815 research outputs found
Successive Combination Jet Algorithm For Hadron Collisions
Jet finding algorithms, as they are used in and hadron collisions,
are reviewed and compared. It is suggested that a successive combination style
algorithm, similar to that used in physics, might be useful also in
hadron collisions, where cone style algorithms have been used previously.Comment: 18 pages plus four uuencoded postscript figures, REVTEX 3.0,
CERN-TH.6860/9
Dijet Production at Large Rapidity Intervals
We examine dijet production at large rapidity intervals at Tevatron energies,
by using the theory of Lipatov and collaborators which resums the leading
powers of the rapidity interval. We analyze the growth of the Mueller-Navelet
-factor in this context and find it to be negligible. However, we do find a
considerable enhancement of jet production at large transverse momenta. In
addition, we show that the correlation in transverse momentum and azimuthal
angle of the tagging jets fades away as the rapidity interval is increased.Comment: 12 pages, preprint DESY 93-139, SCIPP 93/3
Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)
We present a next-to-leading order QCD calculation for single-inclusive
high-p_T jet production in longitudinally polarized pp collisions within the
``small-cone'' approximation. The fully analytical expressions obtained for the
underlying partonic hard-scattering cross sections greatly facilitate the
analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet}
for this process in terms of the unknown polarization of gluons in the nucleon.
We simultaneously rederive the corresponding QCD corrections to unpolarized
scattering and confirm the results existing in the literature. We also
numerically compare to results obtained with Monte-Carlo methods and assess the
range of validity of the ``small-cone'' approximation for the kinematics
relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure
FastJet user manual
FastJet is a C++ package that provides a broad range of jet finding and
analysis tools. It includes efficient native implementations of all widely used
2-to-1 sequential recombination jet algorithms for pp and e+e- collisions, as
well as access to 3rd party jet algorithms through a plugin mechanism,
including all currently used cone algorithms. FastJet also provides means to
facilitate the manipulation of jet substructure, including some common boosted
heavy-object taggers, as well as tools for estimation of pileup and
underlying-event noise levels, determination of jet areas and subtraction or
suppression of noise in jets.Comment: 69 pages. FastJet 3 is available from http://fastjet.fr
Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity
It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.Comment: 15 pages LaTeX, 2 eps figures include
Jets in Hadron-Hadron Collisions
In this article, we review some of the complexities of jet algorithms and of
the resultant comparisons of data to theory. We review the extensive experience
with jet measurements at the Tevatron, the extrapolation of this acquired
wisdom to the LHC and the differences between the Tevatron and LHC
environments. We also describe a framework (SpartyJet) for the convenient
comparison of results using different jet algorithms.Comment: 68 pages, 54 figure
Analytic Structure of Three-Mass Triangle Coefficients
``Three-mass triangles'' are a class of integral functions appearing in
one-loop gauge theory amplitudes. We discuss how the complex analytic
properties and singularity structures of these amplitudes can be combined with
generalised unitarity techniques to produce compact expressions for three-mass
triangle coefficients. We present formulae for the N=1 contributions to the
n-point NMHV amplitude.Comment: 22 pages; v3: NMHV n=point expression added. 7 point expression
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Diverse pollination systems of the twin-spurred orchid genus Satyrium in African grasslands
The large terrestrial orchid genus Satyrium underwent evolutionary radiations in the Cape floral region and the grasslands of southern and eastern Africa. These radiations were accompanied by tremendous diversification of the unusual twin-spurred flowers that characterize the genus, but pollination data required to interpret these patterns of floral evolution have been lacking for grassland species in the genus. Here we document pollinators, nectar properties, and levels of pollination success for 11 grassland Satyrium species in southern and south-central Africa. Pollinators of these species include bees, beetles, butterflies, hawkmoths, noctuid moths, long-proboscid flies, and sunbirds. Most species appear to be specialized for pollination by one functional pollinator group. Long-proboscid fly pollination systems are reported for the first time in Satyrium (in S. macrophyllum and a high-altitude form of S. neglectum). Floral morphology, especially spur length and rostellum structure, differs markedly among plants with different pollinators, while nectar volume, concentration, and sugar composition are fairly uniform across species. Most taxa exhibited high levels of pollination success (>50% of flowers pollinated), a trend that can be attributed to the presence of nectar in the twin spurs
BFKL versus O(\alpha_s^3) Corrections to Large-rapidity Dijet Production
We examine dijet production at large rapidity intervals at Tevatron energies
by comparing an exact calculation with the BFKL
approximation, which resums the leading powers of the rapidity interval to
all orders in . We analyze the dependence of the exact calculation on the jet cone-size as a function of , and use
this cross section to define an ``effective rapidity'' which reduces
the error that the large- approximation induces on the kinematics. Using
in the BFKL resummation, we reexamine jet production at large
transverse momenta and the transverse momentum decorrelation of the tagging
jets. We find less dramatic, but still significant, effects than found
previously using the large- approximation.Comment: 23 pages (6 uu-compressed encapsulated PS figures appended), DESY
94-114, SCIPP 94/1
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