286 research outputs found
Status of atmospheric neutrino(mu)<-->neutrino(tau) oscillations and decoherence after the first K2K spectral data
We review the status of nu_mu-->nu_tau flavor transitions of atmospheric
neutrinos in the 92 kton-year data sample collected in the first phase of the
Super-Kamiokande (SK) experiment, in combination with the recent spectral data
from the KEK-to-Kamioka (K2K) accelerator experiment (including 29 single-ring
muon events). We consider a theoretical framework which embeds flavor
oscillations plus hypothetical decoherence effects, and where both standard
oscillations and pure decoherence represent limiting cases. It is found that
standard oscillations provide the best description of the SK+K2K data, and that
the associated mass-mixing parameters are determined at 1 sigma (and d.o.f.=1)
as: Delta m^2=(2.6 +- 0.4)x10^{-3} eV^2 and sin^2(2theta)=1.00+0.00-0.05. As
compared with standard oscillations, the case of pure decoherence is
disfavored, although it cannot be ruled out yet. In the general case,
additional decoherence effects in the nu_mu-->nu_tau channel do not improve the
fit to the SK and K2K data, and upper bounds can be placed on the associated
decoherence parameter. Such indications, presently dominated by SK, could be
strengthened by further K2K data, provided that the current spectral features
are confirmed with higher statistics. A detailed description of the statistical
analysis of SK and K2K data is also given, using the so-called ``pull''
approach to systematic uncertainties.Comment: 18 pages (RevTeX) + 12 figures (PostScript
The physics impact of proton track identification in future megaton-scale water Cherenkov detectors
In this paper, we investigate the impact in future megaton-scale water
Cherenkov detectors of identifying proton Cherenkov rings. We estimate the
expected event rates for detected neutral current and charged current
quasi-elastic neutrino interactions from atmospheric neutrinos in a
megaton-scale Super-Kamiokande-like detector with both 40% and 20%
photo-cathode coverage. With this sample we examine the prospects for measuring
the neutrino oscillation pattern, and searching for sterile neutrinos. We also
determine the size of selected charged current quasi-elastic samples in a
300-kton fiducial volume Super-Kamiokande-like detector from examples of both
conventional super-beams and beta-beams proposed in the literature. With these
samples, it is shown that full kinematic neutrino reconstruction using the
outgoing proton can improve the reconstructed energy resolution, and give good
neutrino versus anti-neutrino tagging capabilities, adding important
capabilities to water Cherenkov detectors in future projects. We determine the
beam parameters necessary to make use of this technique and present
distributions of neutrino and anti-neutrino selection efficiencies.Comment: 21 pages, 8 figures. Revised version with improved figures, text and
structure, published in JHE
Evolution of electronic and ionic structure of Mg-clusters with the growth cluster size
The optimized structure and electronic properties of neutral and singly
charged magnesium clusters have been investigated using ab initio theoretical
methods based on density-functional theory and systematic post-Hartree-Fock
many-body perturbation theory accounting for all electrons in the system. We
have systematically calculated the optimized geometries of neutral and singly
charged magnesium clusters consisting of up to 21 atoms, electronic shell
closures, binding energies per atom, ionization potentials and the gap between
the highest occupied and the lowest unoccupied molecular orbitals. We have
investigated the transition to the hcp structure and metallic evolution of the
magnesium clusters, as well as the stability of linear chains and rings of
magnesium atoms. The results obtained are compared with the available
experimental data and the results of other theoretical works.Comment: 30 pages, 10 figures, 3 table
Recent results on multiplicative noise
Recent developments in the analysis of Langevin equations with multiplicative
noise (MN) are reported. In particular, we:
(i) present numerical simulations in three dimensions showing that the MN
equation exhibits, like the Kardar-Parisi-Zhang (KPZ) equation both a weak
coupling fixed point and a strong coupling phase, supporting the proposed
relation between MN and KPZ;
(ii) present dimensional, and mean field analysis of the MN equation to
compute critical exponents;
(iii) show that the phenomenon of the noise induced ordering transition
associated with the MN equation appears only in the Stratonovich representation
and not in the Ito one, and
(iv) report the presence of a new first-order like phase transition at zero
spatial coupling, supporting the fact that this is the minimum model for noise
