Review of Double Beta Experiments Sarazin, X
Journal of physics. Conference series,
04/2015, Letnik:
593, Številka:
1
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
This paper gives a review of the double beta experimental techniques and projects, in the search for the Majorana neutrino. The purpose of this review is to detail, for each technique, the different ...origins of background, how they can be identified, and how they can be reduced. Advantages and limitations of the different techniques are discussed.
H.A. Wilson, then R.H. Dicke, proposed to describe gravitation by a spatial change of the refractive index of the vacuum around a gravitational mass. Dicke extended this formalism in order to ...describe the apparent expansion of the universe by a cosmological time dependence of the global vacuum index. In this paper, we develop Dicke’s formalism. The metric expansion in standard cosmology (the time-dependent scale factor of the Friedmann–Lemaître curved spacetime metric) is replaced by a flat and static Euclidean metric with a change with time of the vacuum index. We show that a vacuum index increasing with time produces both the cosmological redshift and time dilation, and that the predicted evolution of the energy density of the cosmological microwave background is consistent with the standard cosmology. We then show that the type Ia supernovæ data, from the joint SDSS-II and SNLS SNe-Ia samples, are well modeled by a vacuum index varying exponentially as
n
(
t
)
=
e
x
p
(
t
/
τ
0
)
, where
τ
0
=
8
.
0
-
0.8
+
0.2
Gyr. The main consequence of this formalism is that the cosmological redshift should affect any atom, with a relative decrease of the energy levels of about
-
2
10
-
18
s
-
1
. Possibilities for an experimental investigation of this prediction are discussed.
In the prefrontal cortex (PFC), higher-order cognitive functions and adaptive flexible behaviors rely on continuous dynamical sequences of spiking activity that constitute neural trajectories in the ...state space of activity. Neural trajectories subserve diverse representations, from explicit mappings in physical spaces to generalized mappings in the task space, and up to complex abstract transformations such as working memory, decision-making and behavioral planning. Computational models have separately assessed learning and replay of neural trajectories, often using unrealistic learning rules or decoupling simulations for learning from replay. Hence, the question remains open of how neural trajectories are learned, memorized and replayed online, with permanently acting biological plasticity rules. The asynchronous irregular regime characterizing cortical dynamics in awake conditions exerts a major source of disorder that may jeopardize plasticity and replay of locally ordered activity. Here, we show that a recurrent model of local PFC circuitry endowed with realistic synaptic spike timing-dependent plasticity and scaling processes can learn, memorize and replay large-size neural trajectories online under asynchronous irregular dynamics, at regular or fast (sped-up) timescale. Presented trajectories are quickly learned (within seconds) as synaptic engrams in the network, and the model is able to chunk overlapping trajectories presented separately. These trajectory engrams last long-term (dozen hours) and trajectory replays can be triggered over an hour. In turn, we show the conditions under which trajectory engrams and replays preserve asynchronous irregular dynamics in the network. Functionally, spiking activity during trajectory replays at regular timescale accounts for both dynamical coding with temporal tuning in individual neurons, persistent activity at the population level, and large levels of variability consistent with observed cognitive-related PFC dynamics. Together, these results offer a consistent theoretical framework accounting for how neural trajectories can be learned, memorized and replayed in PFC networks circuits to subserve flexible dynamic representations and adaptive behaviors.
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
.
Using data from the NEMO-3 experiment, we have measured the two-neutrino double beta decay ( Formula omitted) half-life of Formula omittedSe as Formula omitted y under the single-state dominance ...hypothesis for this nuclear transition. The corresponding nuclear matrix element is Formula omitted. In addition, a search for neutrinoless double beta decay ( Formula omitted) using 0.93 kg of Formula omittedSe observed for a total of 5.25 y has been conducted and no evidence for a signal has been found. The resulting half-life limit of Formula omitted for the light neutrino exchange mechanism leads to a constraint on the effective Majorana neutrino mass of Formula omitted, where the range reflects Formula omitted nuclear matrix element values from different calculations. Furthermore, constraints on lepton number violating parameters for other Formula omitted mechanisms, such as right-handed currents, majoron emission and R-parity violating supersymmetry modes have been set.
The BiPo-3 detector Loaiza, P.; Barabash, A.S.; Basharina-Freshville, A. ...
Applied radiation and isotopes,
05/2017, Letnik:
123
Journal Article
Recenzirano
The BiPo-3 detector is a low radioactive detector dedicated to measuring ultra-low natural contaminations of 208Tl and 214Bi in thin materials, initially developed to measure the radiopurity of the ...double β decay source foils of the SuperNEMO experiment at the μBq/kg level. The BiPo-3 technique consists in installing the foil of interest between two thin ultra-radiopure scintillators coupled to low radioactive photomultipliers. The design and performances of the detector are presented.
In this paper, the final results of the 208Tl and 214Bi activity measurements of the first enriched 82Se foils are reported for the first time, showing the capability of the detector to reach sensitivities in the range of some μBq/kg.
•BiPo3 : low radioactive detector to measure ultra-low levels of 208Tl and 214Bi.•Backgrounds characterized.•Surface background : A(208Tl) =(0.9±0.2)μBq/m2 and A(214Bi) =(1.0±0.3)μBq/m2.•First SuperNemo double β source foils measured : A(208Tl) =(21±11)μBq/kg and A(214Bi) < 290μBq/kg at 90% C.L.•Shows capability to measure 208Tl in the range of some μBq/kg.
Optical properties of the DIRC fused silica Cherenkov radiator Cohen-Tanugi, J.; Convery, M.; Ratcliff, B. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/2003, Letnik:
515, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The DIRC is a new type of Cherenkov detector that is successfully operating as the hadronic particle identification system for the BABAR experiment at SLAC. The fused silica bars that serve as the ...DIRC's Cherenkov radiators must transmit the light over long optical pathlengths with a large number of internal reflections. This imposes a number of stringent and novel requirements on the bar properties. This note summarizes a large amount of R&D that was performed both to develop specifications and production methods and to determine whether commercially produced bars could meet the requirements. One of the major outcomes of this R&D work is an understanding of methods to select radiation hard and optically uniform fused silica material. Others include measurement of the wavelength dependency of the internal reflection coefficient, and its sensitivity to surface contaminants, development of radiator support methods, and selection of good optical glue.
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 Formula omittedMo to the ground state of Formula omittedRu, Formula omitted ...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 Formula omitted events and a signal-to-background ratio of Formula omitted 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 Formula omitted, 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 quantum vacuum as the origin of the speed of light Urban, Marcel; Couchot, François; Sarazin, Xavier ...
The European physical journal. D, Atomic, molecular, and optical physics,
03/2013, Letnik:
67, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We show that the vacuum permeability
μ
0
and permittivity
ε
0
may originate from the magnetization and the polarization of continuously appearing and disappearing fermion pairs. We then show that if ...we simply model the propagation of the photon in vacuum as a series of transient captures within these ephemeral pairs, we can derive a finite photon velocity. Requiring that this velocity is equal to the speed of light constrains our model of vacuum. Within this approach, the propagation of a photon is a statistical process at scales much larger than the Planck scale. Therefore we expect its time of flight to fluctuate. We propose an experimental test of this prediction.
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