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J. D. Vergados

Publications and source records attributed to J. D. Vergados.

At least 55 records · Page 3Linked to original sources
arXiv2011

On the search of sterile neutrinos by oscillometry measurements

It is shown that the "new" neutrino with a high mass squared difference and a small mixing angle should reveal itself in the oscillometry measurements. For a judicious monochromatic neutrino source the "new" oscillation length $L_{42}$ is expected shorter than 1.5 m. Thus the needed measurements can be implemented with a gaseous spherical TPC of modest dimensions with a very good energy and position resolution. The best candidates for oscillometry are discussed and the sensitivity to the mixing angle $θ_{14}$ has been estimated: $\sin^2{(2θ_{14})}$=0.05 (99{%}) for two months of data handling with $^{51}$Cr.

hep-ph↗
arXiv2011

A scheme for the extraction of WIMP-nucleon scattering cross sections from total event rates

We propose a scheme that allows to analytically determine the three elementary cross sections and connect the solutions to the relative sign between the proton and the neutron spin scattering amplitudes once the measurements of total event rate from three appropriate targets become available. In this way it is thus possible to extract the maximum information on the supersymmetric parameter space obtainable from direct detection experiments, in the case that the dark matter particle is the lightest neutralino. Our scheme is based on suitably normalized form of the isospin momentum dependent structure functions entering in the spin-dependent elastic neutralino-nucleus cross section. We compare these functions with the commonly used ones and discuss their advantages: in particular, these allow in the spin-dependent cross section to factorize the particle physics degrees of freedom from the momentum transfer dependent nuclear structure functions as it happens in the spin-independent cross section with the nuclear form factor.

hep-ph↗
arXiv2011

Probing the fourth neutrino existence by neutral current oscillometry in the spherical gaseous TPC

It is shown that, if the "new neutrino" implied by the Reactor Neutrino Anomaly exists and is in fact characterized by the suggested relatively high mass squared difference and reasonably large mixing angle, it should clearly reveal itself in the oscillometry measurements. For a judicious neutrino source the "new oscillation length L14 is expected shorter than 3m. Thus the needed measurements can be implemented with a gaseous spherical TPC of modest dimensions with a very good energy and position resolution, detecting nuclear recoils following the coherent neutrino-nucleus elastic scattering. The best candidates for oscillometry, yielding both monochromatic neutrinos as well as antineutrinos, are discussed. A sensitivity in the mixing angle theta14, (sin(2\theta14))^2=0.1 (99 %), can be reached after a few months of data handling.

hep-ph↗
arXiv2010

Neutrino Oscillometry

Neutrino oscillations are studied employing sources of low energy monoenergetic neutrinos following electron capture by the nucleus and measuring electron recoils. Since the neutrino energy is very low the oscillation length appearing in this electronic neutrino disappearance experiment can be so small that the full oscillation can take place inside the detector. Thus one may determine very accurately all the neutrino oscillation parameters. In particular one can measure or set a better limit on the unknown parameter theta13. One, however, has to pay the price that the expected counting rates are very small. Thus one needs a very intensive neutrino source and a large detector with as low as possible energy threshold and high energy and position resolution. Both spherical gaseous and cylindrical liquid detectors are studied. Different source candidates are considered

hep-ph↗
arXiv2010

Ultra low energy results and their impact to dark matter and low energy neutrino physics

We present ultra low energy results taken with the novel Spherical Proportional Counter. The energy threshold has been pushed down to about 25 eV and single electrons are clearly collected and detected. To reach such performance low energy calibration systems have been successfully developed: - A pulsed UV lamp extracting photoelectrons from the inner surface of the detector - Various radioactive sources allowing low energy peaks through fluorescence processes. The bench mark result is the observation of a well resolved peak at 270 eV due to carbon fluorescence which is unique performance for such large-massive detector. It opens a new window in dark matter and low energy neutrino search and may allow detection of neutrinos from a nuclear reactor or from supernova via neutrino-nucleus elastic scattering

physics.ins-det↗
arXiv2010

Direct dark matter detection: The diurnal variation in directional experiments

We present some theoretical results relevant to the direct dark matter detection experiments, paying particular attention to directional experiments, i.e. experiments in which, not only the energy but the direction of the recoiling nucleus is observed. In directional experiments the detection rate depends on the angle between the line observation and the sun's direction of motion. Since, however, the direction of observation is fixed with respect the earth, while the Earth is rotating around its axis, in a directional experiment the angle between the direction of observation and the Sun's direction of motion will change during the day. So the observed signal in such experiments will exhibit a very interesting and characteristic periodic diurnal variation.

