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NEUTRINOS AND NEUTRINO DETECTION
Erin O’SullivanDuke University
CGWAS 2015Friday, July 10, 15
THIS TALK, IN FOUR PARTS
Part 1: Neutrino history
Part 2: Neutrino sources/neutrinos as probes
Part 3: Neutrinos oscillate!
Part 4: Neutrino detection
2
Friday, July 10, 15
N E U T R I N O H I S T O RY3
Friday, July 10, 15
Cosmic Gall
by John Updike
Neutrinos, they are very small.They have no charge and have no mass
And do not interact at all.The earth is just a silly ball
To them, through which they simply pass,Like dustmaids down a drafty hall
Or photons through a sheet of glass.They snub the most exquisite gas,Ignore the most substantial wall,
Cold-shoulder steel and sounding brass,Insult the stallion in his stall,
And, scorning barriers of class,Infiltrate you and me! Like tall
And painless guillotines, they fallDown through our heads into the grass.
At night, they enter at NepalAnd pierce the lover and his lass
From underneath the bed—you callIt wonderful; I call it crass.
4
(corrected)
rarely
sometimes interact in
100 trillion neutrinos/s
Friday, July 10, 15
5
1899 - Beta decay is discovered
n p
Beta Decay
A continuous energy spectrum was observed
Friday, July 10, 15
Wolfgang Ernst Pauli (1900 – 1958)
1930 - The neutrino is proposed as a solution to missing energy observed in radioactive decays
6
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7
1950s - How to measure neutrinos?Look for inverse beta decay in liquid scintillator
Need a strong source of neutrinos...
Friday, July 10, 15
8
1950s - How to measure neutrinos?
Initial design for detecting neutrinos
Plan A: Detonate a nuclear bomb
(El Monstro)
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1959 - First experimental observation of the (anti)neutrino
Fred Reines (left, 1918 – 1998) and Clyde Cowan Jr (right, 1919-1974) at the Hanford
Reactor site
Neutrino detector at Savannah River, a nuclear facility in Augusta, GA
9
WaterScintillator
Photodetectors
Plan B: Set up a detector near a nuclear reactor
Friday, July 10, 15
1962 - The muon neutrino is discovered
10
Melvin Schwartz(1932 – 2006)
Leon Lederman(1922 – )
Jack Steinberger(1921 – )
A spark chamber measures a muon produced from a
neutrino interaction
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2000 - The tau neutrino is discovered
11
Tau neutrinos produced through
tau decays
Tau neutrinos produce taus in the
detector
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12
2006 - Only 3 neutrino flavours allowed from Z boson decay measurements
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13
Modern picture of neutrinos
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Neutrinos are created in weak interactions
http://wwweth.cern.ch/~disserto/IPPaboutUs/ParticlePhysics_eng.html14
Friday, July 10, 15
A few examples of weak interactions that create neutrinos
Beta-minus decay Beta-plus decay
Muon decay Pion decay
15
Electron capture
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Present day - Open questions in neutrino physics
16
Are neutrinos their own antiparticle?What are the neutrino masses?
Any other flavours of neutrinos? We know they can’t take part in weak interactions, so known as sterile neutrinos.
CP violation in the lepton sector?
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N E U T R I N O S O U R C E S / N E U T R I N O S A S P R O B E S
17
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With X-rays, which penetrate much more than ordinary light, you can see
inside your hand. With neutrinos, which penetrate much more even than X-rays,
you can look inside the Sun.~Ray Davis Jr. 1914-2006
18
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Reactor neutrinos: created by fission products
19
Beta-minus decay
Nuclear fission creates unstable products that beta decay
Friday, July 10, 15
Reactor neutrinos: probes for detecting nuclear facilities
20
Proposed portable neutrino detector that could be used for nonproliferation studies
Hypothetical 10 Mton neutrino detector that could be built in China to search for reactors in
North Korea
A. Bernstein et al 2009 arXiv:0908.4338
Friday, July 10, 15
Geoneutrinos: produced through U and Th chain radioactive decays in the Earth’s crust and mantle
21
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Geoneutrinos: probing the composition of the Earth
22
neutrino detectors
(Japan) (Italy)
Radioactivity is homogeneous in the mantle
Radioactivity is all at the core-mantle
interface
Nature Geoscience 4, 647–651 (2011)
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23
Accelerator Neutrinos: intense neutrino source created by proton beams that produce pion decays
Supersymmetry Magazine. Artwork by Sandbox Studio, Chicago with Ana Kova
Friday, July 10, 15
23
Accelerator Neutrinos: intense neutrino source created by proton beams that produce pion decays
Supersymmetry Magazine. Artwork by Sandbox Studio, Chicago with Ana Kova
Friday, July 10, 15
Accelerator Neutrinos: probing the origin of matter/antimatter asymmetry
24
Neutrinos violate charge conjugation symmetry
(C-symmetry)
Neutrino violate parity symmetry
(P-symmetry)
Neutrinos obey CP-symmetry (as far as we can tell)
BUT, if CP-symmetry always true, reaction rates for matter should be the same for anti-matter. So why do we live in a
matter-dominated universe?
