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

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

A. Ivanov, Top Quark Symposium 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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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’ Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

Run 1: Search for tt Resonances Dominant background is from W + jets Likelihood fit is performed using X->tt templates with various masses Apr-08-2005 A. Ivanov, Top Quark Symposium

No Evidence for tt Resonance in Run 1 Phys.Rev.Lett. 92, 221804 (2004) Phys.Rev.Lett. 85, 2062 (2000) Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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) Apr-08-2005 A. Ivanov, Top Quark Symposium

Run 2: Search for Resonances Using Matrix Element Generator Level Reconstructed events better reconstruction Employ matrix element (similar to the top mass measurement) information to weigh each parton configuration for direct Mtt reconstruction Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

Run 1: Top Quark pT Spectrum True pT Bin (d/dpT) /  Measurement SM Expectation R1 0.41 R2 0.43 R3 0.13 R4 0.025 R1+R2 0.84 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) Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

Run 1: Anomalies in the Top Dilepton Sample? 1 ev. 7 ev. Flavor asymmetry: an excess of em events An excess of events with large missing transverse ET and lepton pT Apr-08-2005 A. Ivanov, Top Quark Symposium

A Subset of Run 1 Dilepton Events In better agreement with decays of SUSY quarks with masses around 300 GeV - hep-ph/9609313 [Barnett and Hall, Phys. Rev. Lett. 77 3506 (1996)] MEt+Et(l1)+Et(l2) [GeV] max(MT1,MT2) [GeV] sqrt(MT1*MT2) [GeV] ql [deg] CDFI D0 tt MC SUSY MC Data: Stnd Model D0 SUSY ??? CDF Apr-08-2005 A. Ivanov, Top Quark Symposium

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?!) SUSY fraction Chance to find 3 evidence 50% 30% 25% 10% 7 % Sensitivity given 13 events observed (kinematics only) Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

Run 2 Dilepton events FERMILAB-PUB-04-396-E 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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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) Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

A. Ivanov, Top Quark Symposium 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) Apr-08-2005 A. Ivanov, Top Quark Symposium

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 b d u B0 p- p+ Apr-08-2005 A. Ivanov, Top Quark Symposium

Top Quark Charge Measurement Sensitivity Study: Limit depends on lepton- b-jet mismatching (fraction of mismatches) Jet Charge Algorithm: Qjet = qi pTia/  pTia Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium

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 Apr-08-2005 A. Ivanov, Top Quark Symposium