Transcript Neutrinos: Little Neutrons. Not! Richard E. Hughes Neutrinos; p.1

Neutrinos: Little Neutrons. Not!
Richard E. Hughes
Neutrinos; p.1
Discovery of Radioactivity
 In 1895 Roentgen discovered
that when electrons accelerated
by very high voltages struck hard
surfaces, any photographic plate
in the vicinity would get exposed
and fluorescent materials in the
region around would glow.
Roentgen thus concluded that
some radiation was being emitted
and called it X-rays.
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Radiograph made by roentgen in
1895 of his wife’s hand
For this discovery, he receives the
first physics Nobel price in 1901.
Today, those "X rays" are well known
to be a particular type of light, that
is photons of high energy
Others (Bequerel and Rutherford)
discover that uranium emits a kind
of radiation called alpha and beta
rays.
Richard E. Hughes
Neutrinos; p.2
Beta Decay
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In certain types of radioactive
decay, an electron or positron is
emitted. The electron (or positron)
was referred to as a “beta” particle
before people knew what it was, and
this type of process is referred to
as “beta decay”
 Example: Copper decaying to nickel
When this decay was first studied,
it looked like one particle (the
copper atom) decayed to just 2
other particles: the nickel and the
positron.
If this were the case, then the
positron would have a very distinct
energy. But when it is measured, the
positron energy varies over a large
range.
This is not possible if energy and
momentum are to be conserved!
http://hyperphysics.phyastr.gsu.edu/hbase/nuclear/beta.ht
ml
Richard E. Hughes
Neutrinos; p.3
Pauli & neutrino
 Wolfgang Pauli came up with a
solution to save Conservation of
Energy: he proposed a completely
new particle, which as far as he
knew, didn’t exist!
 He was so unsure of this that he
didn’t even name his own particle.
 Enrico Fermi named it: the
Neutrino (little neutral one)
Dear Radioactive Ladies and Gentlemen,
….., how because of the "wrong" statistics of the N and Li6 nuclei and the
continuous beta spectrum, I have hit upon a desperate remedy to save the
"exchange theorem" of statistics and the law of conservation of energy. Namely,
the possibility that there could exist in the nuclei electrically neutral particles,
that I wish to call neutrons, ….I agree that my remedy could seem incredible
because one should have seen these neutrons much earlier if they really exist.
Richard E. Hughes
http://www.ethbib.ethz.ch/exhibit/pauli/neutrino_e.html Neutrinos; p.4
How to Find Neutrinos?
 Although Pauli’s neutrino was a good
solution, no one knew if it was the
right solution!
 The big problem is that neutrinos
are very weakly interacting:
 A neutrino would not “notice” a lead
barrier 50 light-years thick!
 But physicists started incorporating
the neutrino into their calculations
 In 1945, the first atomic bomb
explodes. Despite of the horror it
inspires, it is for the physicists a
remarkable powerful source of
neutrinos (assuming they exist).
 Frederick Reines, who is working at
Los Alamos, speaks to Fermi in 1951
about his project to place a neutrino
detector near an atomic explosion.
Richard E. Hughes
http://wwwlapp.in2p3.fr/neutrinos/anhistory.html
Neutrinos; p.5
Reines & Cowan
 In 1952, Reines and Clyde Cowan decide to use a more peaceful source
of neutrinos: the nuclear plant of Hanford, Washington.
 They use a target made of around 400 liters of a mixture of water and
cadmium chloride.
 The anti-neutrino coming from the nuclear reactor interacts with a
proton of the target matter, making a positron and a neutron.
 The positron annihilates with an electron of the surrounding material, giving
two simultaneous photons
 the neutron slows down until it is eventually captured by a cadmium nucleus,
implying the emission of photons some 15 microseconds after those of the
positron annihilation.
 All those photons are detected and the 15 microseconds identify the
neutrino interaction.
 The neutrino is detected in 1956!
Reines receives Nobel
prize in 1995
Richard E. Hughes
Neutrinos; p.6
Observation of neutrinos
 http://hyperphysics.phy-astr.gsu.edu/hbase/particles/cowan.html
Richard E. Hughes
Neutrinos; p.7
What other kinds of neutrinos are there?
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It turns out that Reines and Cowan
discovered the anti-electronneutrino.