matter → antimatterleft handed → right handed
Friday, July 10, 15
Accelerator Neutrinos: probing the origin of matter/antimatter asymmetry
25
By comparing the reactions using the neutrino beam and the reactions using the antineutrino beam, you can probe if there is any matter/antimatter asymmetry in the neutrino sector.
Neutrino beam
Antineutrino beam
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Atmospheric neutrinos: created in cosmic ray showers in the Earth’s atmosphere
26
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Atmospheric neutrinos: probes for neutrino oscillations
27
Using neutrinos produced in the atmosphere, a
neutrino experiment in Japan showed that they
saw a deficit of neutrinos correlated with the
distance the neutrino travelled.
More on how neutrino oscillations work later
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28
Interlude: Advantages of using neutrinos as astrophysical probes
Neutrinos interact much more weakly than photons or charged particles. As a consequence:- we see neutrinos sooner- neutrinos travel undistorted from the source to our detector- neutrinos will also interact less in the astrophysical source, which allows us to probe the core rather than just the surface.
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Solar neutrinos: Produced in the thermonuclear reactions in the Sun
29
pp chain CNO cycle
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Solar neutrinos: Probes for metallicity in the Sun
30
(Pena-Garay and Serenelli 2008)
arXiv:0811.2424
Low metallicity model (AGS) uses
photospheric absorption lines. High metallicity model (GS) uses helioseismology.
CNO neutrinos could determine which
metallicity model is correct.
Friday, July 10, 15
Supernova neutrinos: created in supernova explosions
31
e+ + e- ν + ν
p + e- n + νe
Infall Neutronization burst
Accretion Cooling
Modified from Janka et al 2007 (arXiv:astro-ph/0612072)
p + e- n + νen + e+ p + νe
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32
Supernova neutrinos: probing the core-collapse mechanismObserving the full time spectrum from the SN emission could give us information about
each stage of the explosion
Infall&phase&
Neutroniza2on&burst&&
Neutroniza2on&burst&&
Accre2on&phase& Cooling&phase&
Astrophys.J. 496 (1998) 216-225
Livermore model
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Supernova neutrinos: probing the core-collapse mechanism
33
Neutrinos can give us info about the progenitor of a SN
Modified from O’Connor and Ott 2012 (arXiv:1207.1100)Different progenitor masses
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34
Supernova neutrinos: probing the core-collapse mechanismNeutrinos are a supernova early warning system
Neutrino detectors connected to the SNEWS system
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35
Supernova neutrinos: probing the core-collapse mechanismNeutrinos are (maybe) a supernova early early warning
system
Before explosion
Kamland sensitivity
Some models predict neutrino emission in the
Silicon burning stage
This could give some advance warning of a (nearby) SN. Ex. for
Betelgeuse in Kamland ~ 2 days
Asakura et al. arXiv1506.01175
Friday, July 10, 15
High energy astrophysical neutrinos: created in high energy processes
36Active galactic nuclei
Gamma ray bursts
Possible dark matter annihilation in dwarf galaxies
Candidates for neutrino emission (not been conclusively observed from any specific source)
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Astrophysical neutrinos: probing properties of astrophysical systems
37
DM annihilation cross section
Mass of DM particle
Annihilation channel of DM
An example: By searching for neutrinos from dark matter, we could put constraints on the:
Friday, July 10, 15
38
Astrophysical neutrino detection: SN1987a
In 1987, photons (and neutrinos!) from a supernova in a nearby dwarf galaxy reached
earth.- first measurement of neutrinos from outside our solar system- only a handful of neutrinos,
but hundreds of papers written
Friday, July 10, 15
39
Astrophysical neutrino detection: IceCube
1 PeV Aug 2011 1.1 PeV Jan 2012 2.2 PeV Dec 2012
Highest energy neutrinos ever
measured
Bert Ernie Big Bird
Any significant clustering? Not yet, need more statistics.
Friday, July 10, 15
Neutrino sources have distinct energy domains
40
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N E U T R I N O S O S C I L L AT E !41
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42
The solar neutrino problem: where are the missing neutrinos?
