6,154 research outputs found
Mixed top-bottom squark production at the LHC
We calculate cross sections for mixed stop-sbottom pair production at the
LHC, analogous to single-top production, a weak process involving the
W-t(i)-b(j) vertex. While coupling-suppressed relative to QCD same-flavor
squark pair production, the signal is distinctive due to heavy-flavor tagging
along with a possible same-sign lepton pair in the final state. SUSY
backgrounds can often be suppressed many orders of magnitude by taking
advantage of distinct kinematic differences from the signal. Measuring the rate
of this process would add significant additional information to that gathered
from other SUSY processes. If the stop and sbottom mixings can be determined
elsewhere, stop-sbottom production would provide for a measurement of the weak
squark gauge coupling and super-CKM vertex factor.Comment: typo corrected, comment on W-associated channel added, version to
appear in PR
Photon State Tomography for Two-Mode Correlated Itinerant Microwave Fields
Continuous variable entanglement between two modes of a radiation field is
usually studied at optical frequencies. As an important step towards the
observation of entanglement between propagating microwave photons we
demonstrate the experimental state reconstruction of two field modes in the
microwave domain. In particular, we generate two-mode correlated states with a
Josephson parametric amplifier and detect all four quadrature components
simultaneously in a two-channel heterodyne setup using amplitude detectors.
Analyzing two-dimensional phase space histograms for all possible pairs of
quadratures allows us to determine the full covariance matrix and reconstruct
the four-dimensional Wigner function. We demonstrate strong correlations
between the quadrature amplitude noise in the two modes. Under ideal conditions
two-mode squeezing below the standard quantum limit should be observable in
future experiments.Comment: 4 pages, 4 figure
Direct Measurement of the Top Quark Charge at Hadron Colliders
We consider photon radiation in tbar-t events at the upgraded Fermilab
Tevatron and the CERN Large Hadron Collider (LHC) as a tool to measure the
electric charge of the top quark. We analyze the contributions of tbar-t-gamma
production and radiative top quark decays to p-p, pbar-p -> gamma l^+/- nu
bbar-b jj, assuming that both b-quarks are tagged. With 20~fb^{-1} at the
Tevatron, the possibility that the ``top quark'' discovered in Run I is
actually an exotic charge -4/3 quark can be ruled out at the 95% confidence
level. At the LHC, it will be possible to determine the charge of the top quark
with an accuracy of about 10%.Comment: Revtex, 24 pages, 2 tables, 9 figure
Perceived challenges in business development of smallholder dairy farmers in three Malawian regions
Dairy farmers face various challenges in developing their businesses. The current literature identifies several constraints towards a more efficient dairy sector that relate mostly to on-farm management practices. The available studies analyze constraints mostly from the objective viewpoint of the researcher, whereas very little is known about what farmers themselves perceive to be challenging. To better understand the farmers’ perspective and what they perceive to be challenging, and how these challenges differ across regions, this paper builds on a survey of 529 dairy farmers in Malawi. In the survey, respondents were asked in an open question to name their three main challenges. Based on the responses, a three-level coding scheme was elaborated. Data were then coded by two researchers to ensure reliability of coding. Codes were then used to calculate relative frequencies for the different challenges and to perform chi-square tests to check for regional differences in frequencies. Results suggest that farmers perceive low milk price and milk yield, animal health, availability of feedstock, and the costs for drugs as the main challenges. The analysis also revealed that the challenges vary strongly between the three main regions in the country – Blantyre (south), Lilongwe (central), and Mzuzu (north). The perceived challenges reflect the different production systems in the regions. In Blantyre, dairy farming is low in intensity, and farmers thus perceive inputs, in particular the availability of fodder, as well as outputs, in particular milk yields more frequently as a challenge than farmers in Lilongwe and Mzuzu. In contrast, dairy farming in Lilongwe is the most intense. Accordingly, farmers in Lilongwe perceive costs, in particular for inputs such as mash and concentrates as major constraints. Farmers in Mzuzu, which is a rather remote region, consider a lack of assistance, in particular concerning extension services significantly more challenging than the farmers in the other two regions do. Considering these insights, development work and extensions services may be able to increase outcomes in the dairy sector by targeting the regional challenges.Keywords: Challenges, dairy production, smallholders, Malawi, qualitative study, region
