COBAND プロジェクト

TCHoU
成果報告会 2018/6/4

武内 勇司

1

COBAND (COsmic BAckground Neutrino Decay)
Search for Neutrino decay in Cosmic background neutrino➔To be observed as photons in neutrino decaysin
𝜈2
𝜈1
𝜈3
𝜈2
𝜈3

𝜈3

𝜈1

𝜈3
𝜈1
𝜈3𝜸𝜸
𝜈22

3

COBAND Collaboration Members (As of Mar. 2018)
Shin-Hong Kim, Yuji Takeuchi, Takashi Iida, Kenichi Takemasa,
Kazuki Nagata, Chisa Asano，Rena Wakasa, Akihiro Kasajima,
Hironobu Kanno, Yoichi Otsuka (Univ. of Tsukuba),
Hirokazu Ikeda, Takehiko Wada, Koichi Nagase (JAXA/ISAS),
Shuji Matsuura (Kwansei gakuin Univ),
Yasuo Arai, Ikuo Kurachi, Masashi Hazumi (KEK),
Takuo Yoshida，Takahiro Nakamura, Makoto Sakai , Wataru
Nishimura (Univ. of Fukui),Satoru Mima (RIKEN), Kenji Kiuchi (University of Tokyo),
H.Ishino, A.Kibayashi (Okayama Univ.),
Yukihiro Kato (Kindai University),
Go Fujii, Shigetomo Shiki, Masahiro Ukibe, Masataka Ohkubo (AIST),
Shoji Kawahito (Shizuoka Univ.),
Erik Ramberg, Paul Rubinov, Dmitri Sergatskov (Fermilab)，
Soo-Bong Kim (Seoul National University)3Expected photon wavelength spectrum from CB decays distribution in ν3 → 𝜈2 + 𝛾
dN/d(a.u.)

Sharp Edge with1.9K smearing

𝒎𝟑 = 𝟓𝟎 𝐦𝐞𝐕Red Shift effect

10
100500 [m]100502010

If assume𝑚1 ≪ 𝑚2 < 𝑚3 ,𝑚3 ~50𝑚𝑒𝑉 fromneutrino oscillation
measurements

5E [meV]

50𝜇𝑚(25meV)No other source has such a sharp edge structure!!
4

Surface brightness I [MJy/sr]

Neutrino Decay signal and backgrounds
100 CIB summary from Matsuura et al.(2011)

Zodiacal Emission

CMB1010.1

Zodiacal Light

0.01ISD

0.001 DGL

0.0001

1Zodiacal
Emission
𝑰𝒁𝑬 =8MJy/srSLCB decay

NeutrinoDecay𝑰𝝂 =25kJy/sr

Integrated flux from galaxy counts

𝜏 = 1 × 1014 yr𝑠
1000
10010𝒎𝟑 = 𝟓𝟎 𝐦𝐞𝐕
wavelength [m]No other source has such a sharp edge structure!!

5

Proposal for COBAND Rocket Experiment
Aiming at a sensitivity to 𝜈 lifetime for 𝜏 𝜈3 = Ο 1014 yr𝑠
JAXA sounding rocket S-520
 Telescope with 15cm diameter and 1m focal length At the focal point, a diffraction grating covering =40-80m
and an array of photo-detector pixels of 50() x 8() areplaced.
 Each pixel has 100mx100m sensitive area.

𝜃6

COBAND rocket experiment sensitivity

L-R SM =0.02, M(W2)=715GeVCOBAND rocket
200sec meas.

mi < 0.23eV

200-sec measurements with a sounding rocket
15cm dia. and 1m focal length telescope and grating in 40~80m range
Each pixel in 100m100m850pix. array counts number of photons
m312 = 2.510-3eV2•••x100 improvement!
S.H.Kim et. al (2012)Mirizzi et. al (2007)7

Requirements for the photo-sensor in COBAND rocket experiment• Sensitive area of 100m100m for each pixel• High detection efficiency for a far-infrared single-photon in
=40m～80m• Dark count rate less than 300Hz (expected real photon rate)➔NEP = 𝜖𝛾 2𝑓𝛾 ~ 110−19 𝑊 Τ 𝐻𝑧

We are trying to achieve NEP ~10−19 𝑊 Τ 𝐻𝑧 by using• Superconducting Tunneling Junction detector• Cryogenic amplifier readout8Superconducting Tunnel Junction (STJ)
Superconductor / Insulator /Superconductor
Josephson junction device

Superconductor
Insulator

E2
300nm

Ns(E)
Superconductor
Superconductor
Insulator

Δ: Superconducting gap energy
A constant bias voltage (|V|<2Δ) is applied across the junction.
A photon absorbed in the superconductor breaks Cooper pairs and createstunneling current of quasi-particles proportional to the deposited photon energy.

