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Searches for Anomalous Top Quark Production at the Tevatron

This presentation discusses the search for exotic phenomena in top quark production at the Tevatron, including searches for new particles, anomalous kinematics, and resonance structures. The top quark's special properties make it a valuable tool for studying physics beyond the Standard Model.

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Searches for Anomalous Top Quark Production at the Tevatron

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  1. Searches for Anomalous Top Quark Production at the Tevatron Andrew Ivanov University of California, Davis for the CDF and D0 Collaborations Top Quark Symposium April 08, 2005

  2. Why the top quark is so special … • Mass of order electroweak scale • May play a special role in the dynamics of EWSB • Serves as a powerful probe of physics beyond the SM A. Ivanov, Top Quark Symposium

  3. Is the top quark ordinary or exotic ? Exotic in some way ?! New Physics might reveal itself through • Oblique radiative corrections • Exotic top quark decay modes (scalar bosons, FCNC) • Exotic intermediate heavy states – new gauge bosons or resonances Ordinary ? Becomes a major background to new physics • Top sample might contain an admixture of exotic processes A. Ivanov, Top Quark Symposium

  4. Is the top quark ordinary or exotic ? Exotic in some way ?! New Physics might reveal itself through • Oblique radiative corrections • Exotic top quark decay modes (scalar bosons, FCNC) • Exotic intermediate heavy states – new gauge bosons or resonances Ordinary ? Becomes a major background to new physics • Top sample might contain an admixture of exotic processes Focus of this talk A. Ivanov, Top Quark Symposium

  5. Outline: Searches for • Resonance in mass of ttbar system • Top quark pT • Anomalous kinematics in top dilepton sample • Anomalous kinematics in lepton + jets sample • Top Charge A. Ivanov, Top Quark Symposium

  6. Why search for structure in the Mtt spectrum? • Various exotic models predict the existence of particles decaying to tt Topcolor-Assisted Technicolor (Hill, Phys Lett. B345, 483 (1995); Hill and Parke Phys. Rev. D49, 4454 (1994)) • Extends technicolor models and attempts to explain EWSB by introducing a new strong interaction • Predicts new massive bosons “topgluons” and a topcolor Z’ A. Ivanov, Top Quark Symposium

  7. Run 1: Search for tt Resonances • Each lepton+jets event fit to ttbar hypothesis by constraining W and top masses • Distribution smeared by: • ambiguity in correct jet-parton assignment • detector resolution • B-tagging reduces combinatorics • Select configuration with best 2 fit A. Ivanov, Top Quark Symposium

  8. Run 1: Search for tt Resonances Dominant background is from W + jets Likelihood fit is performed using X->tt templates with various masses A. Ivanov, Top Quark Symposium

  9. No Evidence for tt Resonance in Run 1 Phys.Rev.Lett. 92, 221804 (2004) Phys.Rev.Lett. 85, 2062 (2000) A. Ivanov, Top Quark Symposium

  10. Run 1: Limits on Mass of the Topcolor Boson Model independent search for a narrow resonance Xtt exclude a narrow, leptophobic X boson with a natural width of GX = 0.012 MX MX < 560 GeV/c2 and MX < 480 GeV/c2 MX < 780 GeV/c2 for GX= 0.04 MX A. Ivanov, Top Quark Symposium

  11. Run 2: Search continues … MX = 500 GeV/c2 GX= 0.012 MX  = 1pb MX = 700 GeV/c2 SM ttbar W + >= 3 jets Monte Carlo • Use Neural Nets trained with different X masses • Use large statistics - lepton + >=3 jets events sample (no b-tag information) Fit Mtt distribution to combination of shapes (lepton + jets, use b-tag) A. Ivanov, Top Quark Symposium

  12. Run 2: Search for Resonances Using Matrix Element Generator Level Reconstructed events Employ matrix element (similar to the top mass measurement) information to weigh each parton configuration for direct Mtt reconstruction better reconstruction A. Ivanov, Top Quark Symposium

  13. Why search for structure in top quark pT spectrum ? Many exotic models predict sizeable enhancements in the tt cross section at high transverse momenta pT > 200 GeV/c (T.G. Rizzo , hep-ph/9902273; K. Lane, Phys. Rev. D52, 1546 (1995)) e.g. Anomalous chromomagnetic moment A. Ivanov, Top Quark Symposium

  14. Run 1: Top Quark pT Spectrum Response functions • Use an iterative procedure to unsmear the distribution of reconstructed top pT momentum • Perform a likelihood fit to extract true top pT • Use superposition of response functions in 4 bins of pT and background template A. Ivanov, Top Quark Symposium

  15. Run 1: Top Quark pT Spectrum Top Quark pT Spectrum Upper limit: R4(225<Pt<425GeV/c)<0.16 @ 95% C.L. CDF Run 1 Phys.Rev.Lett. 87, 102001 (2001) A. Ivanov, Top Quark Symposium

