Measurements of the top-quark mass using charged particle tracking

We present three measurements of the top-quark mass in the lepton plus jets channel with approximately 1.9 fb-1 of integrated luminosity collected with the CDF II detector using quantities with minimal dependence on the jet energy scale. One measurement exploits the transverse decay length of b-tagged jets to determine a top-quark mass of 166.9+9.5-8.5 (stat) +/- 2.9 (syst) GeV/c2, and another the transverse momentum of electrons and muons from W-boson decays to determine a top-quark mass of 173.5+8.8-8.9 (stat) +/- 3.8 (syst) GeV/c2. These quantities are combined in a third, simultaneous mass measurement to determine a top-quark mass of 170.7 +/- 6.3 (stat) +/- 2.6 (syst) GeV/c2.

On the ignition and extinction problems in forced convection systems

In this paper the problem of ignition and extinction has been formulated for the flow of a compressible fluid with Prandtl and Schmidt numbers taken as unity. In particular, the problems of (i) a jet impinging on a wall of combustible material and (ii) the opposed jet diffusion flame have been studied. In the wall jet case, three approximations in the momentum equation namely, (i) potential flow, (ii) viscous flow, (ii) viscous incompressible with k = 1 and (iii) Lees' approximation (taking pressure gradient terms zero) are studied. It is shown that the predictions of the mass flow rates at extinction are not very sensitive to the approximations made in the momentum equation. The effects of varying the wall temperature in the case (i) and the jet temperature in the case (ii) on the extinction speeds have been studied. The effects of varying the activation energy and the free stream oxidant concentration in case (ii), have also been investigated.

Search for the associated production of the standard-model Higgs boson in the all-hadronic channel

"We report on a search for the standard-model Higgs boson in pp collisions at s=1.96 TeV using an integrated luminosity of 2.0 fb(-1). We look for production of the Higgs boson decaying to a pair of bottom quarks in association with a vector boson V (W or Z) decaying to quarks, resulting in a four-jet final state. Two of the jets are required to have secondary vertices consistent with B-hadron decays. We set the first 95% confidence level upper limit on the VH production cross section with V(-> qq/qq('))H(-> bb) decay for Higgs boson masses of 100-150 GeV/c(2) using data from run II at the Fermilab Tevatron. For m(H)=120 GeV/c(2), we exclude cross sections larger than 38 times the standard-model prediction."

Exclusion of an Exotic Top Quark with -4/3 Electric Charge Using Soft Lepton Tagging

We present a measurement of the electric charge of the top quark using $\ppbar$ collisions corresponding to an integrated luminosity of 2.7~fb$^{-1}$ at the CDF II detector. We reconstruct $\ttbar$ events in the lepton+jets final state and use kinematic information to determine which $b$-jet is associated with the leptonically- or hadronically-decaying $t$-quark. Soft lepton taggers are used to determine the $b$-jet flavor. Along with the charge of the $W$ boson decay lepton, this information permits the reconstruction of the top quark's electric charge. Out of 45 reconstructed events with $2.4\pm0.8$ expected background events, 29 are reconstructed as $\ttbar$ with the standard model $+$2/3 charge, whereas 16 are reconstructed as $\ttbar$ with an exotic $-4/3$ charge. This is consistent with the standard model and excludes the exotic scenario at 95\% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose.

Direct Top-Quark Width Measurement at CDF

We present a measurement of the top-quark width using $t\bar{t}$ events produced in $p\bar{p}$ collisions at Fermilab's Tevatron collider and collected by the CDF II detector. In the mode where the top quark decays to a $W$ boson and a bottom quark, we select events in which one $W$ decays leptonically and the other hadronically~(lepton + jets channel) . 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 $W$ boson that decays hadronically are reconstructed for each event and compared with templates of different top-quark widths~($\Gamma_t$) and deviations from nominal jet energy scale~($\Delta_{JES}$) to perform a simultaneous fit for both parameters, where $\Delta_{JES}$ is used for the {\it 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 $\Gamma_t $

Measurement of the top quark mass and pp̅ →tt̅ cross section in the all-hadronic mode with the CDF II detector

