Atmospheric Neutrinos As the Background for Proton Decay, a Significant Deficit of Atmospheric Νµ Events Was Observed

KAGRA

Takaaki Kajita Boston Institute for Cosmic Ray Research, The Univ. of Tokyo Feb. 18, 2017 1 Outline • Where is Kamioka? • Initial research in Kamioka: Neutrinos • Kamiokande • Super-Kamiokande • Discovery of atmospheric neutrino oscillations • Contribution to the discovery of solar neutrino oscillations • New research in Kamioka: Gravitational waves • KAGRA project • Summary

2 Where is Kamioka?

3 Initial research in Kamioka: Neutrinos

4 What are neutrinos? • Neutrinos; • are elementary particles like electrons and quarks, • have no electric charge, • have, like the other particles, 3 types (flavors), namely electron-neutrinos (νe), muon-neutrinos (νµ) and tau-neutrinos (ντ), • are produced in various places, such as the Earth’s atmosphere, …. • can easily penetrate through the Earth, • In the very successful Standard Model of particle physics, neutrinos are assumed to have no mass. Neutrino @NASA 5 Kamiokande

6 Kamioka Nucleon Decay Experiment (Kamiokande)  Kamiokande was constructed to observe proton decays.  The predicted lifetime of proton was about 1030 years.

Kamiokande (3000 ton water tank) Detector wall Elec. room

Cherenkov Water system light Photo detectors Charged particle

7 Kamiokande construction team (Spring 1983)

M. Takita TK A. Suzuki T.Suda M. Nakahata K. Arisaka

M. Koshiba Y. Totsuka (2002 Nobel Prize) T. Kifune 8 Construction of the Kamiokande detector (spring 1983)

The Kamiokande experiment began in July 1983.

9 SN1987A (Feb. 23, 1987) K. Hirata et al., Phys. Rev. Lett. 58 (1987) 1490. SN1987A (at LMC)

Supernova neutrinos Number of of Number PMThits

 2002 Nobel prize in Physics to Prof. M. Koshiba (The IMB experiment also observed the neutrino signal.) 10 Atmospheric neutrino deficit (1988)

COSMIC INCOMING RAY COSMIC RAYS AIR NUCLEUS

PION MUON ELECTRON 2 muon- neutrinos 1 electron- neutrino During the studies of atmospheric neutrinos as the background for proton decay, a significant deficit of atmospheric νµ events was observed. © David Fierstein, originally published in Scientific American, August 1999 11 Super-Kamiokande

13 Super-Kamiokande detector 50,000 ton water Cherenkov detector (22,500 ton fiducial volume)

More than 20 times larger mass

~160 collaborators ４２ｍ

３９ｍ１０００ｍ underground

14 Constructing the Super-Kamiokande detector (spring 1995)

Y. Totsuka

15 Filling water in Super-Kamiokande Jan. 1996

16 Discovery of atmospheric neutrino oscillations

17 Neutrino oscillations If neutrinos have masses, neutrinos change their flavor (type) from one flavor (type) to the other. For example, a mu-neutrino may change the flavor (type) to a tau-neutrino.

http://dchooz.titech.jp.hep.net/nu_oscillation.html (slightly modified)

mu-neutrino tau-neutrino mu-neutrino tau-neutrino

The distance for a neutrino to change the type depends on the neutrino mass.  If the distance to change the neutrino type to the other neutrino is measured, we get the information on the neutrino mass.

(Neutrino oscillation was predicted by Z. Maki, M. Nakagawa, S. Sakata and independently B. Pontecorvo.)

12 What will happen if the νµ deficit is due to neutrino oscillations

Cosmic ray Not long enough to oscillate ?

Long enough to oscillate ?

A deficit of upward going νµ’s might be observed!

Cosmic ray 18 Evidence for neutrino oscillations (Super-Kamiokande @Neutrino ’98) Y. Fukuda et al., PRL 81 (1998) 1562

Super-K Muon-neutrino Tau-neutrino

19 Remarks by President Clinton at MIT

・・・・・Just yesterday in Japan, physicists announced a discovery that tiny neutrinos have mass. Now, that may not mean much to most Americans, but it may change our most fundamental theories -- from the nature of the smallest subatomic particles to how the universe itself works, and indeed how it expands. ・・・・・

Wikimedia Commons

20 Contribution to the discovery of solar neutrino oscillations

21 Solar neutrino problem

http://www.sns.ias.edu/~jnb/ J. N. Bahcall https://www.bnl.gov/bnlweb/raydavis/ R. Davis Jr. http://www.astronomynotes.com/starsun/s4.htm 600 ton

C2Cl4 Pioneering Homestake solar neutrino experiment observed only about 1/3 of the predicted solar neutrinos (1960’s).

