C02: Investigation of Supernova Mechanism via Neutrinos. Mark Vagins Kavli IPMU, UTokyo

Transcription

1 C02: Investigation of Supernova Mechanism via Neutrinos Mark Vagins Kavli IPMU, UTokyo GW Genesis 1 st Annual Symposium University of Tokyo, Kashiwa March 7, 2018

2 Supernova explosions play an absolutely central role in understanding the genesis of gravitational waves. Not only do some SNe emit GWs, but the inspiralling neutron stars and black holes which produce the classic chirp GW signals were themselves born during supernova explosions.

3 A-02 Gravitational wave physics/astronomy : Genesis

4 Neutrino emission (Nakazato)

5 A core-collapse supernova is a nearly perfect neutrino bomb. Within ten seconds of collapse it releases >98% of its huge energy (equal to 一兆,or 10 12, hydrogen bombs exploding per second since the beginning of the universe!) as neutrinos. Neutrinos, along with gravitational waves, provide the only possible windows into core collapses inner dynamics.

6 Kamiokande s Burst Time Structure Kamiokande 16:35:41 JST on February 24 th, 1987 SN1987A s neutrinos also seen simultaneously by IMB (in the US) and Baksan (in the Soviet Union)

7 41.4m 40m The Super-Kamiokande neutrino detector, in Mozumi, Japan.

8 50,000 tons of ultra-pure H 2 O 13,000 light detectors One kilometer underground Observes particles from the Sun, supernovas, and cosmic rays Also looks for proton decay

9 Why seeing galactic SN ν's in SK would be great: Fine-grained, high statistics SN neutrino data are a unique probe of many important particle physics topics (neutrino ocsillations, mass hierarchy, sterile neutrinos, extra dimensions, Lorentz violation, neutrino-neutrino self-interactions) They would also provide valuable insight into key astrophysical subjects (supernova explosion mechanism, neutron star/black hole formation, nucleosynthesis, stellar evolution) Super-K data in concert with that from DUNE and IceCube detectors would allow instant triangulation based on first event arrival times (though ~10X less accurate than eventual elastic scattering analysis) SK's ES would provide the world's most accurate pre-optical direction (if the analysis and announcement can be automated, guide astronomers) Serve as an accurate time-zero for gravitational wave observations (gravitational wave signal is less certain compared to neutrino signal) Very good public relations value, especially if SN is a naked-eye object

10 We would very much like to collect some more supernova neutrinos! But it has already been thirty-one years since SN1987A, and exactly 413 years and 149 days since a supernova was last definitely observed within our own galaxy.

11 Yes, it s been a long, cold winter for SN neutrinos but there is hope!

12 So, how can we be certain to see more supernova neutrinos without having to wait too long?

13 This is not the typical view of a supernova! Which, of course is good. Yes, nearby supernova explosions may be rare, but supernova explosions are extremely common.

14 Here s how most of them look to us (video is looped). There are thousands of supernova explosions per hour in the universe as a whole! These produce a diffuse supernova neutrino background [DSNB], also known as the supernova relic neutrinos [SRN].

15 גדוליניום Gadol = Great! Very much in the spirit of this Innovative Area, theorist John Beacom and I wrote the original GADZOOKS! (Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!) paper. It proposed loading big WC detectors, specifically Super-K, with water soluble gadolinium, and evaluated the physics potential and backgrounds of a giant antineutrino detector. [Beacom and Vagins, Phys. Rev. Lett., 93:171101, 2004] (320 citations one every 16 days for fourteen years)

16 Inverse Beta Decay with Gadolinium ν e p n p γ Possibility 1: 10% or less n+p d + γ 2.2 MeV γ-ray e + Gd Positron and gamma ray vertices are within ~50cm. Possibility 2: 90% or more n+gd ~8MeV γ T = ~30 µsec ν e can be identified by delayed coincidence. γ

