Showing papers by "M. J. Shochet published in 1995"

Observation of top quark production in p̄p collisions with the collider detector at fermilab

Abstract: We establish the existence of the top quark using a $67{\mathrm{pb}}^{\ensuremath{-}1}$ data sample of $\overline{p}p$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\mathrm{TeV}$ collected with the Collider Detector at Fermilab (CDF). Employing techniques similar to those we previously published, we observe a signal consistent with $t\overline{t}$ decay to $\mathrm{WWb}\overline{b}$, but inconsistent with the background prediction by $4.8\ensuremath{\sigma}$. Additional evidence for the top quark is provided by a peak in the reconstructed mass distribution. We measure the top quark mass to be $176\ifmmode\pm\else\textpm\fi{}8(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}10(\mathrm{syst})\mathrm{GeV}{/c}^{2}$, and the $t\overline{t}$ production cross section to be ${6.8}_{\ensuremath{-}2.4}^{+3.6}\mathrm{pb}$.

Search for New Gauge Bosons Decaying into Dileptons in p̄p Collisions at s} = 1.8 TeV

Abstract: We have searched for heavy neutral gauge bosons (2’) in jjp collisions at Js = 1.8 TeV. The data were obtained using the CDF detector during 19921993 run corresponding to an integrated luminosity of 19.7f0.7 pb-‘. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons as a function of 2’ mass. Assuming Standard Model coupling strengths, we exclude a 2’ with mass less than 505 GeV/c 2. We also present lower mass limits for 2’ bosons from & models and the Alternative Left-Right Model. PACS numbers: 13.85.Rm, 12.15.Cc, 14.80.Er Neutral gauge bosons in addition to the 2’ are expected in many extensions of the Standard Model [l]. These models typically specify the strengths of the couplings of such bosons to quarks and leptons but make no mass predictions [2]. In up collisions, 2’ bosons may be observed directly via their decay to lepton pairs. Observation of a 2’ boson would provide dramatic evidence for physics beyond the Standard Model. To date there is no experimental evidence for the existence of any 2’ [3]. The current experimental 2’ mass limit Mzt > 412 GeV/c2 (95% C.L.) was established by the CDF collaboration [4] with the assumption that the coupling strengths of the 2’ to quarks and leptons were the same as those for the Standard Model (SM) 2’. This result was based upon data collected during the 1988-89 run with an integrated luminosity of 4 pb-’ and used both the dielectron [5] and dimuon decay modes. We report an extension of this search using 19.7 pb* of integrated luminosity from the 1992-93 run. Results reported here are obtained using only the dielectron decay mode. We present a 95% confidence level upper limit on the production cross section times branching ratio of 2’ decaying into dielectrons (g(Z) . B(Z’ + ee)). Mass limits are 5 again derived assuming SM coupling strengths. In addition, we present 2’ mass limits using several different theoretical models based on the Es symmetry group [6][‘7] and one limit based upon an Alternative Left-Right Model [8]. The CDF detector has been described in detail elsewhere [9]. We give a brief description of the components relevant to this analysis. Momenta of charged particles are measured in the Central Tracking Chamber (CTC), which is immersed in a 1.4 T axial magnetic field. Outside the CTC, electromagnetic and hadronic calorimeters are arranged in a projective tower geometry. There are three separate pseudorapidity (7) regions of calorimeters, central, end-plug, and forward, where 7 = ln(tan $) and 0 is the polar angle with respect to the direction of the proton beam. Each region has an electromagnetic calorimeter and behind it a hadronic calorimeter. For this analysis we use electrons detected in the central (CEM) or end-plug (PEM) regions. The CEM covers ]q] 9 GeV or an energy cluster in the PEM with ET > 20 GeV. If the cluster was in the CEM the trigger also required a coincidence with a track of transverse momentum PT > 9.2 GeV/c. In addition, the trigger required that the ratio of hadronic to electromagnetic energy (HAD/EM) in the trigger cluster be less than 12.5%. For electrons with 25 150 GeV), the energy deposited

Measurement of the B meson differential cross section dσ/dpT in pp̄ collisions at s = 1.8 TeV

Abstract: This paper presents the first direct measurement of the $B$ meson differential cross section $d\ensuremath{\sigma}{/dp}_{T}$ in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8$ TeV using a sample of $19.3\ifmmode\pm\else\textpm\fi{}0.7$ p${\mathrm{b}}^{--1}$ accumulated by the Collider Detector at Fermilab. The cross section is measured in the central rapidity region $|y|l1$ for ${p}_{T}\left(B\right)g6.0$ GeV $/c$ by fully reconstructing the $B$ meson decays ${B}^{+}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{+}$ and ${B}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{K}^{*0}\left(892\right)$, where $J/\ensuremath{\psi}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and ${K}^{*0}\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$. A comparison is made to the theoretical QCD prediction calculated at next-to-leading order.

