“The Story of the neutrino” Does the missing matter matter? or
Dec 20, 2015
“The Story of the neutrino”
Does the missing matter matter?
or
21st/22nd March 2002 Particle Physics MasterclassOxford University
2
An Introduction
Sudbury Neutrino Observatory (SNO)
2km underground
To observe the To observe the Sun !Sun !
21st/22nd March 2002 Particle Physics MasterclassOxford University
3
Discovery of RadioactivityHenri Becquerel, 1896
Accidentally left photographic plates in a dark drawer with some uranium salts...
The plates became “fogged”
The Uranium was emitting something which was interacting with the film...
21st/22nd March 2002 Particle Physics MasterclassOxford University
4
Radioactivity and momentum conservation
Unstable nucleus
Recoiling (more) stable nucleus
• A* is at rest (PTOTAL = 0)
•A and B must have equal and opposite momenta:
p + (-p) = 0
• But, E2 = p2 + m2 and the total energy loss is fixed...
• So, there can be only one value of the energy of the escaping particle...
A*
A
B
p
-p
MA
mB
Conservation of momentum
Einstein: Relativity
21st/22nd March 2002 Particle Physics MasterclassOxford University
5
The Beta-decay puzzle
A*
A
e-
Beta-particle energy
N
A nucleus decays giving out an electron...
Something must be wrongwith the picture...?
The electron has arange of energies
Energy and momentum aren’t conserved!?
21st/22nd March 2002 Particle Physics MasterclassOxford University
6
The “neutrino” hypothesisWhat Pauli “saw”:
“What if the missing energy is carried off by an otherwise “invisible” particle...?”
Wolfgang Pauli, 1930
A*
A
e-
C
21st/22nd March 2002 Particle Physics MasterclassOxford University
7
The birth of the neutrino
Pauli: “I have done a terrible thing. I have invented a particle which cannot be detected...”
• It must be very lightvery light, possibly massless:(sometimes, the electron takes all the energy in the decay)
• It must be electrically neutralelectrically neutral:(charge conservation in beta decay)
• It is produced along with an electron:(they can’t be made on their own...)
• It must interact very rarelyinteract very rarely:(it always escapes the detector without being seen)
21st/22nd March 2002 Particle Physics MasterclassOxford University
8
25 years later: Hard but not impossible
Beta decay in a nuclear reactor
n p
e-
e
“Inverse” Beta decay
p n
e+e
It would take 1019 m (300 light years) of water to absorb a single neutrino.
Therefore we need many neutrinos...
…and a very large detector
...and it’s the sametype of reaction in“reverse”
21st/22nd March 2002 Particle Physics MasterclassOxford University
9
Neutrinos from the Sun
p
p
pn
e
e+
The biggest nuclear reactorThe biggest nuclear reactorof them all...of them all...
Two protons fuse togive a “deuteron”, a positron and an electron neutrino
10 billion neutrinos from 10 billion neutrinos from the sun pass through the sun pass through your finger tip every your finger tip every
second!second!
21st/22nd March 2002 Particle Physics MasterclassOxford University
10
380,000 bottles of cleaning fluid
Neutrinos can change chlorine atoms to argon atoms by Inverse Beta Decay
Cl + Cl + ee Ar + e Ar + e--
Measure the amount of argon produced in one month......find 10 atoms in 1030!
n + ee p + e p + e--
21st/22nd March 2002 Particle Physics MasterclassOxford University
11
Some of our neutrinos are missing...
• We “understand” how each nuclear reaction works...
• We can measure how much energy the sun gives out...
• We can accurately predict the number of neutrinos we expect!
p + p p + n + e + e + (Energy)
SunTotal energy
“Light detector”
Nneutrinos = Total energy Reaction energy
Something must be wrong with the neutrinos...
21st/22nd March 2002 Particle Physics MasterclassOxford University
12
Neutrinos as waves... Oscillations!
• What if neutrinos were made up of two quantum waves with different wavelengths...?
• These waves would interfere
• Electron neutrinos disappear depending on the distance and mass difference of the neutrinos
Quantum waves interfering over 100
million miles!
21st/22nd March 2002 Particle Physics MasterclassOxford University
13
SNO - two measurements at once
1000 tonnes of heavy water (D20)
10,000 light detectors
100 million km to the sun
2039m to surface
21st/22nd March 2002 Particle Physics MasterclassOxford University
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Sudbury Neutrino Observatory
21st/22nd March 2002 Particle Physics MasterclassOxford University
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SNO - two measurements at once
•Reaction like beta decay to detect electron neutrinos
e + d p + p + ee
•All neutrinos can break up deuterons (electron, muon or tau)
any + d p + any + nn
•See ee or nn from flash of light
•If oscillation occurs:Number of e
Number of any <1
21st/22nd March 2002 Particle Physics MasterclassOxford University
16
Cosmic encounters...
proton• High energy protons from space in all directions
• Hit the atmosphere and produce a “shower” of particles
• This shower includes muons
• These particles decay like beta decay to give...
...neutrinos!
100 particles m-2s-1
This is why all This is why all neutrino neutrino
detectors are detectors are undergroundunderground
21st/22nd March 2002 Particle Physics MasterclassOxford University
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Atmospheric neutrinos
“Showerparticle”
muonmuon
neutrino
e
electronneutrino
muonneutrino
• Muons and electrons can’t just be made or decay on their own...
•Particle “type” must be conserved
• A shower particle produces a muon and a muon neutrino.
• The muon decays to a muon neutrino... ...and an electron along with an electron neutrino
2 2 : : 1 1 ee
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Detecting neutrino oscillations...
Knowing what ratio of neutrino types to expect...
...count neutrinos after different distances
See how many neutrinosof each type havedisappeared (oscillated)
Atmospheric neutrinos
Compare “up” and “down”
Soudan 2
21st/22nd March 2002 Particle Physics MasterclassOxford University
19
Soudan 2: Disappearing neutrinos...
e
1000 tonnes of iron!
What do electron and muon neutrino interactions look like?
Interacting electron neutrinos produce electrons
Electrons create e+e- pairs“Electromagnetic Showers”
Interacting muon neutrinos produce muons
Muons are heavier than electrons Straight track until it runs out of energy
muon
e
21st/22nd March 2002 Particle Physics MasterclassOxford University
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What we (don’t) know...
• There are three types of neutrino, each associated with a “lepton”
• They appear to change (oscillate) between neutrino types
• Real quantum waves in action over millions of miles!
e
nu-e
mu
nu-mu
tau
nu-tau