The electron-neutrino is discovered
in 1957 by Goldhaber, Grodzins and
Sunyar
Muon neutrinos are discovered in
1962 by Leon Lederman, Mel
Schwartz, Jack Steinberger and
colleagues at Brookhaven National
Laboratories and it is confirmed
that they are different from
electron neutrinos
The tau lepton is discovered by
Martin Perl and colleagues at SLAC
in Stanford, California. After
several years, analysis of tau decay
modes leads to the conclusion that
tau is accompanied by its own tau
neutrino
As far as we know, there are only
these 3 neutrinos.
Richard E. Hughes
Neutrinos; p.8
The mass of the neutrinos
 As each neutrino was discovered, physicists tried to measure their
mass.
 But they only got so far as to say: they are very very light
 In fact, the Standard Model which describes all of the fundamental
particles has the neutrinos as having ZERO mass
 An important implication: if neutrinos are massless, then they MUST
travel at the speed of light!
(Keep this in mind: it will become important later!)
Richard E. Hughes
Neutrinos; p.9
Neutrino sources
Solar neutrinos
From the process of thermonuclear fusion inside a star. Also produced copiously by
supernovae. Our sun produces about 2x1038 per second total.
Neutrinos from nuclear reactors and accelerators
A standard nuclear power plant radiates about 5x 1020 neutrinos per second) and their
energy is around 4 MeV.
Neutrinos from natural radioactivity on the earth
The power coming from this natural radioactivity is estimated at about 20,000 Giga
Watts (about 20,000 nuclear plants!) and the neutrinos coming from this radioactivity are
numerous: about 6 millions per second and per cm2.
Neutrinos from cosmic rays
When a cosmic ray (proton coming from somewhere in space) penetrates the atmosphere,
it interacts with an atomic nucleus and this generates a particles shower. They are
called "atmospheric neutrinos".
Neutrinos from the Big-Bang
The "standard" model of the Big-Bang predicts, like for the photons, a cosmic background
of neutrinos. There are about 330 neutrinos per cm3. But their energy is theoretically so
little (about 0.0004 eV), that no experiment, even very huge, has been able to detect
them.
Richard E. Hughes
http://wwwlapp.in2p3.fr/neutrinos/ansources.html
Neutrinos; p.10
Importance of Neutrinos
 In the universe, there are:
about 1 billion photons per cubic meter
About 100 million per cubic meter of neutrinos of
each type (electron,muon, tau), or 300 million
total
About 0.5 protons per cubic meter
Richard E. Hughes
Neutrinos; p.11
Solar Fusion
 The evidence is strong that the overall reaction is "burning"
hydrogen to make helium:
 4H + 2 e --> 4He + 2 neutrinos + 6 photons
 Why do we think that this is what goes on?
 Energy output of millions of eV per reaction is needed if the Sun has
been producing energy at the observed rate over billions of years.
 The reactions exist. (They have been studied in the laboratory.)
 There is a consistent step-by-step theory for the reaction.
http://ideaplace.org/Why/FusionE.html
Richard E. Hughes
Neutrinos; p.12
Solar Neutrinos
 We know how many of these
reactions happen per second in
the Sun because we know how
much energy each reaction
releases and we know the solar
luminosity. Thus we know how
many neutrinos the Sun is
producing per second: about
2x1038
 Then we can calculate how many
neutrinos are arriving at Earth.
The answer is about 10^14 per
square meter per second - all
moving away from the Sun at the
speed of light.
 Wait one second: a thousand
trillion solar neutrinos just went
through your body! Ouch!
http://zebu.uoregon.edu/~soper/Sun/solarneutrinos.html
Richard E. Hughes
Neutrinos; p.13
Homestake Gold Mine
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Ray Davis decides to “see” neutrinoes
from the sun.
To do this he filled a huge vat with
cleaning fluid. I am not making this
up!
The pioneering experiment in this
direction was performed deep in the
Homestake Gold Mine in South Dakota
starting in the early 1970's. The
experiment is deep underground to
protect it from high energy particles
from outer space called cosmic rays. The
detection method was based on the
reaction
 37Cl + neutrino --> 37Ar + electron.
 Chlorine, Cl has 17 protons while argon, Ar
has 18 protons. Thus one neutron got
converted into a proton.
After a few days, the argon decays back
to chlorine:
 37Ar --> 37Cl + neutrino + antielectron .
