We search for Z' bosons in dielectron events produced in pp collisions at square root of s = 1.96 TeV, using 0.45 fb(-1) of data accumulated with the Collider Detector at Fermilab II detector at the ...Fermilab Tevatron. To identify the Z' --> e+ e- signal, both the dielectron invariant mass distribution and the angular distribution of the electron pair are used. No evidence of a signal is found, and 95% confidence level lower limits are set on the Z' mass for several models. Limits are also placed on the mass and gauge coupling of a generic Z', as well as on the contact-interaction mass scales for different helicity structure scenarios.
We present a measurement of the W-boson mass, M sub(W), using data corresponding to 2.2 fb super(-1) of integrated luminosity collected in pp collisions at radicals = 1.96 TeV with the CDF II ...detector at the Fermilab Tevatron. The selected sample of 470 126 W arrow right enu candidates and 624 708 W arrow right mu nu candidates yields the measurement M sub(W) = 80387 + or - 12 (stat) + or - 15 (syst) = 80387 + or - 19 MeV /c super(2). This is the most precise single measurement of the W-boson mass to date.
We present a precision measurement of the top-quark mass using the full sample of Tevatron √s = 1.96 TeV proton-antiproton collisions collected by the CDF II detector, corresponding to an integrated ...luminosity of 8.7 fb(-1). Using a sample of tt¯ candidate events decaying into the lepton+jets channel, we obtain distributions of the top-quark masses and the invariant mass of two jets from the W boson decays from data. We then compare these distributions to templates derived from signal and background samples to extract the top-quark mass and the energy scale of the calorimeter jets with in situ calibration. The likelihood fit of the templates from signal and background events to the data yields the single most-precise measurement of the top-quark mass, M(top)=172.85±0.71(stat)±0.85(syst) GeV/c(2).
We report the most restrictive direct limits on masses of fourth-generation down-type quarks b{'}, and quarklike composite fermions (B or T{5/3}), decaying promptly to tW{-/+}. We search for a ...significant excess of events with two same-charge leptons (e, mu), several hadronic jets, and missing transverse energy. An analysis of data from pp collisions with an integrated luminosity of 2.7 fb{-1} collected with the CDF II detector at Fermilab yields no evidence for such a signal, setting mass limits m{b{'}}, m{B}>338 GeV/c{2} and m{T{5/3}}>365 GeV/c{2} at 95% confidence level.
We present a combination of searches for the standard model Higgs boson using the full CDF run II data set, which corresponds to an integrated luminosity of 9.45-10.0 fb super(-1) collected from ...radicals = 1.96 TeV pp collisions at the Fermilab Tevatron. The searches consider Higgs boson production from gluon-gluon fusion, vector-boson fusion, and associated production with either a W or Z boson or a tt pair. Depending on the production mode, Higgs boson decays to W super(+)W super(-), ZZ, bb, tau super(+)tau super(-), and gamma gamma are examined. We search for a Higgs boson with masses (m sub(H)) in the range 90-200 GeV /c super(2). In the absence of a signal, we expect based on combined search sensitivity to exclude at the 95% credibility level the mass regions 90 < m sub(H) < 94 GeV /c super(2), 96 < m sub(H) < 106 GeV /c super(2), and 153 < m sub(H) < 175 GeV /c super(2). The observed exclusion regions are 90 < m sub(H) < 102 GeV /c super(2) and 149 < m sub(H) < 172 GeV /c super(2). A moderate excess of signal-like events relative to the background expectation at the level of 2.0 standard deviations is present in the data for the m sub(H) = 125 GeV /c super(2) search hypothesis. We also present interpretations of the data within the context of a fermiophobic model and an alternative standard model incorporating a fourth generation of fermions. Finally, for the hypothesis of a new particle with mass 125 GeV /c super(2), we constrain the coupling strengths of the new particle to W super(+ or -) bosons, Z bosons, and fermions.
We measure the inclusive forward-backward asymmetry of the charged-lepton pseudorapidities from top-quark pairs produced in proton-antiproton collisions and decaying to final states that contain two ...charged leptons (electrons or muons). The data are collected with the Collider Detector at Fermilab and correspond to an integrated luminosity of 9.1 fb(-1). We measure the leptonic forward-backward asymmetry, A(FB)(ℓ), to be 0.072 ± 0.060 and the leptonic pair forward-backward asymmetry, A(FB)(ℓℓ), to be 0.076 ± 0.082. The measured values can be compared with the standard model predictions of A(FB)(ℓ) = 0.038 ± 0.003 and A(FB)(ℓℓ) = 0.048 ± 0.004, respectively. Additionally, we combine the A(FB)(ℓ) result with a previous determination from a final state with a single lepton and hadronic jets and obtain A(FB)(ℓ) = 0.090(-0.026)(+0.028).
We present the final combination of CDF and D0 measurements of cross sections for single-top-quark production in proton-antiproton collisions at a center-of-mass energy of 1.96 TeV. The data ...correspond to total integrated luminosities of up to 9.7 fb(-1) per experiment. The t-channel cross section is measured to be sigma(t) = 2.25(-0.31)(+0.29) pb. We also present the combinations of the two-dimensional measurements of the s- vs t-channel cross section. In addition, we give the combination of the s + t channel cross section measurement resulting in sigma(s+t) = 3.30(-0.40)(+0.52) pb, without assuming the standard model value for the ratio sigma(s)/sigma(t). The resulting value of the magnitude of the top-to-bottom quark coupling is vertical bar V-tb vertical bar = 1.02(-0.05)(+0.06), corresponding to vertical bar V-tb vertical bar > 0.92 at the 95% C. L.
We perform a study of stellar flares for the 24,809 stars observed with 2 minute cadence during the first two months of the TESS mission. Flares may erode exoplanets' atmospheres and impact their ...habitability, but might also trigger the genesis of life around small stars. TESS provides a new sample of bright dwarf stars in our galactic neighborhood, collecting data for thousands of M dwarfs that might host habitable exoplanets. Here, we use an automated search for flares accompanied by visual inspection. Then, our public allesfitter code robustly selects the appropriate model for potentially complex flares via Bayesian evidence. We identify 1228 flaring stars, 673 of which are M dwarfs. Among 8695 flares in total, the largest superflare increased the stellar brightness by a factor of 16.1. Bolometric flare energies range from 1031.0 to 1036.9 erg, with a median of 1033.1 erg. Furthermore, we study the flare rate and energy as a function of stellar type and rotation period. We solidify past findings that fast rotating M dwarfs are the most likely to flare and that their flare amplitude is independent of the rotation period. Finally, we link our results to criteria for prebiotic chemistry, atmospheric loss through coronal mass ejections, and ozone sterilization. Four of our flaring M dwarfs host exoplanet candidates alerted on by TESS, for which we discuss how these effects can impact life. With upcoming TESS data releases, our flare analysis can be expanded to almost all bright small stars, aiding in defining criteria for exoplanet habitability.
We report the observation and measurement of the mass of the bottom, strange baryon Xi-_b through the decay chain Xi-_b --> J/psi Xi-, where J/psi --> mu+ mu-, Xi- --> Lambda pi+-, and Lambda --> p ...pi+-, and Lambda --> p pi+-. Evidence for observation is based on a signal whose probability of arising from the estimated background is 6.6 x 10-15, or 7.7 Gaussian standard deviations. The Xi-_b mass is measured to be 5792.9 +/- 2.5 (stat.) +/-1.7 (syst.) MeV/c2.
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