Showing papers by "Kostantinos Kordas published in 1996"

Measurement of dijet angular distributions by the collider detector at fermilab

Abstract: We have used 106 pb^-1 of data collected in proton-antiproton collisions at sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular distributions in events with two jets in the final state. The angular distributions agree with next to leading order (NLO) predictions of Quantum Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at 95% confidence level (CL) a model of quark substructure in which only up and down quarks are composite and the contact interaction scale is Lambda_ud(+) < 1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6 TeV.

Measurement of correlated μ-b¯ jet cross sections in pp¯ collisions at s=1.8 TeV

Abstract: We report on measurements of differential $\mu - {\bar b}$ cross sections, where the muon is from a semi-leptonic $b$ decay and the ${\bar b}$ is identified using precision track reconstruction in jets. The semi-differential correlated cross sections, d$\sigma$/d$\Et^{{\bar b}}$, d$\sigma$/d$\pt^{{\bar b}}$, and d$\sigma$/d$\delta\phi(\mu - {\bar b})$ for $\pt^{\mu}>$~9 GeV/c, $|\eta^{\mu}| $~10 GeV, $|\eta^{{\bar b}}|<$~1.5, are presented and compared to next-to-leading order QCD calculations.

Measurement of σB(W→ev) and σB(Z0→e+e-) in pp̄ collisions at √s = 1.8 TeV

Abstract: We present a measurement of $\sigma \cdot B(W \to e u)$ and $\sigma \cdot B(Z^0 \to e^+e^-)$ in proton - antiproton collisions at $\sqrt{s} =1.8$ TeV using a significantly improved understanding of the integrated luminosity. The data represent an integrated luminosity of 19.7 pb$^{-1}$ from the 1992-1993 run with the Collider Detector at Fermilab (CDF). We find $\sigma \cdot B(W \to e u) = 2.49 \pm 0.12$~nb and $\sigma \cdot B(Z^0 \to e^+e^-) = 0.231 \pm 0.012$~nb.

Ratios of bottom meson branching fractions involving J/ psi mesons and determination of b quark fragmentation fractions.

Abstract: We report a measurement of the ratios of the decay rates of the ${B}^{+}$, ${B}^{0}$, and ${B}_{s}^{0}$ mesons into exclusive final states containing a $\frac{J}{\ensuremath{\psi}}$ meson. The final states were selected from 19.6 pb-1 of $p\overline{p}$ collisions recorded by the Collider Detector at Fermilab. These data are interpreted to determine the $b$ quark fragmentation fractions ${f}_{u}$, ${f}_{d}$, and ${f}_{s}$. We also determine the branching fractions for the decay modes ${B}^{+}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{+}}$, ${B}^{+}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{*}{(892)}^{+}}$, ${B}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{0}}$, ${B}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}{K}^{*}{(892)}^{0}}$, and ${B}_{s}^{0}\ensuremath{\rightarrow}\frac{J}{\ensuremath{\psi}\ensuremath{\varphi}(1020)}$. We discuss the implications of these measurements to $B$ meson decay models.

Search for charged Higgs boson decays of the top quark using hadronic τ decays

Abstract: We present the result of a search for charged Higgs boson decays of the top quark, produced in $p\overline{p}$ collisions at $\sqrt{s}=1.8$ TeV. When the charged Higgs boson is heavy and decays to a $\ensuremath{\tau}$ lepton, which subsequently decays hadronically, the resulting events have a unique signature: large missing transverse energy and the low-charged-multiplicity $\ensuremath{\tau}$. Data collected in 1992 and 1993 at the Collider Detector at Fermilab, corresponding to 18.7\ifmmode\pm\else\textpm\fi{}0.7 ${\mathrm{pb}}^{\ensuremath{-}1}$, exclude new regions of combined top quark and charged Higgs boson mass, in extensions to the standard model with two Higgs doublets.

