2019 Fiscal Year Annual Research Report
Studying supernova explosions via their neutrino emissions
| Project Area | Gravitational wave physics and astronomy: Genesis |
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| Project/Area Number |
17H06365
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| Research Institution | The University of Tokyo |
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Principal Investigator |
ヴァギンズ マーク 東京大学, カブリ数物連携宇宙研究機構, 教授 (90509902)
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| Co-Investigator(Kenkyū-buntansha) |
松古 栄夫 大学共同利用機関法人高エネルギー加速器研究機構, 計算科学センター, 助教 (10373185)
住吉 光介 沼津工業高等専門学校, 教養科, 教授 (30280720)
小汐 由介 岡山大学, 自然科学研究科, 准教授 (80292960)
原田 了 東京大学, 宇宙線研究所, 特任研究員 (80844795)
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| Project Period (FY) |
2017-06-30 – 2022-03-31
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| Keywords | gravitational wave / supernova explosion / neutrino / neutron detection / hydrodynamic simulation |
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| Outline of Annual Research Achievements |
Core collapse supernova [SN] explosions comprise one of the primary sources of near-field gravitational waves [GW]. SN neutrinos carry information regarding the end state of the star: for explosions within our galaxy, collapses into neutron stars or black holes, the eventual sources of far-field GW, can be differentiated via observations of neutrino emissions.
(EXPERIMENT)
During FY2019 we continued upgrading the existing Super-Kamiokande [SK] detector to become an advanced-technology, gadolinium [Gd] loaded SN neutrino detector. Following FY2018's extensive refurbishment campaign, which required over 3000 person-hours of in-tank work and resulted in the successful repair of a longstanding water leak, in FY2019 our major focus involved the commissioning of a new Gd-capable selective water filtration system. Its ability to maintain the clarity of SK's pure water was demonstrated; this was the final major hardware step required in making the detector ready for enrichment with gadolinium.
（THEORY)
On the theory side, we performed new simulations of supernova explosions with novel developments of the equation of state and the 3D Boltzmann-Hydro code. As a result, we found an early motion of proto-neutron stars through a new mechanism via asymmetric neutrino emission. We made comprehensive analyses of neutrino light curves with Super-Kamiokande and proposed a backward time analysis to extract neutron star properties. We applied the simulation data to the analysis of neutrino bursts, gravitational waves, and collective oscillations.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Our ultimate goal is to make theory and experiment work together so we will be ready to make the best possible observations of the next galactic explosion and maximize our extraction of information on the explosion mechanism, progenitor, and nuclear physics ingredients.
(EXPERIMENT)
For almost twenty years, the prospect of adding gadolinium to Super-Kamiokande to enhance its ability to detect supernova neutrinos has fueled intensive R&D work in Kamioka and elsewhere around Japan and the world. Now, with the detector refurbished and refilled with pure water, and the new Gd-capable filtration system working well, we are finally ready to go forward with the addition of Gd to the water of SK.
(THEORY)
Additional simulations of core-collapse supernovae on the K-computer are progressing smoothly, exploring the influence of equation of state and rotation. We have applied simulation data in new ways to predict neutrino and gravitational wave signals and to explore collective neutrino oscillations. We have successfully prepared a basic set of time evolutions of expected supernova neutrino events at Super-Kamiokande from supernova and proto-neutron star numerical simulations, and made progress toward the goals of the supernova neutrino burst project.
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| Strategy for Future Research Activity |
(EXPERIMENT)
In FY2020 we plan to finally - the idea was first proposed in 2002 - add the very first gadolinium to the water of Super-Kamiokande. This initial Gd-loading phase, referred to internally within the SK Collaboration as T_1, will see approximately 13 tons of specially developed, ultra-radiopure gadolinium sulfate octahydrate (Gd2(SO4)3)*8H2O) dissolved and injected into the 50,000 tons of SK's pure water. This is designed to bring the concentration of aqueous Gd3+ ions to 0.01% by mass in the SK water. Doing so should allow the collection and event-by-event identification of subtle, currently hidden supernova neutrino interactions from extremely distant (z=1) explosions at roughly 50% efficiency. If all goes well, increased Gd loading of SK is expected beyond FY2020.
(THEORY)
We plan to perform new simulations of core-collapse supernovae using the Boltzmann-Hydro code, adopting a new equation of state and different rotational rates to identify their effects in the explosion mechanism and neutrino signals. We will continue the collaboration of theory and experiment members to construct templates of neutrino light curves for supernovae by examining the uncertainties due to the equation of state and the stellar mass. We are eager to establish the protocol to extract information about supernovae from the burst data by finding universal features of the signal.
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