Ray Davis Jr and John Bahcall (1914 – 2006) and (1935 - 2005)
Electron neutrinos are created in the SunElectron neutrinos were detected Davis’
experiment at Earth
Pred
icte
dO
bser
ved
In an experiment which ran from 1967-1985, Davis observed ~1/3 the amount of neutrinos predicted by Bahcall’s solar neutrino model
Friday, July 10, 15
43
The solar neutrino problem: where are the missing neutrinos?
Some explanations for the solar neutrino problem:- We don’t know the Sun well enough to make robust neutrino models- Measuring neutrinos is tough, so maybe something in the experiment is wrong- Maybe there is something about the neutrinos themselves that we don’t understand
Friday, July 10, 15
44
The solar neutrino problem: where are the missing neutrinos?
Pred
icte
dO
bser
ved
Pred
icte
dO
bser
ved
Pred
icte
d
Obs
erve
d
Obs
erve
d
19851967 (Davis) 1991 & 1990Year measurement began:
Other experiments measure neutrinos and find less than the prediction (and don’t agree with each other!)
Friday, July 10, 15
45
Experimental evidence for neutrino oscillationsPions produce a set ratio of neutrinos in cosmic ray
interactions
≃ 2
1998: Super-Kamiokande publish a paper (Phys. Rev. Lett. 81 (1998) 1562-1567)
that showed:- the ratio they measure is less than 2
(Rdata/Rexpected ≃ 0.6)- the discrepancy was dependent on
neutrino path length (neutrinos entering the bottom of the detector vs. the top of
the detector)- that the missing neutrinos were muon
type neutrinosThe paper concluded that the
behaviour fit all the hallmarks of neutrino oscillation and they calculated
a best fit value for νμ → ντ mixing parameters
Friday, July 10, 15
46
An elegant solution to the solar neutrino problem
2002: The Sudbury Neutrino Observatory (SNO) was the first
experiment to measure solar neutrinos using a detection channel that
was equally sensitive to all flavours. The result measured the expected
flux from theory.
Sensitive to all neutrino flavoursSensitive to electron flavour only
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Our modern understanding: neutrino flavour is not static
p + e- n + νe νe? νμ ? ντ?
A neutrino is created in a
definite flavour state
As the neutrino
propagates, it oscillates between flavours
When the neutrino reaches the detector, it can exist in one of
the other flavour states
Friday, July 10, 15
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Neutrino oscillations: first proposed by Bruno Pontecorvo
Pontecorvo was fascinated by the idea of neutrino oscillations.
1957: Can a neutrino oscillate into an antineutrino? Can a neutrino oscillate
into a “sterile” neutrino?1967: Can an electron neutrino oscillate
into a muon neutrino?Pontecorvo died in 1993, just 5 years
before neutrino oscillations were experimentally observed.
Bruno Pontecorvo(1913 – 1993)
Friday, July 10, 15
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Mathematical framework for oscillations
Mass eigenstates Flavour eigenstates
θ12, θ23, θ13: mixing parameters, δ: CP violation parameter
ν1
ν2
ν3
νe
νμ
ντ
Mass states Flavour states
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Vacuum oscillations
Mass eigenstates propagate with different speeds.
The probability that you will measure
the original flavour varies with path
length
Because neutrinos oscillate, they must have
mass!
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Oscillations in matter
This potential term will affect the neutrino oscillation behaviour.
Neutrinos oscillations are affected by matter
How neutrinos propagate through space
Hamiltonian in the flavour basis
Electron density
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Neutrino mass hierarchy
Neutrinos oscillations are affected by hierarchy
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53
What we know
Mixing Parameters (from the PDG)-∆m221 = 7.58 (+0.22/-0.26)×10−5 eV2 measured by reactor
neutrino experiments (in particular Kamland)-∆m232 = 2.35(+0.12/-0.09) × 10−3 eV2 measured by accelerator
neutrino experiments (in particular MINOS)-sin2θ12 = 0.306(+0.018/-0.015) measured by solar neutrino
experiments -sin2θ23 = 0.42(+0.08/-0.03) measured by atmospheric neutrino
experiments-sin2 (2θ13) = 0.096±0.013 measured by accelerator and reactor
neutrino experiments
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N E U T R I N O D E T E C T I O N54
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55
Detecting neutrinosNeutrinos experiments are built underground to shield
the detectors from muons and other backgrounds. We also need to have clean, low background experiments.
Walk through a mine End up in a clean room
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The reactions: Interactions on nuclei (CC, NC)
56
- CC reaction gives a way to measure the flavour if you can identify the lepton. Mediated
by the W boson.-NC reaction measures all
neutrino flavours equally. This gives a way to measure the total neutrino flux without
considering oscillations. Mediated by the Z boson.
