Plant evolution can mediate negative effects from honey bees on wild pollinators

Pollinators are introduced to agroecosystems to provide pollination services. Introductions of managed pollinators often promote ecosystem services, but it remains largely unknown whether they also affect evolutionary mutualisms between wild pollinators and plants. Here, we developed a model to assess effects of managed honey bees on mutualisms between plants and wild pollinators. Our model tracked how interactions among wild pollinators and honey bees affected pollinator and plant populations. We show that when managed honey bees have a competitive advantage over wild pollinators, or a greater carrying capacity, the honey bees displace the wild pollinator. This leads to reduced plant density because plants benefit less by visits from honey bees than wild pollinators that coevolved with the plants. As wild pollinators are displaced, plants evolve by increasing investment in traits that are attractive for honey bees but not wild pollinators. This evolutionary switch promotes wild pollinator displacement. However, higher mutualism investment costs by the plant to the honey bee can promote pollinator coexistence. Our results show plant evolution can promote displacement of wild pollinators by managed honey bees, while limited plant evolution may lead to pollinator coexistence. More broadly, effects of honey bees on wild pollinators in agroecosystems, and effects on ecosystem services, may depend on the capacity of plant populations to evolve

Search for Narrow Diphoton Resonances and for gamma-gamma+W/Z Signatures in p\bar p Collisions at sqrt(s)=1.8 TeV

We present results of searches for diphoton resonances produced both inclusively and also in association with a vector boson (W or Z) using 100 pb^{-1} of p\bar p collisions using the CDF detector. We set upper limits on the product of cross section times branching ratio for both p\bar p\to\gamma\gamma + X and p\bar p\to\gamma\gamma + W/Z. Comparing the inclusive production to the expectations from heavy sgoldstinos we derive limits on the supersymmetry-breaking scale sqrt{F} in the TeV range, depending on the sgoldstino mass and the choice of other parameters. Also, using a NLO prediction for the associated production of a Higgs boson with a W or Z boson, we set an upper limit on the branching ratio for H\to\gamma\gamma. Finally, we set a lower limit on the mass of a `bosophilic' Higgs boson (e.g. one which couples only to \gamma, W, and Z$ bosons with standard model couplings) of 82 GeV/c^2 at 95% confidence level.Comment: 30 pages, 11 figure

Measurement of the Strong Coupling Constant from Inclusive Jet Production at the Tevatron pˉp\bar pp Collider

We report a measurement of the strong coupling constant, $\alpha_s(M_Z)$, extracted from inclusive jet production in $p\bar{p}$ collisions at $\sqrt{s}=$1800 GeV. The QCD prediction for the evolution of $\alpha_s$ with jet transverse energy $E_T$ is tested over the range 40<$E_T$<450 GeV using $E_T$ for the renormalization scale. The data show good agreement with QCD in the region below 250 GeV. In the text we discuss the data-theory comparison in the region from 250 to 450 GeV. The value of $\alpha_s$ at the mass of the $Z^0$ boson averaged over the range 40<$E_T$<250 GeV is found to be $\alpha_s(M_{Z})= 0.1178 \pm 0.0001{(\rm stat)}^{+0.0081}_{-0.0095}{\rm (exp. syst)}$. The associated theoretical uncertainties are mainly due to the choice of renormalization scale (^{+6%}_{-4%}) and input parton distribution functions (5%).Comment: 7 pages, 3 figures, using RevTeX. Submitted to Physical Review Letter

Search for the Supersymmetric Partner of the Top-Quark in ppˉp \bar{p} Collisions at s=1.8TeV\sqrt{s} = 1.8 {\rm TeV}

We report on a search for the supersymmetric partner of the top quark (stop) produced in $t \bar{t}$ events using $110 {\rm pb}^{-1}$ of $p \bar{p}$ collisions at $\sqrt{s} = 1.8 {\rm TeV}$ recorded with the Collider Detector at Fermilab. In the case of a light stop squark, the decay of the top quark into stop plus the lightest supersymmetric particle (LSP) could have a significant branching ratio. The observed events are consistent with Standard Model $t \bar{t}$ production and decay. Hence, we set limits on the branching ratio of the top quark decaying into stop plus LSP, excluding branching ratios above 45% for a LSP mass up to 40 {\rm GeV/c}$^{2}$.Comment: 11 pages, 4 figure

Measurement of the Associated γ+μ±\gamma + \mu^\pm Production Cross Section in ppˉp \bar p Collisions at s=1.8\sqrt{s} = 1.8 TeV

