2,018 research outputs found
Fish Assemblages and Benthic Biota Associated with Natural Hard-Bottom Areas in the Northwestern Gulf of Mexico
We report new observations of fish and benthic invertebrate assemblages at shallow-water (\u3c35 m depth), hard-bottom sites in the northwestern Gulf of Mexico. The biota of these previously unstudied areas and of three high-relief features in deeper water was observed during May 1980 using a combination of diver reconnaissance, videotape surveys, still-camera photography, and collection of invertebrates for identification. The six hard-bottom sites in shallow water typically comprised, small, often patchy, rock outcrops, and the associated sessile invertebrates included hydroids, bryozoans, sponges, octocorals, and ahermatypic stony corals. Sea urchins and arrow crabs were the most common motile epifauna. Fish assemblages were typified by red snapper, Atlantic spadefish, blue runner gray triggerfish, sheepshead, and tomtate. Three deeper stations had many of the same fish and invertebrate species, but also possessed a more tropical assemblage including fire corals, antipatharians, spiny lobsters, and a variety of tropical fish species. Hermatypic corals characteristic of some large, offshore banks were not abundant at any of the sites.
Differences in the composition of fish assemblages between nearshore and deeper stations parallel those previously observed at petroleum platforms in the area. Shallow-water stations presumably experience a greater seasonal temperature range and lower absolute temperatures in winter and may be exposed to stresses such a lowered salinity and depleted oxygen levels due to their relative proximity to Mississippi River discharge. The fauna of these shallow hard-bottom sites has predominantly warm-temperate rather than tropical affinities
The Heavy Photon Search test detector
The Heavy Photon Search (HPS), an experiment to search for a hidden sector photon in fixed target electroproduction, is preparing for installation at the Thomas Jefferson National Accelerator Facility (JLab) in the Fall of 2014. As the first stage of this project, the HPS Test Run apparatus was constructed and operated in 2012 to demonstrate the experiment׳s technical feasibility and to confirm that the trigger rates and occupancies are as expected. This paper describes the HPS Test Run apparatus and readout electronics and its performance. In this setting, a heavy photon can be identified as a narrow peak in the e+e− invariant mass spectrum above the trident background or as a narrow invariant mass peak with a decay vertex displaced from the production target, so charged particle tracking and vertexing are needed for its detection. In the HPS Test Run, charged particles are measured with a compact forward silicon microstrip tracker inside a dipole magnet. Electromagnetic showers are detected in a PbW04 crystal calorimeter situated behind the magnet, and are used to trigger the experiment and identify electrons and positrons. Both detectors are placed close to the beam line and split top-bottom. This arrangement provides sensitivity to low-mass heavy photons, allows clear passage of the unscattered beam, and avoids the spray of degraded electrons coming from the target. The discrimination between prompt and displaced e+e− pairs requires the first layer of silicon sensors be placed only 10 cm downstream of the target. The expected signal is small, and the trident background huge, so the experiment requires very large statistics. Accordingly, the HPS Test Run utilizes high-rate readout and data acquisition electronics and a fast trigger to exploit the essentially 100% duty cycle of the CEBAF accelerator at JLab
Search for Neutral Higgs Bosons in Events with Multiple Bottom Quarks at the Tevatron
The combination of searches performed by the CDF and D0 collaborations at the
Fermilab Tevatron Collider for neutral Higgs bosons produced in association
with b quarks is reported. The data, corresponding to 2.6 fb-1 of integrated
luminosity at CDF and 5.2 fb-1 at D0, have been collected in final states
containing three or more b jets. Upper limits are set on the cross section
multiplied by the branching ratio varying between 44 pb and 0.7 pb in the Higgs
boson mass range 90 to 300 GeV, assuming production of a narrow scalar boson.
