Jets Channel Research Articles

MEASUREMENT OF R = B(t→Wb)/B(t→Wq) AT DØ

A measurement of the ratio of branching fractions, R = B(t→Wb)/B(t→Wq), with q being any quark with I3 = -1/2 and Q = -1/3, is presented. This analysis considers samples of single- and double-tagged lepton+jets events obtained with the DØ detector, corresponding to integrated luminosities of 169 pb-1 and 158 pb-1, respectively in the e+jets and μ+jets channels. Two different lifetime taggers, CSIP and SVT, are used.

Measurement of the W helicity in $t{\bar t}$ decays at $\sqrt{s} = 1.96\ {\rm TeV}$ in the Lepton+jets Final States

Two measurements of the W-helicity in [Formula: see text] decays at [Formula: see text] have been carried out using data collected by the DØ detector. Semileptonic [Formula: see text] events in the electron and muon channel were used. In these events the distribution of the angle between the lepton and the direction of the top measured in the rest frame of the intermediate W boson is sensitive to the helicity of the W. The two analyses differ in the usage of lifetime tag information in the event selection. With an integrated luminosity of 169 pb-1 and 158 pb-1 in the e+jets and μ+jets channels respectively, an upper limit on the fraction f+ of positive helicity W's of f+<0.244 is set by both analyses at 90% confidence level.

Search for Production of Single Top Quarks in the Electron+Jets Channel at DØ

We present a search for the electroweak production of single top quarks using 156-169 pb-1 of electron+jets data collected by the DØ detector, at [Formula: see text], at the Tevatron proton-antiproton collider at Fermilab. In the absence of any significant evidence for single top production we set upper limits on the cross section at 95% C.L., of 14 pb for s-channel, 20 pb for t-channel, and 18 pb for the combined s + t channel.

The Search for Single Top Quark Production in the Muon plus Jets Channel at DØ

We have performed a search for the electroweak production of single top quarks in [Formula: see text] collisions at the Fermilab Tevatron at a center of mass energy of [Formula: see text]. The search was performed in the muon plus jets decay channel requiring at least one b-tagged jet. The data were collected using the DØ detector between August 2002 and September 2003 corresponding to an integrated luminosity of 158 pb-1. The resulting 95% C.L. upper limits on the production cross sections are 27 pb in the s-channel, 41 pb in the t-channel, and 36 pb in the combined s + t channel using the secondary vertex tagger (SVT) algorithm. We also present results from the combined electron and muon channel search using the DØ detector.

MEASUREMENT OF THE TOP QUARK PAIR PRODUCTION CROSS SECTION IN LEPTON+JETS FINAL STATES AT DØ USING A MULTIVARIATE TECHNIQUE

A measurement of the [Formula: see text] production cross-section at [Formula: see text] with the DØ detector at the Fermilab Tevatron, based on the application of a multivariate topological method is presented. The integrated luminosity corresponds to 143.9 pb-1 in the μ+jets and 141.2 pb-1 in the e+jets channel. The preliminary cross-section is measured to be [Formula: see text].

Search for narrow tt resonances in pp collisions at square root of (s)=1.8 TeV.

A search for narrow resonances that decay into tt pairs has been performed using 130 pb(-1) of data in the lepton + jets channel collected by the Dphi detector in pp collisions at square root of (s)=1.8 TeV. There is no significant deviation observed from the standard-model predictions at a top-quark mass of 175 GeV/c2. We therefore present upper limits at the 95% confidence level on the product of the production cross section and branching fraction to tt for narrow resonances as a function of the resonance mass MX. These limits are used to exclude the existence of a leptophobic top-color particle with mass MX<560 GeV/c2, using a theoretical cross section for a width GammaX=0.012MX.

Measurement of the top quark mass with the collider detector at Fermilab

This report describes a measurement of the top quark mass in $\ppbar$ collisions at a center of mass energy of 1.8 TeV. The data sample was collected with the CDF detector during the 1992--95 collider run at the Fermilab Tevatron, and corresponds to an integrated luminosity of 106 \pb. Candidate $t\bar{t}$ events in the ``lepton+jets'' decay channel provide our most precise measurement of the top quark mass. For each event a top mass is determined by using energy and momentum constraints on the production of the $\ttbar$ pair and its subsequent decay. A likelihood fit to the distribution of reconstructed masses in the data sample gives a top mass in the lepton+jets channel of $176.1\pm 5.1 (stat.)\pm 5.3 (syst.) \gevcc$. Combining this result with measurements from the ``all-hadronic'' and ``dilepton'' decay topologies yields a top mass of $176.1\pm 6.6 \gevcc$.

