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Top as a Window to New Physics

Top as a Window to New Physics. Robin D. Erbacher University of California, Davis. Aspen Winter Conference -- January 9, 2007. Mark Kruse gave us the big picture…. New Physics?!?. Just beginning to study top. Top can reveal new physics….

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Top as a Window to New Physics

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  1. Top as a Window to New Physics Robin D. Erbacher University of California, Davis Aspen Winter Conference -- January 9, 2007

  2. Mark Kruse gave us the big picture…

  3. New Physics?!? Just beginning to study top

  4. Top can reveal new physics… Top can be our window beyond the Standard Model in various ways: • Top results point to new physics: • Properties lead to expectations of partners or other new particles. • Top is Not what we expect: • Measured top properties are anomalous, contrary to SM. • Top is Not all that we find: New physics mimicks top signatures.

  5. Top as Indicator of Where New Physics Lies Measured top parameters could point to something new.

  6. Top mass points to a new paradigm? • Rainer Wallny’s Talk: Precise top mass (and W) places constraints on Higgs boson mass. • Further, top important constraint to models of any new BSM paradigm. • Top mass in the coming decade(s) precise enough to provide important consistency checks?: if SM top, what is the interplay with the new physics we are seeing?

  7. What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. (talk by Wallny)

  8. What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. • LHC:Pushing for Mtop~1 GeV. • Assume MW~15 MeV, 2004 central • values. SM constraint on Higgs: MH = 63 ± 20 GeV (mH/mH  32%) Winter 07 constraint: MH = 80 ± 31 GeV (mH/mH  39%)

  9. What can we expect for Mtop? • Tevatron: Expect 1% combined by end… progress makes us optimistic… pushing lower. • LHC:Pushing for Mtop~1 GeV. • Assume MW~15 MeV, 2004 central • values. • ILC:Will benefit from a scan in • √s, allowing a threshold scan for • top production. Expect to • Improve uncertainty such that • Mtop~100 MeV!

  10. Top mass for different decay channels Rainer’s talk yesterday: • Are the channels consistent? • We compare them taking into account their correlated systematic uncertainties => Determination of Mtop from the 3 different channels is consistent with one another Mtop(All Jets) = 173.4 ± 4.3 GeV/c2 Mtop(Dilepton) = 167.0 ± 4.3 GeV/c2 Mtop(Lepton+Jets) = 171.3 ± 2.2 GeV/c2

  11. Is Top Produced as Expected? • Measure ratio of qq/gg top pair production. (M. Kruse) • Tevatron: 85% qq annihilation, 15% gg fusion. • LHC: 13% qq annihilation, 87% gg fusion. • Signs of new, heavy particles decaying to t-tbar: • Heavy Z’ boson decaying to ttbar (TopColor) • MSSM Higgs, strong EWSB, technicolor • RS gravitons or other resonances decaying to ttbar • Some theories with heavy top t’ decay to top(talk by L. Wang)

  12. Resonances decaying to top pairs • Invariant mass of t-tbar system: • Compare with Standard Model expectations. • Add signal of new physics, such as a narrow leptophobic Z’ resonance.

  13. Resonances decaying to top pairs Excludea narrow leptophobic Z’ resonance. 680 pb-1 MX < 725 GeV 370 pb-1 MX< 680 GeV • 955 pb-1 • MX <~725 GeV!

  14. Resonances decaying to top pairs 1.6 TeV resonance xBR required for a discovery σxBR [fb] 30 fb-1 830 fb Mtt 300 fb-1 mtt [GeV/c2] 1 TeV • LHC: Atlas studied resonance X once x, x and BR(Xtt) is known. • Reconstruction efficiency for semileptonic (L+J): • 20% mtt = 400 GeV • 15% mtt = 2 TeV