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Result: About 1/3 of the expected
number of reactions occurred.
http://zebu.uoregon.edu/~soper/Sun/sol
arneutrinos.html
Richard E. Hughes
Neutrinos; p.14
Kamiokande
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Masatoshi Koshiba followed up on
the measurements made by Ray
Davis by developing a large waterfilled detector, called Kamiokande, in
a Japanese mine. Kamiokande was
direction sensitive and could confirm
Davis' discovery that neutrinos came
from the sun. The Kamiokande water
tank was lined with photomultipliers.
When neutrinos enter the tank, they
can interact with electrons. These
produce flashes of light, which are
registered by the photomultipliers.
 Result: Neutrino reactions
detected, but not as many as
expected based on the
theoretical calculations.
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But Kamiokande also saw something
else even more surprising!
Richard E. Hughes http://www.nobel.se/physics/laureates/2002/illpres/kamiokande.html
Neutrinos; p.15
Seeing a SuperNova with Neutrinos!
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Kamiokande was operating on 23
February 1987 and detected 12
neutrinos emitted by supernova
1987A when it exploded 170,000
light years from the earth – the
first clear observation of neutrinos
produced outside our galaxy.
If you were in a Jupiter-type orbit a
billion kilometers from SN1987A
when it exploded and were protected
from the other effects of the
supernova, you would be killed by the
radiation damage from neutrinos
streaming through your body
SN1987A probably produced 1058
neutrinos
Based on the number and energy of
the neutrinos, the energy released
by the SN was about 10^53 ergs/sec
compared to sun 10^33 erg/sec
But the neutrinos don’t all arrive at
the same time!
Richard E. Hughes
Based on the direction, they came
from Large Megellenic cloud
Neutrinos; p.16
1987 all growed up!
Richard E. Hughes
Neutrinos; p.17
Atmospheric neutrinos
 Kamiokande, and other
experiments like it (like IMB)
also looked for “atmospheric
neutrinos”, which come from
cosmic rays – not the sun.
 All of these experiments looked
for electron neutrinos, and muon
neutrinos.
 Problem: they did not see as
many muon neutrinos as
expected: this is the “anomaly”
 When physicists have a problem
like this, there is only one thing
to do: build a bigger experiment!
 And give it a snappy name:
SuperK!
Richard E. Hughes
Neutrinos; p.18
SuperKamioka
 In 1990, in order to make more progress int hese fields of research,
construction was started on the 50,000 ton water Cerenkov detector,
Super-Kamiokande (Super-KAMIOKA Nucleon Decay Experiment or
Neutrino Detection Experiment). Super-Kamiokande is bigger and has
greater photocathode coverage than Kamiokande. Construction was
completed in 1995 and observation began in April of 1996.
Richard E. Hughes
Neutrinos; p.19
SuperK Event
 481 MeV muon neutrino (MC) produces 394 MeV muon which later
decays at rest into 52 MeV electron.
 Size of PMT corresponds to amount of light seen by the PMT. PMTs are
drawn as a flat squares even though in reality they look more like huge
flattened golden light bulbs.
Muon neutrino
muon
electron
Richard E. Hughes
http://www.ps.uci.edu/~tomba/sk/tscan/pictures.html
Neutrinos; p.20
Events point at the sun
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Super-K detects Boron-8 neutrinos when
they scatter off of atomic electrons in
the water. The recoil electron direction
is oriented along the direction of
neutrino travel (as in the banner at the
top of this page). The electron makes a
weak Cherenkov ring in the detector- only
40-50 PMT hits are expected for a 8
MeV electron (in a narrow time window,
shown as bright green hits in this event
display). At this low energy, there is
considerable random background, mostly
from radon gas in the water. So we count
solar neutrinos by making an angular
distribution with respect to the sun's
known direction. This is shown if the
figure below; the sharp peak near cosine
equals one is due to solar neutrinos. The
area under the peak, after subtracting
background, is the measured number of
solar neutrinos.
http://hep.bu.edu/~superk/solar.html
Richard E. Hughes
Pointing away
from sun
Pointing
at sun
Neutrinos; p.21
SuperKamioka
 Only(!) 500 days worth of data was
needed to produce this "neutrino
image" of the Sun, using Super-K
to detect the neutrinos from
nuclear fusion in the solar interior.
Centered on the Sun's postion, the
picture covers a significant
fraction of the sky (90x90
degrees in R.A. and Dec.). Brighter
colors represent a larger flux of
neutrinos.