Observation of rapidity gaps in pp collisions at 1.8 tev

Abstract: In $p\overline{p}$ collisions at $\sqrt{s}=1.8$ TeV we find jet events with a rapidity gap topology. The number of hadrons in the rapidity interval $\ensuremath{\Delta}{\ensuremath{\eta}}_{D}$ between leading-jet cones was sampled by charged tracks with ${P}_{T}g400$ MeV/c. We find excess trackless events beyond that expected in a smooth multiplicity distribution. In a control region outside $\ensuremath{\Delta}{\ensuremath{\eta}}_{D}$ we see no excess. For $\ensuremath{\Delta}{\ensuremath{\eta}}_{D}g0.8$, the fraction of excess trackless events, consistent with estimates based on exchange of color-singlet digluons, is $R(\mathrm{gap})=\frac{{\ensuremath{\sigma}}_{\mathrm{jet}}(\mathrm{gap})}{{\ensuremath{\sigma}}_{\mathrm{jet}}}=0.0085\ifmmode\pm\else\textpm\fi{}{0.0012(\mathrm{stat})}_{\ensuremath{-}0.0012}^{+0.0024}(\mathrm{syst})$.

Measurement of theWboson mass

Abstract: This paper presents a measurement of the mass of the W boson using data collected with the CDF detector during the 1992--1993 collider run at the Fermilab Tevatron. A fit to the transverse mass spectrum of a sample of 3268 W\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{ u} events recorded in an integrated luminosity of 19.7 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ gives ${\mathit{M}}_{\mathit{W}}^{\mathrm{\ensuremath{\mu}}}$=80.310\ifmmode\pm\else\textpm\fi{}0.205 (stat)\ifmmode\pm\else\textpm\fi{}0.130 (syst) GeV/${\mathit{c}}^{2}$. A fit to the transverse mass spectrum of a sample of 5718 W\ensuremath{\rightarrow}e\ensuremath{ u} events recorded in 18.2 ${\mathrm{pb}}^{\mathrm{\ensuremath{-}}1}$ gives ${\mathit{M}}_{\mathit{W}}^{\mathit{e}}$=80.490\ifmmode\pm\else\textpm\fi{}0.145 (stat)\ifmmode\pm\else\textpm\fi{}0.175 (syst) GeV/${\mathit{c}}^{2}$. Combining the muon and electron results, accounting for correlated uncertainties, yields ${\mathit{M}}_{\mathit{W}}$=80.410\ifmmode\pm\else\textpm\fi{}0.180 GeV/${\mathit{c}}^{2}$.

Search for New Particles Decaying to Dijets in pp̄ Collisions at √s = 1.8 TeV

Abstract: We have used 19 pb**-1 of data collected with the Collider Detector at Fermilab to search for new particles decaying to dijets. We exclude at 95% confidence level models containing the following new particles: axigluons with mass between 200 and 870 GeV, excited quarks with mass between 80 and 570 GeV, and color octet technirhos with mass between 320 and 480 GeV.

Measurement of W-photon couplings in p- p collisions at s=1.8 TeV

Abstract: We report on a study of [ital W]+ photon production in approximately 20 pb[sup [minus]1] of [ital p][minus][ital [bar p]] collisions at [radical][ital s]=1.8 TeV recorded with the Collider Detector at Fermilab. Our results are in good agreement with standard model expectations and are used to obtain limits on anomalous [ital CP]-conserving [ital WW][gamma] couplings of [minus]2.3[lt][Delta][kappa][lt]2.2 for [lambda]=0 and [minus]0.7[lt][lambda][lt]0.7 for [Delta][kappa]=0 at 95% C.L. We obtain the same limits for [ital CP]-violating couplings. These results provide limits on the higher-order electromagnetic moments of the [ital W] boson of 0.8[lt][ital g][sub [ital W]][lt]3.1 for [ital q][sup [ital e]][sub [ital W]]=1 and [minus]0.6[lt][ital q][sup [ital e]][sub [ital W]][lt]2.7 for [ital g][sub [ital W]]=2 at 95% C.L.

ϒProduction inpp¯Collisions ats=1.8TeV

Abstract: We report on measurements of the $\ensuremath{\Upsilon}(1S)$, $\ensuremath{\Upsilon}(2S)$, and $\ensuremath{\Upsilon}(3S)$ differential, ${(\frac{{d}^{2}\ensuremath{\sigma}}{d{P}_{t}\mathrm{dy}})}_{y=0}$, and integrated cross sections in $p\overline{p}$ collisions at $\sqrt{s}=1.8$ TeV using a sample of 16.6 \ifmmode\pm\else\textpm\fi{} 0.6 ${\mathrm{pb}}^{\ensuremath{-}1}$ collected by the Collider Detector at Fermilab. The three resonances were reconstructed through the decay $\ensuremath{\Upsilon}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$. Comparison is made to a leading order QCD prediction.

