APPC12July 17, 2013

Shin-Hong Kim (University of Tsukuba)
for Neutrino Decay collaboration
Neutrino Decay Collaboration
S.H. Kim, Y. Takeuchi, K. Nagata, K. Kasahara, T. Okudaira (University of Tsukuba),
H. Ikeda, S. Matsuura, T. Wada (JAXA/ISAS), H. Ishino, A. Kibayashi (Okayama University),
S. Mima (RIKEN), T. Yoshida(University of Fukui), Y. Kato (Kinki University), M. Hazumi,
Y. Arai (KEK), E. Ramberg, J.H. Yoo (Fermilab), S. B.Kim (Seoul National University)● Introduction
Motivation
Cosmic Infrared Background Measurement by COBE and AKARI● Proposal on Search for Cosmic Background Neutrino Decay
Preparatory Rocket experiment● R&D of Superconducting Tunnel Junction (STJ) Detector Only neutrino mass is unknown in elementary particles. Detection of neutrino decay
enables us to measure an independent quantity of m2 measured by neutrino
oscillation experiments.
Thus we can obtain neutrino mass itself
from these two independentmeasurements.

3W

,2   322m 32  m 22 m 23E 
2m 32m 32Using m 23 ( 2.43  0.09)  10  3 eV2E  10～25 meV at  3 rest frame.
(Far - Infrared region   50～125  ) As the neutrino lifetime is very long, we need use cosmic background neutrino
to observe the neutrino decay. To observe this decay of the cosmic background neutrinomeans a discovery of the cosmic background neutrino predicted by cosmology.

In the Left - Right S ymmetricModel S U(2)L  S U(2)R  U(1)( PRL 38, 1252(1977), PRD 17, 1395(1978) NP B206, 359(1982)) ,there are two Weak Boson mass eigenstates :W1  W Lcosz  W Rsinz ,W2  W Lsinz  W Rcosz .
WL and WR are fields withpure V-A and V+A couplings,
respectively, and z is a mixingangle.

Using a lower mass limit M (W R )  715GeV/c 2 , a mixing angle limitz  0.013,
and m3  50meV,

 (     )  1.5  1017 year32

( 2.1  1043 year in S tandard Model )Measured neutrino lifetime limit τ < 3 x 1012 year
from CIB results measured by COBE and AKARICOBE: M. G. Hauser et al. ApJ 508 (1998) 25. D. P. Finkbeiner et al. ApJ 544 (2000) 81.
AKARI: S. Matsuura et al. ApJ. 737 (2011) 2.
Search Region
Zodiacal LightCIB measurements
Rocket Experiment

Surface brightness I( AKARI,  COBE)

Galaxy evolution model

Galactic dust emission

Integrated flux from galaxy counts
Wavelength[m]A. Mirizzi, D. Montanino and P. Serpico PRD76, 053007 (2007)
Neutrino lifetime τ < (1.6~3.1)x1012 year from CIB results by COBE
S.H. Kim, K. Takemasa, Y. Takeuchi and S. Matsuura JPSJ 81, 024101 (2012)
Neutrino lifetime τ < (3.1~3.8)x1012 year from CIB results by AKARI and SPITZER

Cosmic Infrared Background

10-hour running witha telescope with 20cm diameter,a viewing angle of 0.1 degrees
and 100% detection efficiency( Satellite Experiment )Neutrino Decay （τ＝1.5 x 1017year）
Sharp edge with 1.9K smearing
with detector resolution of 0% to 5%
Red shift effect

dN/dEγ

- d2Nγ/dEγ2
6.7σ● Need the energy resolution better
than 2%.
● Can observe the ν3 decay witha mass of 50meV, and a lifetime of
1.5 x 1017year at 6.7σ.

SU(2)L x SU(2)R x U(1) model Lifetime
Prediction

Search Region ( Satellite Experiment)
Rocket Experiment

S.H. Kim, K. Takemasa, Y. Takeuchi and S. Matsuura

JPSJ 81, 024101 (2012)

Search Region: λ＝ 40～150μm （Eγ ＝ 8～30meV）In Rocket experiment, λ＝ 40～80μm （Eγ ＝ 15～30meV）
Nb/Al-STJ sensisitive region > 8meV ( Nquasi-particles = 60 )Plan: 5minutes data acquisition at 200 km height in 2016.
Improve lifetime limit by two orders of magnitude ( ~1014year).
JAXA Rocket CIB Experiment（Feb 2, 1992）

Nb/Al-STJ
Goal: detection of a single far-infrared photon in energy range between 15meV and30meV for the rocket experiment for neutrino decay search.
Signal of Nb/Al-STJ (100 x 100μm2) toinfrared (1.31μm) light at 1.9K.

Time spread at FWHM is 1μsec.
The number of photon : 93±11( from the spread of
the signal charge distribution ).
the response of Nb/Al-STJ (4μm2 ) to the visible
light (456nm) at 1.9K.
a single photon peak is separated from pedestal by1σ.
The signal charge distribution (Red histogram) is
fitted by four Gaussians of 0, 1, 2 and 3 photon
peaks. Single photon peak has a mean of 0.4fC
and σ of 0.4fC.

