Showing papers by "Kostantinos Kordas published in 1997"
TL;DR: In this article, a strong signal for double parton (DP) scattering is observed in a 16pb−1 sample of p¯p→γ/π0+3jets+X data from the CDF experiment at the Fermilab Tevatron.
Abstract: A strong signal for double parton (DP) scattering is observed in a 16pb−1 sample of p¯p→γ/π0+3jets+X data from the CDF experiment at the Fermilab Tevatron. In DP events, two separate hard scatterings take place in a single p¯p collision. We isolate a large sample of data (∼14000events) of which 53% are found to be DP. The process-independent parameter of double parton scattering, σeff, is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings in separate p¯p collisions. The result σeff=(14.5±1.7−2.3+1.7)mb represents a significant improvement over previous measurements, and is used to constrain simple models of parton spatial density. The Feynman x dependence of σeff is investigated and none is apparent. Further, no evidence is found for kinematic correlations between the two scatterings in DP events.
241 citations
TL;DR: In this article, the authors present a study of $J/\ensuremath{\psi}$ and $ENSSI(2S)$ production in collisions, at the CDF detector at Fermilab.
Abstract: We present a study of $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)$ production in $p\overline{p}$ collisions, at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ with the CDF detector at Fermilab. The $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)$ mesons are reconstructed using their ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decay modes. We have measured the inclusive production cross section for both mesons as a function of their transverse momentum in the central region, $|\ensuremath{\eta}|l0.6$. We also measure the fraction of these events originating from $b$ hadrons. We thus extract individual cross sections for $J/\ensuremath{\psi}$ and $\ensuremath{\psi}(2S)$ mesons from $b$-quark decays and prompt production. We find a large excess (approximately a factor of 50) of direct $\ensuremath{\psi}(2S)$ production compared with predictions from the color singlet model.
210 citations
TL;DR: In this paper, a strong signal for double parton scattering (DP) is observed in a 16 pb{sup {minus}1} sample of {bar p}p{r_arrow}{gamma}+3 jets+X data from the CDF experiment at the Fermilab Tevatron.
Abstract: A strong signal for double parton scattering (DP) is observed in a 16 pb{sup {minus}1} sample of {bar p}p{r_arrow}{gamma}+3 jets+X data from the CDF experiment at the Fermilab Tevatron. The process-independent DP parameter, {sigma}{sub eff}, is obtained without reference to theoretical calculations by comparing observed DP events to events with hard scatterings at separate {bar p}p collisions. The result, {sigma}{sub eff}=(14.5{plus_minus}1.7{sup +1 .7}{sub {minus}2.3}) mb , represents a significant improvement over previous measurements. For the first time, the Feynman x dependence of the {sigma}{sub eff} parameter is investigated, and no dependence is seen. {copyright} {ital 1997} {ital The American Physical Society}
102 citations
TL;DR: The first observation of diffractively produced W bosons was reported in this article, where the diffractive to nondiffractive W production ratio was found to be R{sub W}=(1.15{plus_minus}0.55 ) percent.
Abstract: We report the first observation of diffractively produced W bosons. In a sample of W{r_arrow}e{nu} events produced in p{bar p} collisions at {radical}(s)=1.8TeV, we find an excess of events with a forward rapidity gap, which is attributed to diffraction. The probability that this excess is consistent with nondiffractive production is 1.1{times}10{sup -4} (3.8{sigma}). The relatively low fraction of W+jet events observed within this excess implies that mainly quarks from the Pomeron, which mediates diffraction, participate in W production. The diffractive to nondiffractive W production ratio is found to be R{sub W}=(1.15{plus_minus}0.55){percent}. {copyright} {ital 1997} {ital The American Physical Society}
83 citations
TL;DR: In this article, the authors used 106 pb{sup {minus}1} of data collected with the Collider Detector at Fermilab to search for new particles decaying to dijets.
