2,491 research outputs found
Exact relativistic beta decay endpoint spectrum
The exact relativistic form for the beta decay endpoint spectrum is derived
and presented in a simple factorized form. We show that our exact formula can
be well approximated to yield the endpoint form used in the fit method of the
KATRIN collaboration. We also discuss the three neutrino case and how
information from neutrino oscillation experiments may be useful in analyzing
future beta decay endpoint experiments.Comment: 12 pages, 3 figure
A microwave plasma cleaning apparatus
In a microwave electron cyclotron resonance plasma source, reactive plasmas of oxygen and its mixtures of argon have been used for evaluating plasma cleaning technologies. Small aluminum samples (0.95 x 1.9 cm) were coated with thin films (less than or equal to 20 micrometers in thickness) of Shell Vitrea oil and cleaned with reactive plasmas. The discharge parameters, such as gas pressure, magnetic field, substrate biasing, and microwave power, were varied to change cleaning conditions. A mass spectroscopy (or residual gas analyzer) was used to monitor the status of plasma cleaning. Mass loss of the samples after plasma cleaning was measured to estimate cleaning rates. Measured cleaning rates of low-pressure (0.5-m torr) argon/oxygen plasmas were as high as 2.7 micrometers/min. X-ray photoelectron spectroscopy was used to determine cleanliness of the sample surfaces. In this paper, significant results of the plasma cleaning are reported and discussed
Role of Light Vector Mesons in the Heavy Particle Chiral Lagrangian
We give the general framework for adding "light" vector particles to the
heavy hadron effective chiral Lagrangian. This has strong motivations both from
the phenomenological and aesthetic standpoints. An application to the already
observed D \rightarrow \overbar{K^*} weak transition amplitude is discussed.Comment: 19 pages, LaTeX documen
Spontaneous breaking of a global symmetry in a 331 model
In a 331 model in which the lepton masses arise from a scalar sextet it is
possible to break spontaneously a global symmetry implying in a pseudoscalar
majoron-like Goldstone boson. This majoron does not mix with any other scalar
fields and for this reason it does not couple, at the tree level, neither to
the charged leptons nor to the quarks. Moreover, its interaction with neutrinos
is diagonal. We also argue that there is a set of the parameters in which that
the model can be consistent with the invisible Z^0-width and that heavy
neutrinos can decay sufficiently rapid by majoron emission having a lifetime
shorter than the age of the universe.Comment: RevTex, 10 pages, one .eps figur
A centrifuge CO2 pellet cleaning system
An advanced turbine/CO2 pellet accelerator is being evaluated as a depaint technology at Oak Ridge National Laboratory (ORNL). The program, sponsored by Warner Robins Air Logistics Center (ALC), Robins Air Force Base, Georgia, has developed a robot-compatible apparatus that efficiently accelerates pellets of dry ice with a high-speed rotating wheel. In comparison to the more conventional compressed air 'sandblast' pellet accelerators, the turbine system can achieve higher pellet speeds, has precise speed control, and is more than ten times as efficient. A preliminary study of the apparatus as a depaint technology has been undertaken. Depaint rates of military epoxy/urethane paint systems on 2024 and 7075 aluminum panels as a function of pellet speed and throughput have been measured. In addition, methods of enhancing the strip rate by combining infra-red heat lamps with pellet blasting and by combining the use of environmentally benign solvents with the pellet blasting have also been studied. The design and operation of the apparatus will be discussed along with data obtained from the depaint studies
Chandra Detects a Rapid Flare in the Gravitationally Lensed Mini-BALQSO RX J0911.4+0551
The mini Broad Absorption Line (BAL) quasar RX J0911.4+0551 was observed with
the Advanced CCD Imaging Spectrometer (ACIS) of the Chandra X-ray Observatory
for ~ 29 ks as part of a gravitational lens (GL) survey aimed at measuring
time-delays. Timing analysis of the light-curve of the lensed image A2 shows a
rapid flux variation with a duration of about 2000s. A Kolmogorov-Smirnov test
