23 research outputs found
Precision high voltage divider for the KATRIN experiment
The Karlsruhe Tritium Neutrino Experiment (KATRIN) aims to determine the
absolute mass of the electron antineutrino from a precise measurement of the
tritium beta-spectrum near its endpoint at 18.6 keV with a sensitivity of 0.2
eV. KATRIN uses an electrostatic retardation spectrometer of MAC-E filter type
for which it is crucial to monitor high voltages of up to 35 kV with a
precision and long-term stability at the ppm level. Since devices capable of
this precision are not commercially available, a new high voltage divider for
direct voltages of up to 35 kV has been designed, following the new concept of
the standard divider for direct voltages of up to 100 kV developed at the
Physikalisch-Technische Bundesanstalt (PTB). The electrical and mechanical
design of the divider, the screening procedure for the selection of the
precision resistors, and the results of the investigation and calibration at
PTB are reported here. During the latter, uncertainties at the low ppm level
have been deduced for the new divider, thus qualifying it for the precision
measurements of the KATRIN experiment.Comment: 22 pages, 12 figure
Statistical Analysis of future Neutrino Mass Experiments including Neutrino-less Double Beta Decay
We perform a statistical analysis with the prospective results of future
experiments on neutrino-less double beta decay, direct searches for neutrino
mass (KATRIN) and cosmological observations. Realistic errors are used and the
nuclear matrix element uncertainty for neutrino-less double beta decay is also
taken into account. Three benchmark scenarios are introduced, corresponding to
quasi-degenerate, inverse hierarchical neutrinos, and an intermediate case. We
investigate to what extend these scenarios can be reconstructed. Furthermore,
we check the compatibility of the scenarios with the claimed evidence of
neutrino-less double beta decay.Comment: Matches published version: Europhys.Lett.85:51002 (2009). Format
changed suitably for ArXi
On a model with two zeros in the neutrino mass matrix
We consider a Majorana neutrino mass matrix with
, in the basis
where the charged-lepton mass matrix is diagonal. We show that this pattern for
the lepton mass matrices can be enforced by extending the Standard Model with
three scalar SU(2) triplets and by using a horizontal symmetry group
\mathbbm{Z}_4. The Ma--Sarkar (type-II seesaw) mechanism leads to very small
vacuum expectation values for the triplets, thus explaining the smallness of
the neutrino masses; at the same time, that mechanism renders the physical
scalars originating in the triplets very heavy. We show that the conditions
allow both for
a normal neutrino mass spectrum and for an inverted one. In the first case, the
neutrino masses must be larger than and the atmospheric mixing angle
must be practically equal to . In the second case, the
product must be of order one or
larger, thus correlating the large or maximal atmospheric neutrino mixing with
the smallness of the mixing angle .Comment: 13 pages, no figures, plain LaTeX; one equation added, published
references updated, final version for J. Phys.
Neutrino-less Double Beta Decay and Particle Physics
We review the particle physics aspects of neutrino-less double beta decay.
This process can be mediated by light massive Majorana neutrinos (standard
interpretation) or by something else (non-standard interpretations). The
physics potential of both interpretations is summarized and the consequences of
future measurements or improved limits on the half-life of neutrino-less double
beta decay are discussed. We try to cover all proposed alternative realizations
of the decay, including light sterile neutrinos, supersymmetric or left-right
symmetric theories, Majorons, and other exotic possibilities. Ways to
distinguish the mechanisms from one another are discussed. Experimental and
nuclear physics aspects are also briefly touched, alternative processes to
double beta decay are discussed, and an extensive list of references is
provided.Comment: 96 pages, 38 figures. Published versio
Majorana Neutrino Mixing
The most plausible see-saw explanation of the smallness of the neutrino
masses is based on the assumption that total lepton number is violated at a
large scale and neutrinos with definite masses are Majorana particles. In this
review we consider in details difference between Dirac and Majorana neutrino
mixing and possibilities of revealing Majorana nature of neutrinos with
definite masses
Theory of neutrinoless double beta decay
Neutrinoless double beta decay, which is a very old and yet elusive process,
is reviewed. Its observation will signal that lepton number is not conserved
and the neutrinos are Majorana particles. More importantly it is our best hope
for determining the absolute neutrino mass scale at the level of a few tens of
meV. To achieve the last goal certain hurdles have to be overcome involving
particle, nuclear and experimental physics. Nuclear physics is important for
extracting the useful information from the data. One must accurately evaluate
the relevant nuclear matrix elements, a formidable task. To this end, we review
the sophisticated nuclear structure approaches recently been developed, which
give confidence that the needed nuclear matrix elements can be reliably
calculated. From an experimental point of view it is challenging, since the
life times are long and one has to fight against formidable backgrounds. If a
signal is found, it will be a tremendous accomplishment. Then, of course, the
real task is going to be the extraction of the neutrino mass from the
observations. This is not trivial, since current particle models predict the
presence of many mechanisms other than the neutrino mass, which may contribute
or even dominate this process. We will, in particular, consider the following
processes: (i)The neutrino induced, but neutrino mass independent contribution.