  16. Run 2 Search: Top Quarks Kinematics • Variables of interest: • hadronic/leptonic top pT, • ttbar system pT and, •  of the two top quarks, … Additional jets are source of combinatorial background A. Ivanov, Top Quark Symposium

  17. Run 1: Anomalies in the Top Dilepton Sample? 1 ev. 1 ev. 7 ev. Flavor asymmetry: an excess of em events An excess of events with large missing transverse ET and lepton pT A. Ivanov, Top Quark Symposium

  18. CDFI D0 CDFI - In better agreement with decays of SUSY quarks with masses around 300 GeV MEt+Et(l1)+Et(l2) [GeV] ql [deg] sqrt(MT1*MT2) [GeV] max(MT1,MT2) [GeV] A Subset of Run 1 Dilepton Events hep-ph/9609313 [Barnett and Hall, Phys. Rev. Lett.77 3506 (1996)] tt MC SUSY MC Data: Stnd Model D0 SUSY ??? CDF A. Ivanov, Top Quark Symposium

  19. SM Kinematic Test with Run 2 Dilepton Events • Stay model-independent • Choose a-priori potentially sensitive to new physics kinematic variables • Perform Kolmogorov-Smirnov consistency test between data and Monte Carlo expectation • Search for and isolate a subset with the most non-SM features (SUSY events?!) Sensitivity given 13 events observed (kinematics only) A. Ivanov, Top Quark Symposium

  20. Kinematics in Run 2 Top Dilepton Sample Missing ET Leading lepton pT ? Df (leading lepton, met) “topness” = ttbar decay goodness-of-fit more top-like Overall agreement of 1.0-4.5% mainly due to an excess at low lepton pT A. Ivanov, Top Quark Symposium

  21. Run 2 Dilepton events Phys.Rev.Lett. 93, 142001 (2004) FERMILAB-PUB-04-396-E ( Subm. to Phys.Rev.Lett.) 1 ev. 3 ev. 9 ev. “topness” Low pT-lepton events are accompanied with b-jets - likely being from tt Flavor asymmetry remains?!.. More data to come A. Ivanov, Top Quark Symposium

  22. New Particles Decaying to Wq? • Can be a fourth generation up-type quark He/Polonsky/Su (hep-ph/0102144) a generic 4th chiral generation is consistent with EWK data; accommodates a heavy Higgs (500 GeV) without any other new physics • “Beautiful Mirrors” model Wagner et al (hep-ph/ 0109097) predicts a new heavy up-type quark decaying to Wb; naturally accomodates the LEP b forward-backward asymmetry results • From the precision EWK data the mass splitting between a t' and a b' quark is relatively small. Therefore if Mt’ < Mb’ + MW: t' -> l  b' (virtual W) A. Ivanov, Top Quark Symposium

  23. Run 2: Search for t’->Wq • Lepton + jets channel • Use the variable HT = sum of transverse momenta of all objects in the event • Sensitive to any new high-pT physics • Perform a likelihood fit and set a limit on non-SM processes Data does not prefer t’ contribution A. Ivanov, Top Quark Symposium

  24. Projected Limits: Higher Luminosity / New NN Analysis HT likelihood sensitivity study • Use Neural Nets trained with different t’ masses • Perform likelihood fit with the NN output variable t’->Wb ttbar W + >= 3 jets A. Ivanov, Top Quark Symposium

  25. Top Charge Is it the Standard Model top ? W.-F. Chang et al.,hep-ph/9810531 proposes an exotic doublet of quarks (Q1, Q4) with charges (-1/3,-4/3) and M ~ 175 GeV/c2 while Mtop ~ 274 GeV/c2 q = -4/3 is consistent with EW data, new b-couplings improve the EW fit (E. Ma et al. , hep-ph/9909537) A. Ivanov, Top Quark Symposium

  26. b B0 b d d p- u u b B0 b d d p+ u u Top Quark Charge Measurement • Determine: • charge of W (lepton) • pairing between W and b • flavor of b-jet Use both dilepton and lepton + jets samples Variables to use for flavor b-tagging: • sign of max pT track in b-jet cone • jet charge - sum of charge for tracks inside of the cone • sign of min pT track • sign of fragmentation track Expect with 500 pb-1 to rule out q = -4/3 A. Ivanov, Top Quark Symposium

  27. Top Quark Charge Measurement Sensitivity Study: Limit depends on lepton- b-jet mismatching (fraction of mismatches) Jet Charge Algorithm: Qjet = qi pTia/  pTia A. Ivanov, Top Quark Symposium

  28. Near Future is Very Exciting ... Current Run 2 top analyses in progress utilize datasets of integrated luminosity ~340 pb-1 Results with this amount of data are expected to be reported at the Summer conferences A lot of work was performed on reducing systematic uncertainties in the past months Expect better limits and more precise measurements very soon Many new analyses testing various top properties are in preparation A. Ivanov, Top Quark Symposium

  29. More Distant Future is Even More Exciting… More data is on tape Peak Luminosity beats new records every day Improved trigger system guarantees a higher purity data Stay Tuned A. Ivanov, Top Quark Symposium

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