• Much lower gap energy (Δ) than FIR photon ➔ Can detect FIR photon• Faster response (~s) ➔ Suitable for single-photon counting
9STJ candidates
Nb/Al-STJ• Well-establishedSiNbAlHf9.231.200.165

1100 1.550

0.172

0.020

Tc[K]
Δ[meV]• Δ~0.6meV by the proximity effect from Al• Operation temperature <400mK• Back-tunnelling gain GAl~10• Nq.p.=25meV/1.7ΔGAl~ 250
E/E~10% for E=25meV➔25meV single-photon detection is feasible in principle➔Developing for the rocket experiment
Hf-STJ• Not established as a practical photo-detector yet by any group• Nq.p.=25meV/1.7Δ~ 735
E/E<2% for E=25meV➔Spectrum measurement without a diffraction grating➔Developing for a future satellite experiment10Hf-STJ development

We successfully made a device with SIS in 2010. We need tosuppress leakage down to ~pA for practical usage.
Hf-STJ(RMS=2.5nm)
200m200m
~25eV
T~140mK

200𝜇𝑚 × 200𝜇𝑚

200m sq. Hf-STJ in 2010

200m sq. Hf-STJ in 2017
Detailed status in K.Takemasa’s talk11

Nb/Al-STJ development at CRAVITY
I

100nA

T~300mKw/ B field

10nA

500pA/DIVLeakage

VLeakage

50m sq. Nb/Al-STJ fabricated at CRAVITY

0.1nA

1nA
100pA

0.2mV/DIV

Temperature(K)
0.3

0.4

0.5

0.6

0.7Ileak~200pA for 50m sq. STJ, and achieved 50pA for 20m sq.

➔ This satisfies our requirement!

Far-infrared single photon detection is feasible with thisNb/Al-STJ sensor and a cryogenic amplifier which canbe deployed in close proximity to the STJ.
12

STJ energy resolution for near infrared photon

P. Verhoeve et. al 1997
◼ 30m sq. Ta/Al-STJ◼ E~130meV @ E=620meV(=2m)◼ Charge sensitive amplifier at room temp.
 Electronic noise ~ 100meVIn sub-eV ~ several-eV region, STJ gives the best energy resolution amongsuperconductor based detectors, but limited by readout electronic noise.
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FD-SOI-MOSFET at cryogenic temperature
FD-SOI : Fully Depleted – Silicon On Insulator

ChannelWidth : W

Channel Length : L~50nm

 Very thin channel layer in MOSFET on SiO2
 No floating body effect caused by charge
accumulation in the body FD-SOI-MOSFET is reported to work at 4K
JAXA/ISIS AIPC 1185,286-289(2009)
J Low Temp Phys 167, 602 (2012)

Id-Vg curve of W/L=10m/0.4m at |Vds|=1.8V

Ids1mA

1mA-Ids

1A
1nA

1A

̶ ROOM
̶ 3Kp-MOS

1nAn-MOS

Vgs (V)

1pA

̶ ROOM̶ 3K-2-1.5-1-0.5

0Vgs (V)
00.5

11.5

2

Both p-MOS and n-MOS show excellent performance at 3K and below.
14

10mV

SOI prototype amplifier for demonstration test
T=350mK

1nF
Ｖ

Testpulse

Amplifier Buffer
stagestage

150mV

8mV

INPUT

100s
OUTPUT

Test pulse input through C=1nF at
T=3K and 350mK• Power consumption: ~100μW• Output load: 1M and ~0.5nF

We can compensate the effect of shifts in the thresholds by adjusting bias
voltages.
15

Amplification of STJ response to laser pulse on cold stage
10MSTJ

Vdd

4.7F

cold stage
T~350mKVss

465nm laser
pulse throughoptical fiber

3He sorption

GND

STJ SOI
Cold amp.
output4.7F
Cold amp.
input monitor

We connect 20m sq. Nb/Al-STJ and SOI amplifier on the cold stage
through a capacitance16Voltage [μV]

Voltage [μV]

Amplification of STJ response to laser pulse on cold stage

Laser pulse(=465nm)

