Speaker
Dr
Saori UMEHARA
(Osaka University)
Description
CANDLES is the project to search for neutrino-less double beta
decay (0$\nu\beta\beta$) of $^{48}$Ca.
0$\nu\beta\beta$ is acquiring great interest
after the confirmation of neutrino oscillation
which demonstrated nonzero neutrino mass.
Measurement of 0$\nu\beta\beta$ provides a test for the Majorana
nature of neutrinos
and gives an absolute scale of the effective neutrino mass.
In order to search for 0$\nu\beta\beta$ of $^{48}$Ca,
we proposed CANDLES system by using CaF$_{2}$ scintillators.
The CANDLES system aims at a high sensitive measurement
by a characteristic detector structure and $^{48}$Ca enrichment.
The detector structure realizes a complete 4$\pi$ active shield
by immersion of the CaF$_{2}$ scintillators in liquid scintillator.
The active shield by the liquid scintillator
leads to a low background condition for the measurement.
On the other band,
$^{48}$Ca enrichment is also effective for the high sensitive measurement,
because natural abundance of $^{48}$Ca is very low (0.19\%).
This means that an improvement of sensitivity by enrichment
is a maximum of 20 times for the neutrino mass.
However $^{48}$Ca enrichment is generally difficult and expensive.
Therefore we started the study of $^{48}$Ca enrichment
and succeeded in obtaining enriched $^{48}$Ca although it is a small amount.
We have developed the CANDLES III system,
which contained 350 g of $^{48}$Ca without enrichment,
at the Kamioka underground laboratory.
In 2012
we installed a light-concentration system in the CANDLES III system
in order to improve a energy resolution.
A photo-coverage was about twice larger than the one
without the light-concentration system.
And we started a 0$\nu\beta\beta$ measurement
and have data of a measurement time for 3 months.
Here we will report the detector performance
for background rejection,
the result of the measurement
and the expected sensitivity with the light-concentration system.
Primary author
Dr
Saori UMEHARA
(Osaka University)
Co-authors
Prof.
Sei Yoshida
(Osaka University)
Prof.
Tadafumi Kishimoto
(Osaka University)
Prof.
masaharu Nomachi
(Osaka University)