Probing Trilinear Gauge Boson Interactions via Single Electroweak Gauge Boson Production at the LHC
We analyze the potential of the CERN Large Hadron Collider (LHC) to study
anomalous trilinear vector-boson interactions W^+ W^- \gamma and W^+ W^- Z
through the single production of electroweak gauge bosons via the weak boson
fusion processes q q -> q q W (-> \ell^\pm \nu) and q q -> q q Z(-> \ell^+
\ell^-) with \ell = e or \mu. After a careful study of the standard model
backgrounds, we show that the single production of electroweak bosons at the
LHC can provide stringent tests on deviations of these vertices from the
standard model prediction. In particular, we show that single gauge boson
production exhibits a sensitivity to the couplings \Delta \kappa_{Z,\gamma}
similar to that attainable from the analysis of electroweak boson pair
production.Comment: 20 pages, 6 figure
The lightest Higgs boson production at photon colliders in the 2HDM-III
The branching ratios of the lightest CP-even Higgs boson , in the
framework of the General Two Higgs Doublet Model are calculated. Different
scenarios are presented taking into account constraints obtained in previous
works on the flavor changing neutral currents factors. Plausible scenarios with
flavour changing processes at tree level like and are
analyzed for relevant region of parameters. The loop-induced Higgs couplings to
photon pairs can be tested with a photon collider. The number of events of
as a resonance in photon colliders are calculated taking into account its
corresponding background signal in TESLA, CLIC and NLC.Comment: 1. Universidad Nacional de Colombia, Bogota, Colombia. (2)
Universidad de Valencia, Valencia, Spain. 21 pages, 5 figures, RevTe
Amplitude Zeros in Production
We demonstrate that the Standard Model amplitude for at the Born-level exhibits an approximate zero located at
at
high energies, where the () are the left-handed couplings
of the -boson to fermions and is the center of mass scattering
angle of the -boson. The approximate zero is the combined result of an exact
zero in the dominant helicity amplitudes and strong gauge
cancelations in the remaining amplitudes. For non-standard couplings
these cancelations no longer occur and the approximate amplitude zero is
eliminated.Comment: 11 pages, 4 figures submitted separately as uuencoded tar-ed
postscript files, FSU-HEP-940307, UCD-94-
Crystal Structure of the Sodium Cobaltate Deuterate Superconductor NaxCoO2o4xD2O (x=1/3)
Neutron and x-ray powder diffraction have been used to investigate the
crystal structures of a sample of the newly-discovered superconducting sodium
cobaltate deuterate compound with composition Na0.31(3)CoO2o1.25(2)D2O and its
anhydrous parent compound Na0.61(1)CoO2. The deuterate superconducting compound
is formed by coordinating four D2O molecules (two above and two below) to each
Na ion in a way that gives Na-O distances nearly equal to those in the parent
compound. One deuteron of the D2O molecule is hydrogen bonded to an oxygen atom
in the CoO2 plane and the oxygen atom and the second deuteron of each D2O
molecule lie approximately in a plane between the Na layer and the CoO2 layers.
This coordination of Na by four D2O molecules leads to ordering of the Na ions
and D2O molecules. The sample studied here, which has Tc=4.5 K, has a refined
composition of Na0.31(3)CoO2o1.25(2)D2O, in agreement with the expected 1:4
ratio of Na to D2O. These results show that the optimal superconducting
composition should be viewed as a specific hydrated compound, not a solid
solution of Na and D2O (H2O) in NaxCoO2oyD2O. Studies of physical properties
vs. Na or D2O composition should be viewed with caution until it is verified
that the compound remains in the same phase over the composition range of the
study.Comment: 22 pages, 8 figure
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