The NEMO-3 results for the double-
β
decay of
150
Nd to the 0
1
+
and 2
1
+
excited states of
150
Sm are reported. The data recorded during 5.25 year with 36.6 g of the isotope
150
Nd are used in the ...analysis. The signal of the
2
ν
β
β
transition to the 0
1
+
excited state is detected with a statistical significance exceeding 5
σ
. The half-life is measured to be
T
1
/
2
2
ν
β
β
(
0
1
+
)
=
1
.
11
-
0.14
+
0.19
stat
-
0.15
+
0.17
syst
×
10
20
year, which is the most precise value that has been measured to date. 90% confidence-level limits are set for the other decay modes. For the
2
ν
β
β
decay to the 2
1
+
level the limit is
T
1
/
2
2
ν
β
β
(
2
1
+
)
>
2.42
×
10
20
year
. The limits on the
0
ν
β
β
decay to the 0
1
+
and 2
1
+
levels of
150
Sm are significantly improved to
T
1
/
2
0
ν
β
β
(
0
1
+
)
>
1.36
×
10
22
year
and
T
1
/
2
0
ν
β
β
(
2
1
+
)
>
1.26
×
10
22
year
.
Abstract The full data set of the NEMO-3 experiment has been used to measure the half-life of the two-neutrino double beta decay of $$^{100}$$ 100 Mo to the ground state of $$^{100}$$ 100 Ru, ...$$T_{1/2} = \left 6.81 \pm 0.01\,\left( \text{ stat }\right) ^{+0.38}_{-0.40}\,\left( \text{ syst }\right) \right \times 10^{18}$$ T1/2=6.81±0.01stat-0.40+0.38syst×1018 year. The two-electron energy sum, single electron energy spectra and distribution of the angle between the electrons are presented with an unprecedented statistics of $$5\times 10^5$$ 5×105 events and a signal-to-background ratio of $$\sim $$ ∼ 80. Clear evidence for the Single State Dominance model is found for this nuclear transition. Limits on Majoron emitting neutrinoless double beta decay modes with spectral indices of $$\mathrm{n}=2,3,7$$ n=2,3,7 , as well as constraints on Lorentz invariance violation and on the bosonic neutrino contribution to the two-neutrino double beta decay mode are obtained.
The mass number dependence of the WIMP–nucleus scattering offers a method for identifying a true WIMP signal over a neutron background. In this Letter we present a study on using a combination of ...ZnWO4 and CaWO4 absorbers to exploit this materials signature for WIMP detection. Using monochromatic X-ray radiation we examined the temperature variation of the luminescence properties for both materials and showed that at low temperature (8 K) ZnWO4 exhibits ∼10% higher light yield than CaWO4. Analysis of relevant optical properties indicates that ZnWO4 is a suitable cryogenic scintillator. We show that already modest exposure in the region of ∼5 kg yr should allow the detection of WIMP interaction for cross sections at the level of current experimental sensitivities. The combination of these two tungstates could form the basis of the first multi-target detector capable of WIMP identification through materials signature.
We present first significant limits on WIMP dark matter by the phonon-light technique, where combined phonon and light signals from a scintillating cryogenic detector are used. Data from early 2004 ...with two 300g CRESST-II prototype detector modules are presented, with a net exposure of 20.5kg days. The modules consist of a CaWO4 scintillating “target” crystal and a smaller cryogenic light detector. The combination of phonon and light signals leads to a strong suppression of non-nuclear recoil backgrounds. Using this information to define an acceptance region for nuclear recoils we have 16 events from the two modules, corresponding to a rate for nuclear recoils between 12 and 40keV of (0.87±0.22) events/(kgday). This is compatible with the rate expected from neutron background, and most of these events lie in the region of the phonon-light plane anticipated for neutron-induced recoils. A particularly strong limit for WIMPs with coherent scattering results from selecting a region of the phonon-light plane corresponding to tungsten recoils, where the best module shows zero events.
A local principal curve algorithm has been implemented in three dimensions for automated track and shower reconstruction of neutrino interactions in a liquid argon time projection chamber. We present ...details of the algorithm and characterise its performance on simulated data sets.
A Cellular Automaton algorithm has been implemented in three dimensions for automated track reconstruction of neutrino interactions in a Liquid Argon Time Projection Chamber. We present details of ...the algorithm and characterise its performance on simulated data sets.
By exploiting structural differences between electromagnetic and hadronic showers in a multivariate analysis we present an efficient Electron-Hadron discrimination algorithm for liquid argon time ...projection chambers, validated using Geant4 simulated data.
The recent trend of proposing dark matter direct detection experiments using detector masses of the order of one ton initiated this study about its merits and restrictions for WIMP signature ...detection. It is shown that measurements of the modulation signature would become a sensitive method to study WIMP halo properties using detector masses of the order of one ton in case the DAMA evidence is confirmed. On the other hand, as soon as experiments improve limits by roughly one order of magnitude one will have to test signatures different from the WIMP modulation signature. This paper discusses data analysis techniques to reveal the modulation signature for WIMP direct detection experiments. A periodogram approach, adopted from astronomy, least squares and maximum likelihood techniques are applied to the problem of detecting a weak periodic signal in unevenly sampled noisy data. The systematics of WIMP modulation analysis is discussed and a comparison of evidence regions to limits for selected target materials is carried out.
PDF
