Transcript Neutrinos: What we’ve learned and what we still want to

Neutrinos: What we’ve
learned and what we still want
to find out
Jessica Clayton
Astronomy Club
November 10, 2008
Neutrinos, they are
very small,
they have no charge
and have no mass†,
and do not interact
at all.
John Updike (2003)
†Almost
no mass.
Back to the Basics
The Standard Model
Something’s missing…
Beta decay
Neutron
proton
electron
Conservation of energy, momentum and
angular momentum require that something
else exists.
?
Birth of a Particle
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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”
Discovery!
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In 1956, Fred Reines and Clyde Cowan
detected the neutrino via inverse beta
decay
+p
n + e+
e-
2 photons in
opposite
directions
Cd
Another photon, 5 x 10-6 sec later
Predictions for neutrinos from
the sun
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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.
Underground in South
Dakota…
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Ray Davis built a neutrino detector one
mile underground in the Homestake
Mine
Large tank of cleaning fluid, C2Cl4
Cl +  -> Ar + eCount the number of Ar atoms to find
the number of neutrinos
The Solar Neutrino Problem
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The number of neutrinos measured by
Davis was only 1/3 of what Bahcall
predicted.
It was 1968.
Davis and Bahcall at
Homestake. Photo from
Three possibilities:
nobelprize.org.
1) problem with detector
2) problem with solar theory of fusion and neutrino production
3) something is wrong with the Standard Model.
Searching for answers…
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Kamiokande detector was built in Japan
and detects about half of the neutrinos
that Bahcall predicted.
GALLEX, SAGE and SuperKamiokande confirmed the deficit in
neutrinos over different energy ranges
… but still, the theory doesn’t
match the observations…
http://www-sk.icrr.u-tokyo.ac.jp/sk/index-e.html
SNO breakthrough in 2001
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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.
Neutrinos change flavors!
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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!
Vindicated… after 40 years.
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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.
Supernova 1987a
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Neutrinos were detected from
Supernova 1987a by Kamiokande and
IMB
Within 12 seconds,
Kamiokande saw 12 events
(6-35 MeV) and IMB saw 8
events (19-39 MeV).
Credit: C Burrows (ESA/STScI), HST, NASA
First optical observations were
the next day.
Neutrinos in our midst…
Big Bang
sun
A trillion
neutrinos pass
harmlessly
through your
body every
second!
Nuclear reactors
Supernova
1987a
atmosphere
Human
body
Accelerators
Earth’s radioactivity
A New Window on the Universe
NRAO
Anglo-Australian Obs.
Ultraviolet Imaging Tel.
Radio image of the
Crab Nebula
Optical image of
the Crab Nebula
Ultraviolet image of
the Crab Nebula
Gravitational
waves?
Neutrinos?
Chandra X-ray Obs.
X-ray image of the Crab Nebula
Neutrinos travel in a straight lines.
Because they have no electric charge,
they are not deflected by magnetic fields
in space.
NEUTRINO
PHOTON
(LIGHT)
INTERSTELLAR
DUST
COSMIC RAY
PROTON
Neutrinos: many open
questions
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What’s accelerating neutrinos?
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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: what we think now
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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
Why do we study neutrinos?
“A particle that is almost
nothing may tell us
everything about the
Universe.”
Christine Sutton