 The little blue dot is what the size
of the sun would look like in the
visible spectrum (using photons)
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http://antwrp.gsfc.nasa.gov/apod/ap980605.html
Richard E. Hughes
Credit: R. Svoboda and K. Gordan
(LSU) Jun 5, 1998
Neutrinos; p.22
What else did SuperK do with Neutrinos?
 Also looked at “Atmospheric
Neutrinos”
 Predictions exist for how many
they should see
 SuperK discovered a deficit in
muon neutrinos! They
“disappeared”!
 And discovered that muon
neutrinos which come “upward”
(through the earth) are more
likely to “disappear”. Hmmm…
 Disappear is not quite right: they
“oscillate” into something else: an
electron neutrino!
 This can only happen if neutrinos
have Mass!
Richard E. Hughes
Neutrinos; p.23
Clinton on Neutrinos
“[W]e must help you to ensure that America continues to lead the revolution in
science and technology. Growth is a prerequisite for opportunity, and
scientific research is a basic prerequisite for growth. Just yesterday in
Japan, physicists announced a discovery that tiny neutrinos have mass.
Now, that may not mean much to most Americans, but it may change our
most fundamental theories -- from the nature of the smallest subatomic
particles to how the universe itself works, and indeed how it expands.
This discovery was made, in Japan, yes, but it had the support of the
investment of the U.S. Department of Energy. This discovery calls into
question the decision made in Washington a couple of years ago to disband
the Super-conducting Supercollider, and it reaffirms the importance of the
work now being done at the Fermi National Acceleration Facility in Illinois.
The larger issue is that these kinds of findings have implications that are not
limited to the laboratory. They affect the whole of society -- not only our
economy, but our very view of life, our understanding of our relations with
others, and our place in time.”
Richard E. Hughes
Neutrinos; p.24
Meanwhile…
BATAVIA, IL--President Bush met with members of the Fermi National
Accelerator Laboratory research team Monday to discuss a mathematical error
he recently discovered in the famed laboratory's "Improved Determination Of
Tau Lepton Paths From Inclusive Semileptonic B-Meson Decays" report.
"I'm somewhat out of my depth here," said Bush, a longtime Fermilab
follower……
Above: Bush shows Fermilab scientists where they went
wrong in their calculations.
Richard E. Hughes
Neutrinos; p.25
Are Neutrinos Dark Matter?
 Neutrinos don’t “shine”. And now we know they have mass.
And there sure are a lot of them. Dark Matter!?
 This mass difference, coupled with absolute neutrino mass
measurements and the Kamiokande's measurements,
indicates that the combined mass of all the neutrinos in the
universe is about equal to the combined mass of all the
visible stars. That means neutrinos cannot account for all
the "dark matter" known to make up most of the mass of
the universe.
Richard E. Hughes
Neutrinos; p.26
Summary
What we know:
 There are 3 “light” neutrinos
 The sun is a copious source of neutrinos
 Supernovae produce a lot of neutrinos
 Neutrinos have mass
What we don’t know:
 What are the masses of the 3 neutrinos reallY?
How do we find out?
 Would be great if there was a way to control the neutrinos
to study them in more detail
 But wait! There is! Fermilab can make a lot of neutrinos
too!
Richard E. Hughes
Neutrinos; p.27
Making a Beam of Neutrinos
120 GeV protons hit target (1020/Protons per year!)
p+ (“pions”) produced at wide range of angles
Magnetic horns to focus p+
p+ decay to m+n in long evacuated pipe
Left-over hadrons shower in hadron absorber
Rock shield ranges out m+
n beam travels through earth to experiment
But the experiment is hundreds of miles
away!
p+
p
Decay Pipe
Hadron
Absorber
Target Horns
Richard E. Hughes
m+
n
Exp.
Rock
Neutrinos; p.28
Numi-MINOS from the Air
NUMI: Neutrinos at the Main Injector
MINOS: Main Injector Neutrino Oscillation Search
So the neutrinos start out at
Fermilab, and are aimed through the
earth at Minnesota. Why Minnesota?
Richard E. Hughes
Neutrinos; p.29
MINOS Experiment
Two Detector Neutrino
Oscillation Experiment
(Start 2004)
Near Detector: 980 tons
Far Detector: 5400 tons
Det. 2
Det. 1
Richard E. Hughes
Neutrinos; p.30
Beam and “Near” Detector
Tunneling completed
Decay tunnel
before
installation of
decay pipe
Detector elements built
Installation starts later this year
First beam December 2004
MINOS Service
Target Service
Bldg .
