Search for the neutral current top quark decay t→Zc using the ratio of Z-boson+4jets to W-boson+4jets production
Physical Review D - Particles, Fields, Gravitation and Cosmology 80:5 (2009)
Abstract:
We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay t→Zc using a technique employing ratios of W and Z production, measured in pp̄ data corresponding to an integrated luminosity of 1.52fb-1. The analysis uses a comparison of two decay chains, pp̄→tt̄→WbWb→νbjjb and pp̄→tt̄→ZcWb→cjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multiyear data set using another ratio of W and Z production, in this case the observed ratio of inclusive production of W to Z bosons. To improve the discrimination against standard model backgrounds to top-quark decays, we calculate the top-quark mass for each event with two leptons and four jets assuming it is a tt̄ event with one of the top quarks decaying to Zc. For additional background discrimination we require at least one jet to be identified as originating from a b quark. No significant signal is found and we set an upper limit on the FCNC branching ratio Br(t→Zc) using a likelihood constructed from the cjjb top-quark mass distribution and the number of νbjjb events. Limits are set as a function of the helicity of the Z boson produced in the FCNC decay. For 100% longitudinally-polarized Z bosons we find limits of 8.3% and 9.3% (95% C.L.) depending on the assumptions regarding the theoretical top-quark pair production cross section. © 2009 The American Physical Society.Search for a standard model Higgs boson in WH --> lvbb in pp collisions at square root s = 1.96 TeV.
Phys Rev Lett 103:10 (2009) 101802
Abstract:
We present a search for a standard model Higgs boson produced in association with a W boson using 2.7 fb(-1) of integrated luminosity of pp collision data taken at square root s = 1.96 TeV. Limits on the Higgs boson production rate are obtained for masses between 100 and 150 GeV/c(2). Through the use of multivariate techniques, the analysis achieves an observed (expected) 95% confidence level upper limit of 5.6 (4.8) times the theoretically expected production cross section for a standard model Higgs boson with a mass of 115 GeV/c(2).Search for charged Higgs bosons in decays of top quarks in pp collisions at square root s = 1.96 TeV.
Phys Rev Lett 103:10 (2009) 101803
Abstract:
We report on the first direct search for charged Higgs bosons decaying into cs in tt events produced by pp collisions at square root s = 1.96 TeV. The search uses a data sample corresponding to an integrated luminosity of 2.2 fb(-1) collected by the CDF II detector at Fermilab and looks for a resonance in the invariant mass distribution of two jets in the lepton + jets sample of tt candidates. We observe no evidence of charged Higgs bosons in top quark decays. Hence, 95% upper limits on the top quark decay branching ratio are placed at B(t --> H(+)b)< 0.1 to 0.3 for charged Higgs boson masses of 60 to 150 GeV/c(2) assuming B(H(+) --> cs)=1.0. The upper limits on B(t --> H(+)b) are also used as model-independent limits on the decay branching ratio of top quarks to generic scalar charged bosons beyond the standard model.Ds+ exclusive hadronic decays involving ω
Physical Review D - Particles, Fields, Gravitation and Cosmology 80:5 (2009)
Abstract:
Using data collected near the Ds* ± Ds Ds peak production energy E cm 4170 MeV by the CLEO-c detector, we search for Ds+ exclusive hadronic decays involving. We find B Ds+ n+ w 0.21 ± 0.09 ± %, B Ds+ n+ 2.78 ± 0.65 ± 0.25 %, Ds+ n+ n+ n- 1.58 ± 0.09%. Ds+ n+ 0.85± 0.54 ± 0.06%. K+. n+ n- 0.54%, and The upper limits are at 90% confidence level.Search for a standard model Higgs boson in WH→ℓ vbb̄ in pp̄ collisions at s=1.96TeV
Physical Review Letters 103:10 (2009)