Search for excited quarks with the ATLAS experiment at the CERN LHC: Double jets channel

Search for excited quarks with the ATLAS experiment at the CERN LHC: Double jets channel

Reach of Fermilab Tevatron upgrades for SU(5) supergravity models with nonuniversal gaugino masses

We explore the reach of luminosity upgrades of the Fermilab Tevatron collider for SU(5) supergravity models in which non-universal GUT-scale gaugino masses arise via a vacuum expectation value for the auxiliary component of a superfield that transforms as a 24, 75 or 200 dimensional representation of SU(5). This results in a different pattern of sparticle masses and mixing angles from what is expected in the minimal supergravity model (mSUGRA) with universal GUT scale gaugino masses. We find that the resulting signal cross sections, and hence the reach of the Tevatron, are sensitive to the gaugino masses at the GUT scale. In the 24 model, the large splitting amongst the two lightest neutralinos leads to SUSY events containing many isolated leptons, including events with a real leptonic Z boson plus jets plus missing energy signal which is visible over much of parameter space. In contrast, in the 75 and 200 models, the reach via leptonic SUSY signals is greatly reduced relative to mSUGRA, and the signal is usually visible only via the canonical $\eslt +$jets channel.

Search for second-generation leptoquark pairs in &pmacr;p collisions at radicals = 1.8 TeV

We have searched for second-generation leptoquark (LQ) pairs in the &mgr;&mgr;+jets channel using 94+/-5 pb(-1) of &pmacr;p collider data collected by the D0 experiment at the Fermilab Tevatron during 1993-1996. No evidence for a signal is observed. These results are combined with those from the &mgr;nu+jets and nunu+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and beta, the branching fraction of a LQ decay into a charged lepton and a quark. Lower limits of 200(180) GeV/c(2) for beta = 1(1 / 2) are set at the 95% C.L. on the mass of scalar LQ. Mass limits are also set on vector leptoquarks as a function of beta.

Top quark physics and searches for new phenomena at the Tevatron

The CDF and DØ collaborations each have collected over 110pb −1 of data. The following article will describe near final results from two currently topical analyses: results from top quark physics and searches for first generation leptoquarks (LQ), using the entire statistics of these large data sets. After careful selection, both collaborations have collected top quark data samples consisting of several dozen events each. From these events both experiments have measured the top quark mass and pair production cross section in a variety of decay channels, including the so-called dilepton, lepton plus jets, and all jets channels. The combined top quark mass from both experiments in the lepton plus jets channels is m t = 175.6 ± 5.5GeV/ c 2. CDF and DØ have also performed optimized searches for the pair production of first generation leptoquarks. No candidate events were found. Combining the results from the ee+jets, eν+jets, and νν+jets channels both experiments set 95% confidence level (CL) upper limits on the LQ pair production cross section as a function of mass and of β, the branching fraction to a charged lepton.

Top quark results from the Tevatron

The CDF and DØ collaborations have collected top quark data samples consisting of several dozen events each. Using these data samples, the two Tevatron experiments have measured the top quark mass and pair production cross section in a variety of decay channels, including the so-called dilepton, lepton plus jets and all jets channels. The combined top quark mass from both experiments in the lepton plus jets channels is m t = 175.6 ± 5.5 GeV/ c 2. Additionally, upper limits have been obtained for certain rare or nonstandard (FCNC and charge Higgs) top quark decays.

Search for First Generation Scalar Leptoquark Pairs inpp¯Collisions ats=1.8TeV

We have searched for first generation scalar leptoquark (LQ) pairs in the eν+jets channel using pp¯ collider data (∫Ldt≈115pb−1) collected by the D0 experiment at the Fermilab Tevatron during 1992–1996. The analysis yields no candidate events. We combine the results with those from the ee+jets and νν+jets channels to obtain 95% confidence level (C.L.) upper limits on the LQ pair production cross section as a function of mass and of β, the branching fraction to a charged lepton. Comparing with the next-to-leading order theory, we set 95% C.L. lower limits on the LQ mass of 225, 204, and 79GeV/c2 for β=1, 12, and 0, respectively.Received 30 October 1997DOI:https://doi.org/10.1103/PhysRevLett.80.2051©1998 American Physical Society

CDF top-quark production and mass

The top search in the dilepton and lepton plus jets channels with the Collider Detector at Fermilab is presented. The analysis uses a 67 pb{sup {minus}1} sample of p{bar p} collisions at 1.8 TeV. A 4.8{sigma} excess of candidate events establishes the existence of the top quark. The t{bar t} production cross section is measured to be {sigma}{sub t{bar t}} = 7.6{sub {minus}2.0}{sup +2.4} pb with branching Br(t {yields} Wb) = 0.87{sub {minus}0.30}{sup +0.13}(stat) {sub {minus}0.11}{sup +0.13}(syst). The measured mass is M{sub top} = 176{plus_minus}8{plus_minus}10 GeV.

Top physics at the Tevatron

The DØ and CDF collaborations recently reported the observation of the top quark in pp¯ collisions at √ s =1.8. This review focuses on results which are newer, in particular the reconstruction of the hadronic W mass in lepton+jets events, multivariate analyses, studies of the all jets channel, and a preliminary mass from dilepton events.