Beam Absorber Access Tunnel
Target Shaft Area
600ft
225ft
MINOS Shaft Area
2,200ft
1,100ft
Target Service
EAV-1
Near detector hall
EAV-2&3
MINOS
Service Bldg .
EAV-4
Extraction Hall
Decay Tunnel
(21’6”D + 4’walkway)
Carrier Tunnel
(10’ x 10’)
Target Hall
(25’W x 30-60’H x 175’L)
Beam Absorber
MINOS Hall Tunnel
Muon Detectors
MINOS Hall
(35’W x 32’H x 150’L)
MINOS Near Detector
Richard E. Hughes
Neutrinos; p.31
The “Far” Detector
Richard E. Hughes
Neutrinos; p.32
Minos Plans
 The basic plan of MINOS is to
use the controlled source of
neutrinos from Fermilab to really
show that muon neutrinos can
oscillate into electron neutrinos
 Compare interactions in the near
detector with the far detector
 Both detectors will be able to
determine the type of neutrinos
 Basic measurement: the mass
difference between the two
neutrinos (not the actual masses)
 Will the experiment soar to
great heights?
 Or will it come crashing down to
earth?
Richard E. Hughes
Neutrinos; p.33
Richard E. Hughes
Neutrinos; p.34
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Solar neutrinos are produced by the nuclear reactions
that power the Sun. The fusion of proton plus proton
(pp) to deuterium plus positron plus neutrino is
responsible for 98% of the energy production of the
sun. Therefore these pp-neutrinos are the most
plentiful, and the most reliably estimated. About 60
billion pp-neutrinos pass through a square centimeter
at the Earth each second. They are relatively low
energy, however, with a continuous spectrum that ends
at 420 keV. In addition, there are several rarer
reactions which also produce neutrinos. The electron
capture on Beryllium-7 produces a sharp line of
Beryllium-7 neutrinos at 861 keV. A small fraction of
the time, Beryllium-7 captures a proton instead of an
electron, to form Boron-8. The beta decay of Boron-8:
8B -> 8Be + e+ + nu_e
produces a continuous spectrum of neutrino energies
that extends to 15 MeV. Super-K is sensitive to these
rare but high energy Boron-8 neutrinos.
Super-K detects Boron-8 neutrinos when they
scatter off of atomic electrons in the water. The recoil
electron direction is oriented along the direction of
neutrino travel (as in the banner at the top of this
page). The electron makes a weak Cherenkov ring in the
detector- only 40-50 PMT hits are expected for a 8
MeV electron (in a narrow time window, shown as bright
green hits in this event display). At this low energy,
there is considerable random background, mostly from
radon gas in the water. So we count solar neutrinos by
making an angular distribution with respect to the sun's
known direction. This is shown if the figure below; the
sharp peak near cosine equals one is due to solar
neutrinos. The area under the peak, after subtracting
background, is the measured number of solar neutrinos.
http://hep.bu.edu/~superk/solar.html
Richard E. Hughes
Neutrinos; p.35
Did Kamioka See the Sun?
Richard E. Hughes
Neutrinos; p.36
That bright thing in the sky!
Richard E. Hughes
Neutrinos; p.37
Richard E. Hughes
Neutrinos; p.38
Kamioka
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Brief History
Kamioka Underground Observatory, the predecessor of the present Kamioka Observatory,
Institute for Cosmic Ray Reserch, University of Tokyo, was established in 1983. The
original purpose of this observatory was to verify the Grand Unified Theories, one of the
most impenetrable matters of elementary particle physics, through a Nucleon Decay
Experiment. Thus, the water Cerenkov detector which was used for this experiment was
named Kamiokande (KAMIOKA Nucleon Decay Experiment).
The 4,500 ton water Cerenkov detector was placed at 1,000 m underground of Mozumi
Mine of the Kamioka Mining and Smelting Co. located in Kamioka-cho, Gifu, Japan. The
original purpose of Kamiokande was to investigate the stability of matter, one of the most
fundamental questions of elementary particle physics. An upgrade of Kamiokande was
started in 1985 to observe particles called neutrino (Solar, Atmospheric and other
neutrinos) which come from astrophysical sources and cosmic ray interactions. As a result
of this upgrade, the detector had become highly sensitive. In February, 1987,Kamiokande
had succeeded in detecting neutrinos from a supernova explosion which occurred in the
Large Magellanic Cloud. Solar neutrinos were detected in 1988 adding to the advancements
in neutrino astronomy and neutrino astrophysics.
