Showing papers by "Kostantinos Kordas published in 1998"

Search for flavor-changing neutral current decays of the top quark in pp collisions at s = 1.8 tev

Abstract: We search for the flavor-changing neutral current decays of the top quark $t\ensuremath{\rightarrow}q\ensuremath{\gamma}$ and $t\ensuremath{\rightarrow}\mathrm{qZ}$ (here $q$ represents the $c$ and $u$ quarks) in $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$. We use a dataset $(\ensuremath{\int}L\mathrm{dt}\ensuremath{\sim}110{\mathrm{pb}}^{\ensuremath{-}1})$ collected during the 1992--1995 run of the Collider Detector at Fermilab. We set 95% confidence level limits on the branching fractions $B(t\ensuremath{\rightarrow}q\ensuremath{\gamma})l3.2%$ and $B(t\ensuremath{\rightarrow}\mathrm{qZ})l33%$, consistent with the standard model.

Observation of Bc mesons in pp̄ collisions at √s = 1.8 TeV

Abstract: We report the observation of bottom-charmed mesons B_c in 1.8 TeV p-bar p collisions using the CDF detector at the Fermilab Tevatron. The B_c mesons were found through their semileptonic decays, B_c -> J/psi lepton X. A fit to the J/psi lepton mass distribution yielded 20.4 +6.2 -5.5 events from B_c mesons. A test of the null hypothesis, i.e. an attempt to fit the data with background alone, was rejected at the level of 4.8 standard deviations. By studying the quality of the fit as a function of the assumed B_c mass, we determined M(B_c) = 6.40 +- 0.39 +- 0.13 GeV/c^2. From the distribution of trilepton intersection points in the plane transverse to the beam direction we measured the B_c lifetime to be tau(B_c) = 0.46 +0.18 -0.16 +- 0.03 ps. We also measured the ratio of production cross section times branching fraction for B_c -> J/psi lepton neutrino relative to that for B+ -> J/psi K to be: 0.132 +0.041 -0.037 (stat) +- 0.031 (syst) +0.032 -0.020 (lifetime)

Dijet production by color-singlet exchange at the Fermilab Tevatron

Abstract: We report a new measurement of dijet production by color-singlet exchange in p{ovr p} collisions at {radical}(s)=1.8 TeV at the Fermilab Tevatron. In a sample of events with two jets of transverse energy E{sup jet}{sub T}{gt}20 GeV , pseudorapidity in the range 1.8{lt}{vert_bar}{eta}{sup jet}{vert_bar}{lt}3.5 , and {eta}{sub 1}{eta}{sub 2}{lt}0 , we find that a fraction R=[1.13{plus_minus}0.12(stat){plus_minus} 0.11(syst)]{percent} has a pseudorapidity gap within {vert_bar}{eta}{vert_bar}{lt}1 between the jets that can be attributed to color-singlet exchnage. The fraction R shows no significant dependence on E{sup jet}{sub T} or on the pseudorapidity separation between the jets. {copyright} {ital 1998} {ital The American Physical Society}

Measurement of the Bd0-B̄d0 flavor oscillation frequency and study of same side flavor tagging of B mesons in pp̄ collisions

Abstract: ${B}_{d}^{0}\ensuremath{-}{B}_{d}^{0}$ oscillations are observed in ``self-tagged'' samples of partially reconstructed $B$ mesons decaying into a lepton and a charmed meson collected in $p\overline{p}$ collisions at $\sqrt{s}=18\mathrm{TeV}$ A flavor tagging technique is employed which relies upon the correlation between the flavor of $B$ mesons and the charge of a nearby particle We measure the flavor oscillation frequency to be $\ensuremath{\Delta}{m}_{d}{=0471}_{\ensuremath{-}0068}^{+0078}\ifmmode\pm\else\textpm\fi{}0034{\mathrm{ps}}^{\mathrm{\ensuremath{-}}1}$ The tagging method is also demonstrated in exclusive samples of ${B}_{u}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+}$ and ${B}_{d}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{*0}(892),$ where similar flavor-charge correlations are observed The tagging characteristics of the various samples are compared with each other, and with Monte Carlo simulations

Search for chargino-neutralino associated production at the Fermilab tevatron collider

Abstract: We have searched in p (p) over bar collisions at root s = 1.8 TeV for events with three charged leptons and missing transverse energy. In the minimal supersymmetric standard model, we expect trilepton events from chargino-neutralino ( (+/-)(1) (0)(2) pair production, with subsequent decay into leptons. We observe no candidate e(+)e(-)e(+/-), e(+)e(-)mu(+/-), e(+/-)mu(+)mu(-), or mu(+)mu(-)mu(+/-) events in 106 pb(-1) integrated luminosity. We present limits on the sum of the branching ratios times cross section for the four channels: sigma( 1)(+/-)( 2)B-0( (+/-)(1) (0)(2) --> 3l + X) 1)(+/-) > 81.5 GeV/c(2), and M( 2)(0) > 82.2 GeV/c(2) for tan beta = 2, mu = -600 GeV/c(2), and M-(q over tilde) = M-(g over tilde).