Charge Asymmetry in W-Boson Decays Produced in pp¯ Collisions at s=1.8 TeV

Abstract: Charge asymmetry has been measured using 19 039 [ital W] decays recorded by the Collider Detector at Fermilab during the 1992--93 run of the Tevatron Collider. The asymmetry is sensitive to the ratio of [ital d] and [ital u] quark distributions to [ital x][lt]0.01 at [ital Q][sup 2][approx][ital M][sup 2][sub [ital W]], where nonperturbative effects are minimal. It is found that of the two current sets of parton distributions, those of Martin, Roberts, and Stirling are favored over the sets most recently produced by the CTEQ Collaboration. The [ital W] asymmetry data provide stronger constraints on [ital d]/[ital u] ratio than the recent measurements of [ital F][sub 2][sup [mu][ital n]]/[ital F][sub 2][sup [mu][ital p]], which are limited by uncertainties originating from deuteron corrections.

Search for charged bosons heavier than the W boson in pp̄ collisions at s=1800 GeV

Abstract: We have searched for new, heavy, charged bosons {ital W}{prime} through the decay {ital W}{prime}{r_arrow}{ital e}{nu} in {ital pp}{ovr bar} collisions at {radical}{ital s}=1.8 TeV. The data used in the search represent 19.7 pb{sup --1}collected by the Collider Detector at Fermilab. Limits are placed on {sigma}{ital B}({ital pp}{ovr bar}{r_arrow}{ital W}{prime}{r_arrow}{ital e}{nu}) as a function of {ital M}{sub {ital W}{prime}}. Assuming standard couplings of the {ital W}{prime} to fermions, we establish the limit {ital M}{sub {ital W}{prime}}{gt}652 GeV/{ital c}{sup 2} (95% C.L.).

Limits on Z-photon couplings from p- p interactions at s=1.8 TeV

Abstract: We report limits on anomalous [ital ZZ][gamma] and [ital Z][gamma][gamma] couplings derived from an analysis of [ital Z]+photon production based upon approximately 20pb[sup [minus]1] of the [bar p] collision data recorded by the Collider Detector at Fermilab. We observe good agreement with the standard model expectation that all [ital Z][gamma] couplings are zero. Confidence level intervals for individual couplings and contours for pairs of [ital CP]-conserving/violating [ital ZZ][gamma] and [ital Z][gamma][gamma] couplings are presented.

Measurement of the Polarization in the Decays Bd → J/ψ K*0 and Bs → J/ψ φ

Abstract: This Letter reports on measurements of the longitudinal polarization fractions in the decays {ital B}{sub {ital d}}{r_arrow}{ital J}/{psi}{ital K}{sup *0} and {ital B}{sub {ital s}}{r_arrow}{ital J}/{psi}{phi} using data collected with the Collider Detector at Fermilab. {ital B}{sub {ital d}} mesons are reconstructed through the decay chain {ital B}{sub {ital d}}{r_arrow}{ital J}/{psi}{ital K}*, {ital J}/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}}, {ital K}{sup *0}{r_arrow}{ital K}{sup +}{pi}{sup {minus}}. A sample of 65{plus_minus}10{ital B}{sub {ital d}} events is used to obtain a longitudinal polarization fraction of {Gamma}{sub {ital L}}/{Gamma}=0.65{plus_minus}0.10(stat){plus_minus}0.04(syst). {ital B}{sub {ital s}} mesons are reconstructed through the decay chain {ital B}{sub {ital s}}{r_arrow}{ital J}/{psi}{phi}, {ital J}/{psi}{r_arrow}{mu}{sup +}{mu}{sup {minus}}, {phi}{r_arrow}{ital K}{sup +}{ital K}{sup {minus}}. A sample of 19{plus_minus}5{ital B}{sub {ital s}} events is used to obtain the result {Gamma}{sub {ital L}}/{Gamma}=0.56{plus_minus}0.21(stat){sub {minus}0.04}{sup +0.02}(syst). Copyright {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Search for second generation leptoquarks in pp collisions at s=1.8 TeV

Abstract: We present the results of a search for second generation leptoquarks ${S}_{2}$ using $19.3{\mathrm{pb}}^{\ensuremath{-}1}$ of data collected at the Collider Detector at Fermilab (CDF) in $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8$ TeV during the 1992--93 collider run. We have searched for ${S}_{2}\overline{{S}_{2}}$ pairs assuming that each leptoquark decays to a muon $+$ quark with a branching ratio $\ensuremath{\beta}$. We find two candidate events, consistent with an expected background of $1.11\ifmmode\pm\else\textpm\fi{}0.48$. We obtain upper limits on $\ensuremath{\sigma}(p\overline{p}\ensuremath{\rightarrow}{S}_{2}\overline{{S}_{2}}){\ensuremath{\beta}}^{2}$ as a function of ${M}_{{S}_{2}}$. Using a Monte Carlo prediction for ${S}_{2}\overline{{S}_{2}}$ pair production, we exclude ${M}_{{S}_{2}}l131\phantom{\rule{0ex}{0ex}}\mathrm{GeV}/{c}^{2}$ for $\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ and ${M}_{{S}_{2}}l96\phantom{\rule{0ex}{0ex}}\mathrm{GeV}/{c}^{2}$ for $\ensuremath{\beta}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.5$ at 95% C.L.

