Plan of Rocket Experiment R&D of STJ Detector

We also looked at the response of Nb/Al-STJ (4μm2 ) to the visible light (456nm) at 1.9K, and found that a single photon peak is separatedfrom pedestal by 1σ. 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.As we aim at 5σ separation of one photon signal from pedestal, we need some low noise preamplifier working around 1K such as SOI.

Feasibility of Photon Detection from Cosmic Background Neutrino

Search for Cosmic Background Neutrino DecayShin-Hong Kim (University of Tsukuba)

For Neutrino Decay collaborationS. H. Kim, Y. Takeuchi, K. Nagata, K. Kasahara, T. Okudaira (Univ. of Tsukuba) , H. Ikeda, S. Matsuura, T. Wada (JAXA/ISAS) , H. Ishino, A. Kibayashi (Okayama Univ.) , S. Mima (RIKEN),  T. Yoshida, S. Kobayashi, K. Origasa (Fukui Univ.) , Y. Kato (Kinki Univ.), M. Hazumi, Y. Arai (KEK), E. Ramberg, J. H. Yoo, M. Kozlovsky, P. Rubinov, D. Sergatskov (FNAL), S. B. Kim (Seoul National Univ.) SPICA Conference, Jun. 18-21, 2013 at University of Tokyo 　

SOI-STJ We have processed Nb/Al-STJ on a SOI wafer, and confirmed that both Nb/Al-STJ detector and SOI MOSFET worked normally at 700mK.

In the next step, we will look at the response signal of SOI-STJ to photons.

Introduction

Only neutrino mass is unknown in the present elementary particles. To determine the neutrino masses is an important key issue to reveal the mass origin as well as the study of Higgs characteristics.Δm2

ij have been measured accurately by various

neutrino oscillation experiments. but neutrinomass itself has not been measured. Detection of neutrino decay enables us to measure an independent quantity. Thus we can obtain neutrino mass itself from these two independent measurements.

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 neutrino means a discovery of the cosmic background neutrino predicted by cosmology.

The current lifetime limit is about 3 x 1012 year obtained from COBE and AKARI CIB data.

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Cosmic Infrared Background

Neutrino Decay (τ ＝ 1.5 x 1017year ）Sharp edge with 1.9K smearing and detector resolution of 0% to 5%

5σ observation sensitivity

Search Region: λ ＝　 35 ～ 250μm 　（ Eγ ＝　 35 ～5meV ）In Rocket experiment, λ ＝　 40 ～ 80μm 　（ Eγ ＝　 31 ～15meV ）

23

dN/dEγ

　 d2Nγ/dEγ2 for energy resolutions of

0~3% 　

Rate/50pixel-spectrometer = 　 1.4 kHz ( 28Hz/pixel)Measurements for 200 s → 　 280 k events /50pixel-spectrometer. Using 8 x 50pixel-spectrometer,σ/N=0.066% 2σ = 0.13% x 0.5μW/m2/sr = 0.65nW/m2/sr 　(1.3% times present limit 50nW/m2/sr ）

CMB

𝑘𝑇 1MeV

The photon energy spectrum from CB decay is expected to have a sharp edge at ( is assumed) with smearing and tail in lower energyside due to the red shift effect. We can search for this sharp edge in the cosmic infrared background (CIB) photon energy spectrum.

Simulation (JPSJ 81 (2012) 024101)If we assume• No zodiacal emission

background• 10 hour measurement• 20cm diameter and 0.1o

viewing angle telescope• A photon detector with 2%

energy resolution

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Wavelength[m]

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CIB measurements( AKARI, COBE) Astrophys. J. 737 (2011) 2

Red shift effect

6.7

We plan to perform a rocket experiment with a superconducting tunneling junction (STJ) based detector in 2016 in the earliest, aiming at improving the current experimental lower limit of the neutrino lifetime by 2 order in a 5-minute measurement: (3)>O(1014 yr) . We will also aim at a measurement of (3)>O(1017yr) for the neutrino lifetime in a 10-hour satellite based measurement in further future.Detector design We are developing the following single photon detectors to cope with 2% energy resolution at .• Multi-pixel Nb/Al-STJ with diffractive grating for the photon in • Hafnium based STJ (Hf-STJ)

CB

Summary• It is feasible to observe cosmic background neutrino decay (), if we assume Left-Right

symmetric model.• We are developing STJ-based detectors to detect a photon from cosmic background

neutrino decay.• A rocket experiment using the STJ detectors for neutrino decay search is in preparation.

Hf-STJ Since hafnium has much smaller superconducting gap energy () than niobium (), Hf-STJ can generate enough statistics of quasi-particles from cooper pair breakings to achieve 2% energy resolution for photon with . We are developing Hf-STJ and have established to process SIS structure by hafnium in 2011, which could be confirmed by the Josephson current. Currently, our trial pieces of Hf-STJ has a large leak current, and need more improvement to function as a far infrared photon detector.

Nb/Al-STJ We aim at detecting a single infrared photon for the neutrino decay search experiment. We measured the response of Nb/Al-STJ (100μ x 100μ) to the infrared (1.31μm) light at 1.9K. Time spread at FWHM is 1μsec. The number of photon was estimated to be 93±11 from the spread of the signal charge distribution.

Square is 2.9 mm on a side.

200nA /DIV.

leak current of Nb/Al-STJ is about

6nA at 0.5mV .

pedestal Signal chargedistribution

50μV

/DIV

0.8μs/DIV

Signal chargedistribution

Source

Drain

Gate

STJ2mV /DIV.

After applying150 Gauss to STJ.

Signal shape (1.31μ, N(photon)=93±11)

we can detect CB decay photon for and at 6.7 significance.