neutrinos: what we’ve learned and what we still want to find out jessica clayton astronomy club...
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Neutrinos: What we’ve learned and what we still want to find out
Jessica Clayton
Astronomy Club
November 10, 2008
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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)
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Back to the Basics
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The Standard Model
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Something’s missing…
Neutron proton electron
?Conservation of energy, momentum and angular momentum require that something else exists.
Beta decay
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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”
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+ p n + e+
Discovery! In 1956, Fred Reines and Clyde Cowan
detected the neutrino via inverse beta decay
e-
2 photons in opposite directions
CdAnother photon, 5 x 10-6 sec later
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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.
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Underground in South Dakota… Ray Davis built a neutrino detector one
mile underground in the Homestake Mine
Large tank of cleaning fluid, C2Cl4 Cl + -> Ar + e-
Count the number of Ar atoms to find the number of neutrinos
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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.
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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…
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http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html
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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.
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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!
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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.
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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.
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Neutrinos in our midst…
Earth’s radioactivityNuclear reactors
Human body
atmosphere
Accelerators
sun Supernova 1987a
Big Bang
A trillion neutrinos pass harmlessly through your body every second!
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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?
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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.
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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
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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
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“A particle that is almost nothing may tell us everything about the Universe.”
Christine Sutton
Why do we study neutrinos?