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Transcript
Seeing the Sky Underground The Birth of Neutrino Astronomy Chiaki Yanagisawa Stony Brook University October 13, 2007 Custer Institute History of Cosmic Rays/Neutrino Astronomy Researches 1921 Hess discovered cosmic rays (CRs) 1932 Anderson found the first antimatter : anti-electron (positron) 1937 Discovery of muon by Anderson Birth of elementary particle physics 1949 Fermi’s theory of CR acceleration 1962 Cosmic Microwave Background (CMB) Relic from Big Bang radiation discovered 1 eV: Energy acquired by an electron in 1 V First 1020 eV CR detected 1966 Proposal of GZK cutoff p + gCMB -> Np : Ecutoff=5x1019 eV Interaction of CR proton with CMB radiation 1019 eV 1020 eV History of Cosmic Rays/Neutrino Astronomy Researches 1967 Ray Davis detected first solar neutrinos Birth of neutrino astronomy CR Masatoshi Koshiba 1979 Masatoshi Koshiba got a new idea using water for proton decays 1981 Kamiokande started 1987 Neutrinos from Supernova SN1987A observed by Kamiokande/IMB CR Ray Davis 1991 Super-Kamiokande (SK) construction started Fly’s Eye detected 3x1020 eV CR Probably CRs hit their heads? 1994 AGASA detected 2x1020 eV CR 1996 SK started to take data 1998 Discovery of atmospheric neutrino oscillation by SK 2002 Confirmation of solar neutrino oscillation by SNO Nobel Prize to Davis,Koshiba,&Giacconi Particle Physics What is the world made of? nucleus Model of Atoms proton Old view electrons e- quarks nucleus Modern view Semi-modern view Particle Physics What is matter made of? Building Blocks of Matter Discoveries of too many “elementary” particles lead to more fundamental model the Standard Model. Proton p : uud Neutron n : udd + Pion p : ud Particles made of quarks are called hadrons Particle Physics How many kinds of forces are there? Fundamental Forces There are four know fundamental forces: An example: Free neutron decay Particle Physics Fundamental Forces An example of weak interaction - Free neutron decay: n p + e- + ne Particle Physics What is our dream? Unification of Forces Grand Unified Theories (GUTs) Strong Electric Electromagnetic Magnetic Electroweak Weak 20th c. hard Gravitational GUTs 19th c. 21st c.? GUTs predict: Nucleon decays Neutrino mass/oscillation Particle Physics What is neutrino oscillation? Neutrino Oscillation There are three kinds of neutrinos: ne nm nt (flavors) If neutrinos have mass, they can change their identities (flavors) ne A simple example: nt Probability nm nt nm = cos q n1 - sin q n nt = sin q n1 + cos q n2 n1,2 2 neutrinos with definite mass Probability 1-Probability Neutrino pathlength (km) nm nm nm nm nt ~Earth’s diameter 12,000 km It depends on neutrino energy, masses and q Atmospheric Neutrinos Source of atmospheric neutrinos Earth’s atmosphere is constantly bombarded by cosmic rays. Energetic cosmic rays (mostly protons) interact with atoms in the air. These interactions produce many particles-air showers. Neutrinos are produced in decays of pions and muons. Atmospheric Neutrinos Underground Experiments Ray Davis experiment detected the first solar neutrinos using Chlorine Cl at Homestake to avoid most of cosmic rays Kamiokande detected the first neutrinos from a supernova using water (3,000 tons). Atmospheric Neutrinos Super-Kamiokande: The successor of highly successful Kamiokande 40 m height 50,000 tons of pure water equipped with 12,000 50 cm photomultipliers and 2,800 20 cm photomultipliers (PMTs). 1,000 m deep 40 m diameter Physicists are having fun on a boat in Super-Kamiokande A physicist is checking installed photomultipliers Physicists are preparing photomultipliers: See how big they are! Atmospheric Neutrinos How does a water Cherenkov detector work? Water Cherenkov Detector: Kamiokande,IMB,Super-Kamiokande,SNO Water is cheap and easy to handle! When the speed of a charged particle exceeds that of light IN WATER, electric shock waves in form of light are generated similar to sonic boom sound by super-sonic jet plane . These light waves form a cone and are detected as a ring by a plane equipped by photosensors. Atmospheric Neutrinos