Abstract: We have used 106 pb{sup {minus}1} of data collected with the Collider Detector at Fermilab to search for new particles decaying to dijets. We exclude at the 95{percent} confidence level models containing the following new particles: axigluons and flavor universal colorons with a mass between 200 and 980 GeV/c{sup 2}, excited quarks with a mass between 80 and 570 GeV/c{sup 2} and between 580 and 760 GeV/c{sup 2}, color octet techni-{rho}`s with a mass between 260 and 480 GeV/c{sup 2}, W{sup {prime}} bosons with a mass between 300 and 420 GeV/c{sup 2}, and E{sub 6} diquarks with a mass between 290 and 420 GeV/c{sup 2}. {copyright} {ital 1997} {ital The American Physical Society}
82 citations
TL;DR: In this paper, a direct search for charged Higgs boson production in p{ovr p} collisions at {radical}(s)=1.8 TeV recorded by the Collider Detector at Fermilab was described.
Abstract: This Letter describes a direct search for charged Higgs boson production in p{ovr p} collisions at {radical}(s)=1.8 TeV recorded by the Collider Detector at Fermilab. Two-Higgs-double extensions to the standard model predict the existence of charged Higgs bosons (H{sup {plus_minus}}) . In such models, the branching fraction for top quarks scr(B)(t{r_arrow}H{sup +}b{r_arrow}{tau}{sup +} {nu}b) can be large. This search uses the hadronic decays of the tau lepton in this channel to significantly extend previous limits on H{sup {plus_minus}} production. {copyright} {ital 1997} {ital The American Physical Society}
74 citations
TL;DR: In this article, the authors reported the observation and measurement of diffractive dijet production at the Fermilab Tevatron p¯p collider at s=1.8TeV.
Abstract: We report the observation and measurement of the rate of diffractive dijet production at the Fermilab Tevatron p¯p collider at s=1.8TeV. In events with two jets of ET>20GeV, 1.8 0, we find that the diffractive to nondiffractive production ratio is RJJ=[0.75±0.05(stat)±0.09(syst)]%. By comparing this result, in combination with our measured rate for diffractive W boson production reported previously, with predictions based on a hard partonic pomeron structure, we determine the pomeron gluon fraction to be fg=0.7±0.2.
69 citations
TL;DR: In this paper, the authors present measurements of correlated $b\overline{b}$ cross sections, $\ensuremath{\mu}\ensuresuremath{-}\ensureMath{\mu}$ correlations, the average mixing parameter, and a limit on the CP-violating parameter, which they use muon pairs from double semileptonic decays.
Abstract: We present measurements of correlated $b\overline{b}$ cross sections, $\ensuremath{\mu}\ensuremath{-}\ensuremath{\mu}$ correlations, the average ${B}^{0}{\overline{B}}^{0}$ mixing parameter $\overline{\ensuremath{\chi}}$, and a limit on the CP-violating parameter ${\ensuremath{\epsilon}}_{B}.$ For these measurements, we use muon pairs from $b\overline{b}$ double semileptonic decays. The data used in this analysis were taken with the Collider Detector at Fermilab and represent an integrated luminosity of $17.4\ifmmode\pm\else\textpm\fi{}0.6$ pb${}^{\ensuremath{-}1}$. The results concerning $b\overline{b}$ production correlations are compared to predictions of next-to-leading order QCD computations.
60 citations
TL;DR: In this article, the first observation of the all hadronic decay of t{ovr t} pairs was performed using 109 pb{sup -1} of p{ov r p} collisions at sqrt[s] = 1.8 TeV collected with the Collider Detector at Fermilab.
Abstract: We present the first observation of the all hadronic decay of t{ovr t} pairs. The analysis is performed using 109 pb{sup -1} of p{ovr p} collisions at sqrt[s] = 1.8 TeV collected with the Collider Detector at Fermilab. We observe an excess of events with five or more jets, including one or two b jets, relative to background expectations. Based on this excess we evaluate the production cross section to be in agreement with previous results. We measure the top mass to be 186{+-}10{+-}12 GeV/c{sup 2}.
46 citations
TL;DR: The results of a search for first generation scalar leptoquarks pairs (S-1 (S)over-bar(1)) in 110 +/- 7 pb(-1) of data collected by the Collider Detector at Fermilab are presented in this article.
Abstract: We present the results of a search for first generation scalar leptoquarks pairs (S-1 (S)over-bar(1)) in 110 +/- 7 pb(-1) of data collected by the Collider Detector at Fermilab. We assume both leptoquarks decay to an electron and a quark. Three candidate events, with masses below 140 GeV/c(2) and consistent with background expectations, are observed. We obtain a 95% confidence level upper limit on the production cross section as a function of the leptoquark mass. Using a next-to-leading order calculation of S-1 (S)over-bar(1) production, we exclude scalar leptoquarks with mass less than 213 GeV/c(2) at 95% C.L. for a branching ratio into eq equal to 1.
