Search

We report the results of a search for the anomalous production of a massive particle decaying to four electrons via two $Z^0$ bosons in $1.1{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF II detector at Fermilab. We employ optimized electron identification criteria to maximize acceptance and efficiency. We estimate the backgrounds in the invariant mass range $500–1000\mathrm{GeV}/c^2$ to be $0.028\pm 0.009(\mathrm{stat})\pm 0.011(\mathrm{syst})$ events. We observe zero events in this search region. Assuming a Randall-Sundrum graviton production model, we set 95% C.L. limits on $\sigma \times \mathrm{BF}(G\to Z^0{Z}^0)<4–6\mathrm{pb}$, depending on the graviton mass.

A measurement of the $t\overline{t}$ production cross section in $p\overline{p}$ collisions at $\sqrt{\mathrm{s}}=1.96\mathrm{TeV}$ using events with two leptons, missing transverse energy, and jets is reported. The data were collected with the CDF II detector. The result in a data sample corresponding to an integrated luminosity $2.8{\mathrm{fb}}^{-1}$ is ${\sigma }_{t\overline{t}}=6.27\pm 0.73(\mathrm{stat})\pm 0.63(\mathrm{syst})\pm 0.39(\mathrm{lum})\mathrm{pb}.$ for an assumed top mass of $175\mathrm{GeV}/c^2$.

A search for new physics using three-lepton (trilepton) data collected with the CDF II detector and corresponding to an integrated luminosity of 976 ${\mathrm{pb}}^{-1}$ is presented. The standard model predicts a low rate of trilepton events, which makes some supersymmetric processes, such as chargino-neutralino production, measurable in this channel. The $\mu \mu +\ell$ signature is investigated, where $\ell$ is an electron or a muon, with the additional requirement of large missing transverse energy. In this analysis, the lepton transverse momenta with respect to the beam direction ($p_T$) are as low as $5\mathrm{GeV}/c$, a selection that improves the sensitivity to particles that are light as well as to ones that result in leptonically decaying tau leptons. At the same time, this low-$p_T$ selection presents additional challenges due to the non-negligible heavy-quark background at low lepton momenta. This background is measured with an innovative technique using experimental data. Several dimuon and trilepton control regions are investigated, and good agreement between experimental results and standard-model predictions is observed. In the signal region, we observe one three-muon event and expect $0.4\pm 0.1\mu \mu +\ell$ events from standard-model processes.

We present a measurement of the $WW+WZ$ production cross section observed in a final state consisting of an identified electron or muon, two jets, and missing transverse energy. The measurement is carried out in a data sample corresponding to up to $4.6{\mathrm{fb}}^{-1}$ of integrated luminosity at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the CDF II detector. Matrix element calculations are used to separate the diboson signal from the large backgrounds. The $WW+WZ$ cross section is measured to be $17.4\pm 3.3\mathrm{pb}$ in agreement with standard model predictions. A fit to the dijet invariant mass spectrum yields a compatible cross section measurement.

We present a measurement of the top-quark pair-production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ using a data sample corresponding to $1.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the Collider Detector at Fermilab. We reconstruct $t\overline{t}$ events in the $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ channel, consisting of $e\nu +\mathrm{\text{jets}}$ and $\mu \nu +\mathrm{\text{jets}}$ final states. The dominant background is the production of $W$ bosons in association with multiple jets. To suppress this background, we identify electrons from the semileptonic decay of heavy-flavor jets (“soft electron tags”). From a sample of 2196 candidate events, we obtain 120 tagged events with a background expectation of $51\pm 3$ events, corresponding to a cross section of ${\sigma }_{t\overline{t}}=7.8\pm 2.4(\mathrm{stat})\pm 1.6(\mathrm{syst})\pm 0.5(\mathrm{lumi})\mathrm{pb}$. We assume a top-quark mass of $175\mathrm{GeV}/c^2$. This is the first measurement of the $t\overline{t}$ cross section with soft electron tags in run II of the Tevatron.