(ii)Heavy left and/or right handed neutrino mass contributions.
(iii)Intermediate scalars (doubly charged etc). (iv)Supersymmetric (SUSY)
contributions. We will show that it is possible to disentangle the various
mechanisms and unambiguously extract the important neutrino mass scale, if all
the signatures of the reaction are searched in a sufficient number of nuclear
isotopes.Comment: 104 pages, 6 tables, 25 figures.References added. To appear in ROP
(Reports on Progress in Physics), copyright RO
A See-Saw model for fermion masses and mixings
We present a supersymmetric see-saw model giving rise to the most
general neutrino mass matrix compatible with Tri-Bimaximal mixing. We adopt the
flavour symmetry, broken by suitable vacuum expectation values
of a small number of flavon fields. We show that the vacuum alignment is a
natural solution of the most general superpotential allowed by the flavour
symmetry, without introducing any soft breaking terms. In the charged lepton
sector, mass hierarchies are controlled by the spontaneous breaking of the
flavour symmetry caused by the vevs of one doublet and one triplet flavon
fields instead of using the Froggatt-Nielsen U(1) mechanism. The next to
leading order corrections to both charged lepton mass matrix and flavon vevs
generate corrections to the mixing angles as large as .
Applied to the quark sector, the symmetry group can give a
leading order proportional to the identity as well as a matrix with
coefficients in the Cabibbo submatrix. Higher order
corrections produce non vanishing entries in the other entries which
are generically of .Comment: 30 pages, 3 figures, minor changes to match the published versio
Gravitational clustering of relic neutrinos and implications for their detection
We study the gravitational clustering of big bang relic neutrinos onto
existing cold dark matter (CDM) and baryonic structures within the flat
CDM model, using both numerical simulations and a semi-analytical
linear technique, with the aim of understanding the neutrinos' clustering
properties for direct detection purposes. In a comparative analysis, we find
that the linear technique systematically underestimates the amount of
clustering for a wide range of CDM halo and neutrino masses. This invalidates
earlier claims of the technique's applicability. We then compute the exact
phase space distribution of relic neutrinos in our neighbourhood at Earth, and
estimate the large scale neutrino density contrasts within the local
Greisen--Zatsepin--Kuzmin zone. With these findings, we discuss the
implications of gravitational neutrino clustering for scattering-based
detection methods, ranging from flux detection via Cavendish-type torsion
balances, to target detection using accelerator beams and cosmic rays. For
emission spectroscopy via resonant annihilation of extremely energetic cosmic
neutrinos on the relic neutrino background, we give new estimates for the
expected enhancement in the event rates in the direction of the Virgo cluster.Comment: 38 pages, 8 embedded figures, iopart.cls; v2: references added, minor
changes in text, to appear in JCA
Commissioning of the vacuum system of the KATRIN Main Spectrometer
The KATRIN experiment will probe the neutrino mass by measuring the
beta-electron energy spectrum near the endpoint of tritium beta-decay. An
integral energy analysis will be performed by an electro-static spectrometer
(Main Spectrometer), an ultra-high vacuum vessel with a length of 23.2 m, a
volume of 1240 m^3, and a complex inner electrode system with about 120000
individual parts. The strong magnetic field that guides the beta-electrons is
provided by super-conducting solenoids at both ends of the spectrometer. Its
influence on turbo-molecular pumps and vacuum gauges had to be considered. A
system consisting of 6 turbo-molecular pumps and 3 km of non-evaporable getter
strips has been deployed and was tested during the commissioning of the
spectrometer. In this paper the configuration, the commissioning with bake-out
at 300{\deg}C, and the performance of this system are presented in detail. The
vacuum system has to maintain a pressure in the 10^{-11} mbar range. It is
demonstrated that the performance of the system is already close to these
stringent functional requirements for the KATRIN experiment, which will start
at the end of 2016.Comment: submitted for publication in JINST, 39 pages, 15 figure
Reduction of stored-particle background by a magnetic pulse method at the KATRIN experiment
The KATRIN experiment aims to determine the effective electron neutrino mass with a sensitivity of 0.2 eV/c2 (%90 CL) by precision measurement of the shape of the tritium β-spectrum in the endpoint region. The energy analysis of the decay electrons is achieved by a MAC-E filter spectrometer. A common background source in this setup is the decay of short-lived isotopes, such as 219Rn and 220Rn, in the spectrometer volume. Active and passive countermeasures have been implemented and tested at the KATRIN main spectrometer. One of these is the magnetic pulse method, which employs the existing air coil system to reduce the magnetic guiding field in the spectrometer on a short timescale in order to remove low- and high-energy stored electrons. Here we describe the working principle of this method and present results from commissioning measurements at the main spectrometer. Simulations with the particle-tracking software Kassiopeia were carried out to gain a detailed understanding of the electron storage conditions and removal processes