1,400 research outputs found
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
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.
Longitudinally Polarized Photoproduction of Inclusive Hadrons Beyond the Leading Order
We present a complete next-to-leading order QCD calculation for
single-inclusive large-pT hadron production in longitudinally polarized
lepton-nucleon collisions, consistently including ``direct'' and ``resolved''
photon contributions. This process could be studied experimentally at a future
polarized lepton-proton collider like eRHIC at BNL. We examine the sensitivity
of such measurements to the so far completely unknown parton content of
circularly polarized photons.Comment: 15 pages, 7 eps figure
Polarized Parton Distribution in Neutrino Induced Heavy Flavor Production
In order to examine polarized strange quark distribution, semi-inclusive
D/\Dbar production in neutrino deep inelastic scattering is studied including
corrections. Cross section and spin asymmetry are
calculated by using various parametrizations of polarized parton distribution
functions. It is found that \Dbar production is promising to directly extract
the polarized strange sea.Comment: 3 pages, 2 figures. Talk given at the NuFact02 workshop, London, UK,
July 1-6, 200
Impact of Neutron Decay Experiments on non-Standard Model Physics
This paper gives a brief overview of the present and expected future limits
on physics beyond the Standard Model (SM) from neutron beta decay, which is
described by two parameters only within the SM. Since more than two observables
are accessible, the problem is over-determined. Thus, precise measurements of
correlations in neutron decay can be used to study the SM as well to search for
evidence of possible extensions to it. Of particular interest in this context
are the search for right-handed currents or for scalar and tensor interactions.
Precision measurements of neutron decay observables address important open
questions of particle physics and cosmology, and are generally complementary to
direct searches for new physics beyond the SM in high-energy physics. Free
neutron decay is therefore a very active field, with a number of new
measurements underway worldwide. We present the impact of recent developments.Comment: 13 pages, 6 figures; Proceedings of the 5th International BEYOND 2010
Conference, Cape Town, South Africa (2010), World Scientific, accepted for
publication; Corrected typo
Has the QCD RG-Improved Parton Content of Virtual Photons been Observed?
It is demonstrated that present and DIS ep data on the structure of
the virtual photon can be understood entirely in terms of the standard `naive'
quark--parton model box approach. Thus the QCD renormalization group (RG)
improved parton distributions of virtual photons, in particular their gluonic
component, have not yet been observed. The appropriate kinematical regions for
their future observation are pointed out as well as suitable measurements which
may demonstrate their relevance.Comment: 24 pages, LaTeX, 5 figure
Dynamical parton distributions of the nucleon and very small-x physics
Utilizing recent DIS measurements (F_{2,L}) and data on dilepton and
high-E_{T} jet production we determine the dynamical parton distributions of
the nucleon generated radiatively from valence-like positive input
distributions at optimally chosen low resolution scales. These are compared
with `standard' distributions generated from positive input distributions at
some fixed and higher resolution scale. It is shown that up to the next to
leading order NLO(\bar{MS}, DIS) of perturbative QCD considered in this paper,
the uncertainties of the dynamical distributions are, as expected, smaller than
those of their standard counterparts. This holds true in particular in the
presently unexplored extremely small-x region relevant for evaluating ultrahigh
energy cross sections in astrophysical applications. It is noted that our new
dynamical distributions are compatible, within the presently determined
uncertainties, with previously determined dynamical parton distributions.Comment: 21 pages, 2 tables, 16 figures, v2: added Ref.[60], replaced Fig.
The curvature of as a probe of the range of validity of perturbative QCD evolutions in the small- region
Perturbative NLO and NNLO QCD evolutions of parton distributions are studied,
in particular in the (very) small- region, where they are in very good
agreement with all recent precision measurements of . These
predictions turn out to be also rather insensitive to the specific choice of
the factorization scheme ( or DIS). A characteristic feature of
perturbative QCD evolutions is a {\em{positive}} curvature of which
increases as decreases. This perturbatively stable prediction provides a
sensitive test of the range of validity of perturbative QCD.Comment: 17 pages, 6 figures, 2 tables; minor corrections, to appear in EPJ
Modeling of electron emission processes accompanying Radon--decays within electrostatic spectrometers
Electrostatic spectrometers utilized in high-resolution beta-spectroscopy
studies such as in the Karlsruhe Tritium Neutrino (KATRIN) experiment have to
operate with a background level of less than 10^(-2) counts per second. This
limit can be exceeded by even a small number of Rn-219 or Rn-220 atoms being
emanated into the volume and undergoing alpha-decay there. In this paper we
present a detailed model of the underlying background-generating processes via
electron emission by internal conversion, shake-off and relaxation processes in
the atomic shells of the Po-215 and Po-216 daughters. The model yields electron
energy spectra up to 400 keV and electron multiplicities of up to 20 which are
compared to experimental data.Comment: 7 figure
Generalized parton distributions of the nucleon in constituent quark models
Generalized parton distributions (GPDs) are studied at the hadronic
(nonperturbative) scale within different assumptions based on a relativistic
constituent quark model. In particular, by means of a meson-cloud model we
investigate the role of nonperturbative antiquark degrees of freedom and the
valence quark contribution. A QCD evolution of the obtained GPDs is used to add
perturbative effects and to investigate the GPDs' sensitivity to the
nonperturbative ingredients of the calculation at larger (experimental) scale.Comment: 4 pages, 1 figure, presented at the Baryon-04 Conference, Palaiseau
(France), October 25-29, 2004. Nuclear Physics A, to be publishe
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