22 Solving the solar neutrino problem (2001-2002)

- SNO SNO νeDe pp νe flux ν +ν flux !! Super-K ES µ τ (ν ν ν e + µ + τ νeνe flux) SNO

νe +νµ +ντ νDνpn flux

Flux (106/cm2/sec) 1000 ton of heavy water (D O) Neutrino oscillation: electron neutrinos 2 Art McDonald to the other neutrinos. Photo: K. MacFarlane. Queen's University /SNOLAB 23 KamLAND KamLAND is a 1kton liq. scintillator Many nuclear power stations detector, and was constructed at around KamLAND at the the location of Kamiokande after its distance of about 180 km. completion.  Neutrino osc. experiment with reactor neutrinos.

1kton liq. scintillator

@ Research center for neutrino science, Tohoku University

24 Really neutrino oscillations ! KamLAND data on neutrino oscillations from nuclear power stations.

KamLAND PRD 83 (2011) 052002

Atsuto Suzuki

Really neutrino oscillations!

25 What have we learned? Why are neutrinos important?

3rd generation

2nd generation

Neutrinos Quarks 1st generation ？ (with some assumptions) Charged leptons (electrons, etc.)

0.01 1 100 104 106 108 1010 1012 1014 Mass（eV/c2） The neutrino masses are approximately (or more than) 10 billion (10 orders of magnitude) smaller than the corresponding masses of quarks and charged leptons! We believe this is the key to better understand elementary particles and the Universe.

26 New research in Kamioka: Gravitational waves

27 Gravitational waves A. Einstein predicted gravitational waves in 1916 base on his theory of general relativity.

Black hole

Image of the gravitational wave emission from a binary black hole system. These back holes merge and a new heavier black hole will be created.

28 Simulation of the merger of two black holes

湯製紙

https://www.ligo.caltech.edu/news/ligo20160211 29 How to measure gravitational waves

Gravitational waves

L1 and L2 changes (If L1 gets longer (shorter), L2 gets shorter (longer) )

Mirror Intensity of the interference light Mirror L1 Signal L2

レーザー Laser

30 Discovery of GW in LIGO Feb. 11, 2016 LIGO Scientific Collaboration and Virgo Collaboration, PRL, 116, 061102 (2016)

Data

Simulation

Data told us that 2 blackholes of 36 MSun Great discovery! Congratulations! and 29 MSun each merged at the distance Now it is clear that we can do of 1.3 Billion lightyears, newly forming a 62 science with GW, if we do it right. MSun blackhole. 31 Not easy to detect GWs

150,000,000 km

If strong gravitational waves come to the solar system, the distance between the Sun and the Earth will change by about 0.00000001cm (10-8cm). Therefore every gravitational wave detector has to be sensitive to this length change…

Please note that the present GW detectors have the arm length of only 3-4 km. Therefore, these detectors must be sensitive to the length change of 0.0000000000000001cm (10-16cm) in 3-4 km.

32 Mysteries to be solved with GW

Merger of binary Merger of binary Supernova explosion neutron stars. blackholes  How the heavy  What is the origin of  How the blackholes stars finish their life? the heavy metals in the were formed? Universe.?

(And…, how the Universe itself began?)

33 The KAGRA project

34 KAGRA “Kamioka” has been contributing a lot to neutrino physics. We realized that “underground” is very useful for basic science. A new detector, called KAGRA, on KAGRA gravitational waves is under construction in Kamioka underground. 35 KAGRA: key features and plans

Sapphire mirror (22cm(φ) X 15cm(t), 23kg) Mirrors will be cooled down to The detector is under construction in underground Kamioka. 20K to reduce the thermal  Reduction of seismic noise (to approximately 1/100). noise. KAGRA plans the first interferometer operation with the cryogenic mirrors in the spring of 2018, and the high sensitivity run in ~2019-2020.

36 International GW network

LIGO KAGRA

Virgo

IndIGO/LIGO-India

2LIGO+Virgo 2LIGO+Virgo+LIGO-India+KAGRA

S. Fairhurst, J. Phys. Conf. Ser. 484 (2014) 012007

37 Summary • “Kamioka” has been contributing a lot to basic science in the last 30 years. • In the early 1980’s, Kamiokande began trying to observe proton decays, and unexpectedly observed supernova neutrinos, atmospheric neutrino deficit and solar neutrinos (not discussed). • In 1998, Super-Kamiokande discovered atmospheric neutrino oscillations. • KamLAND and Super-K contributed significantly to the solar neutrino oscillation. • KAGRA is a new project trying to observe gravitational wave signals. KAGRA would like to begin the observation in a few years. • “Kamioka” is expected to contribute more to basic science.