collaborations July 25-29, 1999 (soon to be at University of Washington)

2 Gordon Watts (Brown University) Top Status 7/28/99 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 p T distributions W Helicity M tt  Extended Top Higgs Disappear

3 Gordon Watts (Brown University) Top Status 7/28/99 The Tevatron Tevatron Main Injector (Run 2) Located just west of Chicago

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

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

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

7 Gordon Watts (Brown University) Top Status 7/28/99  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 Top Cross-Section CDF has updated the b-tagging 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% for SVX

8 Gordon Watts (Brown University) Top Status 7/28/99 Top Cross-Section CDF  Other  (tt) changes since 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 No Excess pb DØ CDF’s old value: Preliminary

9 Gordon Watts (Brown University) Top Status 7/28/99  e  is a golden channel Low Backgrounds But, low BR (2.5%)  Long standing standard analysis Can multivariate techniques do better? Neural Net Analysis of tt  e  Standard Analysis  Cuts on E T of electron, muon, missing E T, jets, and total energy in event (H T ). NN Analysis:  Release the jet E T and missing E T cuts  Remove the H T requirement  Feed forward NN trained on simulated signal and background QCD, Z  e , and WW  e  Variables:

10 Gordon Watts (Brown University) Top Status 7/28/99 Neural Net Analysis of t  e   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 AnalysisConventional Analysis Relative Uncertainly: 60%Relative Uncertainly: 68%

11 Gordon Watts (Brown University) Top Status 7/28/99 MtMt  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 M t =176.0 ± 6.5 GeV/c 2 DØ M t =172.1 ± 7.1 GeV/c 2 DØ CDF

12 Gordon Watts (Brown University) Top Status 7/28/99 Tevatron M t If you believe SuperKamiokande 0 < M < M t 12 orders of magnitude range in mass for the fundamental SM fermions!  Systematic errors are divided into six components with six subparts All correlations are taken into account. m t = ± 5.1 GeV/c 2 Contribution to Central Value

13 Gordon Watts (Brown University) Top Status 7/28/99 MWMW DØ Average  CDF Average  0.079

14 Gordon Watts (Brown University) Top Status 7/28/99 MHMH  Light Higgs Favored Good news for LEP and future collider searches LEPEWWG [summer ‘99 plots]

15 Gordon Watts (Brown University) Top Status 7/28/99 Tevatron Run 2  What is Run II? Start Slow: 3 fb -1 in first couple of years per detector Finish Fast: 5 fb -1 per year till LHC 2 TeV center of mass energy  40% increase in  (tt)  Concentrate on bread & butter at start of Run II Top! Preliminary  Better Detectors in Run II Improved Tracking Better B-tagging efficiency  Large double tag sample Better lepton detection efficiency  Better top efficiency Top Factory Top at Fermilab

16 Gordon Watts (Brown University) Top Status 7/28/99 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?  M t  GeV/c 2  M W  MeV/c 2  M Higgs  40% Run 1 Results:  M t  6.7 GeV/c 2 (each)  M W  MeV/c 2 (each) (per experiment!)

17 Gordon Watts (Brown University) Top Status 7/28/99 Systematic Errors in M t Dilepton systematic errors are the smallest!

18 Gordon Watts (Brown University) Top Status 7/28/99 Search for Single Top Stelzer 1998  Measure top properties in isolation  Signal One or two hard b-jets W decay products  Backgrounds are Wbb, Wcc, Wc, mistags, and tt production. After detector efficiency/acceptance Expect only 1.2 ± 0.3 events! Expected total background: 12.9 ± 2.1 Observe 15 95% CL W-g q W q t b b Signal is W+b+q Preliminary

19 Gordon Watts (Brown University) Top Status 7/28/99 Search for Single Top Smith 1996 After detector efficiency/acceptance Expect only 1.0 ± 0.3 events! Expected total background: 29.7± 2.1 Observe 42 95% CL s-W q W*W* q t b Signal is W+b+b Preliminary