How do we detect atmospheric muon and electron neutrinos ? muon-like ring Major interactions: ne + n -> p + enm + n -> p + mMost of time invisible electron-like ring An event produced by an atmospheric muon neutrino Atmospheric Neutrinos Neutrino pathlength How do we see neutrino oscillation in atmospheric neutrinos? a q cos q = a/b b upward-going downward-going Probability (nm->nm) cos (zenith angle) Actual probability for measured zenith angle due to measurement errors Atmospheric Neutrinos Evidence of neutrino oscillation/mass with oscillation without oscillation low energy ne low energy nm high energy ne high energy nm First crack in the Standard Model!!! Solar Neutrinos How does the Sun shine? Nuclear fusions generate: - energy/heat/light - neutrinos Kamiokande 1 MeV = 1x106 eV Solar Neutrinos How do we detect solar neutrinos? Ray Davis Homestake Experiment: 615 tons Kamiokande,Super-Kamiokande: 3,000 tons , 50,000 tons - Detect the recoil electron which is kicked by a solar neutrino out of a water molecule. Counts the number of 37Ar using a chemical methods - Can measure the energy and direction of the recoil electron. Solar Neutrinos How do we see the Sun? Image of Sun by Super-Kamiokande Solar neutrinos background e e Seeing the Sun undergraound Solar Neutrinos Seeing the Earth’s Orbit Underground! Distance Earth-Sun Summer: 4 Jul. 156 million km Winter : 3 Jan. 146 million km Solar neutrino flux ~ (1/distance)2 Note: Flux less than half of expected (deficit)!!! Solar Neutrinos How do we see neutrino oscillation with solar neutrinos? Flux: measured/expected Homestake : 0.27+- 0.06 Kamiokande : 0.44+- 0.06 Super-Kamiokande : 0.465+-0.005+0.016-0.015 nm is not visible to all experiments above Neutrino deficit!!! Solar Neutrinos How can we prove it’s neutrino oscillation? Neutral current SNO experiment uses heavy water D2O instead of normal water H2O Solar Neutrinos How does the neutral current confirm neutrino oscillation? Elastic scattering -This reaction is available only for n e . -Available for both water and heavy water. Neutral current interaction -This reaction is flavour blind and is available for all kinds of neutrinos. - Available only for heavy water. Solar Neutrinos Confirmation of solar neutrino oscillation by SNO nm is visible only to SNO But not to Homestake, Kamiokande or SuperKamiokande. Even if solar neutrino ne changes its flavour to nm or nt total flux of solar neutrino can be measured by SNO Solar flux measured: 6.4+-1.6 x 106 cm-2 s-1 Solar flux predicted : 5.1+-1.0 x 106 cm-2 s-1 Solar neutrinos oscillate!!!! Supernova Supernova Supernova SN 1987A, Feb.23, 1987 in Large Magellanic Cloud At about 170,000 light years away Before After 12 events 8 events Neutrinos from this SN were observed by Kamiokande and IMB 10 sec Supernova How do we know detected neutrinos are from a supernova? Birth of a supernova witnessed with neutrinos Number of photomultipliers fired A few hours before optical observation Kamiokande Background level Taken by Hubble Telescope ( 1990) Supernova Why is detection of supernova neutrinos important? We learn: - Properties of neutrinos: its mass (or limit of it), magnetic moment,electric charge, etc. - Details of supernova explosion: how a star dies - How a neutron star or a black hole is formed if it happens Nobel Prize for Physics in 2002 The first detection of solar neutrinos by Ray Davis’s chlorine experiment, and the subsequent confirmation by Kamiokande using real-time directional information and the first detection of supernova neutrinos opened up a new exciting field of neutrino astronomy. For these great achievements Ray Davis and Masatoshi Koshiba shared a Nobel Prize with Riccardo Giaconni who is the founding father of x-ray astronomy. Ray Davis Masatoshi Koshiba Riccardo Giocconi Nobel Prize for Physics in 2002 At Kamioka with Prof.Koshiba At Stony Brook with Dr.Davis What’s Next? Are all the mysteries solved? -Where is all the missing mass? - Are there any other neutrino point sources? ANTARES - Origin of ultra high energy cosmic rays around and beyond cutoff GZK cutoff Auger Project ?