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.

Strong Evidence for ZZ Production in pp̅ Collisions at √s=1.96 TeV

We report the first measurement of the cross section for Z boson pair production at a hadron collider. This result is based on a data sample corresponding to 1.9 fb-1 of integrated luminosity from ppbar collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the Fermilab Tevatron. In the llll channel, we observe three ZZ candidates with an expected background of 0.096^{+0.092}_{-0.063} events. In the llnunu channel, we use a leading-order calculation of the relative ZZ and WW event probabilities to discriminate between signal and background. In the combination of llll and llnunu channels, we observe an excess of events with a probability of $5.1\times 10^{-6}$ to be due to the expected background. This corresponds to a significance of 4.4 standard deviations. The measured cross section is sigma(ppbar -> ZZ) = 1.4^{+0.7}_{-0.6} (stat.+syst.) pb, consistent with the standard model expectation.

First measurement of the ratio of branching fractions B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-)

This article presents the first measurement of the ratio of branching fractions B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-). Measurements in two control samples using the same technique B(B̅ 0→D+μ-ν̅ μ)/B(B̅ 0→D+π-) and B(B̅ 0→D*(2010)+μ-ν̅ μ)/B(B̅ 0→D*(2010)+π-) are also reported. The analysis uses data from an integrated luminosity of approximately 172  pb-1 of pp̅ collisions at √s=1.96  TeV, collected with the CDF II detector at the Fermilab Tevatron. The relative branching fractions are measured to be B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-)=16.6±3.0(stat)±1.0(syst)+2.6/-3.4(PDG)±0.3(EBR), B(B̅ 0→D+μ-ν̅ μ)/B(B̅ 0→D+π-)= 9.9±1.0(stat)±0.6(syst)±0.4(PDG)±0.5(EBR), and B(B̅ 0→D*(2010)+μ-ν̅ μ)/B(B̅ 0→D*(2010)+π-)=16.5±2.3(stat)± 0.6(syst)±0.5(PDG)±0.8(EBR). The uncertainties are from statistics (stat), internal systematics (syst), world averages of measurements published by the Particle Data Group or subsidiary measurements in this analysis (PDG), and unmeasured branching fractions estimated from theory (EBR), respectively. This article also presents measurements of the branching fractions of four new Λb0 semileptonic decays: Λb0→Λc(2595)+μ-ν̅ μ, Λb0→Λc(2625)+μ-ν̅ μ, Λb0→Σc(2455)0π+μ-ν̅ μ, and Λb0→Σc(2455)++π-μ-ν̅ μ, relative to the branching fraction of the Λb0→Λc+μ-ν̅ μ decay. Finally, the transverse-momentum distribution of Λb0 baryons produced in pp̅ collisions is measured and found to be significantly different from that of B̅ 0 mesons, which results in a modification in the production cross-section ratio σΛb0/σB̅ 0 with respect to the CDF I measurement.

First Observation of B̅ s0→Ds±K∓ and Measurement of the Ratio of Branching Fractions B(B̅ s0→Ds±K∓)/B(B̅ s0→Ds+π-)

A combined mass and particle identification fit is used to make the first observation of the decay B̅ s0→Ds±K∓ and measure the branching fraction of B̅ s0→Ds±K∓ relative to B̅ s0→Ds+π-. This analysis uses 1.2  fb-1 integrated luminosity of pp̅ collisions at √s=1.96  TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a B̅ s0→Ds±K∓ signal with a statistical significance of 8.1σ and measure B(B̅ s0→Ds±K∓)/B(B̅ s0→Ds+π-)=0.097±0.018(stat)±0.009(syst).

Search for the rare decays B+→μ+μ-K+, B0→μ+μ-K*(892)0, and Bs0→μ+μ-ϕ at CDF

We search for b→sμ+μ- transitions in B meson (B+, B0, or Bs0) decays with 924  pb-1 of pp̅ collisions at √s=1.96  TeV collected with the CDF II detector at the Fermilab Tevatron. We find excesses with significances of 4.5, 2.9, and 2.4 standard deviations in the B+→μ+μ-K+, B0→μ+μ-K*(892)0, and Bs0→μ+μ-ϕ decay modes, respectively. Using B→J/ψh (h=K+, K*(892)0, ϕ) decays as normalization channels, we report branching fractions for the previously observed B+ and B0 decays, B(B+→μ+μ-K+)=(0.59±0.15±0.04)×10-6, and B(B0→μ+μ-K*(892)0)=(0.81±0.30±0.10)×10-6, where the first uncertainty is statistical, and the second is systematic. We set an upper limit on the relative branching fraction B(Bs0→μ+μ-ϕ)/B(Bs0→J/ψϕ)<2.6(2.3)×10-3 at the 95(90)% confidence level, which is the most stringent to date.

Inhomogeneous Structures in Holographic Superfluids I

We begin an investigation of inhomogeneous structures in holographic superfluids. As a first example, we study domain wall like defects in the 3+1 dimensional Einstein-Maxwell-Higgs theory, which was developed as a dual model for a holographic superconductor. In [1], we reported on such "dark solitons" in holographic superfluids. In this work, we present an extensive numerical study of their properties, working in the probe limit. We construct dark solitons for two possible condensing operators, and find that both of them share common features with their standard superfluid counterparts. However, both are characterized by two distinct coherence length scales (one for order parameter, one for charge condensate). We study the relative charge depletion factor and find that solitons in the two different condensates have very distinct depletion characteristics. We also study quasiparticle excitations above the holographic superfluid, and find that the scale of the excitations is comparable to the soliton coherence length scales.