  15. Expected EWK top production s-channel t-channel (Wg fusion) W-associated Tevatron: 0.9 pb 2 pb 0 pb LHC: 10 pb 62 pb 245 pb • Small signals (~1/2 ttbar production) at Tevatron together with large W+2jets background make it difficult to find. • Similar signatures as Higgs, demonstrational challenge: increase acceptance, multivariate methods, modeling, resolutions, sophisticated techniques get us there… Tevatron: See Single Top talks by Sullivan & Coaddou tomorrow

  16. Expected EWK top production • Single top: primary access to top CC interaction. Already test the W-t-b weak interaction (W helicity), and measure |Vtb| indirectly through branching ratios. • We know |Vtb| to four decimal places: CKM unitarity. New physics (eg: 4th gen) would modify this. Other new physics (charged Higgs, FCNC) modifies channels differently. (Tait, Yuan ‘01) LHC can get t-channel to / ~9% with 10 fb-1. s, Wt channels more difficult.

  17. Does top decay as expected? • Top decay branching ratios (Tevatron) shown by Kruse, gives us |Vtb|. Precision poor, improves at LHC. • Light charged Higgs? • CDF looked for tH+b • affecting four channels • in a correlated way, • excluding when • data inconsistent: • Topdilepton (ee, , e)+jets • Topdilepton (e, )+jets • Toplepton(e)+jets+1 b-tag • Toplepton(e)+jets+2 b-tags Varying model parameters changes: BR(tH+b) BR(H+) BR(H+cs) BR(H+t*b) BR(H+W+h0) BR(H+W+A0) Shown here: Variations as a function of tan particular set of MSSM parameters

  18. Does top decay as expected? • Calculate BR(tH+b) and H+ BR’s as function of MA and tan • 6 MSSM benchmarks used, #1 is shown below. No evidence yet! Collab with M. Carena, thanks!

  19. Anomalies in Top Properties Is it simply Standard Model top?

  20. Many properties could show anomalies… Dil+LJ 200 pb-1 750 pb-1 Dilepton only 200 pb-1 • Top charge(Kruse: D0 results, CDF soon!): -4/3e close to ruled out. LHC gets 5 separation with 24 pb-1, easy. • W helicityKruse: D0/CDF consistent with V-A within statistics, still poor. LHC gets F+ (FR) to 0.02 with 10 fb-1. However… • Separate channel fits still look funny!

  21. Forward-backward asymmetry in top pair production • Afb typically associated with parity-violating weak processes • Not expected in top, but for BSM. • Diagram interference at NLO predicts 3.8% effect.(Kuhn, Rodrigo 99) • Massive neutral gauge boson Z’ could produce an asymmetry. • Look for Moriond results from the Tevatron. mc@NLO 500 GeV Z’

  22. Flavor-changing Neutral Currents Tree level FCNC No FCNCs in SM at tree level • Allowed in higher order penguins Light quark penguins observed • e.g. b→sγ observed by CLEO in 1995, BR O(10-4) Not yet observed for top • SM BR: O(10-12) New Physics models predict BRs up to O(10-2) • SUSY, Higgs doublet, Warped extra dimensions(J. A. Aguilar-Saavedra, Acta Phys. Polon. B35 (2004) 2695) Penguin

  23. FCNC limits so far… Search in tt sample, tZ,  CDF Run I: • ttWb qZ, Wjj, Zl+l- • Limit: BR(tqZ)< 33% @95% CL • ttWb q • Limit: BR(tq)< 3.2% @95% CL Search for single top, LEP: • e+e- γ*/Z* t q • Limit: BR(tqZ)< 13.7% @ 95% CL • Best limit so far for tZ

  24. FCNC from Tevatron, LHC CMS sensitivity: Expected sensitivity (5): • BR ~ 1.5 x 10-3 (L=10 fb-1) • BR ~ 4 x 10-4 (L=100 fb-1) New CDF search, ~1fb-1: example exclusion (not final) Expected limit at 95% C.L. (no signal): • Anti-tagged sample: 23-30% • Tagged sample: 18-24% • Combined: 10-15% • Previous limits: 13.7% (LEP), 33% (CDF Run I)

  25. More top properties to look for anomalies… • Properties that we are measuring (and LHC/ILC are studying that I didn’t have time to discuss): • Top anti-top spin correlations: top decays as a bare quark, transfers properties to decay products. • EWK Top couplings (ttZ, tt): (LHC/ILC) form factors: vector, axial vector, anom mag moment, electric (weak) dipole mom. • Anomalous top couplings: W helicity: right-handed PR New coupling: no righ-handed, Interference effects (tough!)