CDF RESULTS ON TOP

CDF has established the existence of the top quark. Results from [Formula: see text] collisions at [Formula: see text] TeV are presented. In the dilepton final state we find seven events with a background of 1.3±0.3. In the e, μ+v+jets channel with a b identified via a secondary vertex detector (SVX), we find 21 events with a background of 5.5±1.8. We measure the top quark mass to be 176±8 (stat) ±10 (syst) GeV/c2, and the [Formula: see text] production cross section to be [Formula: see text] . The integrated luminosity for the results presented in this paper is 67 pb−1. The CDF detector needs to be upgraded for our next run. The integrated luminosity for the next run is expected to be more than 1000 pb −1.

A LIGHT TOP-SQUARK AND ITS CONSEQUENCES AT HIGH ENERGY COLLIDERS

An interesting prediction of a string-inspired one-parameter SU (5)× U (1) supergravity model, is the fact that the lightest member [Formula: see text] of the top-squark doublet [Formula: see text], may be substantially lighter than the top quark. This sparticle [Formula: see text] may be readily pair-produced at the Tevatron and, if [Formula: see text] even be observed at the end of Run IB. Top-squark production may also be a source of top-quark-like signatures in the dilepton and ℓ+ jets channels, if the experimental acceptances are tuned to look for soft leptons. Such a light top-squark is linked with a light supersymmetric spectrum, which can certainly be searched for at the Tevatron through trilepton and squark-gluino searches, and at LEPII through direct [Formula: see text] pair-production and via chargino and Higgs-boson searches.

Evidence for top quark production in p-barp collisions at sqrt s =1.8 TeV.

We present the results of a search for the top quark in 19.3 pb[sup [minus]1] of [ital [bar p]p] collisions at [radical][ital s] =1.8 TeV. The data were collected at the Fermilab Tevatron collider using the Collider Detector at Fermilab (CDF). The search includes standard model [ital t[bar t]] decays to final states [ital ee][nu][bar [nu]], [ital e][mu][nu][bar [nu]], and [mu][mu][nu][bar [nu]] as well as [ital e]+[nu]+jets or [mu]+[nu]+jets. In the ([ital e],[mu])+[nu]+jets channel we search for [ital b] quarks from [ital t] decays via secondary vertex identification and via semileptonic decays of the [ital b] and cascade [ital c] quarks. In the dilepton final states we find two events with a background of 0.56[sub [minus]0.13][sup +0.25] events. In the [ital e],[mu]+[nu]+jets channel with a [ital b] identified via a secondary vertex, we find six events with a background of 2.3[plus minus]0.3. With a [ital b] identified via a semileptonic decay, we find seven events with a background of 3.1[plus minus]0.3. The secondary vertex and semileptonic-decay samples have three events in common. The probability that the observed yield is consistent with the background is estimated to be 0.26%. The statistics are too limited to firmly establish the existence of the more » top quark; however, a natural interpretation of the excess is that it is due to [ital t[bar t]] production. We present several cross-checks. Some support this hypothesis; others do not. Under the assumption that the excess yield over background is due to [ital t[bar t]], constrained fitting on a subset of the events yields a mass of 174[plus minus]10[sub [minus]12][sup +13] GeV/[ital c][sup 2] for the top quark. The [ital t[bar t]] cross section, using this top quark mass to compute the acceptance, is measured to be 13.9[sub [minus]4.8][sup +6.1] pb. « less

Possibilities of discovering a heavy top quark in the lepton-multijet channel

As the Fermilab experiments steadily increase the top quark mass limit, one has to study the top quark discovery in an scenario where its mass is larger than 150 GeV. We will show in this paper that one can apply simple and efficient cuts in the single lepton plus inclusive four jets channel which will reduce the QCD background by a factor of at least 5, while the top quark signal efficiency is more than 70%. With these cuts a discovery limit of 180 GeV can be set for an integrated luminosity of 100 pb −1. This limit is much higher than previously quoted in the literature and does not use the method of heavy quark tagging. The analysis includes energy smearing of the measured jets to simulate the most important detectors effects.

How to tell quark jets from gluon jets.

A method to distinguish between light-quark jets and gluon jets in a calorimeter detector is presented. The method could be used to refine the experimental test of QCD based on the single-jet cross section, by comparing the quark and gluon contributions separately. It could also be used to enhance the signal/background ratio in searching for the top quark in ${\mathit{W}}^{\ifmmode\pm\else\textpm\fi{}}$+jets channels. Optimistically, it might even make it possible to observe the hadronic decays ${\mathit{W}}^{\ifmmode\pm\else\textpm\fi{}}$\ensuremath{\rightarrow}jj and ${\mathit{Z}}^{0}$\ensuremath{\rightarrow}jj, which would allow the W and Z masses to be used as benchmarks for calibrating the calorimeter, and perhaps even provide a useful measurement of ${\mathit{M}}_{\mathit{W}}$/${\mathit{M}}_{\mathit{Z}}$. The method has been developed using Monte Carlo simulations of jet events. Ways to compare it with experiment are discussed. The comparison would provide an important test for QCD shower simulation models.