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 ttbar events from ppbar 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 DJES to calibrate the jet energy scale /in situ/. Using a total of 1087 events, a value of m_t = 173.0 +/- 1.2 GeV/c^2 is measured.

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.

Search for WW and WZ production in lepton plus jets final state at CDF

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 TeV ppbar collisions at the Fermilab Tevatron, using data corresponding to 1.2 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}* BR(W->lnu,W->jets)+ sigma_{WZ}*BR(W->lnu,Z->jets)

Search for High-Mass Resonances Decaying to Dimuons at CDF

We present a search for high-mass neutral resonances using dimuon data corresponding to an integrated luminosity of 2.3 fb$^{-1}$ collected in {$p\bar p$} collisions at {$\sqrt{s}$ = 1.96 TeV} by the CDF II detector at the Fermilab Tevatron. No significant excess above the standard model expectation is observed in the dimuon invariant-mass spectrum. We set 95% confidence level upper limits on $\sigma \cdot BR (p \bar{p} \to X \to \mu \bar{\mu})$, where $X$ is a boson with spin 0, 1, or 2. Using these cross section limits, we determine lower mass limits on sneutrinos in R-parity-violating supersymmetric models, $Z'$ bosons, and Kaluza-Klein gravitons in the Randall-Sundrum model.

Search for Anomalous Production of Events with a Photon, Jet, b-quark Jet, and Missing Transverse Energy

We present a signature-based search for anomalous production of events containing a photon, two jets, of which at least one is identified as originating from a b quark, and missing transverse energy. The search uses data corresponding to 2.0/fb of integrated luminosity from p-pbar collisions at a center-of-mass energy of sqrt(s)=1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. From 6,697,466 events with a photon candidate with transverse energy ET> 25 GeV, we find 617 events with missing transverse energy > 25 GeV and two or more jets with ET> 15 GeV, at least one identified as originating from a b quark, versus an expectation of 607+- 113 events. Increasing the requirement on missing transverse energy to 50 GeV, we find 28 events versus an expectation of 30+-11 events. We find no indications of non-standard-model phenomena.

Precision Measurement of the X(3872) Mass in J/ψπ+π- Decays

We present an analysis of the mass of the X(3872) reconstructed via its decay to J/psi pi+ pi- using 2.4 fb^-1 of integrated luminosity from ppbar collisions at sqrt(s) = 1.96 TeV, collected with the CDF II detector at the Fermilab Tevatron. The possible existence of two nearby mass states is investigated. Within the limits of our experimental resolution the data are consistent with a single state, and having no evidence for two states we set upper limits on the mass difference between two hypothetical states for different assumed ratios of contributions to the observed peak. For equal contributions, the 95% confidence level upper limit on the mass difference is 3.6 MeV/c^2. Under the single-state model the X(3872) mass is measured to be 3871.61 +- 0.16 (stat) +- 0.19 (syst) MeV/c^2, which is the most precise determination to date.

First simultaneous measurement of the top quark mass in the lepton+jets and dilepton channels at CDF

We present a measurement of the mass of the top quark using data corresponding to an integrated luminosity of 1.9fb^-1 of ppbar collisions collected at sqrt{s}=1.96 TeV with the CDF II detector at Fermilab's Tevatron. This is the first measurement of the top quark mass using top-antitop pair candidate events in the lepton + jets and dilepton decay channels simultaneously. We reconstruct two observables in each channel and use a non-parametric kernel density estimation technique to derive two-dimensional probability density functions from simulated signal and background samples. The observables are the top quark mass and the invariant mass of two jets from the W decay in the lepton + jets channel, and the top quark mass and the scalar sum of transverse energy of the event in the dilepton channel. We perform a simultaneous fit for the top quark mass and the jet energy scale, which is constrained in situ by the hadronic W boson mass. Using 332 lepton + jets candidate events and 144 dilepton candidate events, we measure the top quark mass to be mtop=171.9 +/- 1.7 (stat. + JES) +/- 1.1 (syst.) GeV/c^2 = 171.9 +/- 2.0 GeV/c^2.

Measurement of the tt̅ cross section in pp̅ collisions at √s=1.96 TeV using dilepton events with a lepton plus track selection

This paper reports a measurement of the cross section for the pair production of top quarks in ppbar collisions at sqrt(s) = 1.96 TeV at the Fermilab Tevatron. The data was collected from the CDF II detector in a set of runs with a total integrated luminosity of 1.1 fb^{-1}. The cross section is measured in the dilepton channel, the subset of ttbar events in which both top quarks decay through t -> Wb -> l nu b where l = e, mu, or tau. The lepton pair is reconstructed as one identified electron or muon and one isolated track. The use of an isolated track to identify the second lepton increases the ttbar acceptance, particularly for the case in which one W decays as W -> tau nu. The purity of the sample may be further improved at the cost of a reduction in the number of signal events, by requiring an identified b-jet. We present the results of measurements performed with and without the request of an identified b-jet. The former is the first published CDF result for which a b-jet requirement is added to the dilepton selection. In the CDF data there are 129 pretag lepton + track candidate events, of which 69 are tagged. With the tagging information, the sample is divided into tagged and untagged sub-samples, and a combined cross section is calculated by maximizing a likelihood. The result is sigma_{ttbar} = 9.6 +/- 1.2 (stat.) -0.5 +0.6 (sys.) +/- 0.6 (lum.) pb, assuming a branching ratio of BR(W -> ell nu) = 10.8% and a top mass of m_t = 175 GeV/c^2.