We present a measurement of the top-quark mass in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ which uses events with an inclusive signature of missing transverse energy and jets. The event selection is sensitive to $t\overline{t}\to W^{+}b{W}^{-}\overline{b}\to l\nu bq{q}^{\prime }\overline{b}$ independent of the lepton flavor and results in a large acceptance for $W\to \tau \nu$ decays. All-hadronic $t\overline{t}$ decays and events with identified electrons or muons are vetoed to provide a statistically independent sample with respect to all previous measurements. The top-quark mass is inferred from the distribution of the scalar sum of all jet transverse energies and the missing transverse energy. Using $311{\mathrm{pb}}^{-1}$ of integrated luminosity recorded by the Collider Detector at Fermilab, we measure a top-quark mass $m_t={172.3}_{-9.6}^{+10.8}(\mathrm{stat})\pm 10.8(\mathrm{syst})\mathrm{GeV}/c^2$. While the uncertainty on $m_t$ is larger than that of other measurements, the result is statistically uncorrelated with those of other methods and thus can help to reduce the overall $m_t$ uncertainty when combined with other existing measurements.

We searched for scalar bottom quarks in $156{\mathrm{pb}}^{-1}$ of $\overline{p}p$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the Collider Detector at Fermilab II experiment at the Tevatron. Scalar bottom quarks can be produced from gluino decays in $R$-parity conserving models of supersymmetry when the mass of the gluino exceeds that of the scalar bottom quark. Then, a scalar bottom quark can decay into a bottom quark and a neutralino. To search for this scenario, we investigated events with large missing transverse energy and at least three jets, two or more of which were identified as containing a secondary vertex from the hadronization of $b$ quarks. We found four candidate events, where $2.6\pm 0.7$ are expected from standard model processes, and placed 95% confidence level lower limits on gluino and scalar bottom quark masses of up to 280 and $240\mathrm{GeV}/c^2$, respectively.

We present a search for $WW$ and $WZ$ production in final states that contain a charged lepton (electron or muon) and at least two jets, produced in $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collisions at the Fermilab Tevatron, using data corresponding to $1.2{\mathrm{fb}}^{-1}$ of integrated luminosity collected with the CDF II detector. Diboson production in this decay channel has yet to be observed at hadron colliders due to the large single $W$ plus jets background. An artificial neural network has been developed to increase signal sensitivity, as compared with an event selection based on conventional cuts. We set a 95% confidence level upper limit of ${\sigma }_{WW}\times \mathrm{BR}(W\to \ell {\nu }_{\ell },W\to \mathrm{\text{jets}})+{\sigma }_{WZ}\times \mathrm{BR}(W\to \ell {\nu }_{\ell },Z\to \mathrm{\text{jets}})<2.88\mathrm{pb}$, which is consistent with the standard model next-to-leading-order cross section calculation for this decay channel of $2.09\pm 0.12\mathrm{pb}$.

We have performed a search for new particles which decay to two photons using $1.2{\mathrm{fb}}^{-1}$ of integrated luminosity from $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected using the CDF II detector at the Fermilab Tevatron. We find the diphoton mass spectrum to be in agreement with the standard model expectation, and set limits on the cross section times branching ratio for the Randall-Sundrum graviton, as a function of diphoton mass. We subsequently derive lower limits for the graviton mass of $230\mathrm{GeV}/c^2$ and $850\mathrm{GeV}/c^2$, at the 95% confidence level, for coupling parameters ($k/{\overline{M}}_{\mathrm{Pl}}$) of 0.01 and 0.1, respectively.

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of $b$ hadrons. We use $\sim 1{\mathrm{fb}}^{-1}$ integrated luminosity of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the Collider Detector at Fermilab II experiment at the Tevatron. We find 268 (16) single (double) $b$-tagged candidate events, where $248\pm 43$ ($14.4\pm 2.7$) are expected from standard model background processes. We observe no significant excess over the expected background and thus set 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 to $140\mathrm{GeV}/c^2$. For a mass of $115\mathrm{GeV}/c^2$, the observed (expected) limit is 20.4 (14.2) times the standard model prediction.

