In Search of Lonely Top Quarks at the Tevatron

1. In Search of Lonely Top Quarks at the Tevatron Work with Matt Strassler and Matt Bowen (GS) ISMD, Sonoma, CA 7/27/04

2. Outline • What is single-top • Why it is worthwhile to study • What makes it challenging – counting is not enough! • Another approach – Shapes Matter! • Conclusions Note: The Group in Seattle is rebuilding itself as a Particle, Field, String & Phenomenology Group: Aganagic, Ellis, Karch, Nelson, Sharpe, Strassler, Yaffe S. D. Ellis ISMD 2004

3. What is single-top? Two single-top channels are classified by W momentum t-channel s-channel time-like space-like • The top quark was discovered in Run I through • Neither single-top channel has been confirmed in Run II yet Run I limits: t < 13.5 pb, s < 12.9 pb S. D. Ellis ISMD 2004

4. Studying single top quark production because … • Leads to measurement of Vtb • Background to other searches (Higgs, etc.) t-channel, s-channel Vtb S. D. Ellis ISMD 2004

5. Plus top quark may be a special case with big payoff!! Potential for new physics discovery • Extra Scalar Bosons – top-color • Extra Gauge Bosons – top flavor • Extra Dimensions – 5D with gauge bosons in bulk • Extra Generations of Quarks - will change unitarity constraints on CKM elements • Extra couplings (Modified) – top interaction with SM particles. ex: Ztc Affect s-channel Affect t-channel See, for example, T. Tait hep-ph/0007298 S. D. Ellis ISMD 2004

6. Looking for the t-channel Trigger on - • 1 lepton • Missing Transverse Energy (from neutrino) • 1 b-tagged jet • 1 non b-tagged jet (from light quark) jet e+ b ne Similar for s-channel - extra jet from extra radiation! often not seen S. D. Ellis ISMD 2004

7. What else do we see? • , e.g., (last year’s signal is this year’s background); trigger particles + lots of extra activity, but symmetrical event • , e.g., where b tag is fake, or extra q’s are b’s or g becomes a heavy quark during showering/fragmentation • Pure QCD, where nearly everything (leptons and maybe b) is a fake.This is difficult to simulate, but experimentalists (I talk to) say it is small! We will ignore it here. S. D. Ellis ISMD 2004

8. Define “Aggressive” Event Sample for Counting Experiment Basic Cuts : 1 lepton PT > 15 GeV, |η| < 2.0; MET > 15 GeV 1 b-tagged jet with PT > 20 GeV, |η| < 2.0 (at least) 1 other jet with PT > 20 GeV, |η| < 3.5 • Studies done with Madgraph + Pythia + PGS Detector Simulation for 3 fb-1 PGS jets, Rcone =0.4; DR(lepton,jet) > 0.4 Advanced Cuts: Same, except b-tagged jet PT > 60 GeV, other jet PT > 30 GeV Mtop = invariant mass(bln): 160 GeV < Mtop < 190 GeV HT = PTlepton+MET+ Σall jets (jet PT): 180 GeV < HT < 250 GeV (all jets PT > 20 GeV, |η| < 3.5) S. D. Ellis ISMD 2004

9. Aggressive Event sample in 3 fb-1,sum over + , e + m • Basic sig:bkg ratio is 1:15 • Advanced sig:bkg is 1:4 • Systematics prevent discovery S. D. Ellis ISMD 2004

10. Conclude that Life is Hard!!! Contrast with the 1:2 ratio suggested by Stelzer, Sullivan and Willenbrock (SSW), hep-ph/9807340 • SSW more optimistic about the Tevatron energy and the top quark cross section than is now appropriate • SSW were more optimistic about light quark/gluon mistagging (as b) than we are – • Mistagged at ~ 1% rate, PT > 50 GeV • g  c, b at ~ 1-2% rate during (Pythia) showering/fragmentation •  comparable contributions to background rate • SSW were more optimistic about top quark mass reconstruction than we are S. D. Ellis ISMD 2004

11. Look for more handles on data: symmetries, correlations and event shapes • CP symmetry of initial state • Kinematic asymmetry of Initial state: (asymmetric) vs (symmetric) • In t-channel signal there is a correlation between scattered q and final lepton due to LH W vertex and carried by top quark spin (which decays before it interacts), q  t  l S. D. Ellis ISMD 2004

12. CP Invariance of the Tevatron Initial State • pp initial state at Tevatron is CP invariant, but not C or P invariant separately • At leading order, processes that proceed through an s-channel gluon “forget” that they are not separately C and P invariant (tt and QCD) • Processes with W’s “remember” that they are not separately C and P invariant (single top and W+jets) P P Under C or P transformation P P Under CP P P S. D. Ellis ISMD 2004

13. ** **Indicates C or P non-invariance Focus on 2-D distributions in signed rapidity, * A B D C CP invariant • Same correlations in and • Strong correlation in t-channel signal, • Very weak correlation in s-channel and • Weak, but similar correlation in *Used by CDF in 1-D analysis S. D. Ellis ISMD 2004

14. Define “Relaxed” Event Sample for Shape Analysis Basic Cuts :(only) 1 lepton PT>15 GeV, |η|<2.0; MET > 20 GeV 1 b-tagged jet with PT>40 GeV, |η|<2.0 (at least) 1 other jet with PT>30 GeV, |η|<3.5 Advanced Cuts: Mtop = invariant mass(bln): 130 GeV < Mtop < 210 GeV HT = PTlepton+MET+ Σall jets (jet PT): 170 GeV < HT < 300 GeV (all jets PT > 20 GeV, |η|<3.5) Keep more of signal and more background, especially S. D. Ellis ISMD 2004

