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

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N E U T R I N O H I S T O RY3

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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.

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(corrected)

rarely

sometimes interact in

100 trillion neutrinos/s

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1899 - Beta decay is discovered

n p

Beta Decay

A continuous energy spectrum was observed

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Wolfgang Ernst Pauli (1900 – 1958)

1930 - The neutrino is proposed as a solution to missing energy observed in radioactive decays

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1950s - How to measure neutrinos?Look for inverse beta decay in liquid scintillator

Need a strong source of neutrinos...

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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

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WaterScintillator

Photodetectors

Plan B: Set up a detector near a nuclear reactor

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1962 - The muon neutrino is discovered

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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

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Tau neutrinos produced through

tau decays

Tau neutrinos produce taus in the

detector

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2006 - Only 3 neutrino flavours allowed from Z boson decay measurements

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Modern picture of neutrinos

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Neutrinos are created in weak interactions

http://wwweth.cern.ch/~disserto/IPPaboutUs/ParticlePhysics_eng.html14

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A few examples of weak interactions that create neutrinos

Beta-minus decay Beta-plus decay

Muon decay Pion decay

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Electron capture

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Present day - Open questions in neutrino physics

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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

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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

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Reactor neutrinos: created by fission products

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Beta-minus decay

Nuclear fission creates unstable products that beta decay

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Reactor neutrinos: probes for detecting nuclear facilities

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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

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Geoneutrinos: produced through U and Th chain radioactive decays in the Earth’s crust and mantle

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Geoneutrinos: probing the composition of the Earth

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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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Accelerator Neutrinos: intense neutrino source created by proton beams that produce pion decays

Supersymmetry Magazine. Artwork by Sandbox Studio, Chicago with Ana Kova

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Accelerator Neutrinos: intense neutrino source created by proton beams that produce pion decays

Supersymmetry Magazine. Artwork by Sandbox Studio, Chicago with Ana Kova

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Accelerator Neutrinos: probing the origin of matter/antimatter asymmetry

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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

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Accelerator Neutrinos: probing the origin of matter/antimatter asymmetry

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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

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Atmospheric neutrinos: probes for neutrino oscillations

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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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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

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pp chain CNO cycle

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Solar neutrinos: Probes for metallicity in the Sun

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(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.

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Supernova neutrinos: created in supernova explosions

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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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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

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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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Supernova neutrinos: probing the core-collapse mechanismNeutrinos are a supernova early warning system

Neutrino detectors connected to the SNEWS system

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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

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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

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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:

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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

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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.

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Neutrino sources have distinct energy domains

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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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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

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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

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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!)

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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

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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

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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)

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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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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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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)

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- 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

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The reactions: Inverse beta decay (CC)

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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)

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- 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-

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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*

( )

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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

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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)

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Heavy nuclei

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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*

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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

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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).

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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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