  26. New Physics in Top Quark Samples Are top-like events really unknown physics?

  27. Measuring top pair production Nevents - Nbackground (tt) = Luminosity *  Production Cross Section • Why is measuring the rate of top production important? • Higher cross section than predicted could be a sign of non-standard model production mechanisms • Resonant state X tt OR Anomalous couplings in QCD? • It could also mean new physics in the top sample! One of the first things to measure is the top pair production rate.

  28. Run 1: Excess in the b-tagged 2-jet bin sample • Observed excess of b-tags in the 2 jet bin • Too many SVX double tags (more than one b-tagged jet/event) • Too many multiple tags (more than one b-tag/jet) A lot of speculation, but nothing solid.

  29. Lepton+Jets: How’re the double tags? Signal: lepton+ ≥3 jets, MET, ≥2 b-tags! Signal: lepton+ ≥3 jets, MET, ≥1 b-tag L=695pb-1 7-input neural Network, no tag required L=695pb-1 CDF CDF signal signal (tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=8.8±1.2(stat)±1.7(sys)pb

  30. Lepton+Jets channel cross sections Signal: lepton+ ≥3 jets, MET Signal: lepton+ ≥3 jets, MET, ≥1 b-tag L=695pb-1 7-input neural Network, no tag required L=760pb-1 CDF signal CDF Consistency 7% (tt)=8.2±0.6(stat)±1.0(sys) pb (tt)=6.0±0.6(stat)±1.1(sys)pb

  31. Idea: use kinematics again to separate t’ from t New physics in top samples • While on the energy frontier, we look for interesting events on the tails of the top quark distributions • Can a t’exist? Can it mimic top? • Generic 4th chiral generation is consistent with EWK data; can accommodate a heavy Higgs (500 GeV) without any other new physics • Several SUSY models provide for a 4th generation t’ or mimic top-like signatures(Beautiful Mirrors: Choudhury, Tait, Wagner) • Little Higgs models predict a heavy t’ -like particle

  32. Variables are ~model- independent, to maintain sensitivity to many BSM scenarios • We use the top mass fitter, and fit observed 2D data distribution of HT vs Mrecon Search for massive top

  33. Exclude with 95%CL region of t´ masses below258 GeV Limits on t'

  34. 1-d Projection: Fit results for M(t) = 350 GeV 2-d Scatter: Expected (MC) for M(t) = 400 GeV v. data (black), number points for ~7.5 fb-1 Data v. Projections

  35. Couple of strange ones…

  36. Top plus missing ET ET mTW • Search for anomalous events that look like top+MET. • SUSY cascades, TAht (L. Wang), … • Similar (based on) t’ search but optimize for extra MET. • Search underway at CDF.

  37. Physics with top is rich • The top quark is the least known quark, and the most interesting for new physics. • The top physics program is very active at the Tevatron, and studies are vibrant at the LHC and ILC. • Beginning to have sensitivity to the unexpected in particle properties and the data samples!

  38. Forward to the Femtobarn Era! • More data makes us smarter ! • It is not just the luminosity factor. We become more daring and more creative. • New techniques and ideas are making our results more sensitive than expected. • Let’s hope nature is kind and top physics indeed becomes our window beyond the Standard Model! Physics with top quarks is just starting !

  39. Note to Slide Readers: • You are • This talk is best viewed • Fonts may not agree from • Contains animations. • Your mileage may vary.

  40. “Beauty is Truth, and Truth Beauty”-- that is allYe Know on Earth,and All Ye Need to Know!”-Keats

  41. Backup Slides

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