15. Relaxed Event sample in 3 fb-1,sum over + , e + m • Basic sig:bkg ratio is 1:12 • Advanced sig:bkg is 1:7 But look at shapes!! S. D. Ellis ISMD 2004

16. Contour plots of 4 channels – as predicted ! Sig Bkg S. D. Ellis ISMD 2004

17. Focus on Shape with following basis functions Complete & Orthogonal • Uncorrelated bits cancel in F+ S. D. Ellis ISMD 2004

18. Uncorrelated and P even • Uncorrelated – • P even •   Cancel in F+ and F- S. D. Ellis ISMD 2004

19. S. D. Ellis ISMD 2004

20. Different shapes S. D. Ellis ISMD 2004

21. S. D. Ellis ISMD 2004

22. 325 -11 -6 29 -3 19 31 3 343 11 76 19 -19 38 3 11 281 -31 6 -3 -11 286 41 19 Quantify this by again looking at the sum over + , e + m in the 4 quadrants for 3 fb-1 Signal = t + s-channels Background = tt + Wjj  But use the shapes! F+  Note signs F-  S. D. Ellis ISMD 2004

23. Signal/Background _   F   |F+| |F-| S. D. Ellis ISMD 2004

24. Suggests that we can separate Signal and Background, If we use the Shape information! • Systematic issue #1: Do we understand the shape of the Wjj background in detail? • Answer: Not Yet! There are many individual channels with somewhat different shapes, whose relative contribution rates depend largely on mis-tag rates and g  b,c rates. • But we will learn using the many different handles on the data, e.g., look at Zjj!! S. D. Ellis ISMD 2004

25. We can improve further by choosing specific “windows” – helps also with statistical N issues • Uncertainty in NF+ : in any region of  plane • Uncertainty in NF- : S. D. Ellis ISMD 2004

26. N/ N (appropriate) _ F 1.7 1.8 F- F+ S. D. Ellis ISMD 2004

27. Can also consider a likelihood analysis based on the difference in shapes •  = NSig/NTot 0.13 (all of phase space) • Uncertainty S. D. Ellis ISMD 2004

28. Conclusions • Phenomenology at hadron colliders is tough! • Shape variables are very useful/essential for finding the single top quark signal • We need to understand the shapes of the backgrounds, especially Wjj (and QCD) S. D. Ellis ISMD 2004

29. Extra Detail Slides S. D. Ellis ISMD 2004

30. Extra (Pseudo-)Scalar Bosons: Top-color models • Scalars (such as Higgs) exist as bound states of top and bottom quarks • For Mπ± = 250 GeV, tR-cR mixing of ~20% s-channel cross-section doubles • No interference as SM is from left-handed light quarks • t-channel contribution is suppressed by 1/Mπ±2 and that π± doesn’t couple to light quarks time-like momentum allows for resonance e.g., He & Yuan: hep-ph/9810367 S. D. Ellis ISMD 2004

31. Extra Gauge Bosons: Top-flavor models SU(3)C x SU(2)h x SU(2)l x U(1)Y e.g., • Postulate a larger gauge group which reduces to the SM gauge group at low energies to explain top mass • 1st and 2nd gen quarks transform under SU(2)l, and 3rd under SU(2)h, add heavy doublet of quarks • SU(2)h gauge couplings mix with SU(2)l according to sin2φ • For MW‘ = 1 TeV, sin2φ =0.05 s-channel increases ~20% • t-channel contribution suppressed by 1/MW‘2 W' S. D. Ellis ISMD 2004

32. Extra Dimensions:5-D Gauge Bosons • Allow only SM gauge bosons to propagate in compactified extra dimension • Permits Kaluza-Klein modes of W (Wkk) • For MWkk= 1TeV, s-channel amplitudes interfere destructively to reduce cross-section by 25% • t-channel contributions are suppressed by 1/MW'2 Wkk S. D. Ellis ISMD 2004

33. Extra quark generations:CKM constraints • For 3 generations, the unitary of the CKM matrix constrains |Vts| < 0.043 • With >3 generations, one possibility is |Vtb|=0.83 and |Vts|=0.55 • Because gluons split to ss far more than bb, the t-channel cross-section rises by 60% • s-channel produces as many tops as before, but less with an additional b quark – so the observable cross-section goes down a little. • Changes decay structure of top s s Vts Without imposing 3 family unitarity, these are the 90% CL direct constraints. S. D. Ellis ISMD 2004

34. Extra Couplings*:FCNC: Z-t-c • Can argue that low energy constraints (κZtc < 0.3) may not apply in the presence of additional new physics • For κZtc = 1, t-channel increases 60% • These couplings change top decay structure • κZtc recently constrained by LEP II data to be < ~ 0.5 (hep-ex/0404014) Z c c *there’s nothing “extra” about these couplings; the appropriate title would be “Modifications to Top Couplings” S. D. Ellis ISMD 2004

35. Shifted cross-sections plot SM prediction 3σ theoretical deviation Charged top-pion FCNC Z-t-c vertex 4 gen Top-flavor model Extra dimensions Plot from hep-ph/0007298 t-channel CS has changed to 1.98pb ED from hep-ph/0207178 S. D. Ellis ISMD 2004

36. Lessons • t-channel is affected by modifications to top quark couplings • s-channel is affected by heavy particles • Many other models to consider, good practice for general searches Therefore, measuring the t- and s-channels separately is important and could potentially be a “Window to Physics Beyond the SM” S. D. Ellis ISMD 2004