We present the first measurement of associated direct photon + muon production in hadronic collisions, from a sample of 1.8 TeV $p \bar p$ collisions recorded with the Collider Detector at Fermilab. Quantum chromodynamics (QCD) predicts that these events are primarily from the Compton scattering process $cg \to c\gamma$, with the final state charm quark producing a muon. Hence this measurement is sensitive to the charm quark content of the proton. The measured cross section of $29\pm 9 pb^{-1}$ is compared to a leading-order QCD parton shower model as well as a next-to-leading-order QCD calculation.Comment: 12 pages, 4 figures Added more detailed description of muon background estimat

Measurement of the Helicity of W Bosons in Top Quark Decays

We use the transverse momentum spectrum of leptons in the decay chain t-->bW with W-->l nu to measure the helicity of the W bosons in the top quark rest frame. Our measurement uses a ttbar sample isolated in 106 +/- 4 inverse picobarns of data collected in ppbar collisions at sqrt(s)=1.8 TeV with the CDF detector at the Fermilab Tevatron. Assuming a standard V--A weak decay, we find that the fraction of W's with zero helicity in the top rest frame is F_0 = 0.91 +/- 0.37 (stat) +/- 0.13 (syst), consistent with the standard model prediction of F_0=0.70 for a top mass of 175 GeV/c**2.Comment: Submitted to PRL. 8 pages, 2 figure

Measurement of Rapidity Distribution for High Mass Drell-Yan ee Pairs at CDF

We report on the first measurement of the rapidity distribution dsigma/dy over nearly the entire kinematic region of rapidity for e^+e^- pairs in the Z-boson region of 66116 GeV/c^2. The data sample consists of 108 pb^{-1} of ppbar collisions at \sqrt{s}=1.8 TeV taken by the Collider Detector at Fermilab during 1992--1995. The total cross section in the $Z$-boson region is measured to be 252 +- 11 pb. The measured total cross section and d\sigma/dy are compared with quantum chromodynamics calculations in leading and higher orders.Comment: 7 pages, 3 figures. Submitted to Physical Review Letter

Search for a Fourth-Generation Quark More Massive than the Z0 Boson in ppbar Collisions at sqrt(s) = 1.8 TeV

We present the results of a search for pair production of a fourth-generation charge -1/3 quark (b') in sqrt(s)=1.8 TeV ppbar collisions using 88 pb^(-1) of data obtained with the Collider Detector at Fermilab. We assume that both quarks decay via the flavor-changing neutral current process b' -> bZ and that the b' mass is greater than m_Z + m_b. We studied the decay mode b'b'bar -> ZZ b bbar where one Z0 decays into e^+e^- or mu^+ mu^- and the other decays hadronically, giving a signature of two leptons plus jets. An upper limit on the cross section of ppbar -> b'b'bar times [BR (b' -> bZ)]^2 is established as a function of the b' mass. We exclude at 95% confidence level a b' quark with mass between 100 and 199 GeV/c^2 for BR(b' -> bZ) = 100%.Comment: 12 pages, 2 figures, submitted to Phys. Rev. Letters on 9/12/9

Measurement of the Decay Amplitudes of B0 --> J/psi K* and B0s --> J/psi phi Decays

A full angular analysis has been performed for the pseudo-scalar to vector-vector decays, B0 --> J/psi K* and B_s --> J/psi phi, to determine the amplitudes for decays with parity-even longitudinal and transverse polarization and parity-odd transverse polarization. The measurements are based on 190 B0 candidates and 40 B_s candidates collected from a data set corresponding to 89 inverse pb of pbarp collisions at root(s) = 1.8 TeV at the Fermilab Tevatron. In both decays the decay amplitude for longitudinal polarization dominates and the parity-odd amplitude is found to be small.Comment: 7 pages, 3 figures, 1 tabl

Limits on Gravitino Production and New Processes with Large Missing Transverse Energy in p-pbar Collisions at sqrt(s)=1.8 TeV

Events collected by the Collider Detector at Fermilab (CDF) with an energetic jet plus large missing transverse energy can be used to search for physics beyond the Standard Model. We see no deviations from the expected background and set upper limits on the production of new processes. We consider in addition the production of light gravitinos within the framework of the Gauge Mediated Supersymmetry Breaking models and set a limit at 95% confidence level on the breaking scale sqrt(F) >= 217 GeV, which excludes gravitino masses smaller than 1.1x10^-5 eV/c^2.Comment: 13 pages, 4 figures. Submitted to Physical Review Letter