shows that the probability that a constant-intensity source would produce the
observed variability is less than ~ 0.2 percent. We discuss possible origins
for the observed short-term X-ray variability. Our gravitational lens models
for the RX J0911.4+0551 GL system predict a time-delay of less than a day
between images A1 and A2. The rapid variability combined with the predicted
short-time delay make RX J0911.4+0551 an ideal system to apply the GL method
for estimating the Hubble constant. We describe the prospects of measuring H_0
within single X-ray observations of GL systems with relatively short time
delays. Modeling of the spectrum of the mini-BAL quasar RX J0911.4+0551
suggests the presence of an intrinsic absorber. Partial covering models are
slightly preferred over models that contain absorption due to intrinsic ionized
or neutral gas.Comment: 17 pages, includes 5 figures, Accepted for publication in Ap
The Shape and Scale of Galactic Rotation from Cepheid Kinematics
A catalog of Cepheid variables is used to probe the kinematics of the
Galactic disk. Radial velocities are measured for eight distant Cepheids toward
l = 300; these new Cepheids provide a particularly good constraint on the
distance to the Galactic center, R_0. We model the disk with both an
axisymmetric rotation curve and one with a weak elliptical component, and find
evidence for an ellipticity of 0.043 +/- 0.016 near the Sun. Using these
models, we derive R_0 = 7.66 +/- 0.32 kpc and v_circ = 237 +/- 12 km/s. The
distance to the Galactic center agrees well with recent determinations from the
distribution of RR Lyrae variables, and disfavors most models with large
ellipticities at the solar orbit.Comment: 36 pages, LaTeX, 10 figure
Leptogenesis in the presence of exact flavor symmetries
In models with flavor symmetries in the leptonic sector leptogenesis can take
place in a very different way compared to the standard leptogenesis scenario.
We study the generation of a asymmetry in these kind of models in the
flavor symmetric phase pointing out that successful leptogenesis requires (i)
the right-handed neutrinos to lie in different representations of the flavor
group; (ii) the flavons to be lighter at least that one of the right-handed
neutrino representations. When these conditions are satisfied leptogenesis
proceeds due to new contributions to the CP violating asymmetry and -depending
on the specific model- in several stages. We demonstrate the validity of these
arguments by studying in detail the generation of the asymmetry in a
scenario of a concrete flavor model realization.Comment: 25 pages, 7 figures; version 2: A few clarifications added. Version
matches publication in JHE
Reactor mixing angle from hybrid neutrino masses
In terms of its eigenvector decomposition, the neutrino mass matrix (in the
basis where the charged lepton mass matrix is diagonal) can be understood as
originating from a tribimaximal dominant structure with small deviations, as
demanded by data. If neutrino masses originate from at least two different
mechanisms, referred to as "hybrid neutrino masses", the experimentally
observed structure naturally emerges provided one mechanism accounts for the
dominant tribimaximal structure while the other is responsible for the
deviations. We demonstrate the feasibility of this picture in a fairly
model-independent way by using lepton-number-violating effective operators,
whose structure we assume becomes dictated by an underlying flavor
symmetry. We show that if a second mechanism is at work, the requirement of
generating a reactor angle within its experimental range always fixes the solar
and atmospheric angles in agreement with data, in contrast to the case where
the deviations are induced by next-to-leading order effective operators. We
prove this idea is viable by constructing an -based ultraviolet
completion, where the dominant tribimaximal structure arises from the type-I
seesaw while the subleading contribution is determined by either type-II or
type-III seesaw driven by a non-trivial singlet (minimal hybrid model).
After finding general criteria, we identify all the symmetries
capable of producing such -based minimal hybrid models.Comment: 18 pages, 5 figures. v3: section including sum rules added, accepted
by JHE
- …