8,407 research outputs found
Investigation into the limits of perturbation theory at low Q^2 using HERA deep inelastic scattering data
A phenomenological study of the final combined HERA data on inclusive deep
inelastic scattering (DIS) has been performed. The data are presented and
investigated for a kinematic range extending from values of the four-momentum
transfer, , above 10 GeV down to the lowest values observable at
HERA of = 0.045 GeV and Bjorken , = 6
10. The data are well described by fits based on perturbative quantum
chromodynamics (QCD) using collinear factorisation and evolution of the parton
densities encompassed in the DGLAP formalism from the highest down to
of a few GeV. The Regge formalism can describe the data up to 0.65 GeV. The complete data set can be described by a new fit
using the ALLM parameterisation. The region between the Regge and the
perturbative QCD regimes is of particular interest.Comment: 38 pages, 13 figure
Prompt neutrino fluxes in the atmosphere with PROSA parton distribution functions
Effects on atmospheric prompt neutrino fluxes of present uncertainties
affecting the nucleon composition are studied by using the PROSA fit to parton
distribution functions (PDFs). The PROSA fit extends the precision of the PDFs
to low x, which is the kinematic region of relevance for high-energy neutrino
production, by taking into account LHCb data on charm and bottom
hadroproduction. In the range of neutrino energies explored by present Very
Large Volume Neutrino Telescopes, it is found that PDF uncertainties are far
smaller with respect to those due to renormalization and factorization scale
variation and to assumptions on the cosmic ray composition, which at present
dominate and limit our knowledge of prompt neutrino fluxes. A discussion is
presented on how these uncertainties affect the expected number of atmospheric
prompt neutrino events in the analysis of high-energy events characterized by
interaction vertices fully contained within the instrumented volume of the
detector, performed by the IceCube collaboration.Comment: 36 pages, 17 figures, 1 tabl
High Q^2 Deep Inelastic Scattering at HERA
High Q^2 NC and CC cross-sections as measured at HERA can give information on
two distinct areas of current interest. Firstly, supposing that all the
electroweak parameters are well known, these cross-sections may be used to give
information on parton distributions at high x and high Q^2. Secondly, supposing
that parton distributions are well known, after evolution in Q^2 from the
kinematic regime where they are already measured, these cross-sections can be
used to give information on electroweak parameters in a process where the
exchanged boson is `spacelike' rather than `timelike'. WG1 addressed itself to
clarifying the limits of our present and possible future knowledge on both
these areas.Comment: 26 pages, 12 figures. Uses iopart.cls, iopart12.clo, axodraw.sty.
Report of WG1 of the 3rd UK Phenomenology Workshop on HERA Physics, Durham
1998. To be published in Journal of Physics
What did HERA teach us about the structure of the proton?
Starting in 2008 the H1 and ZEUS experiments have been combining their data
in order to provide the most complete and accurate set of deep-inelastic data
as the legacy of HERA. The present review presents these combinations, both
published and preliminary, and explores how they have been used to give
information on the structure of the proton. The HERAPDF parton distribution
functions (PDFs) are presented and compared with other current PDFs and with
data from the Tevatron and LHC colliders.Comment: 49 pages, 49 figures, to be published in J.Phys.
Fractal Inspired Models of Quark and Gluon Distributions and Longitudinal Structure Function FL(x, Q2) at small x
In recent years, Fractal Inspired Models of quark and gluon densities at
small x have been proposed. In this paper, we investigate longitudinal
structure function F-L (x, Q2) within this approach. We make predictions using
the QCD based approximate relation between the longitudinal structure function
and the gluon density. As the Altarelli-Martinelli equation for the
longitudinal structure function cannot be applied to Model I due to the
presence of a singularity in the Bjorken x-space we consider Model II only. The
qualitative feature of the prediction of Model II is found to be compatible
with the QCD expectation.Comment: 11 pages, 4 figures, Accepted for publication on 10-07-2010 in Indian
Journal of Physic
Spin dependent structure function g_1 at low x and low Q^2
Theoretical description of the spin dependent structure function g_1(x,Q^2)
in the region of low values of x and Q^2 is presented. It contains the Vector
Meson Dominance contribution and the QCD improved parton model suitably
extended to the low Q^2 domain. Theoretical predictions are compared with the
recent experimental data in the low x, low Q^2 region
Bounds on the dipole moments of the tau-neutrino via the process in a 331 model
We obtain limits on the anomalous magnetic and electric dipole moments of the
through the reaction
and in the framework of a 331 model. We consider initial-state radiation, and
neglect and photon exchange diagrams. The results are based on the data
reported by the L3 Collaboration at LEP, and compare favorably with the limits
obtained in other models, complementing previous studies on the dipole moments.Comment: 13 pages, 4 figures, to be published in The European Physical J C.
arXiv admin note: substantial text overlap with arXiv:hep-ph/060527
Effects of neutrino oscillations and neutrino magnetic moments on elastic neutrino-electron scattering
We consider elastic antineutrino-electron scattering taking into account
possible effects of neutrino masses and mixing and of neutrino magnetic moments
and electric dipole moments. Having in mind antineutrinos produced in a nuclear
reactor we compute, in particular, the weak-electromagnetic interference terms
which are linear in the magnetic (electric dipole) moments and also in the
neutrino masses. We show that these terms are, however, suppressed compared to
the pure weak and electromagnetic cross section. We also comment upon the
possibility of using the electromagnetic cross section to investigate neutrino
oscillations.Comment: 12 pages, REVTEX file, no figures, submitted to Phys.Rev.
DGLAP evolution extends the triple pole pomeron fit
We show that the triple pole pomeron model \cite{CMS} provides an initial
condition for a DGLAP evolution \cite{DGLAP} that produces a fit to high
experimental DIS data. We obtain good for initial scales down to 3
GeV. Values of the initial scale smaller than 1.45 GeV are ruled out at
the 90% confidence level.Comment: 8 pages, 6 figures, uses RevTex 4. Typos corrected, some points
clarifed and 1 figure adde
New parton distributions in fixed flavour factorization scheme from recent deep-inelastic-scattering data
We present our QCD analysis of the proton structure function
to determine the parton distributions at the next-to-leading order (NLO). The
heavy quark contributions to , with = , have been
included in the framework of the `fixed flavour number scheme' (FFNS). The
results obtained in the FFNS are compared with available results such as the
general-mass variable-flavour-number scheme (GM-VFNS) and other prescriptions
used in global fits of PDFs. In the present QCD analysis, we use a wide range
of the inclusive neutral-current deep-inelastic-scattering (NC DIS) data,
including the most recent data for charm , bottom , longitudinal
structure functions and also the reduced DIS cross sections
from HERA experiments. The most recent HERMES data for
proton and deuteron structure functions are also added. We take into account
ZEUS neutral current DIS inclusive jet cross section data from HERA
together with the recent Tevatron Run-II inclusive jet cross section data from
CDF and D{\O}. The impact of these recent DIS data on the PDFs extracted from
the global fits are studied. We present two families of PDFs, {\tt KKT12} and
{\tt KKT12C}, without and with HERA `combined' data sets on DIS. We
find these are in good agreement with the available theoretical models.Comment: 23 pages, 26 figures and 4 tables. V3: Only few comments and
references added in the replaced version, results unchanged. Code can be
found at http://particles.ipm.ir/links/QCD.ht
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