NC channel
CC channel
Stuff(neutron, proton, nucleon)
lepton Other stuff
νl + X → l + Y
ν + X → ν + X’
Nucleon
( )
Excited nucleon or ejected particles
Friday, July 10, 15
The reactions: Inverse beta decay (CC)
57
Electron Antineutrinos
Get a prompt gamma from positron annihilation. Delayed
neutron capture = a good coincidence signal (if you can
detect it)
νe + p → e+ + n
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The reactions: Elastic scattering (CC + NC)
58
- Measures neutrinos and antineutrinos
- The outgoing electron travels in a direction related to the
incoming neutrino, so we get directionality (can point to the location of the neutrino source)
- higher cross section for electron neutrino than other flavours (because of charged current
component)
ν + e- → ν + e-
Friday, July 10, 15
59
Water CherenkovCherenkov radiation: particles traveling faster than the
speed of light (in the medium)
Analogous to a sonic boom (but with light) Nuclear reactors emitting Cherenkov light
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Dominant(Reac,on((
Other(Reac,ons((
Advantages:- water is cheap!
- directional info in the ES channel- flavour info (if you are able to see
the neutron)
Water CherenkovDetect light from Cherenkov radiation in water
Solar neutrinosν + e- → ν + e-
Atmospheric, Accelerator,
Astrophysical neutrinosνl + X → l + Y
Supernova Neutrinos νe + p → e+ + n ν + e- → ν + e-
νe + 16O → e- + 16F* νe + 16O → e+ + 16N* ν + 16O → ν + 16O*
( )
Friday, July 10, 15
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Water CherenkovThis is what a supernova looks like in a water Cherenkov
detector
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Water CherenkovThis is what a supernova looks like in a water Cherenkov
detector
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Water Cherenkov: Super-Kamiokande
H2O (50 kT)
Largest water Cherenkov detector currently operating
Currently operating
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Water Cherenkov + Gadolinium: SK-Gd
H2O+ Gd
Improve capture efficiency for the neutron in inverse beta decay
Near-term operating (5-10 years)
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Water Cherenkov: Hyper-Kamiokande
9900 PMTs which record light
~1 Megaton of water
Future experiment (~2025+)
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Water Cherenkov string detectors: IceCubeCurrently operating
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Solar neutrinosν + e- → ν + e-
Reactor /Geo-Neutrinosνe + p → e+ + n
Supernova Neutrinos νe + p → e+ + n ν + e- → ν + e-
ν + 12C → ν + 12C*Accelerator,
Astrophysical neutrinosνl + X → l + Y
Scintillator
66
Detect light from charged particles in scintillatorνe-
Advantages:- Low energy threshold- IBD neutron capture is
visible- NC reaction gives total
flux information
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Scintillator: JUNONear-term operating (5-10 years)
Friday, July 10, 15
Heavy nuclei
68
Count neutrons from nuclei-neutrino interactions
νPb
Pb* neutron
γ
detector Advantages:- simple detection
technique- high density target
Supernova Neutrinos νe + 208Pb → νe + 208Bi*
ν + 208Pb → ν + 208Pb*
Friday, July 10, 15
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Heavy nuclei: HALO
Lead blocks (76 T)
Proportional counters (neutron detector)
Water shielding
Currently operating
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Liquid argon
70
Detect ionization in a time projection chamber
Advantages:- Good measurement of the
electron neutrino flavour- Good particle identification
Atmospheric, Accelerator, Astrophysical neutrinos
νl + N → l + XSupernova Neutrinos ν + e- → ν + e-
νe + 40Ar → e- + 40K* νe + 40Ar → e+ + 40Cl*
( )
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Liquid argon: DUNE
40 kT Read out position and time info from
wire plane
Future experiment (~2023+)
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Complementarity with GWs
- A neutrino signal could give an early warning for a nearby supernova explosion
- A neutrino burst signal could be used to look back in the GW info and look for a signal (and vice versa)
- Both neutrino signals and GW signals contain similar info (ex. in a SN: mass, distance, direction). Having both
signals together will help to constrain the parameters.
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Conclusions
- Neutrinos have interesting properties (oscillations, very small mass). Because neutrinos are so abundant in our
Universe, their properties are important.- Neutrinos are able to probe systems that are difficult to
measure in other ways (supernovae, high E astrophysics). - Current neutrino detectors employ many different
technologies. Each detector adds something to the puzzle (see the activity this afternoon for more details).
Friday, July 10, 15
FURTHER READING
For a good read about neutrino history: Neutrino by Frank Close (available on Amazon)
For a good neutrino textbook: Fundamentals of Astrophysics by Carlo Giunti and Chung Kim
For information on supernova neutrino detection: Supernova Neutrino Detection by Kate Scholberg (available at http://arxiv.org/pdf/1205.6003.pdf)
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