906 research outputs found
Global QCD Analysis and the CTEQ Parton Distributions
The CTEQ program for the determination of parton distributions through a
global QCD analysis of data for various hard scattering processes is fully
described. A new set of distributions, CTEQ3, incorporating several new types
of data is reported and compared to the two previous sets of CTEQ
distributions. Comparison with current data is discussed in some detail. The
remaining uncertainties in the parton distributions and methods to further
reduce them are assessed. Comparisons with the results of other global analyses
are also presented.Comment: (Change in Latex style only: 2up style removed since many don't have
it.) 35 pages, 23 figures separately submitted as uuencoded compressed
ps-file; Michigan State Report # MSU-HEP/41024 and CTEQ 40
Elastic pp-scattering at \sqrt s=7 TeV with the genuine Orear regime and the dip
The unitarity condition unambigously requires the Orear region to appear in
between the diffraction cone at low transferred momenta and hard parton
scattering regime at high transferred momenta in hadron elastic scattering. It
originates from rescattering of the diffraction cone processes. It is shown
that such region has been observed in the differential cross section of the
elastic pp-scattering at \sqrt s=7 TeV. The Orear region is described by
exponential decrease with the scattering angle and imposed on it damped
oscillations. They explain the steepening at the end of the diffraction cone as
well as the dip and the subsequent maximum observed in TOTEM data. The failure
of several models to describe the data in this region can be understood as
improper account of the unitarity condition. It is shown that the real part of
the amplitude can be as large as the imaginary part in this region. The overlap
function is calculated and shown to be small outside the diffraction peak. Its
negative sign there indicates the important role of phases in the amplitudes of
inelastic processes.Comment: 5 pages, 2 figures, revtex
Global Study of Electron-Quark Contact Interactions
We perform a global fit of data relevant to contact interactions,
including deep inelastic scattering at high from ZEUS and H1, atomic
physics parity violation in Cesium from JILA, polarized on nuclei
scattering experiments at SLAC, Mainz and Bates, Drell-Yan production at the
Tevatron, the total hadronic cross section at LEP, and
neutrino-nucleon scattering from CCFR. With only the new HERA data, the
presence of contact interactions improves the fit compared to the Standard
Model. When other data sets are included, the size of the contact contributions
is reduced and the overall fit represents no real improvement over the Standard
Model.Comment: 26 pages (now single-spaced), Revtex, 2 eps figures, uses epsf.sty.
Some clarifications, minor corrections, 2 new references, also 3 new tables
which present 95% CL bounds on the contact interaction scales Lambd
A Precise Measurement of the Weak Mixing Angle in Neutrino-Nucleon Scattering
We report a precise measurement of the weak mixing angle from the ratio of
neutral current to charged current inclusive cross-sections in deep-inelastic
neutrino-nucleon scattering. The data were gathered at the CCFR neutrino
detector in the Fermilab quadrupole-triplet neutrino beam, with neutrino
energies up to 600 GeV. Using the on-shell definition, , we obtain .Comment: 10 pages, Nevis Preprint #1498 (Submitted to Phys. Rev. Lett.
Neutrino Interactions In Oscillation Experiments
We calculate neutrino induced cross-sections relevant for oscillation
experiments, including the -lepton threshold for quasi-elastic, resonance
and deep inelastic scattering. In addition to threshold effects, we include
nuclear corrections for heavy targets which are moderate for quasi-elastic and
large for single pion production. Nuclear effects for deep inelastic reactions
are small. We present cross sections together with their nuclear corrections
for various channels which are useful for interpreting the experimental results
and for determining parameters of the neutrino sector..Comment: 24 pages, 18 figure
Secondary antiprotons and propagation of cosmic rays in the Galaxy and heliosphere
High-energy collisions of cosmic-ray nuclei with interstellar gas are
believed to be the mechanism producing the majority of cosmic ray antiprotons.