We present a measurement of the top quark mass and of the top-antitop pair production cross section using p-pbar data collected with the CDFII detector at the Tevatron Collider at the Fermi National Accelerator Laboratory and corresponding to an integrated luminosity of 2.9 fb-1. We select events with six or more jets satisfying a number of kinematical requirements imposed by means of a neural network algorithm. At least one of these jets must originate from a b quark, as identified by the reconstruction of a secondary vertex inside the jet. The mass measurement is based on a likelihood fit incorporating reconstructed mass distributions representative of signal and background, where the absolute jet energy scale (JES) is measured simultaneously with the top quark mass. The measurement yields a value of 174.8 +- 2.4(stat+JES) ^{+1.2}_{-1.0}(syst) GeV/c^2, where the uncertainty from the absolute jet energy scale is evaluated together with the statistical uncertainty. The procedure measures also the amount of signal from which we derive a cross section, sigma_{ttbar} = 7.2 +- 0.5(stat) +- 1.0 (syst) +- 0.4 (lum) pb, for the measured values of top quark mass and JES.

Search for single top quark production in pp̅ collisions at √s=1.96 TeV in the missing transverse energy plus jets topology

We report a search for single top quark production with the CDF II detector using 2.1 fb-1 of integrated luminosity of pbar p collisions at sqrt{s}=1.96 TeV. The data selected consist of events characterized by large energy imbalance in the transverse plane and hadronic jets, and no identified electrons and muons, so the sample is enriched in W -> tau nu decays. In order to suppress backgrounds, additional kinematic and topological requirements are imposed through a neural network, and at least one of the jets must be identified as a b-quark jet. We measure an excess of signal-like events in agreement with the standard model prediction, but inconsistent with a model without single top quark production by 2.1 standard deviations (sigma), with a median expected sensitivity of 1.4 sigma. Assuming a top quark mass of 175 GeV/c2 and ascribing the excess to single top quark production, the cross section is measured to be 4.9+2.5-2.2(stat+syst)pb, consistent with measurements performed in independent datasets and with the standard model prediction.

Search for the associated production of the standard-model Higgs boson in the all-hadronic channel

"We report on a search for the standard-model Higgs boson in pp collisions at s=1.96 TeV using an integrated luminosity of 2.0 fb(-1). We look for production of the Higgs boson decaying to a pair of bottom quarks in association with a vector boson V (W or Z) decaying to quarks, resulting in a four-jet final state. Two of the jets are required to have secondary vertices consistent with B-hadron decays. We set the first 95% confidence level upper limit on the VH production cross section with V(-> qq/qq('))H(-> bb) decay for Higgs boson masses of 100-150 GeV/c(2) using data from run II at the Fermilab Tevatron. For m(H)=120 GeV/c(2), we exclude cross sections larger than 38 times the standard-model prediction."

Measurement of the Ratio σtt̅ /σZ/γ*→ll and Precise Extraction of the tt̅ Cross Section

We report a measurement of the ratio of the tt̅ to Z/γ* production cross sections in √s=1.96  TeV pp̅ collisions using data corresponding to an integrated luminosity of up to 4.6  fb-1, collected by the CDF II detector. The tt̅ cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/γ*→ll cross section predicted by the standard model, the extracted tt̅ cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result σtt̅ =7.70±0.52  pb, for a top-quark mass of 172.5  GeV/c2.

Measurement of the kT Distribution of Particles in Jets Produced in pp̅ Collisions at √s=1.96 TeV

We present a measurement of the transverse momentum with respect to the jet axis (kt) of particles in jets produced in pp̅ collisions at √s=1.96  TeV. Results are obtained for charged particles in a cone of 0.5 radians around the jet axis in events with dijet invariant masses between 66 and 737  GeV/c2. The experimental data are compared to theoretical predictions obtained for fragmentation partons within the framework of resummed perturbative QCD using the modified leading log and next-to-modified leading log approximations. The comparison shows that trends in data are successfully described by the theoretical predictions, indicating that the perturbative QCD stage of jet fragmentation is dominant in shaping basic jet characteristics.

