295 research outputs found
Accelerator and Reactor Neutrino Experiments
Present results from neutrino experiments at accelerators and nuclear
reactors are reviewed with emphasis on neutrino oscillation searches. Future
prospects in this field are also discussed.Comment: Review presented at LP9
Quiet Sun X-rays as Signature for New Particles
We have studied published data from the Yohkoh solar X-ray mission, with the
purpose of searching for signals from radiative decays of new, as yet
undiscovered massive neutral particles. This search is based on the prediction
that solar axions of the Kaluza-Klein type should result in the emission of
X-rays from the Sun direction beyond the limb with a characteristic radial
distribution. These X-rays should be observed more easily during periods of
quiet Sun. An additional signature is the observed emission of hard X-rays by
SMM, NEAR and RHESSI. The recent observation made by RHESSI of a continuous
emission from the non-flaring Sun of X-rays in the 3 to ~15 keV range fits the
generic axion scenario. This work also suggests new analyses of existing data,
in order to exclude instrumental effects; it provides the rationale for
targeted observations with present and upcoming (solar) X-ray telescopes, which
can provide the final answer on the nature of the signals considered here. Such
measurements become more promising during the forthcoming solar cycle minimum
with an increased number of quiet Sun periods.Comment: 14 pages, 3 figures; to be published in ApJ. May 20 200
Is CP Violation Observable in Long Baseline Neutrino Oscillation Experiments ?
We have studied CP violation originated by the phase of the neutrino mixing
matrix in the long baseline neutrino oscillation experiments. The direct
measurements of CP violation is the difference of the transition probabilities
between CP-conjugate channels. In those experiments, the CP violating effect is
not suppressed if the highest neutrino mass scale is taken to be 1\sim 5 \eV,
which is appropriate for the cosmological hot dark matter. Assuming the
hierarchy for the neutrino masses, the upper bounds of CP violation have been
caluculated for three cases, in which mixings are constrained by the recent
short baseline ones. The calculated upper bounds are larger than ,
which will be observable in the long baseline accelerator experiments. The
matter effect, which is not CP invariant, has been also estimated in those
experiments.Comment: 28 pages, LaTex file, 6 figures included using epsfig Matter effect
is estimated(Figs.3(a) (b)). Physical parameters are change
Probing possible decoherence effects in atmospheric neutrino oscillations
It is shown that the results of the Super-Kamiokande atmospheric neutrino
experiment, interpreted in terms of nu_munu_tau flavor transitions, can
probe possible decoherence effects induced by new physics (e.g., by quantum
gravity) with high sensitivity, supplementing current laboratory tests based on
kaon oscillations and on neutron interferometry. By varying the (unknown)
energy dependence of such effects, one can either obtain strong limits on their
amplitude, or use them to find an unconventional solution to the atmospheric nu
anomaly based solely on decoherence.Comment: Title changed; major changes in the text; includes the discussion of
a new solution to the atmosheric neutrino anomaly, based on decoherence; a
second figure and a note have been adde
Natural Neutrino Mass Matrix
Naturalness of the neutrino mass hierarchy and mixing is studied. First we
select among 12 neutrino mixing patterns a few patterns, which could form the
natural neutrino mass matrix. Further we show that if the Dirac neutrino mass
matrix is taken as the natural one in the quark sector, then only two mixing
patterns without the large mixing lead to the natural right-handed Majorana
mass matrix. The rest of the chosen patterns with three degenerate mass
solution lead to the unnatural right-handed Majorana mass matrix in the see-saw
mechanism. Notice however, that for the chosen two natural patterns there could
be a huge mass hierarchy such as in order to reproduce
the inverse mass hierarchy of the light neutrinos.Comment: 31 pages, LaTex file, no figures, arguments made more clear, main
conclusions unchanged, version accepted for publication in PRD Reort-no:
Lund-Mph-97/14 Revise
Neutrino Masses and Mixings in a Universal Seesaw Mass Matrix Model
Neutrino masses and mixings are investigated on the basis of a universal
seesaw mass matrix model, in which quark (except for top) and charged lepton
mass matrices M_f and neutrino mass matrix M_\nu are given by M_f \simeq m_L
M_F^{-1} m_R and M_\nu \simeq m_L M_F^{-1} m_L^T (F=N), respectively. For a
simple model which can successfully describe quark masses and mixings, we find
that the observed neutrino data (except for the solar neutrino data) are favor
to the intermediate mass scales O(m_R) = 10^{11} GeV and O(M_F)= 10^{13} GeV
together with O(m_L)= 10^2 GeV. In spite of the largesse of O(m_R), the
observed top quark mass can be consistently understood from the would-be seesaw
mass matrix with these mass scales.Comment: 19 pages (Latex file
First Observation and Measurement of the Decay K+- -> pi+- e+ e- gamma
Using the full data set of the NA48/2 experiment, the decay K+- -> pi+- e+ e-
gamma is observed for the first time, selecting 120 candidates with 7.3 +- 1.7
estimated background events. With K+- -> pi+- pi0D as normalisation channel,
the branching ratio is determined in a model-independent way to be Br(K+- ->
pi+- e+ e- gamma, m_eegamma > 260 MeV/c^2) = (1.19 +- 0.12_stat +- 0.04_syst) x
10^-8. This measured value and the spectrum of the e+ e- gamma invariant mass
allow a comparison with predictions of Chiral Perturbation Theory.Comment: 13 pages, 3 figures. Accepted for publication in Phys.Lett.
Empirical parameterization of the K+- -> pi+- pi0 pi0 decay Dalitz plot
As first observed by the NA48/2 experiment at the CERN SPS, the \p0p0
invariant mass (M00) distribution from \kcnn decay shows a cusp-like anomaly
at M00=2m+, where m+ is the charged pion mass. An analysis to extract the pi pi
scattering lengths in the isospin I=0 and I=2 states, a0 and a2, respectively,
has been recently reported. In the present work the Dalitz plot of this decay
is fitted to a new empirical parameterization suitable for practical purposes,
such as Monte Carlo simulations of K+- -> pi+- pi0 pi0 decays.Comment: 9 pages, 3 figures
Recent NA48/2 and NA62 results
The NA48/2 Collaboration at CERN has accumulated and analysed unprecedented
statistics of rare kaon decays in the modes: () and ()
with nearly one percent background contamination. It leads to the improved
measurement of branching fractions and detailed form factor studies. New final
results from the analysis of 381 rare decay
candidates collected by the NA48/2 and NA62 experiments at CERN are presented.
The results include a decay rate measurement and fits to Chiral Perturbation
Theory (ChPT) description.Comment: Prepared for the Proceedings of "Moriond QCD and High Energy
Interactions. March 22-29 2014." conferenc
ChPT tests at the NA48 and NA62 experiments at CERN
The NA48/2 Collaboration at CERN has accumulated unprecedented statistics of
rare kaon decays in the Ke4 modes: Ke4(+-) ()
and Ke4(00) () with nearly one percent
background contamination. The detailed study of form factors and branching
rates, based on these data, has been completed recently. The results brings new
inputs to low energy strong interactions description and tests of Chiral
Perturbation Theory (ChPT) and lattice QCD calculations. In particular, new
data support the ChPT prediction for a cusp in the invariant mass
spectrum at the two charged pions threshold for Ke4(00) decay. New final
results from an analysis of about 400 rare
decay candidates collected by the NA48/2 and NA62 experiments at CERN during
low intensity runs with minimum bias trigger configurations are presented. The
results include a model-independent decay rate measurement and fits to ChPT
description.Comment: XIIth International Conference on Heavy Quarks and Leptons 2014,
Mainz, German
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