Cecilia Lunardini Institute for Nuclear Theory University of Washington

The subatomic world: particles We are made of atoms Atoms are made of particles Only some particles stay inside atoms  There is a whole “zoo” of free particles

We are particle investigators Billions of particles arrive here every day from space!  Why are they here?  Where do they come from?  What are they? We capture them to learn

The elusive neutrinos They are invisible!  No trace in optical devices (telescopes, etc.) Three species : Electron neutrino Muon neutrinoTau neutrino

They are everywhere! about 300 in a teaspoon volume (1 cubic cm)  from 1 second after the Big Bang 60 billions every second across your thumb’s nail (1 square cm) from the Sun

How we thought they behaved The old theory of neutrino behavior

The mass-less neutrino The mass  myself: 50 Kg (110 lb)  A particle (proton): Most particles have some mass The neutrino was believed to have no mass proton neutrino 50 Kg 80 billions of billions of billions

Mass-less particles have a very ordinary life  Born (e.g., in the Sun)  Travel at speed of light  Get caught (absorbed) by matter (e.g., on Earth)

The puzzle of the missing neutrinos

The neutrino trap Experimenter Raymond Davis decided to count the neutrinos from the Sun  To check the nuclear reactions inside the Sun He made a “neutrino trap” made of cleaning fluid (containing Chlorine)

The trap worked similarly to a colander:

The prediction Theorist John Bahcall calculated the number of neutrinos expected in the trap  Using knowledge of the Sun He found 9 “Solar Units” Photo from

Something was wrong… The counted neutrinos were only 2 and ½ Solar Units !!  Only about 1/3 of the prediction prediction

How they actually do behave The new theory of neutrino behavior

Are we catching everyone? The Sun only emits neutrinos of the electron species The trap is unable to catch the muon and tau species!!

Are neutrinos “mutants”? Theorist Bruno Pontecorvo had an idea… “What if some neutrinos mutate from electron to muon species on the way?”

A lot of thinking was done… Bruno Pontecorvo Alexei Smirnov Lincoln Wolfenstein Stas Mikeyev See for more photoshttp://

New theory: neutrinos with mass Maybe the neutrinos have mass..  If so, the electron neutrino and the muon neutrino could be like two sides of the same object Muon neutrino Electron neutrino

The “oscillations” idea The neutrinos could rotate (“oscillate”)  They rotate while the travel

Those neutrinos that arrive as muon are missed!

You probably know what to do….

Let’s make a better trap! A “colander” that catches everyone:

The technological challenge Thousands of tons of water (and heavy water) were needed Photo: Kamioka Observatory, ICRR, The University of Tokyo Sudbury Neutrino Observatory, Sudbury, Canada

And, finally… bingo!! With an “all species” trap the numbers matched! Neutrinos counted Neutrinos predicted

½ Nobel prize soon came Raymond Davis Masatoshi Koshiba Photo: December 2002

The fundamental meaning Ok, the neutrinos have mass. But, why is this interesting??

Particles have mass if they can “hold hands”: Neutrinos are unable to hold hands  They are all left-armed

Something exotic must happen… Probably a new particle “helps” them!  Indication of a new species!!

Neutrinos outside the solar system A gallery

Exploding stars: supernovae Gravitational energy is converted into neutrinos Huge storm of neutrinos floods the Earth for seconds More powerful than all the stars of the universe together

In 1987 the star Sanduleak (in the Large Magellanic Cloud) went supernova Kamiokande (Japan) and IMB (USA) captured the neutrinos

The gamma ray emitters Exotic supernovae emit powerful flashes of gamma rays  Mistaken for new weapon of the Soviet Union….  Still mysterious Neutrinos come together with the gamma rays  More energetic than any human technology

The dark neutrinos The mysterious Dark Matter contains neutrinos  Primordial, from the Big Bang

The question of the mass Speed of light: C= Km/s ( … mph) Human being: m=80 kg (~ 160 lb)  E =…

Mass and neutrino behavior How much do neutrino weigh?

Even man-made neutrinos go missing

The elusive neutrinos They are invisible!  No trace in optical devices (telescopes, etc.) Three “flavors”