20 Gordon Watts (Brown University) Top Status 7/28/99 Single Top in Run 2  Run events per experiment Increased data set size allows for better selection cuts  Better Signal-to-background ratio  Measurements Partial Widths  (t  WX) V tb (12% error)  10% error) Top Quark Polarization

21 Gordon Watts (Brown University) Top Status 7/28/99 Spin Correlation The top quark decays before it can hadronize M t = 175 GeV/c 2 Typical lifetime ~ 4  seconds Strong interaction has no time to affect spins Decay products will have spin information of top quark Can measure spin of top quark by looking at its decay products Use top dilepton events

22 Gordon Watts (Brown University) Top Status 7/28/99 Spin Correlation Spin has a quantization axis Off diagonal basis [Mahlon and Parke, PLB411, 173 (1997)] Correlation information is in . SM Prediction for TeV ~ 0.9  Top spin is not polarized at Tevatron But spins of the two top quarks are correlated!

23 Gordon Watts (Brown University) Top Status 7/28/99 Spin Correlation  Events are reconstructed using the same method as for the dilepton mass reconstruction Events are underconstrained  6 Dilepton Candidates  Binned 2D likelihood fit  68% CL  =-1  =+1 MC Data

24 Gordon Watts (Brown University) Top Status 7/28/99 Spin Correlation in Run Events per Experiment

25 Gordon Watts (Brown University) Top Status 7/28/99 Top Quark P T Distribution  Look for deviations in the top quark production variable p T Extended Technicolor predicts these deviations R 4 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 p T  Excellent agreement with the SM Work in progress to establish quantitative limits on various models.

26 Gordon Watts (Brown University) Top Status 7/28/99 W Helicity  SM top decays only to longitudinally polarized or left-handed W h W = 0 or -1  Lepton p T distributions in t  bl distinguish the two helicity states. h W =0: perpendicular to W h W =-1: Opposite to W  Lepton p T discriminates Better measured than angular correlations Unaffected by combinatorics or reconstruction

27 Gordon Watts (Brown University) Top Status 7/28/99 W Helicity  Backgrounds include W+jets, fake leptons, HF production, Z , and WW.  Unbinned maximum likelihood fit to the MC predicted expectations for longitudinal and left and background  F right determined by repeating fit with F long constrained to the SM value of 0.7 F right =0.11  0.15 (stat)  0.06 (sys) F long =0.91  0.37 (stat)  0.12 (sys) Run 2:  ~ 6% Signal Background

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

29 Gordon Watts (Brown University) Top Status 7/28/99  Perform binned likelihood fit using M tt templates. Z’  tt SM tt QCD W+Jets  In the region less than 650 GeV/c 2 Existence of a narrow width topcolor Z’ which maximizes the predicted Z’ production cross-section is excluded. M tt In Run 2 we will have a large sample of top in which to do this study

30 Gordon Watts (Brown University) Top Status 7/28/99 Higgs Disappearance  SM has single Higgs doublet One physical Higgs: H 0  Many theories call for two doublets SUSY Other non-SUSY extensions Five physical states: H 0, h 0, A 0, H +, H - EW interactions specified by: m W, M H +, tan  If m H + is light enough, then t  H + b is open

31 Gordon Watts (Brown University) Top Status 7/28/99 Higgs Disappearance  t  H + b will compete with t  W + b Can do a disappearance search based on the Lepton + Jets analysis For each bin in (m H +, tan  ) space simulate many Monte Carlo experiments Compare number of expected events with tt lepton + jets data

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

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

34 Gordon Watts (Brown University) Top Status 7/28/99 Conclusions  The Top Quark is the best measured of any of the known quarks  (tt) CDF = pb  (tt) DØ = 5.9±1.7 pb m t = 174.3±5.1 GeV/c 2  We have moved beyond the discovery phase Are already able to characterize properties of the Top Quark & its decay M tt, p t, spin, W decay, etc.  Run 2 Outlook is bright for top physics at the Tevetron  M,  W,  H  New techniques (Neural Nets) Rare Decays Top Properties (V tb, etc)