Due to the kinematics of the process they are created with a nonzero momentum;
the characteristic spectral shape with a maximum at ~2 GeV and a sharp decrease
towards lower energies makes antiprotons a unique probe of models for particle
propagation in the Galaxy and modulation in the heliosphere. On the other hand,
accurate calculation of the secondary antiproton flux provides a ``background''
for searches for exotic signals from the annihilation of supersymmetric
particles and primordial black hole evaporation. Recently new data with large
statistics on both low and high energy antiproton fluxes have become available
which allow such tests to be performed. We use our propagation code GALPROP to
calculate interstellar cosmic-ray propagation for a variety of models. We show
that there is no simple model capable of accurately describing the whole
variety of data: boron/carbon and sub-iron/iron ratios, spectra of protons,
helium, antiprotons, positrons, electrons, and diffuse gamma rays. We find that
only a model with a break in the diffusion coefficient plus convection can
reproduce measurements of cosmic-ray species, and the reproduction of primaries
(p, He) can be further improved by introducing a break in the primary injection
spectra. For our best-fit model we make predictions of proton and antiproton
fluxes near the Earth for different modulation levels and magnetic polarity
using a steady-state drift model of propagation in the heliosphere.Comment: Many Updates, 20 pages, 15 ps-figures, emulateapj5.sty. To be
published in ApJ v.564 January 10, 2002 issue. More details can be found at
http://www.gamma.mpe-garching.mpg.de/~aws/aws.htm
Inherited biotic protection in a Neotropical pioneer plant
Chelonanthus alatus is a bat-pollinated, pioneer Gentianaceae that clusters in patches where still-standing, dried-out stems are interspersed among live individuals. Flowers bear circum-floral nectaries (CFNs) that are attractive to ants, and seed dispersal is both barochorous and anemochorous. Although, in this study, live individuals never sheltered ant colonies, dried-out hollow stems - that can remain standing for 2 years - did. Workers from species nesting in dried-out stems as well as from ground-nesting species exploited the CFNs of live C. alatus individuals in the same patches during the daytime, but were absent at night (when bat pollination occurs) on 60.5% of the plants. By visiting the CFNs, the ants indirectly protect the flowers - but not the plant foliage - from herbivorous insects. We show that this protection is provided mostly by species nesting in dried-out stems, predominantly Pseudomyrmex gracilis. That dried-out stems remain standing for years and are regularly replaced results in an opportunistic, but stable association where colonies are sheltered by one generation of dead C. alatus while the live individuals nearby, belonging to the next generation, provide them with nectar; in turn, the ants protect their flowers from herbivores. We suggest that the investment in wood by C. alatus individuals permitting stillstanding, dried-out stems to shelter ant colonies constitutes an extended phenotype because foraging workers protect the flowers of live individuals in the same patch. Also, through this process these dried-out stems indirectly favor the reproduction (and so the fitness) of the next generation including both their own offspring and that of their siblings, alladding up to a potential case of inclusive fitness in plants
Leptoproduction of Heavy Quarks II -- A Unified QCD Formulation of Charged and Neutral Current Processes from Fixed-target to Collider Energies
A unified QCD formulation of leptoproduction of massive quarks in charged
current and neutral current processes is described. This involves adopting
consistent factorization and renormalization schemes which encompass both
vector-boson-gluon-fusion (flavor creation) and
vector-boson-massive-quark-scattering (flavor excitation) production
mechanisms. It provides a framework which is valid from the threshold for
producing the massive quark (where gluon-fusion is dominant) to the very high
energy regime when the typical energy scale \mu is much larger than the quark
mass m_Q (where the quark-scattering should be prevalent). This approach
effectively resums all large logarithms of the type (alpha_s(mu)
log(mu^2/m_Q^2)^n which limit the validity of existing fixed-order calculations
to the region mu ~ O(m_Q). We show that the (massive) quark-scattering
contribution (after subtraction of overlaps) is important in most parts of the
(x, Q) plane except near the threshold region. We demonstrate that the
factorization scale dependence of the structure functions calculated in this
approach is substantially less than those obtained in the fixed-order
calculations, as one would expect from a more consistent formulation.Comment: LaTeX format, 29 pages, 11 figures. Revised to make auto-TeX-abl
Impact of Atomic Parity Violation Measurements on Precision Electroweak Physics
The impact of atomic parity violation experiments on determination of the
weak mixing parameter and the Peskin-Takeuchi parameters
and is reassessed in the light of recent electroweak measurements at LEP,
SLAC, and Fermilab. Since the weak charge provides unique information on
, its determination with a factor of four better accuracy than present
levels can have a noticeable effect on global fits. However, the measurement of
for two different isotopes provides primarily information on
. To specify this quantity to an accuracy of ,
comparable to that now provided by other electroweak experiments, one would
have to determine in cesium to about 0.1\% of its value, with
comparable demands for other nuclei. The relative merits of absolute
measurements of and isotope ratios for discovering effects of new gauge
bosons are noted briefly.Comment: 11 pages, latex, 1 uuencoded figure sent separatel
Can lepton flavor violating interactions explain the atmospheric neutrino problem?
We investigate whether flavor changing neutrino interactions (FCNIs) can be
sufficiently large to provide a viable solution to the atmospheric neutrino
problem. Effective operators induced by heavy boson exchange that allow for
flavor changing neutrino scattering off quarks or electrons are related by an
rotation to operators that induce anomalous tau decays. Since
violation is small for New Physics at or above the weak scale, one
can use the upper bounds on lepton flavor violating tau decays or on lepton
universality violation to put severe, model-independent bounds on the relevant
non-standard neutrino interactions. Also -induced flavor changing neutral
currents, due to heavy singlet neutrinos, are too small to be relevant for the
atmospheric neutrino anomaly. We conclude that the FCNI solution to the
atmospheric neutrino problem is ruled out.Comment: 16 pages, no figures, Late
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