4,052 research outputs found
Scheme and Scale Dependence of Charm Production in Neutrino Scattering
We discuss some theoretical uncertainties in the calculation of the cross
section for charm production in charged current deep inelastic neutrino
scattering related to ambiguities in the treatment of terms which are singular
in the limit of a vanishing charm mass. In particular we compare the so-called
variable flavour scheme where these terms are absorbed in the parton
distribution functions containing the charm as an active flavour, with the
so-called fixed flavour scheme with no charm mass subtraction where the charm
appears only in the final state of fixed-order scattering matrix elements.
Using available parametrizations of parton distribution functions we find that
the two schemes lead to largely differing results for separate structure
functions whereas the differences cancel to a large extent in the total cross
section in that kinematical region which has been measured so far.Comment: 20pages, uuencoded postscript, figures include
Dynamical QCD Predictions for Ultrahigh Energy Neutrino Cross Sections
Neutrino-nucleon total cross sections for neutrino energies up to ultrahigh
energies (UHE), E_\nu=10^12 GeV, are evaluated within the framework of the
dynamical (radiative) parton model. The expected uncertainties of these
predictions do not exceed the level of about 20 % at the highest energies where
contributions of parton distributions in the yet unmeasured region around
x\simeq 10^-8 to 10^-9 are non-negligible. This is far more accurate than
estimated uncertainties of about 2^+-1 due to ad hoc extrapolations of parton
distributions to x<10^-5 required for calculating UHE cosmic neutrino event
rates.Comment: 16 pages, LaTeX, 4 figures, uses epsfig and amssymb styl
The Strange Sea Density and Charm Production in Deep Inelastic Charged Current Processes
Charm production as related to the determination of the strange sea density
in deep inelastic charged current processes is studied predominantly in the
framework of the fixed flavor factorization scheme.
Perturbative stability within this formalism is demonstrated. The compatibility
of recent next-to-leading order strange quark distributions with the available
dimuon and data is investigated. It is shown that final
conclusions concerning these distributions afford further analyses of presently
available and/or forthcoming neutrino data.Comment: 12 pages, LaTeX, 4 figure
The furan microsolvation blind challenge for quantum chemical methods: First steps
© 2018 Author(s). Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH-O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication
Library of model components for process simulation relevant to production activities, Prototype 1 versions
Production Economics,
Heavy Quark Initiated Contributions to Deep Inelastic Structure Functions
We present O(alpha_s^1) corrections to deep inelastic scattering amplitudes
on massive quarks obtained within the scheme of Aivazis, Collins, Olness and
Tung (ACOT). After identifying the correct subtraction term the convergence of
these contributions towards the analogous coefficient functions for massless
quarks, obtained within the modified minimal subtraction scheme (MSbar), is
demonstrated. Furthermore, the quantitative relevance of the contributions to
neutral current (NC) and charged current (CC) structure functions is
investigated for several choices of the factorization scale.Comment: 29 pages, 6 figures; uses epsfig.sty, amssymb.sty, axodraw.sty; minor
changes for publication in Phys. Rev.
Photoproduction off Nuclei and Point-like Photon Interactions Part I: Cross Sections and Nuclear Shadowing
High energy photoproduction off nuclear targets is studied within the
Glauber-Gribov approximation. The photon is assumed to interact as a
-system according to the Generalized Vector Dominance Model and as a
``bare photon'' in direct scattering processes with target nucleons. We
calculate total cross sections for interactions of photons with nuclei taking
into account coherence length effects and point-like interactions of the
photon. Results are compared to data on photon-nucleus cross sections, nuclear
shadowing, and quasi- elastic -production. Extrapolations of cross
sections and of the shadowing behaviour to high energies are given.Comment: 15 pages, 12 figure
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
The fully differential single-top-quark cross section in next-to-leading order QCD
We present a new next-to-leading order calculation for fully differential
single-top-quark final states. The calculation is performed using phase space
slicing and dipole subtraction methods. The results of the methods are found to
be in agreement. The dipole subtraction method calculation retains the full
spin dependence of the final state particles. We show a few numerical results
to illustrate the utility and consistency of the resulting computer
implementations.Comment: 37 pages, latex, 2 ps figure
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