This Letter reports a measurement of the cross section of prompt isolated photon pair production in $p\overline{p}$ collisions at a total energy $\sqrt{s}=1.96\mathrm{TeV}$ using data of $5.36{\mathrm{fb}}^{-1}$ integrated luminosity collected with the CDF II detector at the Fermilab Tevatron. The measured cross section, differential in basic kinematic variables, is compared with three perturbative QCD predictions, a leading order parton shower calculation and two next-to-leading order calculations. The next-to-leading order calculations reproduce most aspects of the data. By including photon radiation from quarks before and after hard scattering, the parton shower prediction becomes competitive with the next-to-leading order predictions.

We present results of a search for anomalous production of events containing a charged lepton ($\ell$, either $e$ or $\mu$) and a photon ($\gamma$), both with high transverse momentum, accompanied by additional signatures $X$, including missing transverse energy (${\mathrm{E̸}}_T$) and additional leptons and photons. We use the same selection criteria as in a previous CDF search but with a substantially larger data set, $305\mathrm{p}{\mathrm{b}}^{-1}$, a $p\overline{p}$ collision energy of 1.96 TeV, and the CDF II detector. We find 42 $\ell \gamma {\mathrm{E̸}}_T$ events versus an expectation of $37.3\pm 5.4$ events. We observe 31 $\ell \ell \gamma +X$ events versus an expectation of $23.0\pm 2.7$ events. We find no events similar to the run I $ee\gamma \gamma {\mathrm{E̸}}_T$ event.

We present a search for the standard model Higgs boson produced in association with a $W^{\pm }$ boson. This search uses data corresponding to an integrated luminosity of $7.5{\mathrm{fb}}^{-1}$ collected by the CDF detector at the Tevatron. We select $WH\to \ell \nu b\overline{b}$ candidate events with two jets, large missing transverse energy, and exactly one charged lepton. We further require that at least one jet be identified to originate from a bottom quark. Discrimination between the signal and the large background is achieved through the use of a Bayesian artificial neural network. The number of tagged events and their distributions are consistent with the standard model expectations. We observe no evidence for a Higgs boson signal and set 95% C.L. upper limits on the $WH$ production cross section times the branching ratio to decay to $b\overline{b}$ pairs, $\sigma (p\overline{p}\to W^{\pm }H)\times \mathcal{B}(H\to b\overline{b})$, relative to the rate predicted by the standard model. For the Higgs boson mass range of $100$ to $150\mathrm{GeV}/c^2$ we set observed (expected) upper limits from 1.34 (1.83) to 38.8 (23.4). For $115\mathrm{GeV}/c^2$ the upper limit is 3.64 (2.78). The combination of the present search with an independent analysis that selects events with three jets yields more stringent limits ranging from 1.12 (1.79) to 34.4 (21.6) in the same mass range. For 115 and $125\mathrm{GeV}/c^2$ the upper limits are 2.65 (2.60) and 4.36 (3.69), respectively.

A search for a manifestly exotic $S=-2$ baryon state decaying to ${\mathit{\Xi }}^{-}{\pi }^{-}$, and its neutral partner decaying to ${\mathit{\Xi }}^{-}{\pi }^{+}$, has been performed using $220{\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the Collider Detector at Fermilab. The ${\mathit{\Xi }}^{-}$ trajectories were measured in a silicon tracker before their decay, resulting in a sample with low background and excellent position resolution. No evidence was found for $S=-2$ pentaquark candidates in the invariant mass range of $1600–2100\mathrm{MeV}/c^2$. Upper limits on the product of pentaquark production cross section times its branching fraction to ${\mathit{\Xi }}^{-}{\pi }^{+,-}$, relative to the cross section of the well-established $\mathit{\Xi }(1530)$ resonance, are presented for neutral and doubly negative candidates with $p_T>2\mathrm{GeV}/c$ and $|y|<1$ as a function of pentaquark mass. At $1862\mathrm{MeV}/c^2$, these upper limits for neutral and doubly negative final states were found to be 3.2% and 1.7% at the 90% confidence level, respectively.

