1. Neutrinos: What we’ve learned and what we still want to find out Jessica Clayton Astronomy Club November 10, 2008

2. Neutrinos, they are very small, they have no charge and have no mass †, and do not interact at all. † Almost no mass. John Updike (2003)

3. Back to the Basics

4. The Standard Model

5. Something’s missing… Neutron proton electron ? Conservation of energy, momentum and angular momentum require that something else exists. Beta decay

6. Birth of a Particle 1930: Wolfgang Pauli predicts that there is another particle involved in beta decay First theories about neutrinos were soon after written by Enrico Fermi Fermi coined the term neutrino - meaning “little neutral one”

7. + p n + e+ Discovery! In 1956, Fred Reines and Clyde Cowan detected the neutrino via inverse beta decay e-e- 2 photons in opposite directions Cd Another photon, 5 x 10 -6 sec later

9. Predictions for neutrinos from the sun 4p He + 2e + + 2 e + energy Protons in the sun fuse to form helium In the process, neutrinos and energy are released. Ray Davis and John Bahcall formed a team to study this prediction in 1964.

10. Underground in South Dakota… Ray Davis built a neutrino detector one mile underground in the Homestake Mine Large tank of cleaning fluid, C 2 Cl 4 Cl + -> Ar + e - Count the number of Ar atoms to find the number of neutrinos

11. The Solar Neutrino Problem It was 1968. Three possibilities: 1) problem with detector 2) problem with solar theory of fusion and neutrino production 3) something is wrong with the Standard Model. The number of neutrinos measured by Davis was only 1/3 of what Bahcall predicted. Davis and Bahcall at Homestake. Photo from nobelprize.org.

12. Searching for answers… Kamiokande detector was built in Japan and detects about half of the neutrinos that Bahcall predicted. GALLEX, SAGE and Super- Kamiokande confirmed the deficit in neutrinos over different energy ranges … but still, the theory doesn’t match the observations…

13. http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html

14. SNO breakthrough in 2001 The Sudbury Neutrino Observatory could only measure one flavor of neutrinos, e. Kamiokande was sensitive mostly to e, but also to  and . Results were combined to come up with the total number of solar neutrinos and the number of solar e.

15. Neutrinos change flavors! 1/3 of solar neutrinos are electron flavor by the time they get to Earth The “missing” electron neutrinos oscillate into  or . In order to change flavors, neutrinos must have a non-zero mass. That doesn’t fit into the Standard Model as we know it!

16. Vindicated… after 40 years. Bahcall made his first predictions about the number of neutrinos produced by the sun in the mid-1960s. The Solar Neutrino Problem was born with Davis’ first results in 1968. Neutrinos were studied by several experiments - and were measured from a supernova in 1987 In 2001, SNO results confirmed that neutrino oscillations occur.

17. Supernova 1987a Neutrinos were detected from Supernova 1987a by Kamiokande and IMB Credit: C Burrows (ESA/STScI), HST, NASA Within 12 seconds, Kamiokande saw 12 events (6-35 MeV) and IMB saw 8 events (19-39 MeV). First optical observations were the next day.

18. Neutrinos in our midst… Earth’s radioactivity Nuclear reactors Human body atmosphere Accelerators sun Supernova 1987a Big Bang A trillion neutrinos pass harmlessly through your body every second!

19. A New Window on the Universe NRAO Radio image of the Crab Nebula Anglo-Australian Obs. Optical image of the Crab Nebula Ultraviolet Imaging Tel. Ultraviolet image of the Crab Nebula Chandra X-ray Obs. X-ray image of the Crab Nebula Gravitational waves? Neutrinos?

20. NEUTRINO COSMIC RAY PROTON PHOTON (LIGHT) STAR OR GALAXY ? INTERSTELLAR DUST Neutrinos travel in a straight lines. Because they have no electric charge, they are not deflected by magnetic fields in space.

21. What’s accelerating neutrinos? Gamma-ray bursts (GRBs)? Active Galactic Nuclei (AGN)? What’s the mass of each flavor of neutrino? What’s the value of the oscillation parameters? Are neutrinos and anti-neutrinos the same thing? Neutrinos: many open questions

22. Neutrinos: what we think now Neutral (no charge) Tiny, non-zero mass 3 flavors, which oscillate Very tiny cross-section, meaning that they don’t like to interact with matter Promising new way of studying the Universe

23. “A particle that is almost nothing may tell us everything about the Universe.” Christine Sutton Why do we study neutrinos?