Search for the Higgs Boson Produced in Association with Z→ℓ+ℓ- in pp̅ Collisions at √s=1.96 TeV

We present a search for the Higgs boson in the process $q\bar{q} \to ZH \to \ell^+\ell^- b\bar{b}$. The analysis uses an integrated luminosity of 1 fb$^{-1}$ of $p\bar{p}$ collisions produced at $\sqrt{s} =$ 1.96 TeV and accumulated by the upgraded Collider Detector at Fermilab (CDF II). We employ artificial neural networks both to correct jets mismeasured in the calorimeter, and to distinguish the signal kinematic distributions from those of the background. We see no evidence for Higgs boson production, and set 95% CL upper limits on $\sigma_{ZH} \cdot {\cal B}(H \to b\bar{b}$), ranging from 1.5 pb to 1.2 pb for a Higgs boson mass ($m_H$) of 110 to 150 GeV/$c^2$.

First Measurement of the b-Jet Cross Section in Events with a W Boson in pp̅ Collisions at √s=1.96 TeV

The cross section for jets from b quarks produced with a W boson has been measured in ppbar collision data from 1.9/fb of integrated luminosity recorded by the CDF II detector at the Tevatron. The W+b-jets process poses a significant background in measurements of top quark production and prominent searches for the Higgs boson. We measure a b-jet cross section of 2.74 +- 0.27(stat.) +- 0.42(syst.) pb in association with a single flavor of leptonic W boson decay over a limited kinematic phase space. This measured result cannot be accommodated in several available theoretical predictions.

Measurement of W-Boson Polarization in Top-Quark Decay in pp̅ Collisions at √s=1.96 TeV

We report measurements of the polarization of W bosons from top-quark decays using 2.7 fb^-1 of ppbar collisions collected by the CDF II detector. Assuming a top-quark mass of 175 GeV/c^2, three measurements are performed. A simultaneous measurement of the fraction of longitudinal (f_0) and right-handed (f_+) W bosons yields the model-independent results f_0 = 0.88 \pm 0.11 (stat) \pm 0.06 (syst) and f_+ = -0.15 \pm 0.07 (stat) \pm 0.06 (syst) with a correlation coefficient of -0.59. A measurement of f_0 (f_+) constraining f_+ (f_0) to its standard model value of 0.0 (0.7) yields f_0 = 0.70 \pm 0.07 (stat) \pm 0.04 (syst) (f_+ = -0.01 \pm 0.02 (stat) \pm 0.05 (syst)). All these results are consistent with standard model expectations.

Measurement of the top pair production cross section in the dilepton decay channel in pp̅ collisions at √s=1.96 TeV

A measurement of the $\ttbar$ production cross section in $\ppbar$ collisions at $\sqrt{{\rm s}}$ = 1.96 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 fb$^{-1}$ is: $\sigma_{\ttbar}$ = 6.27 $\pm$ 0.73(stat) $\pm$ 0.63(syst) $\pm$ 0.39(lum) pb. for an assumed top mass of 175 GeV/$c^{2}$.

Search for the Production of Scalar Bottom Quarks in pp̅ Collisions at √s=1.96 TeV

We report on a search for direct scalar bottom quark (sbottom) pair production in $p \bar{p}$ collisions at $\sqrt{s}=1.96$~TeV, in events with large missing transverse energy and two jets of hadrons in the final state, where at least one of the jets is required to be identified as originating from a $b$ quark. The study uses a CDF Run~II data sample corresponding to 2.65~fb${}^{-1}$ of integrated luminosity. The data are in agreement with the standard model. In an R-parity conserving minimal supersymmetric scenario, and assuming that the sbottom decays exclusively into a bottom quark and a neutralino, 95$\%$ confidence-level upper limits on the sbottom pair production cross section of 0.1~pb are obtained. For neutralino masses below 70~GeV/$c^2$, sbottom masses up to 230~GeV/$c^2$ are excluded at 95$\%$ confidence level.