astro-ph.CO↗
arXiv2010

Exploring new features of neutrino oscillations with very low energy monoenergetic neutrinos

In the present work we propose to study neutrino oscillations employing sources of monoenergetic neutrinos following electron capture by the nucleus. Since the neutrino energy is very low the smaller of the two oscillation lengths, L23, appearing in this electronic neutrino disappearance experiment can be so small that the full oscillation can take place inside the detector and one may determine very accurately the neutrino oscillation parameters. Since in this case the oscillation probability is proportional to theta13, one can measure or set a better limit on the unknown parameter theta13. This is quite important, since, if this mixing angle vanishes, there is not going to be CP violation in the leptonic sector. The best way to detect it is by measuring electron recoils in neutrino-electron scattering. One, however, has to pay the price that the expected counting rates are very small. Thus one needs a very intensive neutrino source and a large detector with as low as possible energy threshold and high energy and position resolution. Both spherical gaseous and cylindrical liquid detectors are studied. Different source candidates are considered.

hep-ph↗
arXiv2009

Searching for Dark Matter- Theoretical Rates and Exclusion Plots due to the Spin

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. The nature of the dark matter constituents cannot be determined till they are directly detected. Recent developments in particle physics provide a number of candidates as constituents of dark matter, called Weakly Interacting Massive Particles (WIMPs). Since these interact weakly and are of low energy they cannot excite the target and can only be detected via measuring the recoiling nucleus. For all WIMPs, including the most popular candidate, the lightest supersymmetric particle (LSP), the relevant cross sections arise out of the following mechanisms: i) The coherent mode, due to the scalar interaction. ii) The charge coherent mode, with only proton contribution, as in the recent case of secluded dark matter scenario and iii) The spin contribution arising from the axial current. In this paper we will focus on the spin contribution, which maybe important, especially for light targets.

hep-ph↗
arXiv2009

The Diurnal Variation of the Wimp Detection Event Rates in Directional Experiments

The recent WMAP data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Modern particle theories naturally provide viable cold dark matter candidates with masses in the GeV-TeV region. Supersymmetry provides the lightest supersymmetric particle (LSP), theories in extra dimensions supply the lightest Kaluza-Klein particle (LKP) etc. The nature of dark matter can only be unraveled only by its direct detection in the laboratory. All such candidates will be called WIMPs (Weakly Interacting Massive Particles). In any case the direct dark matter search, which amounts to detecting the recoiling nucleus, following its collision with WIMP, is central to particle physics and cosmology. In this work we briefly review the theoretical elements relevant to the direct dark matter detection experiments, paying particular attention to directional experiments. i.e experiments in which, not only the energy but the direction of the recoiling nucleus is observed. Since the direction of observation is fixed with respect the the earth, while the Earth is rotating around its axes, the directional experiment will sample different parts of the sky at different times during the day. So, since the event rates are different when looking at different parts of the sky, the observed signal in such experiments will exhibit very interesting and characteristic periodic diurnal variation.

astro-ph.CO↗
arXiv2009

Pionic Contribution to Neutrinoless Double Beta Decay

It is well known that neutrinoless double decay is going to play a crucial role in settling the neutrino properties, which cannot be extracted from the neutrino oscillation data. It is, in particular, expected to settle the absolute scale of neutrino mass and determine whether the neutrinos are Majorana particles, i.e. they coincide with their own antiparticles. In order to extract the average neutrino mass from the data one must be able to estimate the contribution all possible high mass intermediate particles. The latter, which occur in practically all extensions of the standard model, can, in principle, be differentiated from the usual mass term, if data from various targets are available. One, however, must first be able reliably calculate the corresponding nuclear matrix elements. Such calculations are extremely difficult since the effective transition operators are very short ranged. For such operators processes like pionic contributions, which are usually negligible, turn out to be dominant. We study such an effect in a non relativistic quark model for the pion and the nucleon.

hep-ph↗
arXiv2009

Searching for Secluded Dark Matter via Direct Detection of Recoiling Nuclei as well as Low Energy Electrons