Signal charge
distribution

SOI-STJ
SOI (Silicon-On-Insulator) preamplifier :Low noise preamplifier working around 1K.
We have processed Nb/Al-STJ on a SOI
transistor board, and confirmed that both
Nb/Al-STJ detector and SOI MOSFET
worked normally at 700mK.

I (1mA /DIV.)

V (2mV /DIV.)In the next step, we will look at the response of SOI-STJ to infrared photons.

Hf-STJ
Goal: Measure energy of a single far-infrared photon for neutrino decay searchexperiment within 2% energy resolution.

I-V curve of Hf-STJ (200x200m2 )• T~80mK, Ic=60μA, Rd=0.2Ω

B=0 Gauss

Hf-STJ (100x100m2) shows smaller leakage
current than Hf-STJ (200x200m2) which wehave established to work as a STJ in 2011.
The work to reduce a large leakage current ofHf-STJ is underway.

B=10 Gauss

I-V curve of Hf-STJ (100x100m2 )• T~40mK, Ic=10μA, Rd=0.6Ω

B=0 Gauss

B=10 Gauss1. It is feasible to observe the cosmic backgroundneutrino decay with a satellite experiment, if we
assume Left-Right Symmetric Model.
2. We are developing STJ-based detectors to detecta far-infrared photon in energy range between 8
and 30meV to search for cosmic backgroundneutrino decay.
3. A rocket experiment using the STJ detectors forneutrino decay search is in preparation. It will
improve the neutrino lifetime sensitivity fromthe present 1012 year to 1014 year.

2013

SuperconductingTun
nel Junction (STJ )Detector
Preamplifier at 2K
and Post-Preamp(Fermilab, JAXA,Tsukuba）
Dispersive Element,Optics (JAXA,Tsukuba)
Cryostat( JAXA, KEK)
Measurements＋
Analysis
（All）

2015

2016

2017

2018

Experiment design with Satellite such as SPICA
Experiment design withFIR Rocket
Design and R&D of
Nb/Al-STJ Detector

Production

Design and R&D of Hf-STJ Detector
Design and R&D

Nb/Al-STJ設計・開発
Production

Design and R&D

Production

Design and R&D

Production

Analysis Program
Simulation

Far-Infrared Observatory Rocket Experiment

Experiment Design201414Analysis

» Superconductor / Insulator / Superconductor Josephson
Junction

At the superconducting junction,
excited electrons (quasi-particles) overtheir energy gap go through tunnel barrier
by a tunnel effect.
By measuring the tunnel current ofelectrons excited by an incident particle,
we measure the energy of the particle.
Excited Electrons

Incident Particle
2ΔCooper PairsSISSTJ Energy Resolution

Δ: Band gap energy E  1.7( FE )F:Using Hf as a superconductor, E:

 E / E  1.7%

at E  25meVMaterialNiobium
9.20
Aluminum 1.14

1.550
0.172

Hafnium

0.021

0.13

Fano factor (= 0.2)
Incident particle energy

Tc : Critical Temperature
Operation is done at a temperaturearound 1/10 of Tc

We reported that Hf-STJ worked as a STJ in
2011.

ATLAS
CDF

GUT
Phase Transition in vacuum

2.7K Cosmic backgroundradiation(420/cm3)
Electroweak
1.9K Cosmic background neutrino
Higgs particle(110/cm3)

M. Beg, W. Marciano and M. Rudeman Phys. Rev. D17 (1978) 1395-1401
R. E. Shrock Nucl. Phys. B206 (1982) 359-379
Calculate the neutrino decay width in SU(2)L ｘ SU(2)R ｘ U(1) modelwith Dirac neutrinos.
M（WR）=∞ and sin z = 0 corresponds to Standard Model.

W 1  W L cos z  W R sin z
W 2  W L sin z  W R cos z
WL and WR are fields withpure V-A and V+A couplings,
respectively, and z is a mixing
angle.

Using a lower mass limit M (W R )  715GeV/c 2 , a mixing angle limit z  0.013,
and m3  50meV,

 (     )  1.5 1017 year
32( 2.110 43 year in Standard M odel )R. E. Schrock, Nucl. Phys. 28 (1982) 359.
Calculate the neutrino decay width in SU(2)L ｘ SU(2)R ｘ U(1) model3

GF 2  m322  2 2
1 m sin 2z
64 4  m3 M W2  0.715TeV, sinz  0.013, m32  2.43 10-3 eV 2 , m  1.78GeV, m3  50meV ,2  1.5 1017 year
In the standard model,
3222

9GF  m32 
22  m1 (mm)
32 2 4 
8192  m3  MW 

2Thus   2.110 43 year

ref. K. Sato and M . Kobayashi, Prog. Theor. Phys.58 (1977) 1775. and others.

Focal plane Instruments
Incident rays are madeparallel throughcylindrical mirrors 1, 2
and a parabolic mirror
before diffracted by agrating, and are finallyfocused on the STJ
detector array by aspherical mirror.

Rate/50pixel-spectrometer = 15 kHz ( 300Hz/pixel)
Measurements for 200 s → 3M events /50pixel-spectrometer.
Using 8 x 50pixel-spectrometer, σ/N=0.02%
2σ = 0.04% x 0.5μW/m2/sr = 0.2nW/m2/sr (0.4% times present limit 50nW/m2/sr ）