Results obtained several years ago using the high-resolution 93.3 keV Mössbauer resonance in
67
ZnO and
β
′
-brass have been reanalyzed with the notion that the clock hypothesis of Special Relativity ...Theory is not sufficient, but that a maximal acceleration
a
m
exists and that an acceleration
a
contributes to the temperature dependence of the center shift by a term ±(1/2)(
a
/
a
m
)
2
. The significance of the sign of this term is discussed in detail. For both substances a lower limit of
a
m
>1.5⋅10
21
m/s
2
is inferred which is more than two orders of magnitude
larger
than - and thus excludes - the value
a
m
=1⋅10
19
m/s
2
suggested by
57
Fe rotor experiments.
The CRESST-II experiment uses cryogenic detectors to search for nuclear recoil events induced by the elastic scattering of dark matter particles in CaWO
4
crystals. Given the low energy threshold of ...our detectors in combination with light target nuclei, low mass dark matter particles can be probed with high sensitivity. In this letter we present the results from data of a single detector module corresponding to 52 kg live days. A blind analysis is carried out. With an energy threshold for nuclear recoils of 307 eV we substantially enhance the sensitivity for light dark matter. Thereby, we extend the reach of direct dark matter experiments to the sub- GeV/
c
2
region and demonstrate that the energy threshold is the key parameter in the search for low mass dark matter particles.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The CRESST-II cryogenic Dark Matter search, aiming at detection of WIMPs via elastic scattering off nuclei in CaWO
4
crystals, completed 730 kg days of data taking in 2011. We present the data ...collected with eight detector modules, each with a two-channel readout; one for a phonon signal and the other for coincidently produced scintillation light. The former provides a precise measure of the energy deposited by an interaction, and the ratio of scintillation light to deposited energy can be used to discriminate different types of interacting particles and thus to distinguish possible signal events from the dominant backgrounds.
Sixty-seven events are found in the acceptance region where a WIMP signal in the form of low energy nuclear recoils would be expected. We estimate background contributions to this observation from four sources: (1) “leakage” from the
e
/
γ
-band (2) “leakage” from the
α
-particle band (3) neutrons and (4)
206
Pb recoils from
210
Po decay. Using a maximum likelihood analysis, we find, at a statistical significance of more than 4
σ
, that these sources alone are not sufficient to explain the data. The addition of a signal due to scattering of relatively light WIMPs could account for this discrepancy, and we determine the associated WIMP parameters.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Coherent elastic neutrino–nucleus scattering (CEνNS) offers a unique way to study neutrino properties and to search for new physics beyond the Standard Model. Nuclear reactors are promising sources ...to explore this process at low energies since they deliver large fluxes of anti-neutrinos with typical energies of a few MeV. In this paper, a new-generation experiment to study CEνNS is described. The NUCLEUS experiment will use cryogenic detectors which feature an unprecedentedly low-energy threshold and a time response fast enough to be operated under above-ground conditions. Both sensitivity to low-energy nuclear recoils and a high event rate tolerance are stringent requirements to measuring CEνNS of reactor anti-neutrinos. A new experimental site, the Very-Near-Site (VNS), at the Chooz nuclear power plant in France is described. The VNS is located between the two 4.25 GWth reactor cores and matches the requirements of NUCLEUS. First results of on-site measurements of neutron and muon backgrounds, the expected dominant background contributions, are given. In this paper a preliminary experimental set-up with dedicated active and passive background reduction techniques and first background estimations are presented. Furthermore, the feasibility to operate the detectors in coincidence with an active muon veto at shallow overburden is studied. The paper concludes with a sensitivity study pointing out the physics potential of NUCLEUS at the Chooz nuclear power plant.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The NUCLEUS experiment aims for the detection of coherent elastic neutrino-nucleus scattering at a nuclear power reactor with gram-scale, ultra-low-threshold cryogenic detectors. This technology ...leads to a miniaturization of neutrino detectors and allows to probe physics beyond the Standard Model of particle physics. A 0.5 g NUCLEUS prototype detector, operated above ground in 2017, reached an energy threshold for nuclear recoils of below 20 eV. This sensitivity is achieved with tungsten transition edge sensors which are operating at temperatures of 15 mK and are mainly sensitive to non-thermal phonons. These small recoil energies become accessible for the first time with this technology, which allows collecting large-statistics neutrino event samples with a moderate detector mass. A first-phase cryogenic detector array with a total mass of 10 g enables a 5-sigma observation of coherent scattering within several weeks. We identified a suitable experimental site at the Chooz Nuclear Power Plant and performed muon and neutron background measurements there. The operation of a NUCLEUS cryogenic detector array at such a site requires highly efficient background suppression. NUCLEUS plans to use an innovative technique consisting of separate cryogenic anticoincidence detectors against surface backgrounds and penetrating (gamma, neutron) radiation. We present first results from prototypes of these veto detectors and their operation in coincidence with a NUCLEUS target detector.
Recoilless resonant capture of monoenergetic electron antineutrinos (Mössbauer antineutrinos) emitted in bound-state β-decay in the system 3H – 3He is discussed. The recoilfree fraction including a ...possible phonon excitation due to local lattice expansion and contraction at the time of the nuclear transition, homogeneous and inhomogeneous line broadening, and the relativistic second-order Doppler effect are considered. It is demonstrated that homogeneous line broadening is essential due to stochastic magnetic relaxation processes in a metallic lattice. Inhomogeneous line broadening plays an equally important role. An essential issue which has been overlooked up to now, is an energy shift of the resonance line due to the direct influence of the binding energies of the 3H and 3He atoms in the lattice on the energy of the electron antineutrinos. This energy shift as well as the second-order Doppler shift exhibit variations in a non-perfect (inhomogeneous) lattice and may seriously jeopardize the observation of Mössbauer antineutrinos. If successful in spite of these enormous difficulties, Mössbauer antineutrino experiments could be used to gain new and deep insights into the nature of neutrino oscillations, determine the neutrino mass hierarchy as well as up to now unknown oscillation parameters, search for sterile neutrinos, and measure the gravitational redshift of electron antineutrinos in the field of the Earth.
We report the complete GNO solar neutrino results for the measuring periods GNO III, GNO II, and GNO I. The result for GNO III (last 15 solar runs) is 54.3−9.3+9.9(stat)±2.3(syst)SNU(1σ) or ...54.3−9.6+10.2(incl. syst) SNU (1σ) with errors combined. The GNO experiment is now terminated after altogether 58 solar exposure runs that were performed between 20 May 1998 and 9 April 2003. The combined result for GNO (I+II+III) is 62.9−5.3+5.5(stat)±2.5(syst) SNU (1σ) or 62.9−5.9+6.0 SNU (1σ) with errors combined in quadrature. Overall, gallium based solar observations at LNGS (first in GALLEX, later in GNO) lasted from 14 May 1991 through 9 April 2003. The joint result from 123 runs in GNO and GALLEX is 69.3±5.5(incl. syst) SNU (1σ). The distribution of the individual run results is consistent with the hypothesis of a neutrino flux that is constant in time. Implications from the data in particle- and astrophysics are reiterated.
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