Further properties of high-mass multijet events at the Fermilab proton-antiproton collider

Abstract: The properties of high-mass multijet events produced at the Fermilab proton-antiproton collider are compared with leading order QCD matrix element predictions, QCD parton shower Monte Carlo predictions, and the predictions from a model in which events are distributed uniformly over the available multibody phase space. Multijet distributions corresponding to (4{ital N}{minus}4) variables that span the {ital N}-body parameter space are found to be well described by the QCD calculations for inclusive three-jet, four-jet, and five-jet events. The agreement between data, QCD matrix element calculations, and QCD parton shower Monte Carlo predictions suggests that 2{r_arrow}2 scattering plus gluon radiation provides a good first approximation to the full LO QCD matrix element for events with three, four, or even five jets in the final state. {copyright} {ital 1996 The American Physical Society.}

Properties of high mass multi - jet events at the Fermilab $p\bar{p}$ collider

Abstract: The properties of two-, three-, four-, five-, and six-jet events with multijet masses > 600 GeV/c’ are compared with QCD predictions. The shapes of the multijet-mass and leadingjet-angular distributions are approximately independent of jet multiplicity and are well IL,scribed by the NJETS matrix element calculation and the HERWIG parton shower lloutr Carlo predictions. The observed jet transverse momentum distributions for threeand fourjet events discriminate between the matrix element and parton shower predictions, the Ilata favoring the matrix element calculation.

Study of tt production in pp collisions using total transverse energy

Abstract: We analyze a sample of {ital W}+jet events collected with the Collider Detector at Fermilab (CDF) in {ital pp} collisions at {radical}{ital s}=1.8 TeV to study {ital tt} production. We employ a simple kinematical variable H, defined as the scalar sum of the transverse energies of the lepton, neutrino, and jets. For events with a {ital W} boson and four or more jets, the shape of the H distribution deviates by 3.8 standard deviations from that expected from known backgrounds to {ital tt} production. However, this distribution agrees well with a linear combination of background and {ital tt} events, the agreement being best for a top mass of 180 GeV/{ital c}{sup 2}. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

Search for squarks and gluinos via radiative decays of neutralinos in proton-antiproton collisions at s=1.8 TeV

Abstract: We have sought evidence for radiative decays of neutralinos produced in proton-antiproton collisions at {radical}{ital s}=1.8TeV. Events containing two photons plus large missing transverse energy were investigated. The observed event rate and the missing transverse energy distribution of the two-photon events are consistent with QCD predictions. Inferred limits on squark and gluino masses depend on the supersymmetry model parameters. The particular choices {mu}={minus}40GeV/{ital c}{sup 2} and tan{beta}=1.5 lead to 90%-confidence-level asymptotic lower limits of 110 GeV/{ital c}{sup 2} and 140 GeV/{ital c}{sup 2} for squarks and gluinos, respectively.

Measurement of the lifetime of the B-s(0) meson using the exclusive decay mode B-s(0)->J/psi phi

Abstract: The lifetime of the ${B}_{s}^{0}$ meson is measured using the exclusive decay mode ${B}_{s}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}\ensuremath{\varphi}$, where $J/\ensuremath{\psi}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ and $\ensuremath{\varphi}\ensuremath{\rightarrow}{K}^{+}{K}^{\ensuremath{-}}$. The data sample consists of $110{\mathrm{pb}}^{\ensuremath{-}1}$ of $p\overline{p}$ collisions at $\sqrt{s}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.8\phantom{\rule{0ex}{0ex}}\mathrm{TeV}$, collected by the CDF detector at the Fermilab Tevatron collider during 1992--1995. We find $58\ifmmode\pm\else\textpm\fi{}12$ signal events, and the ${B}_{s}^{0}$ meson lifetime is determined to be ${\ensuremath{\tau}}_{{B}_{s}^{0}}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.34}_{\ensuremath{-}0.19}^{+0.23}(\mathrm{stat})\ifmmode\pm\else\textpm\fi{}0.05(\mathrm{syst})$ ps. This result is consistent with previous measurements of the ${B}_{s}^{0}$, ${B}^{+}$, and ${B}_{d}^{0}$ meson lifetimes and with theoretical predictions.