Measurement of the Λb0 Lifetime in Λb0→Λc+π- Decays in pp̅ Collisions at √s=1.96 TeV

We report a measurement of the lifetime of the Lambda_b baryon in decays to the Lambda_C+ pi- final state in a sample corresponding to 1.1 fb^-1 collected in p-pbar collisions at sqrt(s) = 1.96 TeV by the CDF II detector at the Tevatron collider. Using a sample of about 3000 fully reconstructed Lambda_b events we measure tau(Lambda_b) = 1.401 +- 0.046 (stat) +- 0.035 (syst) ps (corresponding to c.tau(Lambda_b) = 420.1 +- 13.7 (stat) +- 10.6 (syst) um, where c is the speed of light). The ratio of this result and the world average B^0 lifetime yields tau(Lambda_b)/tau(B^0) = 0.918 +- 0.038 (stat and syst), in good agreement with recent theoretical predictions.

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 Pair Production of Supersymmetric Top Quarks in Dilepton Events from pp̅ Collisions at √s=1.96 TeV

We present the results of a search for pair production of the supersymmetric partner of the top quark (the stop quark $\tilde{t}_{1}$) decaying to a $b$-quark and a chargino $\chargino$ with a subsequent $\chargino$ decay into a neutralino $\neutralino$, lepton $\ell$, and neutrino $\nu$. Using a data sample corresponding to 2.7 fb$^{-1}$ of integrated luminosity of $p\bar{p}$ collisions at $\sqrt{s} = 1.96$ TeV collected by the CDF II detector, we reconstruct the mass of candidate stop events and fit the observed mass spectrum to a combination of standard model processes and stop quark signal. We find no evidence for $\pairstop$ production and set 95% C.L. limits on the masses of the stop quark and the neutralino for several values of the chargino mass and the branching ratio ${\cal B}(\chargino\to\neutralino\ell^{\pm}\nu)$.

Search for R-Parity Violating Decays of Sneutrinos to eμ, μτ, and eτ Pairs in pp̅ Collisions at √s=1.96 TeV

We present a search for tau sneutrino production using the Tevatron ppbar collision data collected with the CDF II detector and corresponding to an integrated luminosity of 1 fb^-1. We focus on the scenarios predicted by the R-parity violating (RPV) supersymmetric models in which tau sneutrinos decay to two charged leptons of different flavor. With the data consistent with the standard model expectations, we set the upper limits on sigma(ppbar -> tau sneutrino)*BR(tau sneutrino ->emu,mutau,etau) and use these results to constrain the RPV couplings as a function of tau sneutrino mass.

Search for WW and WZ Resonances Decaying to Electron, Missing ET, and Two Jets in pp̅ Collisions at √s=1.96 TeV.

Using data from 2.9  fb-1 of integrated luminosity collected with the CDF II detector at the Tevatron, we search for resonances decaying into a pair of on-shell gauge bosons, WW or WZ, where one W decays into an electron and a neutrino, and the other boson decays into two jets. We observed no statistically significant excess above the expected standard model background, and we set cross section limits at 95% confidence level on G* (Randall-Sundrum graviton), Z′, and W′ bosons. By comparing these limits to theoretical cross sections, mass exclusion regions for the three particles are derived. The mass exclusion regions for Z′ and W′ are further evaluated as a function of their gauge coupling strength.

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.

Search for WW and WZ Resonances Decaying to Electron, Missing ET, and Two Jets in pp̅ Collisions at √s=1.96 TeV.

Using data from 2.9/fb of integrated luminosity collected with the CDF II detector at the Tevatron, we search for resonances decaying into a pair of on-shell gauge bosons, WW or WZ, where one W decays into an electron and a neutrino, and the other boson decays into two jets. We observed no statistically significant excess above the expected standard model background, and we set cross section limits at 95% confidence level on G*(Randall-Sundrum graviton), Z', and W' bosons. By comparing these limits to theoretical cross sections, mass exclusion regions for the three particles are derived. The mass exclusion regions for Z' and W' are further evaluated as a function of their gauge coupling strength.

Measurement of the tt̅ production cross section in pp̅ collisions at √s=1.96 TeV using soft electron b-tagging

We present a measurement of the top quark pair production cross section in ppbar collisions at sqrt(s)=1.96 TeV using a data sample corresponding to 1.7/fb of integrated luminosity collected with the Collider Detector at Fermilab. We reconstruct ttbar events in the lepton+jets channel. 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. We measure a production cross section of 7.8 +/- 2.4 (stat) +/- 1.6 (syst) +/- 0.5 (lumi) pb. This is the first measurement of the top pair production cross section with soft electron tags in Run II of the Tevatron.