Measurement of $B$ hadron lifetimes using $J/\psi$ final states at CDF

Abstract: The average bottom-hadron and individual B{sup +}, B{sup 0}, and B{sub s}{sup 0} meson lifetimes have been determined using decays with a J/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}} in the final state. The data sample consists of 110 pb{sup {minus}1} of {bar p}p collisions at {radical} (s) =1.8 TeV collected by the CDF detector at the Fermilab Tevatron collider during 1992{endash}1995. For the average lifetime of B hadrons decaying into J/{psi}+X, we obtain {l_angle}{tau}{sub b}{r_angle}=1.533{plus_minus}0.015(stat){sub {minus}0.031}{sup +0.035}(syst)ps. For the B{sup +} and B{sup 0} meson lifetimes, we determine {tau}(B{sup +})=1.68{plus_minus}0.07(stat){plus_minus}0.02(syst)ps, {tau}(B{sup 0})=1.58{plus_minus}0.09(stat){plus_minus}0.02(syst)ps, and {tau}(B{sup +})/{tau}(B{sup 0})=1.06{plus_minus}0.07(stat){plus_minus}0.02(syst). For the B{sub s}{sup 0} meson lifetime, we find {tau}(B{sub s}{sup 0})=1.34{sub {minus}0.19}{sup +0.23}(stat){plus_minus}0.05(syst) ps. {copyright} {ital 1998} {ital The American Physical Society}

Search for long-lived parents of Z0 bosons in pp̄ collisions at √s = 1.8 TeV

Abstract: We search for new long-lived particles which decay to Z{sup 0} bosons by looking for Z{sup 0}{yields}e{sup +}e{sup -} decays with displaced vertices. We find no evidence for parent particles of the Z{sup 0} with long lifetimes in 90 pb{sup -1} of data from the CDF experiment at Fermilab. We set a cross section limit as a function of the lifetime of the parent particle for both a generic Z{sup 0} parent and a fourth-generation, charge -1/3 quark that decays into Z{sup 0}b.

Observation of B + -->ψ(2S)K + and B 0 -->ψ(2S)K * (892) 0 decays and measurements of B-meson branching fractions into J/ψ and ψ(2S) final states

Abstract: We report the observations of the decays B{sup +}{yields}{psi}(2S)K{sup +} and B{sup 0}{yields}{psi}(2S)K*(892){sup 0} in p{ovr p} collisions at a center-of-mass energy of 1.8 TeV using a 110 pb{sup -1} data sample recorded by the Collider Detector at Fermilab. We also reconstruct the decays B{sup +}{yields}J/{psi}K{sup +} and B{sup 0}{yields}J/{psi}K*(892){sup 0} and measure the six ratios of branching fractions of these four decays. The relative branching-fraction results are shown to be consistent with phenomenological factorization calculations of hadronic B-meson decays. We use the world-average branching fraction B(B{sup +}{yields}J/{psi}K{sup +}) to derive B(B{sup +}{yields}{psi}(2S)K{sup +})=(0.56{+-}0.08{+-}0.10)x10{sup -3}, B(B{sup 0}{yields}{psi}(2S)K*(892){sup 0})=(0.92{+-}0.20{+-}0.16)x10{sup -3}, and B(B{sup 0}{yields}J/{psi}K*(892){sup 0})=(1.78{+-}0.14{+-}0.29)x10{sup -3}, where the first and second uncertainties are statistical and systematic, respectively.

Measurement of the [Formula Presented] and [Formula Presented] meson lifetimes using semileptonic decays

Abstract: The lifetimes of the ${B}^{\ensuremath{-}}$ and ${B}^{0}$ mesons are measured using the partially reconstructed semileptonic decays $\overline{B}\ensuremath{\rightarrow}{\mathrm{Dl}}^{\ensuremath{-}}\overline{\ensuremath{ u}}X,$ where $D$ is either a ${D}^{0}$ or ${D}^{*+}$ meson. The data were collected by the CDF detector at the Fermilab Tevatron collider during 1992--1995 and correspond to about $110{\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ of $\overline{p}p$ collisions at $\sqrt{s}=1.8\mathrm{TeV}.$ We measure decay lengths and extract the lifetimes to be $\ensuremath{\tau}{(B}^{\ensuremath{-}})=1.637\ifmmode\pm\else\textpm\fi{}{0.058}_{\ensuremath{-}0.043}^{+0.045}$ ps and $\ensuremath{\tau}({B}^{0})=1.474\ifmmode\pm\else\textpm\fi{}{0.039}_{\ensuremath{-}0.051}^{+0.052}\mathrm{ps},$ and the ratio of the lifetimes to be $\ensuremath{\tau}{(B}^{\ensuremath{-}})/\ensuremath{\tau}({B}^{0})=1.110\ifmmode\pm\else\textpm\fi{}{0.056}_{\ensuremath{-}0.030}^{+0.033},$ where the first uncertainties are statistical and the second are systematic.

Measurement of the σ(W+≥1Jet)/σ(W) cross section ratio from ¯pp collisions at √s=1.8TeV

Abstract: The ratio of the W + ≥ 1 jet cross section to the inclusive W cross section is measured using W±→ e±v events from p¯p collisions at √ = 1.8 TeV. The data are from 108pb−1of integrated luminosity collected with the Collider Detector at Fermilab. Measurements of the cross section ratio for jet transverse energy thresholds(EminT) ranging from 15 to 95 GeV are compared to theoretical predictions using next-to-leading-order QCD calculations. Data and theory agree well for EminT> 25 GeV, where the predictions lie within 1 standard deviation of the measured values. © 1998 The American Physical Society.

Search for the rare decay W± → Dsplusmnγ in pp̄ collisions at √s = 1.8 TeV

Abstract: We search for the rare decay ${W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{D}_{s}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\gamma}$ in $82{\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ of $p\overline{p}$ collisions recorded with the Collider Detector at Fermilab. At the 95% confidence level, we find an upper limit on the relative branching fraction to be $\ensuremath{\Gamma}{(W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{D}_{s}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\gamma})/\ensuremath{\Gamma}{(W}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{e}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{ u})l1.2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}.$