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Particle Collider Phenomenology at the UW

Particle Collider Phenomenology at the UW. Directly Connected to:. Experiment : D0, ATLAS – Burnett, Lubatti, Watts Students : Haas, Gadfort Model Building : Ann Nelson, David Kaplan String Theory : Andreas Karch (see Matt’s part). Thy Faculty : Matt Strassler and Steve Ellis

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Particle Collider Phenomenology at the UW

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  1. Particle Collider Phenomenology at the UW Directly Connected to: Experiment: D0, ATLAS – Burnett, Lubatti, Watts Students: Haas, Gadfort Model Building: Ann Nelson, David Kaplan String Theory: Andreas Karch (see Matt’s part) Thy Faculty: Matt Strassler and Steve Ellis Thy Graduate Student: Matt Bowen REU Students: Kyle Armour (2004, now back as grad student), Andre Bach (2005) Coming Soon (free!): Chris Lee – INT PD, Jet Expert Wu-Ki Tung – Aff Fac, pdf & heavy flavor expert UW 8/18/05

  2. Goal: • Develop Analysis Tools for the LHC, especially looking for new physics • Practice on Tevatron Data Special Features at UW: • Focus on “Signal-driven” (model-informed but) , model-independent techniques • Engage faculty with a broad range of expertise • Meet weekly with the experimentalists (incl. video conferencing) Recent Theme - Asymmetries S. D. Ellis - DoE Visit 2005

  3. Tools: • Computational: MadGraph, MadEvent • Event Simulation: PYTHIA • Detector Simulation: PGS Event elements: • Charged leptons: e,  () • Neutral Leptons:  (LSP)  MET • Jets (“clumps” of hadronic energy)≈ energetic partons (?) Many caveats – partons are color connected (# of jets  # of partons), depends on details of jet algorithm (work with Joey Huston), internal structure depends on higher orders (work with Bill Kilgore), and kinematics e.g., energetic W’s at the LHC  1 jet (not 2) energetic tops at the LHC  1 jet (not 3) See also Matt’s section S. D. Ellis - DoE Visit 2005

  4. Example: Dark Towers not found by jet algorithms, ~ 5% effect S. D. Ellis - DoE Visit 2005

  5. Distribution of (single) Jet Masses in LHC Olympics “ttbar” data sample W(Z) top S. D. Ellis - DoE Visit 2005

  6. Number of (non-tagged) Jets per ttbar event S. D. Ellis - DoE Visit 2005

  7. Tagging of Heavy Flavor Jets is Essential (typically from seeing decay lepton/displaced vertex) • But not so well understood experimentallyOR • Theoretically, gluon  b bbar in a gluon jet, What is that rate? Example Simulation (meant to be realistic) b-Tags: “real b” ~ 0.5 tanh(PT/36 GeV) [PT = jet PT] “real c” ~ 0.15 tanh(PT/42 GeV) mistag ~ 0.01 tanh(PT/80 GeV) S. D. Ellis - DoE Visit 2005

  8. Asymmetries: • Tied to structure of valence quarks, Both quantum numbers, and Kinematics,  if see asymmetry in new physics, must be connected to valence quarks • Dynamics can both remember and forget the initial asymmetry, e.g., gluons forget flavor quantum numbers • Generalize from special cases! (Still looking for most general description) • EXAMPLES - S. D. Ellis - DoE Visit 2005

  9. CP Invariance of the Tevatron • pp initial state at Tevatron is CP invariant, but not C or P invariant separately • Perturbative Final state is CP invariant, but may violate C or P • Depends on Perturbative Initial state: qg (asym)  gg (sym) • Depends on dynamics: LO s-channel gluon “forgets” asymmetry • Processes with W’s “remember” asymmetries Initial State P P Under C or P transformation P P Under CP P P S. D. Ellis - DoE Visit 2005

  10. Looking for the t-channel Single top quark production at the Tevatron Jet & lepton correlated by kinematics and weak couplings Trigger on - • 1 lepton (only) • 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! [ is too rare] often not seen S. D. Ellis - DoE Visit 2005

  11. What else do we see? Need to be serious about Backgrounds! • , e.g., • , e.g., where b tag is fake, or extra q’s are b’s, or g becomes a heavy quark pair during showering/fragmentation S. D. Ellis - DoE Visit 2005

  12. Lepton and Jet Correlated;CP Correlates t (e+) and tbar (e-) ! Sig Bkg S. D. Ellis - DoE Visit 2005

  13. New Result (Sad) - Democracy of Background Wjj channels Tagging _ _ Small , Large tag rate  Large , Small tag rate S. D. Ellis - DoE Visit 2005

  14. Wjj tag budget _ _ Democracy at work! But different channels have different shapes! S. D. Ellis - DoE Visit 2005

  15. What does the LHC look like? Work by Matt Bowen • Initial state is P invariant, but not separately C or CP invariant • Cross-sections are P invariant, but can also be C invariant Initial State P P Under C or CP transformation P P Under P P P S. D. Ellis - DoE Visit 2005

  16. Now Use Charge AsymmetryLife is Easier! • N+: Number of events with only 1 high pT (> 20 GeV) positively-charged lepton • N-: Number of events with only 1 high pT negatively-charged lepton • Δ: N+ - N- For 10 fb-1, double-tag  Dominated by single top, and statistics are fine S. D. Ellis - DoE Visit 2005

  17. Top Asymmetry at Tevatron:Bowen, Ellis and Rainwater • Color flow asymmetry at Tevatron • In remember the color flow direction at NLO in QCD due to interference effects, t goes opposite to q (and p) if require extra jet (accelerate charge to get radiation)t goes parallel to q (and p) in inclusive sample (and jet veto sample) – virtual correction has opposite sign and is numerically larger • Asymmetry is communicated to leptons in decay  Very interesting physics, but statistics will be tough at the Tevatron, few percent S. D. Ellis - DoE Visit 2005

  18. If asymmetries are so powerful, look at them in much more generality!  Matt • The literature: many applications of asymmetries scattered throughout, but no coherent study emphasizing their general importance. • A charge asymmetry, in any particular new-physics sample, unambiguously indicates this sample is generated from a process involving the valence quarks [other implications follow also, but more complicated to state] • This is a powerful constraint on models (many of which never have significant participation by the valence quarks) and ought to be a forefront model-independent tool at LHC. • Matt is looking for a high impact example to make this point to experimentalists! S. D. Ellis - DoE Visit 2005

  19. Extra Detail Slides S. D. Ellis - DoE Visit 2005

  20. 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 - DoE Visit 2005

  21. 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 - DoE Visit 2005

  22. 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 - DoE Visit 2005

  23. 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 - DoE Visit 2005

  24. 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 - DoE Visit 2005

  25. 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 - DoE Visit 2005

  26. 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 - DoE Visit 2005

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