In 1996, Kamioka Observatory which belongs to the Institute for Cosmic Ray
Research(ICRR), University of Tokyo was established. Kamiokande had been world famous
for its achievements on the observation of supernova neutrinos, solar neutrinos and
atmospheric neutrinos and also the study of the Grand Unified Theories of particles. In
1990, in order to make more progress int hese fields of research, construction was
started on the 50,000 ton water Cerenkov detector, Super-Kamiokande (SuperKAMIOKA Nucleon Decay Experiment or Neutrino Detection Experiment). SuperKamiokande is bigger and has greater photocathode coverage than Kamiokande.
Construction was completed in 1995 and observation began in April of 1996.
Richard E. Hughes
Neutrinos; p.39
Neutrino sources
Solar neutrinos
From the process of thermonuclear fusion inside the stars (our sun or any other star in the universe).
Some other neutrinos could come from very cataclysmic phemomena like explosions of supernovae or neutron stars
coalescences.
Neutrinos from nuclear reactors and accelerators
These are high energy neutrinos produced by the particles accelerators and low energy neutrinos coming out of nuclear
reactors. The first ones, whose energy can reach about 100 GeV, are produced to study the structure of the nucleons
(protons and neutrons composing the atomic nuclei) and to study the weak interaction. The second ones are here
although we did not ask for them. They are an abundant product made by the nuclear reactions inside the reactors
cores (a standard nuclear plant radiate about 5x 10^20 neutrinos per second) and their energy is around 4 MeV.
Neutrinos from natural radioactivity on the earth
The power coming from this natural radioactivity is estimated at about 20.000 Giga Watts (about 20.000 nuclear
plants!) and the neutrinos coming from this radioactivity are numerous: about 6 millions per second and per cm2. But
those neutrinos, despite of their quantity, are often locally drowned in the oceans of neutrinos coming from the nuclear
plants.
Neutrinos from cosmic rays
When a cosmic ray (proton coming from somewhere in space) penetrates the atmosphere, it interacts with an atomic
nucleus and this generates a particles shower. They are called "atmospheric neutrinos".
Neutrinos from the Big-Bang
The "standard" model of the Big-Bang predicts, like for the photons, a cosmic background of neutrinos. Those
neutrinos, nobody has never seen them. They are yet very numerous: about 330 neutrinos per cm3. But their energy is
theoretically so little (about 0.0004 eV), that no experiment, even very huge, has been able to detect them.
http://wwwlapp.in2p3.fr/neutrinos/ansources.html
Richard E. Hughes
Neutrinos; p.40
Timeline
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A NEUTRINO TIMELINE
The following is a short history of neutrinos as it relates to neutrino oscillation studies.
1920-1927 Charles Drummond Ellis (along with James Chadwick and colleagues) establishes clearly that the beta decay spectrum is really continuous, ending all controversies.
1930 Wolfgang Pauli hypothesizes the existence of neutrinos to account for the beta decay energy conservation crisis.
1932 James Chadwick discovers the neutron.
1933 Enrico Fermi writes down the correct theory for beta decay, incorporating the neutrino.
1946 Shoichi Sakata and Takesi Inoue propose the pi-mu scheme with a neutrino to accompany muon.
1956 Fred Reines and Clyde Cowan discover (electron anti-) neutrinos using a nuclear reactor.
1957 Neutrinos found to be left handed by Goldhaber, Grodzins and Sunyar.
1957 Bruno Pontecorvo proposes neutrino-antineutrino oscillations analogously to K0-K0bar, this is the first time neutrino oscillations (of some sort) are hypothesized.
1962 Ziro Maki, Masami Nakagawa and Sakata introduce neutrino flavor mixing and flavor oscillations.
1962 Muon neutrinos are discovered by Leon Lederman, Mel Schwartz, Jack Steinberger and colleagues at Brookhaven National Laboratories and it is confirmed that they are
different from electron neutrinos.
1964 John Bahcall and Ray Davis discuss the feasibility of measuring neutrinos from the sun.
1965 The first natural neutrinos are observed by Reines and colleagues in a gold mine in South Africa, and by Goku Menon and colleagues in Kolar gold fields in India, setting first
astrophysical limits.