induced ordering transitions.Comment: Some improvements respect to the first versio
Tracking Performance of the Scintillating Fiber Detector in the K2K Experiment
The K2K long-baseline neutrino oscillation experiment uses a Scintillating
Fiber Detector (SciFi) to reconstruct charged particles produced in neutrino
interactions in the near detector. We describe the track reconstruction
algorithm and the performance of the SciFi after three years of operation.Comment: 24pages,18 figures, and 1 table. Preprint submitted to NI
Neutral-Current Atmospheric Neutrino Flux Measurement Using Neutrino-Proton Elastic Scattering in Super-Kamiokande
Recent results show that atmospheric oscillate with eV and , and that
conversion into is strongly disfavored. The Super-Kamiokande (SK)
collaboration, using a combination of three techniques, reports that their data
favor over . This distinction
is extremely important for both four-neutrino models and cosmology. We propose
that neutrino-proton elastic scattering () in water
\v{C}erenkov detectors can also distinguish between active and sterile
oscillations. This was not previously recognized as a useful channel since only
about 2% of struck protons are above the \v{C}erenkov threshold. Nevertheless,
in the present SK data there should be about 40 identifiable events. We show
that these events have unique particle identification characteristics, point in
the direction of the incoming neutrinos, and correspond to a narrow range of
neutrino energies (1-3 GeV, oscillating near the horizon). This channel will be
particularly important in Hyper-Kamiokande, with times higher rate.
Our results have other important applications. First, for a similarly small
fraction of atmospheric neutrino quasielastic events, the proton is
relativistic. This uniquely selects (not ) events,
useful for understanding matter effects, and allows determination of the
neutrino energy and direction, useful for the dependence of oscillations.
Second, using accelerator neutrinos, both elastic and quasielastic events with
relativistic protons can be seen in the K2K 1-kton near detector and MiniBooNE.Comment: 10 pages RevTeX, 8 figure
Restricting quark matter models by gravitational wave observation
We consider the possibilities for obtaining information about the equation of
state for quark matter by using future direct observational data on
gravitational waves. We study the nonradial oscillations of both fluid and
spacetime modes of pure quark stars. If we observe the and the lowest
modes from quark stars, by using the simultaneously obtained
radiation radius we can constrain the bag constant with reasonable
accuracy, independently of the quark mass.Comment: To appear in Phys. Rev.
Measurement of the residual energy of muons in the Gran Sasso underground Laboratories
The MACRO detector was located in the Hall B of the Gran Sasso underground
Laboratories under an average rock overburden of 3700 hg/cm^2. A transition
radiation detector composed of three identical modules, covering a total
horizontal area of 36 m^2, was installed inside the empty upper part of the
detector in order to measure the residual energy of muons. This paper presents
the measurement of the residual energy of single and double muons crossing the
apparatus. Our data show that double muons are more energetic than single ones.
This measurement is performed over a standard rock depth range from 3000 to
6500 hg/cm^2.Comment: 28 pages, 9 figure
Muon Energy Estimate Through Multiple Scattering with the Macro Detector
Muon energy measurement represents an important issue for any experiment
addressing neutrino induced upgoing muon studies. Since the neutrino
oscillation probability depends on the neutrino energy, a measurement of the
muon energy adds an important piece of information concerning the neutrino
system. We show in this paper how the MACRO limited streamer tube system can be
operated in drift mode by using the TDC's included in the QTPs, an electronics
designed for magnetic monopole search. An improvement of the space resolution
is obtained, through an analysis of the multiple scattering of muon tracks as
they pass through our detector. This information can be used further to obtain
an estimate of the energy of muons crossing the detector. Here we present the
results of two dedicated tests, performed at CERN PS-T9 and SPS-X7 beam lines,
to provide a full check of the electronics and to exploit the feasibility of
such a multiple scattering analysis. We show that by using a neural network
approach, we are able to reconstruct the muon energy for 40 GeV. The
test beam data provide an absolute energy calibration, which allows us to apply
this method to MACRO data.Comment: 25 pages, 11 figures, Submitted to Nucl. Instr. & Meth.
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