70 Input to SOI amp. from STJ

T=350mK

605018μV

40
1600Output from SOI amp.
1200
800
4000-100 -80 -40 -40 -20

1.2mV

02040

6080100time [μs]Demonstrated to show amplification of Nb/Al-STJ response to laser pulse
by SOI amplifier situated close to STJ at T=350mK

Development of SOI cryogenic amplifier for STJ signal readout
is now moving to the stage of design for practical use !
17

Charge sensitive amplifier
40μA

20μA
20μA

FeedbackBuffer
stage

10μA 2μA
Telescopiccascode18

Response to charge injection5MΩ
3pF𝐶𝑅-Function
generator+CH2
Refrig. DC,1MΩ

×10CH1

𝐼ref 𝑉dd 𝑉ssRoomoutputinput

3K
10mV

50μs

10mV

50μs

0.4mV

0.4mV
200ns

200ns

19

Other R&D components for COBAND rocket experiment

Design of Telescope optics

Prototype rocket-borne
3He sorption refrigerator

Design of antenna for STJ
Coupling of STJ with FIR photon

FIR laser for STJ calibration
20Summary• We propose a sounding rocket experiment to search forneutrino radiative decay in cosmic neutrino background,followed by a future satellite experiment .
• Nb/Al-STJ array with a grating for the rocket experiment.
– Demonstrated STJ signal amplification by a prototype SOI amplifier at
T~350mK– Now we design and develop SOI cryogenic amplifier for practical use• Hf-STJ is under development for future experiment• Development of telescope optics, STJ with antenna, rocketborne refrigerator, and FIR laser source for STJ calibration
are on going as well toward rocket experiment.

21

Backup22

Noise Equivalent Power (NEP) Requirements for the photo-detector
 Neutrino decay (𝑚3 = 50 meV, 𝜏𝜈 = 1014 yrs): 𝑰𝝂 =25kJy/sr @ =50m
𝑷𝑵𝑫 = 𝟐𝟓 𝒌𝑱𝒚Τ𝒔𝒓 × 𝟖 × 𝟏𝟎−𝟖 𝒔𝒓 × 𝝅 𝟏𝟓𝒄𝒎Τ𝟐 𝟐 × 𝚫𝝂
= 𝟑. 𝟑 × 𝟏𝟎−𝟐𝟎 𝑾Τ𝟖𝒑𝒊𝒙
 Zodiacal emission: 𝑰𝝂 =8MJy/sr @ =50m
𝑷𝒁𝑬 = 𝟏. 𝟏 × 𝟏𝟎−𝟏𝟕 𝑾Τ𝟖𝒑𝒊𝒙◆ Shot noise in PZE integrated over an interval t– Fluctuation in number of photons with energy 𝜖𝛾 :𝑁𝐸𝑃2Δ𝑡× Δ𝑡 ≪𝜖𝛾 𝑃𝑍𝐸 Δ𝑡𝜖𝛾 𝑃𝑍𝐸 Δ𝑡 ≪ 𝑃𝑁𝐷 Δ𝑡➔ Δ𝑡>200sec➔ NEP ~O(10−20 ) 𝑊 Τ 𝐻𝑧 for 1pix23

STJ current-voltage curveCurrent
2Δ

B field

Voltage
Signal current
Leak current

I-V curve with light illumination
Optical signal readout
Tunnel current of Cooperpairs (Josephson current)
is suppressed by applying
magnetic field➔ Apply a constant bias voltage (|V|<2Δ)
across the junction and collect tunnelingcurrent of quasi particles created by photons✓ Leak current causes background noise
24

STJ back-tunneling effect• Bi-layer fabricated with superconductors of different gaps
Nb>Al to enhance quasi-particle density near the barrier– Quasi-particle near the barrier can mediate multiple Cooper pairs• Nb/Al-STJ Nb(200nm)/Al(70nm)/AlOx/Al(70nm)/Nb(200nm)• Gain: ～10
Al/AlOx/AlNb
Si wafer

PhotonNb

Nb

AlAlNb25

Charge sensitive amplifierW(m)/L(m)

Iref

Iref

10/10

Iref2
10/10

100/7

Bias

100/7

12/7

100/1

Iref

100/1

Iref/5
2/10
10/10

4/1

20/10

4/10

4/10

Iref2/5

Telescopic
cascode4/1

Iref2/5

Buffer
stage
VDD=-VSS=1.5V
Iref>10A26