1968 Ray Davis and colleagues get first radiochemical solar neutrino results using cleaning fluid in the Homestake Mine in North Dakota, leading to the observed deficit now known
as the "solar neutrino problem".
1976 The tau lepton is discovered by Martin Perl and colleagues at SLAC in Stanford, California. After several years, analysis of tau decay modes leads to the conclusion that tau is
accompanied by its own neutrino, nutau, which is neither nue nor numu.
1980s The IMB, the first massive underground nucleon decay search instrument and neutrino detector is built in a 2000' deep Morton Salt mine near Cleveland, Ohio. The Kamioka
experiment is built in a zinc mine in Japan.
1985 The "atmospheric neutrino anomaly" is observed by IMB and Kamiokande.
1986 Kamiokande group makes first directional counting observation solar of solar neutrinos and confirms deficit.
1987 The Kamiokande and IMB experiments detect burst of neutrinos from Supernova 1987A, heralding the birth of neutrino astronomy, and setting many limits on neutrino
properties, such as mass.
1988 Lederman, Schwartz and Steinberger awarded the Physics Nobel Prize for the discovery of the muon neutrino.
1989 The LEP accelerator experiments in Switzerland and the SLC at SLAC (Stanford) determine that there are only 3 light neutrino species (electron, muon and tau).
1991-2 SAGE (in Russia) and GALLEX (in Italy) confirm the solar neutrino deficit in radiochemical experiments.
1995 Frederick Reines and Martin Perl share the Physics Nobel Prize for discovery of electron neutrinos (and observation of supernove neutrinos) and the tau lepton, respectively.
1996 Super-Kamiokande, the largest particle detector ever, begins searching for neutrino interactions on 1 April at the site of the Kamioka experiment, with a Japan-US team.
1998 After analyzing more than 500 days of data, the Super-Kamiokande team reports finding oscillations in atmospheric neutrinos and, thus, neutrino mass.
1999-2000 The Chooz and Palo Verde reactor experiments report no oscillations, concluding that electron neutrinos are not the dominant participant in the atmospheric neutrino
oscillations.
2000 The DONUT Collaboration working at Fermilab announces observation of tau particles produced by tau neutrinos, making the first direct observation of the tau neutrino.
2000 Super-Kamiokande announces that the oscillating partner to the muon neutrino is not a sterile neutrino, but the tau neutrino.
2001-02 SNO announces observation of neutral currents from solar neutrinos, along with charged currents and elastic scatters, providing convincing evidence that neutrino
oscillations are the cause of the solar neutrino problem.
2002 Masatoshi Koshiba and Raymond Davis win Nobel Prize for measuring solar neutrinos (as well as supernova neutrinos).
2002 KamLAND observes neutrino oscillations consistent with the solar neutrino puzzle using, for the first time, man-made neutrinos.
Modified by Giorgio Gratta from an original by John Leaned and Sandip Pakvasa.
This page is maintained by [email protected].
Richard E. Hughes
Neutrinos; p.41
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It appears established beyond reasonable doubt, through the success of the standard
solar model, that the sun shines from nuclear fusion in its core. A fusion reaction involves
the merging of two atomic nuclei into one. In the sun, a chain of several different fusion
reactions along any of about four different pathways, leads from four hydrogen nuclei
(single protons) to one helium nucleus (two protons and two neutrons). In this process, two
protons have to be converted into neutrons through beta decays. In each beta decay, a
neutrino is emitted (an electron-flavored neutrino, that is). So it is straightforward to
calculate that, if the sun shines through hydrogen fusion, it ought to emit two neutrinos
per fusion chain. And in our standard theory of particle physics, the neutrinos will zip
straight out from the sun, without interacting with the intervening material. The total
flux of neutrinos from the sun ought to be some 200 000 000 000 000 000 000 000 000
000 000 000 000 per second, corresponding to a flux of about 6.5 × 1010 neutrinos per
square centimeter per second hitting the earth.