17 Here s what the coincident signals in Super-K with Gd 2 (SO 4 ) 3 will look like (energy resolution is applied): Most modern DSNB range ν e + p e + + n spatial and temporal separation between prompt e + Cherenkov light and delayed Gd neutron capture gamma cascade: λ=~4cm, τ=~30µs A few clean events/yr in Super-K with Gd

18 Odrzywodek et al. were the first to suggest that late-stage Si burning in very large, very close stars could provide useful early warning of a core collapse supernova in a Gd-loaded Super-Kamiokande. [C. Simpson] e + + e - ν e + ν e (just above inverse beta threshold) ν e + p e + + n (e + barely relativistic) [Odrzywodek, Misiaszek, and Kutschera, Astropart.Phys. 21: , 2004]

19 Gd-loaded Super-Kamiokande s Sensitivity to pre-sn ν s (Super-K internal study) [C. Simpson]

20 Gd-loaded Super-Kamiokande s Sensitivity to pre-sn ν s (Super-K internal study) False alarm rate: 1 per 100 years, from 1800 years simulated Yoshida model Assuming reasonable mass and distance for Betelgeuse Typical unambiguous warning time is 8 days [C. Simpson]

21 EGADS Gd-loaded Super-K Adding water soluble gadolinium to Super-K will greatly enhance its ability to detect supernova neutrinos (and help with many other physics topics like proton decay). EGADS is a dedicated gadolinium demonstrator which includes a working 200 ton scale model of SK. νe n p e+ p Gd EGADS Facility in Kamioka Mine γ γ Beacom and Vagins, Phys. Rev. Lett., 93:171101, 2004 [320 citations] ;. 12/ /2011 8/2013 6/2015

22 Maintaining good water quality in the presence of dissolved gadolinium required the development of an entirely new technology: true selective filtration. I call my resulting system a molecular band-pass filter. It continuously circulates the Gd-loaded water and removes every impurity except gadolinium sulfate. 22

23 Main 200-ton Water Tank ( cm PMT s + 13 HK test tubes) EGADS Laboratory ;. 15-ton Gadolinium Pre-treatment Mixing Tank Selective Water+Gd Filtration System Worldwide, over $10,000,000 dollars (not counting salaries) has been spent developing and proving the viability of the Gd-in-water concept.

24 15 meters and Gd conc. in the 200-ton EGADS tank After two and a half years at full Gd loading, during stable operations EGADS water transparency remains within the SK ultrapure range. No detectable loss of Gd after more than 650 complete turnovers.

25 May 16 th, 2017; This is 0.2% Gd 2 (SO 4 ) 3 water. The EGADS tank had been fully loaded for over two years.

26 November 6 th, 2017; After draining, this view is directed up the side wall from the bottom of the 200-ton tank. Looks great after 2.5 years of exposure to 0.2% Gd 2 (SO 4 ) 3 water!

27 After years of testing and study culminating in these powerful EGADS results no technical showstoppers have been encountered. And so June 27, 2015: The Super-Kamiokande Collaboration approved the addition of gadolinium to the detector, pending discussions with T2K. January 30, 2016: The T2K Collaboration approved addition of gadolinium to Super-Kamiokande, with the precise timing to be jointly determined based on the needs of both projects. July 26, 2017: The official start time of draining the SK tank to prepare for Gd loading is decided to be June 1, 2018.

28 Super-Kamiokande Original Super-K Water System New Gadolinium Water System Hall G (4000 m 3 ) EGADS Hall (2500 m 3 ) The Kamioka Observatory in the Mozumi Mine

29 Hall G being filled with equipment for the gadolinium loading of Super-Kamiokande; January 30th, 2017

30 Expected timeline for SK-Gd Schedule Approved Install New SK Water Systems, Computing, Calibration SK In-Tank Upgrade Work SK Pure Water Running SK Running with 0.01% Gd (50% eff.) Increased Loading, up to 0.1% Gd (90% eff.) We should have collected some new supernova neutrinos for the theorists to study with within three years from today!