Top-quark mass measurement using events with missing transverse energy and jets at CDF

We present a measurement of the top-quark mass using a sample of t ?t events in 5.7 fb(-1) of integrated luminosity from p ?p collisions at the Fermilab Tevatron with √s=1.96 TeV and collected by the CDF II Detector. We select events having large missing transverse energy, and four, five, or six jets with at least one jet tagged as coming from a b quark, and reject events with identified charged leptons. This analysis considers events from the semileptonic t ?t decay channel, including events that contain tau leptons. The measurement is based on a multidimensional template method. We fit the data to signal templates of varying top-quark masses and background templates, and measure a top-quark mass of M(top)=172.32±2.4(stat)±1.0(syst) GeV/c(2).     

Precise measurement of the top-quark mass from lepton + jets events

We measure the mass of the top quark using top-quark pair candidate events in the lepton+jets channel from data corresponding to 1 fb;{-1} of integrated luminosity collected by the D0 experiment at the Fermilab Tevatron collider. We use a likelihood technique that reduces the jet energy scale uncertainty by combining an in situ jet energy calibration with the independent constraint on the jet energy scale (JES) from the calibration derived using photon+jets and dijet samples. We find the mass of the top quark to be 171.5+/-1.8(stat.+JES)+/-1.1(syst.) GeV.     

Precision top-quark mass measurement in the lepton+jets topology in p p collisions at square root s=1.96 TeV

We report two measurements of the top-quark mass M(top) using the CDF II detector at the Fermilab Tevatron in a 318 pb(-1) data sample of tt events in the lepton+jets final state. One method uses an event-based likelihood technique resulting in M(top) = 173.2(-2.4)(+2.6)(stat) +/- 3.2(syst) GeV/c2 or 173.2(-4.0)(+4.1) GeV/c2. The second method reconstructs a top-quark mass in each event using the measured invariant mass of the hadronically decaying W boson to constrain the jet energy scale to obtain a value for M(top)of 173.5(-3.6)(+3.7)(stat) +/- 1.3(syst) GeV/c2 or 173.5(-3.8)(+3.9) GeV/c2 . We take the latter, which is more precise, as our result.     

The top quark, others new phenomena observed at the CDF in {ie359-1} collisions at √s = 1.96 TeV (Review)

Upgraded Tevatron luminosity in Run-II (started 2001) has opened a new level of modern heavy-quark studies compared to that one of Run-I. Now top event samples contain hundreds of event statistics for investigation. This review mainly covers the mass measurements of the top quark produced at √s = 1.96 TeV in {ie359-2} collisions at the Collider Detector of Fermilab with the integrated luminosity samples up to 1 fb^?1. As an example of the top quark mass measurements we consider so-called Matrix Element method in “lepton + jets” and “dilepton” channels of the top-quark decay. The CDF top quark mass obtained in lepton +jets mode is the world most precise single measurement of this important physics parameter. The review summarizes the essential results of the CDF top-quark mass measurement achieved and published for the recent 2003–2008 period. We consider also b-quark baryon discoveries like Σ _b , Σ _b ^* , Θ _b as well as first observation of {ie359-3} oscillations. Let us mention here that a CDF/JINR-group created significant contribution to the new CDF complex and physics investigation.     

Measurement of the tt production cross section in pp collisions at square root s = 1.96 TeV using missing E(T) + jets events with secondary vertex b tagging

We present a measurement of the tt production cross section in pp collisions at square root s = 1.96 TeV which uses events with an inclusive signature of significant missing transverse energy and jets. This is the first measurement which makes no explicit lepton identification requirements, so that sensitivity to W --> tau nu decays is maintained. Heavy flavor jets from top quark decay are identified with a secondary vertex tagging algorithm. From 311 pb(-1) of data collected by the Collider Detector at Fermilab, we measure a production cross section of 5.8 +/- 1.2(stat)(-0.7)(+0.9)(syst) pb for a top quark mass of 178 GeV/c2, in agreement with previous determinations and standard model predictions.     

Measurement of the top-quark mass in all-hadronic decays in pp collisions at CDF II

We present a measurement of the top-quark mass Mtop in the all-hadronic decay channel tt-->W+bW-b-->q1q2bq3q4b. The analysis is performed using 310 pb-1 of sqrt[s]=1.96 TeV pp[over ] collisions collected with the CDF II detector using a multijet trigger. The mass measurement is based on an event-by-event likelihood which depends on both the sample purity and the value of the top-quark mass, using 90 possible jet-to-parton assignments in the six-jet final state. The joint likelihood of 290 selected events yields a value of Mtop=177.1+/-4.9(stat)+/-4.7(syst) GeV/c2.     