Properties of Jets in W Boson Events from 1.8 TeV p¯p Collisions

Abstract: We present a study of events with Z bosons and hadronic jets produced in {bar p}p collisions at a center-of-mass energy of 1.8 TeV. The data consist of 6708 Z{yields}e{sup +}e{sup -} decays from 106 pb{sup -1} of integrated luminosity collected using the CDF detector at the Fermilab Tevatron Collider. The Z+{ge}n jet cross sections and jet production properties have been measured for n = 1 to 4. The data are compared to predictions of leading-order QCD matrix element calculations with added gluon radiation and simulated parton fragmentation.

Search for chargino-neutralino production in pp collisions at s=1.8 tev

Abstract: We have searched for chargino-neutralino production ({tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0}) in 1.8 TeV p{bar p} collisions, followed by their leptonic decays {tilde {xi}}{sub 1}{sup {+-}}{yields}{tilde {xi}}{sub 1}{sup 0}{ell}{sup {+-}}{nu} and {tilde {xi}}{sub 2}{sup 0}{yields}{tilde {xi}}{sub 1}{sup 0}{ell}{sup +}{ell}{sup -}. These trilepton events are expected within a framework of the minimal supersymmetric standard model (MSSM). In a 19.1 pb{sup -1} data sample collected with a Collider Detector at Fermilab, no trilepton events were observed. Upper limits on {sigma}(p{bar p} {yields}{tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0})BR({tilde {xi}}{sub 1}{sup {+-}}{tilde {xi}}{sub 2}{sup 0}{yields}3{ell}+X) were obtained for various MSSM parameter space regions, yielding new 95% confidence level lower limits for the neutralino ({tilde {xi}}{sub 2}{sup 0}) mass which extend as high as 49 GeV/c{sup 2}.

Search for flavor-changing neutral current B meson decays in pp̄ collisions √s = 1.8 Te V

Abstract: We report on a search for the flavor-changing neutral current decays B{sub d,s}{sup 0}{yields}{mu}{sup +}{mu}{sup -}, B{sup +}{yields}{mu}{sup +}{mu}{sup -}K{sup +}, and B{sup 0}{yields}{mu}{sup +}{mu}{sup -}K*{sup 0} using data from p{bar p} collisions at {radical}s= 1.8 TeV, collected with the Collider Detector at Fermilab during the 1992-1993 running period. We find no indication of such decays and we set the following 90% confidence level upper limits on branching ratios: B(B{sup 0}{yields}{mu}{sup +}{mu}{sup -})<1.6x10{sup -6}, B(B{sub s}{sup 0}{yields}{mu}{sup +}{mu}{sup -})<8.4 x 10{sup -6}, B(B{sup +}{yields}{mu}{sup +}{mu}{sup -}K{sup +})<1.0x10{sup -5}, and B(B{sup 0}{yields}{mu}{sup +}{mu}{sup -}K*{sup 0})<2.5x10{sup -5}.

Measurement of the branching fraction B(B+u→J/ψπ+) and Search for B+c→J/ψπ+

Abstract: We report on a measurement of the branching fraction of the Cabibbo-suppressed decay ${B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}$, where $J/\ensuremath{\psi}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. The data were collected by the Collider Detector at Fermilab during 1992--1995 and correspond to an integrated luminosity of $110{\mathrm{pb}}^{\ensuremath{-}1}$ in $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$. A signal of ${28}_{\ensuremath{-}9}^{+10}$ events is observed and we determine the ratio of branching fractions $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})/B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$ to be $[{5.0}_{\ensuremath{-}1.7}^{+1.9}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.1(\mathrm{syst})]%$. Using the world average value for $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$, we calculate the branching fraction $B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})$ to be $({5.0}_{\ensuremath{-}1.9}^{+2.1})\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$. We also search for the decay ${B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}$ and report a $95%$ confidence level limit on $\ensuremath{\sigma}({B}_{c}^{+})B({B}_{c}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+})/\ensuremath{\sigma}({B}_{u}^{+})B({B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+})$ as a function of the ${B}_{c}^{+}$ lifetime.