40 citations
TL;DR: In this article, the authors measured a mass difference between the decay of the Lambda and the B-Lambda in 110 collisions taken at 1.8$ TeV and showed that the mass difference was 0.05(syst).
Abstract: The decay ${\ensuremath{\Lambda}}_{b}^{0}$\ensuremath{\rightarrow}J/\ensuremath{\psi} \ensuremath{\Lambda} is observed in 110 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ of pp\ifmmode\bar\else\textasciimacron\fi{} collisions taken at $\sqrt{s}=1.8$ TeV. These data are used to measure a \ensuremath{\Lambda}${}_{b}^{0}$ mass of 5621\ifmmode\pm\else\textpm\fi{}4(stat)\ifmmode\pm\else\textpm\fi{}3(syst) MeV/${\mathit{c}}^{2}$, and a mass difference between the \ensuremath{\Lambda}${}_{b}^{0}$ and the ${\mathit{B}}^{0}$ of 340\ifmmode\pm\else\textpm\fi{}5(stat)\ifmmode\pm\else\textpm\fi{}1(syst) MeV/${\mathit{c}}^{2}$. The production cross-section times branching fraction for the decay ${\ensuremath{\Lambda}}_{b}^{0}$\ensuremath{\rightarrow}J/\ensuremath{\psi} \ensuremath{\Lambda} relative to that for the decay ${B}^{0}$\ensuremath{\rightarrow}J/\ensuremath{\psi} ${K}_{S}^{0}$ has been measured to be 0.27\ifmmode\pm\else\textpm\fi{}0.12(stat)\ifmmode\pm\else\textpm\fi{}0.05(syst).
TL;DR: In this article, the authors present a search for dilepton events from t{ovr t} production with one electron or muon and one hadronically decaying {tau} lepton from the decay t{n,n,sub l}({tau,nu,sub τ,tau]), using the Collider Detector at Fermilab.
Abstract: We present a search for dilepton events from t{ovr t} production with one electron or muon and one hadronically decaying {tau} lepton from the decay t{ovr t}{yields}(l{nu}{sub l})({tau}{nu}{sub {tau}})b{ovr b}, (l = e,{mu}), using the Collider Detector at Fermilab. In a 109 pb{sup -1} data sample of p{ovr p} collisions at sqrt[s] = 1.8 TeV we expect {approx}1 signal event and a total background of {approx}2 events; we observe 4 candidate events ( 2 e{tau} and 2 {mu}{tau}). Three of these events have jets identified as b candidates, compared to an estimated background of 0.28{+-}0.02 events.
TL;DR: In this article, the authors search for new particles that decay into b{ovr b} and are produced with W bosons in p{ov r p} collisions at sqrt[s] = 1.8 TeV.
Abstract: We search for new particles that decay into b{ovr b} and are produced with W bosons in p{ovr p} collisions at sqrt[s] = 1.8 TeV. The search uses 109 {+-} 7 pb{sup -1} accumulated by the CDF experiment at Fermilab. We select events with an e{nu} or {mu}{nu}, and two jets, one of the b tagged. The number of events and the two-jet mass distribution are consistent with expectations. Using W+Higgs production as a model for the acceptance, we set an upper limit on the production cross section times branching ratio for the new particle ranging from 14 to 19 pb (95% C.L.) as the particle mass varies from 70 to 120 GeV/c{sup 2}.
TL;DR: In this paper, the authors describe the properties of six-jet events at the Fermilab proton-antiproton collider operating at a center-of-mass energy of 1.8 TeV.
Abstract: We describe the properties of six-jet events, with the six-jet mass exceeding 520GeV/c{sup 2}, produced at the Fermilab proton-antiproton collider operating at a center-of-mass energy of 1.8 TeV. Observed distributions for a set of 20 multijet variables are compared with predictions from the HERWIG QCD parton shower Monte Carlo program, the NJETS leading order QCD matrix element Monte Carlo program, and a phase-space model in which six-jet events are distributed uniformly over the kinematically allowed region of the six-body phase space. In general the QCD predictions provide a good description of the observed six-jet distributions. {copyright} {ital 1997} {ital The American Physical Society}