Direct top-quark width measurement at CDF

We present a measurement of the top-quark width in the lepton+jets decay channel of tt events produced in p p collisions at Fermilab's Tevatron collider and collected by the CDF II detector. From a data sample corresponding to 4.3 fb(-1) of integrated luminosity, we identify 756 candidate events. The top-quark mass and the mass of the hadronically decaying W boson that comes from the top-quark decay are reconstructed for each event and compared with templates of different top-quark widths (Γ(t)) and deviations from nominal jet energy scale (Δ(JES)) to perform a simultaneous fit for both parameters, where Δ(JES) is used for the in situ calibration of the jet energy scale. By applying a Feldman-Cousins approach, we establish an upper limit at 95% confidence level (CL) of Γ(t) <7.6 GeV and a two-sided 68% CL interval of 0.3 GeV <Γ(t) <4.4 GeV for a top-quark mass of 172.5 GeV/c(2), which are consistent with the standard model prediction.     

Review of the top quark mass measurement at the CDF in p \bar p collisions at \sqrt s = 1.96 TeV

Upgraded Tevatron RUN-II luminosity has opened a new chapter in a modern heavy quark studies—a top physics: a dozen level of a Tevatron Run-I top events statistic now is being replaced by hundreds events. This work reviews a mass measurement of the top quark produced at $\sqrt s $ = 1.96 TeV in p $\bar p$ collisions at the Collider Detector at Fermilab (CDF) with the integrated luminosity samples up to 359 pb^?1. The review covers the M(top) measurement using mainly the so-called template methods both in the “lepton + jets” and “dilepton” channels of top quark decay. The CDF top quark mass obtained in the lepton + jets mode is currently the world’s most precise single measurement of this important physical parameter. This work summarizes the essential results of the CDF top quark mass measurement achieved and published for the recent 2003–2005 period.     

Model-independent measurement of the W-boson helicity in top-quark decays at D0

We present the first model-independent measurement of the helicity of W bosons produced in top quark decays, based on a 1 fb(-1) sample of candidate tt events in the dilepton and lepton plus jets channels collected by the D0 detector at the Fermilab Tevatron pp Collider. We reconstruct the angle theta(*) between the momenta of the down-type fermion and the top quark in the W boson rest frame for each top quark decay. A fit of the resulting costheta(*) distribution finds that the fraction of longitudinal W bosons f(0)=0.425+/-0.166(stat)+/-0.102(syst) and the fraction of right-handed W bosons f(+)=0.119+/-0.090(stat)+/-0.053(syst), which is consistent at the 30% C.L. with the standard model.     

Measurement of the tt production cross section in pp collisions at square root of s = 1.96 TeV

We present a measurement of the top quark pair production cross section in pp collisions at square root of s = 1.96 TeV using 318 pb(-1) of data collected with the Collider Detector at Fermilab. We select tt[over ] decays into the final states enu+jets and mu nu+ jets, in which at least one b quark from the t-quark decays is identified using a secondary vertex-finding algorithm. Assuming a top quark mass of 178 GeV/c2, we measure a cross section of 8.7 +/- 0.9(stat)(-0.9)+1.1(syst) pb. We also report the first observation of tt[over ] with significance greater than 5sigma in the subsample in which both b quarks are identified, corresponding to a cross section of 10.1(-1.4)+1.6(stat)(-1.3)+2.0(syst) pb.     

Determination of the width of the top quark

We extract the total width of the top quark, Γ(t), from the partial decay width Γ(t → Wb) measured using the t-channel cross section for single top-quark production and from the branching fraction B(t → Wb) measured in tt events using up to 2.3 fb(-1) of integrated luminosity collected by the D0 Collaboration at the Tevatron pp Collider. The result is Γ(t) = 1.99(-0.55)(+0.69) GeV, which translates to a top-quark lifetime of τ(t) = (3.3(-0.9)(+1.3)) × 10(-25) s. Assuming a high mass fourth generation b' quark and unitarity of the four-generation quark-mixing matrix, we set the first upper limit on |V(tb')| < 0.63 at 95% C.L.     

Search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector

A search for new phenomena in tt events with large missing transverse momentum in proton-proton collisions at a center-of-mass energy of 7 TeV is presented. The measurement is based on 1.04 fb(-1) of data collected with the ATLAS detector at the LHC. Contributions to this final state may arise from a number of standard model extensions. The results are interpreted in terms of a model where new top-quark partners are pair produced and each decay to an on-shell top (or antitop) quark and a long-lived undetected neutral particle. The data are found to be consistent with standard model expectations. A limit at 95% confidence level is set excluding a cross section times branching ratio of 1.1 pb for a top-partner mass of 420 GeV and a neutral particle mass less than 10 GeV. In a model of exotic fourth generation quarks, top-partner masses are excluded up to 420 GeV and neutral particle masses up to 140 GeV.     

