4,947 research outputs found
Nuclear modification of valence-quark distributions and its effects on NuTeV sin^2 theta_W anomaly
We investigated a nuclear modification difference between up- and
down-valence quark distributions by analyzing structure function F_2 and
Drell-Yan cross-section ratios. Although nuclear modifications of the
valence-quark distributions themselves are rather well determined, it is
difficult to find their difference from the present data. We estimated such an
effect on the NuTeV sin^2 theta_W value and its uncertainty by the Hessian
method. At this stage, it is not large enough to explain the whole NuTeV
anomaly. However, the modification difference cannot be precisely determined,
so that further studies are needed.Comment: 3 pages, LaTeX, 1 eps file, to be published in Proceedings of the 6th
International Workshop on Neutrino Factories and Superbeams (NuFact04
Can a 3+2 Oscillation Model Explain the NuTeV Electroweak Results?
The weak mixing angle result from NuTeV falls three standard deviations above
the value determined by global electroweak fits. It has been suggested that one
possible explanation for this result could be the oscillation of electron
neutrinos in the NuTeV beam to sterile neutrinos. This article examines several
cases of masses and mixings for 3+2 neutrino oscillation models which fit the
current oscillation data at 99% CL. We conclude that electron to sterile
neutrino oscillations can account for only up to a third of a standard
deviation between the NuTeV determination of the weak mixing angle and the
standard model.Comment: 3 pages, 2 figures, submitted to Brief Report
Modified Paschos-Wolfenstein relation and extraction of weak mixing angle sin^2 theta_W
The NuTeV collaboration reported anomalously large weak mixing angle sin^2
theta_W in comparison with the standard model prediction. Neutrino and
antineutrino charged- and neutral-current events are analyzed for extracting
sin^2 theta_W. Although the Paschos-Wolfenstein relation is not directly used
in the analysis, it plays an important role in the determination. Noting that
the target nucleus, iron, is not an isoscalar nucleus, we derive a
leading-order expression for a modified Paschos-Wolfenstein relation for
nuclei, which may have neutron excess. Then, using charge and baryon-number
conservations for nuclei, we discuss a nuclear correction in the sin^2 theta_W
determination. It is noteworthy that nuclear modifications are different
between valence up- and down-quark distributions. We show this difference
effect on the NuTeV sin^2 theta_W deviation.Comment: 5 pages, REVTeX4.0, revtex4.cls, url.sty, natbib.sty, revsymb.sty,
10pt.rtx, aps.rtx, amssymb.sty, amsfonts.sty, 3 eps figures. Phys. Rev. D in
press. Email: [email protected] See also http://hs.phys.saga-u.ac.j
Ionization signals from electrons and alpha-particles in mixtures of liquid Argon and Nitrogen - perspectives on protons for Gamma Resonant Nuclear Absorption applications
In this paper we report on a detailed study of ionization signals produced by
Compton electrons and alpha-particles in a Time Projection Chamber (TPC) flled
with different mixtures of liquid Argon and Nitrogen. The measurements were
carried out with Nitrogen concentrations up to 15% and a drift electric feld in
the range 0-50 kV/cm. A prediction for proton ionization signals is made by
means of interpolation. This study has been conducted in view of the possible
use of liquid Ar-N2 TPCs for the detection of gamma-rays in the resonant band
of the Nitrogen absorption spectrum, a promising technology for security and
medical applications
30 kV coaxial vacuum-tight feedthrough for operation at cryogenic temperatures
In this paper we describe the technology of building a vacuum-tight high
voltage feedthrough which is able to operate at voltages up to 30 kV. The
feedthrough has a coaxial structure with a grounded sheath which makes it
capable to lead high voltage potentials into cryogenic liquids, without risk of
surface discharges in the gas phase above the liquid level. The feedthrough is
designed to be used in ionization detectors, based on liquefied noble gases,
such as Argon or Xenon
Single Pion production from Nuclei
We have studied charged current one pion production induced by
from some nuclei. The calculations have been done for
the incoherent pion production processes from these nuclear targets in the
dominance model and take into account the effect of Pauli blocking,
Fermi motion and renormalization of properties in the nuclear medium.
The effect of final state interactions of pions has also been taken into
account. The numerical results have been compared with the recent results from
the MiniBooNE experiment for the charged current 1 production, and also
with some of the older experiments in Freon and Freon-Propane from CERN.Comment: 5 pages, 5 figures, 5th International Workshop on Neutrino-Nucleus
Interactions in the few GeV region(NuInt07), Batavia, Illinois, 30May-3June,
200
A First-Principles Study of Zinc Oxide Honeycomb Structures
We present a first-principles study of the atomic, electronic, and magnetic
properties of two-dimensional (2D), single and bilayer ZnO in honeycomb
structure and its armchair and zigzag nanoribbons. In order to reveal the
dimensionality effects, our study includes also bulk ZnO in wurtzite,
zincblende, and hexagonal structures. The stability of 2D ZnO, its nanoribbons
and flakes are analyzed by phonon frequency, as well as by finite temperature
ab initio molecular-dynamics calculations. 2D ZnO in honeycomb structure and
its armchair nanoribbons are nonmagnetic semiconductors but acquire net
magnetic moment upon the creation of zinc-vacancy defect. Zigzag ZnO
nanoribbons are ferromagnetic metals with spins localized at the oxygen atoms
at the edges and have high spin polarization at the Fermi level. However, they
change to nonmagnetic metal upon termination of their edges with hydrogen
atoms. From the phonon calculations, the fourth acoustical mode specified as
twisting mode is also revealed for armchair nanoribbon. Under tensile stress
the nanoribbons are deformed elastically maintaining honeycomblike structure
but yield at high strains. Beyond yielding point honeycomblike structure
undergo a structural change and deform plastically by forming large polygons.
The variation in the electronic and magnetic properties of these nanoribbons
have been examined under strain. It appears that plastically deformed
nanoribbons may offer a new class of materials with diverse properties.Comment: http://prb.aps.org/abstract/PRB/v80/i23/e23511
Measurement of the drift field in the ARGONTUBE LAr TPC with 266~nm pulsed laser beams
ARGONTUBE is a liquid argon time projection chamber (LAr TPC) with a drift
field generated in-situ by a Greinacher voltage multiplier circuit. We present
results on the measurement of the drift-field distribution inside ARGONTUBE
using straight ionization tracks generated by an intense UV laser beam. Our
analysis is based on a simplified model of the charging of a multi-stage
Greinacher circuit to describe the voltages on the field cage rings
Experimental study of electric breakdowns in liquid argon at centimeter scale
In this paper we present results on measurements of the dielectric strength
of liquid argon near its boiling point and cathode-anode distances in the range
of 0.1 mm to 40 mm with spherical cathode and plane anode. We show that at such
distances the applied electric field at which breakdowns occur is as low as 40
kV/cm. Flash-overs across the ribbed dielectric of the high voltage
feed-through are observed for a length of 300 mm starting from a voltage of 55
kV. These results contribute to set reference for the breakdown-free design of
ionization detectors, such as Liquid Argon Time Projection Chambers (LAr TPC)
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