Measurement of the Ratio σtt̅ /σZ/γ*→ll and Precise Extraction of the tt̅ Cross Section

We report a measurement of the ratio of the tt̅ to Z/γ* production cross sections in √s=1.96  TeV pp̅ collisions using data corresponding to an integrated luminosity of up to 4.6  fb-1, collected by the CDF II detector. The tt̅ cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/γ*→ll cross section predicted by the standard model, the extracted tt̅ cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result σtt̅ =7.70±0.52  pb, for a top-quark mass of 172.5  GeV/c2.

Search for the Higgs Boson Using Neural Networks in Events with Missing Energy and b-Quark Jets in pp̅ Collisions at √s=1.96 TeV

We report on a search for the standard model Higgs boson produced in association with a $W$ or $Z$ boson in $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV recorded by the CDF II experiment at the Tevatron in a data sample corresponding to an integrated luminosity of 2.1 fb$^{-1}$. We consider events which have no identified charged leptons, an imbalance in transverse momentum, and two or three jets where at least one jet is consistent with originating from the decay of a $b$ hadron. We find good agreement between data and predictions. We place 95% confidence level upper limits on the production cross section for several Higgs boson masses ranging from 110$\gevm$ to 150$\gevm$. For a mass of 115$\gevm$ the observed (expected) limit is 6.9 (5.6) times the standard model prediction.

Measurement of the Ratio σtt̅ /σZ/γ*→ll and Precise Extraction of the tt̅ Cross Section

We report a measurement of the ratio of the top-antitop to Z/gamma* production cross sections in sqrt(s) = 1.96 TeV proton-antiproton collisions using data corresponding to an integrated luminosity of up to 4.6 fb-1, collected by the CDF II detector. The top-antitop cross section ratio is measured using two complementary methods, a b-jet tagging measurement and a topological approach. By multiplying the ratios by the well-known theoretical Z/gamma*->ll cross section, the extracted top-antitop cross sections are effectively insensitive to the uncertainty on luminosity. A best linear unbiased estimate is used to combine both measurements with the result sigma_(top-antitop) = 7.70 +/- 0.52 pb, for a top-quark mass of 172.5 GeV/c^2.

Search for the supersymmetric partner of the top quark in pp̅ collisions at √s=1.96 TeV

We present a search for the lightest supersymmetric partner of the top quark in proton-antiproton collisions at a center-of-mass energy √s=1.96  TeV. This search was conducted within the framework of the R parity conserving minimal supersymmetric extension of the standard model, assuming the stop decays dominantly to a lepton, a sneutrino, and a bottom quark. We searched for events with two oppositely-charged leptons, at least one jet, and missing transverse energy in a data sample corresponding to an integrated luminosity of 1  fb-1 collected by the Collider Detector at Fermilab experiment. No significant evidence of a stop quark signal was found. Exclusion limits at 95% confidence level in the stop quark versus sneutrino mass plane are set. Stop quark masses up to 180  GeV/c2 are excluded for sneutrino masses around 45  GeV/c2, and sneutrino masses up to 116  GeV/c2 are excluded for stop quark masses around 150  GeV/c2.

Top quark mass measurement in the lepton plus jets channel using a modified matrix element method

We report a measurement of the top quark mass, m_t, obtained from ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron using the CDF II detector. We analyze a sample corresponding to an integrated luminosity of 1.9 fb^-1. We select events with an electron or muon, large missing transverse energy, and exactly four high-energy jets in the central region of the detector, at least one of which is tagged as coming from a b quark. We calculate a signal likelihood using a matrix element integration method, with effective propagators to take into account assumptions on event kinematics. Our event likelihood is a function of m_t and a parameter JES that determines /in situ/ the calibration of the jet energies. We use a neural network discriminant to distinguish signal from background events. We also apply a cut on the peak value of each event likelihood curve to reduce the contribution of background and badly reconstructed events. Using the 318 events that pass all selection criteria, we find m_t = 172.7 +/- 1.8 (stat. + JES) +/- 1.2 (syst.) GeV/c^2.