Most of those neutrinos come from the main energy-producing reaction chain in the sun:
proton-proton fusion. Unfortunately, the neutrinos from proton-proton (pp) fusion have a
very low energy. Energy in this context in measured in electron-volts (1 eV = 1.6 × 10-19
Joule), or millions of electron-volts (MeV), and the energy of the pp neutrinos is less than
0.42 MeV, making them difficult to detect.
Smaller (but still enormous) numbers of higher-energy neutrinos are expected from
various side reactions, notably boron and beryllium decays. There is also an alternative
energy-producing chain, CNO-fusion, where the fusion of hydrogen to helium is catalyzed
by carbon. This CNO-chain is expected to be the main energy source in larger, hotter
stars, but it should only give a modest contribution in the sun. The CNO neutrinos are
otherwise easier to detect than pp-neutrinos, having three to four times more energy
each.
Number of interactions/person/lifetime from solar neutrinos: 1.
http://www.talkorigins.org/faqs/faq-solar.html
Richard E. Hughes
Neutrinos; p.42
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Most physicists and astronomers believe that the sun's heat is produced by
thermonuclear reactions that fuse light elements into heavier ones, thereby
converting mass into energy. To demonstrate the truth of this hypothesis,
however, is still not easy, nearly 50 years after it was suggested by Sir Arthur
Eddington. The difficulty is that the sun's thermonuclear furnace is deep in the
interior, where it is hidden by an enormous mass of cooler material. Hence
conventional astronomical instruments, even when placed in orbit above the
earth, can do no more than record the particles, chiefly photons, emitted by the
outermost layers of the sun.
Of the particles released by the hypothetical thermonuclear reactions in the
solar interior, only one species has the ability to penetrate from the center of
the sun to the surface (a distance of some 400,000 miles) and escape into
space: the neutrino. This massless particle, which travels with the speed of
light, is so unreactive that only one in every 100 billion created in the solar
furnace is stopped or deflected on its flight to the sun's surface. Thus
neutrinos offer us the possibility of ``seeing'' into the solar interior because
they alone escape directly into space. About 3 percent of the total energy
radiated by the sun is in the form of neutrinos. The flux of solar neutrinos at
the earth's surface is on the order of 1011 per square centimeter per second.
Unfortunately the fact that neutrinos escape so easily from the sun implies that
they are difficult to capture.
Richard E. Hughes
Neutrinos; p.43
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Neutrinos were first suggested as hypothetical entities in 1931 after it was noted that small amounts
of mass seemingly vanish in the radioactive decay of certain nuclei. Wolfgang Pauli suggested that the
mass was spirited away in the form of energy by massless particles, for which Enrico Fermi proposed
the name neutrino (``little neutral one''). Fermi also provided a quantitative theory of processes
involving neutrinos. In 1956 Frederick Reines and Clyde L. Cowan, Jr., succeeded in detecting neutrinos
by installing an elaborate apparatus near a large nuclear reactor. Such a reactor emits a prodigious flux
of antineutrinos produced by the radioactive decay of fission products. For purposes of demonstrating
a particle's existence, of course, an antiparticle is as good as a particle.
In the late 1930's Hans A. Bethe of Cornell University followed up Eddington's 1920 suggestion of the
nuclear origin of the sun's energy and outlined how the fusion of atomic nuclei might enable the sun and
other stars to shine for the billions of years required by the age of meteorites and terrestrial rocks.
Since the 1930's the birth, evolution and death of stars have been widely studied. It is generally
assumed that the original main constituent of the universe was hydrogen. Under certain conditions
hydrogen atoms presumably assemble into clouds, or protostars, dense enough to contract by their own
gravitational force. The contraction continues until the pressure and temperature at the center of the
protostar ignite thermonuclear reactions in which hydrogen nuclei combine to form helium nuclei. After
most of the hydrogen has been consumed, the star contracts again gravitationally until its center
becomes hot enough to fuse helium nuclei into still heavier elements. The process of fuel exhaustion
and contraction continues through a number of cycles.
The sun is thought to be in the first stage of nuclear burning. In this stage four hydrogen nuclei
(protons) are fused to create a helium nucleus, consisting of two protons and two neutrons. In the
process two positive charges (originally carried by two of the four protons) emerge as two positive
electrons (antiparticles of the familiar electron). The fusion also releases two neutrinos and some
excess energy, about 25 million electron volts (MeV). This energy corresponds to the amount of mass
lost in the overall reaction, which is to say that a helium nucleus and two electrons weigh slightly less
than four protons. The 25 MeV of energy so released appears as energy of motion in the gas of the
solar furnace and as photons (particles of radiant energy). This energy ultimately diffuses to the
surface of the sun and escapes in the form of sunlight and other radiation.
Richard E. Hughes
Neutrinos; p.44