We measure the branching fraction of the top quark to longitudinally and right-handed polarized $W$ bosons, $F_0$ and $F_{+}$, using approximately $200{\mathrm{pb}}^{-1}$ of $\overline{p}p$ collisions collected by the CDF II detector. We analyze two quantities sensitive to the $W$ helicity: the invariant mass of the charged lepton and the bottom-quark jet in the decay $t\to Wb\to \ell \nu b$ (where $\ell =e$ or $\mu$), and the transverse momentum of the charged lepton. Constrained fits yield $F_0={0.74}_{-0.34}^{+0.22}$, and $F_{+}<0.27$ at the 95% confidence level. These measurements are consistent with the standard model predictions.

We present a measurement of the ratio of the $t\overline{t}$ production cross section via gluon-gluon fusion to the total $t\overline{t}$ production cross section in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ at the Tevatron. Using a data sample with an integrated luminosity of $955{\mathrm{pb}}^{-1}$ recorded by the CDF II detector at Fermilab, we select events based on the $t\overline{t}$ decay to $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$. Using an artificial neural network technique we discriminate between $t\overline{t}$ events produced via $q\overline{q}$ annihilation and $gg$ fusion, and find $G_f=\sigma (gg\to t\overline{t})/\sigma (p\overline{p}\to t\overline{t})<0.33$ at the 68% confidence level. This result is combined with a previous measurement to obtain the most stringent measurement of this quantity by CDF to date, $G_f={0.07}_{-0.07}^{+0.15}$.

We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay $t\to Zc$ using a technique employing ratios of $W$ and $Z$ production, measured in $p\overline{p}$ data corresponding to an integrated luminosity of $1.52{\mathrm{fb}}^{-1}$. The analysis uses a comparison of two decay chains, $p\overline{p}\to t\overline{t}\to WbWb\to \ell \nu bjjb$ and $p\overline{p}\to t\overline{t}\to ZcWb\to \ell \ell cjjb$, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multiyear data set using another ratio of $W$ and $Z$ production, in this case the observed ratio of inclusive production of $W$ to $Z$ bosons. To improve the discrimination against standard model backgrounds to top-quark decays, we calculate the top-quark mass for each event with two leptons and four jets assuming it is a $t\overline{t}$ event with one of the top quarks decaying to $Zc$. For additional background discrimination we require at least one jet to be identified as originating from a $b$ quark. No significant signal is found and we set an upper limit on the FCNC branching ratio $\mathrm{Br}(t\to Zc)$ using a likelihood constructed from the $\ell \ell cjjb$ top-quark mass distribution and the number of $\ell \nu bjjb$ events. Limits are set as a function of the helicity of the $Z$ boson produced in the FCNC decay. For 100% longitudinally-polarized $Z$ bosons we find limits of 8.3% and 9.3% (95% C.L.) depending on the assumptions regarding the theoretical top-quark pair production cross section.

We present the results of a search for new physics in the jets plus missing transverse energy data sample collected from $368{\mathrm{pb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded by the Collider Detector at Fermilab. We compare the number of events observed in the data with a data-based estimate of the standard model backgrounds contributing to this signature. We observe no significant excess of events, and we interpret this null result in terms of lower limits on the fundamental Planck scale for a large extra dimensions scenario.

We report a detailed study of the temperature and magnetic-field dependence of free energy, magnetization, and specific heat of superconducting ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ in the critical fluctuation region near ${\mathit{H}}_{\mathit{c}2}$(T) line. Our approach is to apply the recently developed nonperturbative scaling theory (Tešanović et al.) in high fields to describe the reversible magnetization data taken on a c-axis-oriented superconducting ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{10}$ thin tape. We find good agreement on some of the superconducting parameters obtained in the present study with those derived by applying the Ginzburg-Landau theory to our reversible magnetization data taken outside the critical fluctuation region.