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

S. D. Ellis ISMD Outline 1.What is single-top 2.Why it is worthwhile to study 3.What makes it challenging – counting is not enough! 4.Another approach – Shapes Matter! 5.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 What is single-top? Two single-top channels are classified by W momentum t-channel s-channel  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 time-like space-like

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

S. D. Ellis ISMD 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: Z tc Affect s-channel Affect t-channel See, for example, T. Tait hep-ph/

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

S. D. Ellis ISMD 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 Define “Aggressive” Event Sample for Counting Experiment Advanced Cuts: Same, except b-tagged jet P T > 60 GeV, other jet P T > 30 GeV M top = invariant mass(bl ): 160 GeV 20 GeV, |η| < 3.5)  Studies done with Madgraph + Pythia + PGS Detector Simulation for 3 fb -1 Basic Cuts : 1 lepton P T > 15 GeV, |η| 15 GeV 1 b-tagged jet with P T > 20 GeV, |η| 20 GeV, |η| < 3.5 PGS jets, R cone =0.4;  R(lepton,jet) > 0.4

S. D. Ellis ISMD Aggressive Event sample in 3 fb -1, sum over +, e +  ChannelsEvents for Basic Cuts Advanced cuts Systematic Uncertainty t-channel44332>15% s-channel19216>10% W+jj >10% Tt320048>10% Basic sig:bkg ratio is 1:15 Advanced sig:bkg is 1:4 Systematics prevent discovery

S. D. Ellis ISMD Conclude that Life is Hard!!! Contrast with the 1:2 ratio suggested by Stelzer, Sullivan and Willenbrock (SSW), hep-ph/  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, P T > 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 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 CP Invariance of the Tevatron PP 1.pp initial state at Tevatron is CP invariant, but not C or P invariant separately 2.At leading order, processes that proceed through an s- channel gluon “forget” that they are not separately C and P invariant (tt and QCD) 3.Processes with W’s “remember” that they are not separately C and P invariant (single top and W+jets) Initial State PP Under C or P transformation PP Under CP

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

S. D. Ellis ISMD Define “Relaxed” Event Sample for Shape Analysis Advanced Cuts: M top = invariant mass(bl ): 130 GeV 20 GeV, |η|<3.5) Basic Cuts : (only) 1 lepton P T >15 GeV, |η| 20 GeV 1 b-tagged jet with P T >40 GeV, |η| 30 GeV, |η|<3.5 Keep more of signal and more background, especially

S. D. Ellis ISMD Relaxed Event sample in 3 fb -1, sum over +, e +  ChannelsEvents for Basic Cuts Advanced cuts Systematic Uncertainty t-channel191133>15% s-channel8551>10% W+jj >10% tt >10% Basic sig:bkg ratio is 1:12 Advanced sig:bkg is 1:7 But look at shapes!!

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

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

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

S. D. Ellis ISMD

S. D. Ellis ISMD Different shapes

S. D. Ellis ISMD

S. D. Ellis ISMD Quantify this by again looking at the sum over +, e +  in the 4 quadrants for 3 fb Signal = t + s-channels Background = tt + Wjj But use the shapes!  F-F- F+F   Note signs

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

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

S. D. Ellis ISMD N/  N (appropriate) F _ F+F+ F-F-

S. D. Ellis ISMD Can also consider a likelihood analysis based on the difference in shapes  = N Sig /N Tot  0.13 (all of phase space) Uncertainty

S. D. Ellis ISMD 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 Extra Detail Slides

S. D. Ellis ISMD Extra (Pseudo-)Scalar Bosons: Top-color models Scalars (such as Higgs) exist as bound states of top and bottom quarks For M π± = 250 GeV, t R -c R 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/M π± 2 and that π ± doesn’t couple to light quarks e.g., He & Yuan: hep-ph/ time-like momentum allows for resonance

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

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

S. D. Ellis ISMD Extra quark generations: CKM constraints For 3 generations, the unitary of the CKM matrix constrains |V ts | < With >3 generations, one possibility is |V tb |=0.83 and |V ts |=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 Without imposing 3 family unitarity, these are the 90% CL direct constraints. V ts s s

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

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

S. D. Ellis ISMD Lessons 1)t-channel is affected by modifications to top quark couplings 2)s-channel is affected by heavy particles 3)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”