Motivated by recent cosmic ray experimental results there has been a proposition for a scenario where a secluded dark matter particle annihilates, primarily, into Standard Model leptons through a low mass mediator particle. We consider several varieties of this scenario depending on the type of mixing among gauge bosons and we study the implications in novel direct dark matter experiments for detecting low energy recoiling electrons. We find significant event rates and time modulation effects, especially in the case where the mediator is massless, that may be complementary to those from recoiling nuclei.

hep-ph↗
arXiv2009

Halo Density Profiles Consistent with Asymmetric M-B Velocity Distributions-Implications on Direct Dark Matter Searches

In the present paper we obtain the WIMP velocity distribution in our vicinity starting from spherically symmetric WIMP density profiles in a self consistent way by employing the Eddington approach. By adding a reasonable angular momentum dependent term in the expression of the energy, we obtain axially symmetric WIMP velocity distributions as well. We find that some density profiles lead to approximate Maxwell-Boltzmann distributions, which are automatically defined in a finite domain, i.e. the escape velocity need not be put by hand. The role of such distributions in obtaining the direct WIMP detection rates, including the modulation, is studied in some detail and, in particular, the role of the asymmetry is explored.

astro-ph↗
arXiv2008

Solar Neutrinos as Background in Direct Dark Matter Searches

The coherent contribution of all neutrons in neutrino nucleus scattering due to the neutral current is examined considering the boron solar neutrinos. These neutrinos could potentially become a source of background in the future dark matter searches aiming at nucleon cross sections in the region well below the few events per ton per year.

hep-ph↗
arXiv2008

A novel large-volume Spherical Detector with Proportional Amplification read-out

A new type of radiation detector based on a spherical geometry is presented. The detector consists of a large spherical gas volume with a central electrode forming a radial electric field. Charges deposited in the conversion volume drift to the central sensor where they are amplified and collected. We introduce a small spherical sensor located at the center acting as a proportional amplification structure. It allows high gas gains to be reached and operates in a wide range of gas pressures. Signal development and the absolute amplitude of the response are consistent with predictions. Sub-keV energy threshold with good energy resolution is achieved. This new concept has been proven to operate in a simple and robust way and allows reading large volumes with a single read-out channel. The detector performance presently achieved is already close to fulfill the demands of many challenging projects from low energy neutrino physics to dark matter detection with applications in neutron, alpha and gamma spectroscopy.

physics.ins-det↗
arXiv2008

Can Solar Neutrinos be a Serious Background in Direct Dark Matter Searches?

The coherent contribution of all neutrons in neutrino nucleus scattering due to the neutral current is examined considering the boron solar neutrinos. These neutrinos could potentially become a source of background in the future dark matter searches aiming at nucleon cross sections in the region well below the few events per ton per year.

hep-ph↗
arXiv2007

The impact of going beyond the Maxwell distribution in direct dark matter detection rates

We consider direct dark matter detection rates and investigate the difference between a standard Maxwell-Boltzmann velocity distribution and a "realistic" distribution like the ones extracted from numerical N-body simulations. Sizable differences are observed when such results are compared to the standard Maxwell-Boltzmann distribution. For a light target both the total rate and the annual modulation are reduced by ~25%. For a heavy target the total rate is virtually unchanged, whereas the annual modulation is modified by up to 50%, depending on the WIMP mass and detector energy threshold. We also consider the effect of a possible velocity anisotropy, and the effect is found to be largest for a light target For the realistic velocity distribution the anisotropy may reduce the annual modulation, in contrast to the Maxwell-Boltzmann case.

astro-ph↗
arXiv2007

Review of Low Energy Neutrinos

Some issues regarding low energy neutrinos are reviewed. We focus on three aspects i)We show that by employing very low energy (a few keV) electron neutrinos, neutrino disappearance oscillations can be investigated by detecting recoiling electrons with low threshold spherical gaseous TPC's. In such an experiment, which is sensitive to the small mixing angle theta13, the novel feature is that the oscillation length is so small that the full oscillation takes place inside the detector. Thus one can determine accurately all the oscillation parameters and, in particular, measure or set a good limit on theta13. ii) Low threshold gaseous TPC detectors can also be used in detecting nuclear recoils by exploiting the neutral current interaction. Thus these robust and stable detectors can be employed in supernova neutrino detection. iii) The lepton violating neutrinoless double decay is investigated focusing on how the absolute neutrino mass can be extracted from the data

hep-ph↗