Simultaneous measurement of the ratio R=B(t --> Wb)/B(t --> Wq) and the top-quark pair production cross section with the D0 detector at sqrt(s) = 1.96 TeV

We present the first simultaneous measurement of the ratio of branching fractions, R=B(t --> Wb)/B(t --> Wq), with q being a d, s, or b quark, and the top-quark pair production cross section sigma(tt[over]) in the lepton plus jets channel using 0.9 fb(-1) of pp[over] collision data at sqrt(s)=1.96 TeV collected with the D0 detector. We extract R and sigma(tt[over]) by analyzing samples of events with 0, 1, and > or =2 identified b jets. We measure R=0.97(+0.09)/(-0.08)(stat+syst) and sigma(tt[over])=8.18(+0.09)(-0.84)(stat+syst) +/- 0.50(lumi) pb, in agreement with the standard model prediction.     

Measurement of the mass difference between t and t quarks

We present a direct measurement of the mass difference between t and t quarks using tt candidate events in the lepton+jets channel, collected with the CDF II detector at Fermilab's 1.96 TeV Tevatron pp Collider. We make an event by event estimate of the mass difference to construct templates for top quark pair signal events and background events. The resulting mass difference distribution of data is compared to templates of signals and background using a maximum likelihood fit. From a sample corresponding to an integrated luminosity of 5.6 fb(-1), we measure a mass difference, ΔM(top) = M(t) - M(t) = -3.3 ± 1.4(stat) ± 1.0(syst) GeV/c2, approximately 2 standard deviations away from the CPT hypothesis of zero mass difference.     

First measurement of W boson production in association with a single Charm quark in pp collisions at sqrt(s)=1.96 TeV

We present the first measurement of the production cross section of a W boson with a single charm quark (c) in pp collisions at sqrt(s)=1.96 TeV, using soft muon tagging of c jets. In a data sample of approximately 1.8 fb(-1), recorded with the Collider Detector at Fermilab II detector at the Fermilab Tevatron, we select events with W+1 or 2 jets. We use the charge correlation between the W and the muon from the semileptonic decay of a charm hadron to extract the Wc signal. We measure sigma Wc(PTc >20 GeV/c,|eta c|<1.5) x BR(W-->l nu)=9.8+/-3.2 pb, in agreement with theoretical expectations.     

Status and prospects of top-quark physics

The top quark is the heaviest elementary particle observed to date. Its large mass of about 173 GeV/c² makes the top quark act differently than other elementary fermions, as it decays before it hadronises, passing its spin information on to its decay products. In addition, the top quark plays an important role in higher order loop corrections to standard model processes, which makes the top-quark mass a crucial parameter for precision tests of the electroweak theory. The top quark is also a powerful probe for new phenomena beyond the standard model.During the time of discovery at the Tevatron in 1995 only a few properties of the top quark could be measured. In recent years, since the start of Tevatron Run II, the field of top-quark physics has changed and entered a precision era. This report summarises the latest measurements and studies of top-quark properties and gives prospects for future measurements at the Large Hadron Collider (LHC).     

Search for anomalous heavy-flavor quark production in association with W bosons

We search for anomalous production of heavy-flavor quark jets in association with W bosons at the Fermilab Tevatron pp Collider in final states in which the heavy-flavor quark content is enhanced by requiring at least one tagged jet in an event. Jets are tagged using one algorithm based on semileptonic decays of b/c hadrons, and another on their lifetimes. We compare e+jets (164 pb(-1)) and mu+jets (145 pb(-1)) channels collected with the D0 detector at sqrt[s]=1.96 TeV to expectations from the standard model and set upper limits on anomalous production of such events.     

Top-quark mass measurement from dilepton events at CDF II

We report a measurement of the top-quark mass using events collected by the CDF II detector from pp collisions at square root of s = 1.96 TeV at the Fermilab Tevatron. We calculate a likelihood function for the top-quark mass in events that are consistent with tt --> bl(-)nu(l)bl'+ nu'(l) decays. The likelihood is formed as the convolution of the leading-order matrix element and detector resolution functions. The joint likelihood is the product of likelihoods for each of 33 events collected in 340 pb(-1) of integrated luminosity, yielding a top-quark mass M(t) = 165.2 +/- 6.1(stat) +/- 3.4(syst) GeV/c2. This first application of a matrix-element technique to tt --> bl+ nu(l)bl'- nu(l') decays gives the most precise single measurement of M(t) in dilepton events. Combined with other CDF run II measurements using dilepton events, we measure M(t) = 167.9 +/- 5.2(stat) +/- 3.7(syst) GeV/c2.     

Top quark mass measurement in the lepton + jets channel using a matrix element method and in situ jet energy calibration

A precision measurement of the top quark mass m(t) is obtained using a sample of tt events from pp collisions at the Fermilab Tevatron with the CDF II detector. Selected events require an electron or muon, large missing transverse energy, and exactly four high-energy jets, at least one of which is tagged as coming from a b quark. A likelihood is calculated using a matrix element method with quasi-Monte Carlo integration taking into account finite detector resolution and jet mass effects. The event likelihood is a function of m(t) and a parameter Δ(JES) used to calibrate the jet energy scale in situ. Using a total of 1087 events in 5.6 fb(-1) of integrated luminosity, a value of m(t)=173.0 ± 1.2 GeV/c(2) is measured.