Significant enhancements to the production of Higgs bosons can be found in
theories beyond the standard model, for example in supersymmetry. The results
are interpreted as upper limits in the parameter space of the minimal
supersymmetric standard model in a benchmark scenario favoring this decay mode.Comment: 10 pages, 2 figure
Search for Kaluza-Klein Graviton Emission in Collisions at TeV using the Missing Energy Signature
We report on a search for direct Kaluza-Klein graviton production in a data
sample of 84 of \ppb collisions at = 1.8 TeV, recorded
by the Collider Detector at Fermilab. We investigate the final state of large
missing transverse energy and one or two high energy jets. We compare the data
with the predictions from a -dimensional Kaluza-Klein scenario in which
gravity becomes strong at the TeV scale. At 95% confidence level (C.L.) for
=2, 4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and 0.71
TeV, respectively.Comment: Submitted to PRL, 7 pages 4 figures/Revision includes 5 figure
Search for the standard model Higgs boson decaying to a pair in events with no charged leptons and large missing transverse energy using the full CDF data set
We report on a search for the standard model Higgs boson produced in
association with a vector boson in the full data set of proton-antiproton
collisions at TeV recorded by the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45 fb. We
consider events having no identified charged lepton, a transverse energy
imbalance, and two or three jets, of which at least one is consistent with
originating from the decay of a quark. We place 95% credibility level upper
limits on the production cross section times standard model branching fraction
for several mass hypotheses between 90 and . For a Higgs
boson mass of , the observed (expected) limit is 6.7
(3.6) times the standard model prediction.Comment: Accepted by Phys. Rev. Let
A Study of B0 -> J/psi K(*)0 pi+ pi- Decays with the Collider Detector at Fermilab
We report a study of the decays B0 -> J/psi K(*)0 pi+ pi-, which involve the
creation of a u u-bar or d d-bar quark pair in addition to a b-bar -> c-bar(c
s-bar) decay. The data sample consists of 110 1/pb of p p-bar collisions at
sqrt{s} = 1.8 TeV collected by the CDF detector at the Fermilab Tevatron
collider during 1992-1995. We measure the branching ratios to be BR(B0 -> J/psi
K*0 pi+ pi-) = (8.0 +- 2.2 +- 1.5) * 10^{-4} and BR(B0 -> J/psi K0 pi+ pi-) =
(1.1 +- 0.4 +- 0.2) * 10^{-3}. Contributions to these decays are seen from
psi(2S) K(*)0, J/psi K0 rho0, J/psi K*+ pi-, and J/psi K1(1270)
Measurement of the average time-integrated mixing probability of b-flavored hadrons produced at the Tevatron
We have measured the number of like-sign (LS) and opposite-sign (OS) lepton
pairs arising from double semileptonic decays of and -hadrons,
pair-produced at the Fermilab Tevatron collider. The data samples were
collected with the Collider Detector at Fermilab (CDF) during the 1992-1995
collider run by triggering on the existence of and candidates
in an event. The observed ratio of LS to OS dileptons leads to a measurement of
the average time-integrated mixing probability of all produced -flavored
hadrons which decay weakly, (stat.)
(syst.), that is significantly larger than the world average .Comment: 47 pages, 10 figures, 15 tables Submitted to Phys. Rev.
Search for the standard model Higgs boson decaying to a bb pair in events with one charged lepton and large missing transverse energy using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a W boson in sqrt(s) = 1.96 TeV p-pbar collision data
collected with the CDF II detector at the Tevatron corresponding to an
integrated luminosity of 9.45 fb-1. In events consistent with the decay of the
Higgs boson to a bottom-quark pair and the W boson to an electron or muon and a
neutrino, we set 95% credibility level upper limits on the WH production cross
section times the H->bb branching ratio as a function of Higgs boson mass. At a
Higgs boson mass of 125 GeV/c2 we observe (expect) a limit of 4.9 (2.8) times
the standard model value.Comment: Submitted to Phys. Rev. Lett (v2 contains clarifications suggested by
PRL
Search for the standard model Higgs boson decaying to a bb pair in events with two oppositely-charged leptons using the full CDF data set
We present a search for the standard model Higgs boson produced in
association with a Z boson in data collected with the CDF II detector at the
Tevatron, corresponding to an integrated luminosity of 9.45/fb. In events
consistent with the decay of the Higgs boson to a bottom-quark pair and the Z
boson to electron or muon pairs, we set 95% credibility level upper limits on
the ZH production cross section times the H -> bb branching ratio as a function
of Higgs boson mass. At a Higgs boson mass of 125 GeV/c^2 we observe (expect) a
limit of 7.1 (3.9) times the standard model value.Comment: To be submitted to Phys. Rev. Let
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