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Neutrino Physics

Joe GrangeUPS c/o 2006Univ. of Florida PhD candidate

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Today

What are neutrinos?

Neutrino history

New physics! The oscillating neutrino

Modern neutrino detectors

What can neutrinos tell us about our universe?

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n History:

Early 20th century physicists thought the things that make up our macroscopic world (nuclei, electrons, photons) were the only things that make up the universe

If that’s the case, then the common radioactive “beta (electron) decay” involves only a proton and an electron

npeAssuming energy + momentum

conservation, electron would have the same energy in every decay

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Intersection of data and theory

Hypothesis was wrong! So either: the decay involves more

than two particles or energy is not conserved

Data

Latter option might sound drastic, but, e.g. Niels Bohr (right) was ready to abandon E conservation

Wolfgang Pauli (left) chose the former

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“A desperate remedy”

1930, Pauli proposed a light, electrically neutral particle carried away the missing energy “I dare not publish this idea…but only those who

wager can win…” “I have done a terrible thing. I have postulated a

particle that cannot be detected”

A few years later, Enrico Fermi further incorporated this particle into present theory, named it “Neutr-”: neutral “-ino”: little one

n

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Neutr- “ino”: how small?

Not totally sure! Active area to find the absolute mass, but from indirect measurements we know it’s ~0.1 eV (electron-volts)

Analogy: if a n weighs as much as a penny…

An electron would weigh as much as a car,

a proton would weigh as much as a space shuttle,

and a human would weigh 20x Jupiter!

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Why “cannot be detected”?

Can be detected, it just turned out to be very hard hadn’t seen it before, must have extremely low

probability to interact

Of the four fundamental forces (gravitation, strong nuclear, electricity & magnetism, weak), neutrinos only interact weakly. Aptly named!

at the dentist’s office, a vest with a few mm of lead stops x-rays, meanwhile you’d need ~1 light year (10 trillion miles) of lead to stop a n!

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First proposed expt: “El Monstro”

First proposed n experiment used an atomic bomb as the source of n’s! different times!

To shield the detector from the blast, simultaneously drop it with the explosion

Ultimately went with a more responsible source of nuclear reactor

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Finding n’s

So folks thought n’s carried away the missing energy in beta decay

Just like any other physical reaction, ought to be able to “reverse” the reaction

npe-n

n

e- n

p W

n p

W ne+

pe+n

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First n detection: 1956

Discovery of n ~25 years after proposed by W. Pauli

Detection:e+ annihilates with e- in medium, detect g rays

neutron captures in medium, releases g’s

Basic rule of n detection: nothing comes in outgoing particles

consistent with n interaction

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n “flavors”

That the neutrinos from nuclear reactors produce electrons important!

Three “flavors” of neutrinos (+antineutrinos) that dictate what they can produce “electron-type” ne

“muon-type” nm

“tau-type” nt

Lepton flavor conservation that is, only a nt can produce a t, etc.

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How n’s interact with matter

Charged-partner conversion Scattering

nm m-

N

N’

nm

N

N

nm

ne t-

N

N’

No way!

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1960s: let’s look for more n’s!

The sun predicted to be a very hot source of ne’s (and only ne’s)

Ray Davis stuck a giant (600t) vat of cleaning fluid (C2Cl4) inside a mine

ne’s from the sun should interact with Cl, turn it to Ar

Count the Ar atoms!

2/3 are missing?

Prediction: 5.7 ± 0.9 Ar/day

Data: 1.9 ± 0.2 Ar/day

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1990s: data confirmed

Using modern n detection techniques (more later), the ne deficit confirmed

What’s happening?! Three options:Are independent experiments wrong?

Do we not understand the physics of the sun?Is something happening to the n’s?

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A new way of testing n’s

2001: An experiment with unique sensitivity to ne but also all n flavors (ne, nm, nt) releases data

sensitive to ne’s exclusively(tests previous expts) look at all n flavors

(tests total n flux)

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A new way of testing n’s

2001: An experiment with unique sensitivity to ne but also all n flavors (ne, nm, nt) releases data

sensitive to ne’s exclusively(tests previous expts) look at all n flavors

(tests total n flux)

only way of “looking” at nm, nt from the sun!

n energy too low (~10 MeV) to create m, t

particles

Me = 0.5 MeVMm = 105 MeVMt = 1800 MeV

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Solution!

Data confirms both theory and previous experiments!

We know the n’s have flavor ne when created in the sun, yet 2/3 have flavor either nm or nt on earth!

This was the first definitive evidence that n’s oscillate! that is, they can be “born” one flavor, and detected as

another

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n oscillation

What does this mean?! (quantum mechanics ahead!)

The n propagation state (i.e. Hamiltonian or mass eigenstate) is NOT the n flavor state (i.e. interaction eigenstate)

Rather, the propagation states (n1, n2, n3) are quantum mechanical admixtures of the three flavor (ne, nm, nt) states

n’s are constantly in an entangled state of ne, nm, nt! Immediate implications: n’s have mass! Previously thought to have m = 0 lepton flavor not always conserved!

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n oscillation

Just like the famous example of Schrödinger's cat: if the cat has an equal probability of being alive or dead

Then, quantum mechanically, it exists in superposition of both states. In some sense, simultaneously alive and dead!

Any n is simultaneously ne, nm, and nt!

P = ½ ( ) + ½( )

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Going a little deeper

For simplicity, let’s pretend only 2 flavor and propagation states

Simplifying assumptions: n’s travel near speed of light n mass is small compared to it’s energy

Then, after travelling distance L, a ne of energy E has

€

ν eν μ

⎛

⎝ ⎜

⎞

⎠ ⎟=

cosθ sinθ

−sinθ cosθ

⎛

⎝ ⎜

⎞

⎠ ⎟ν 1

ν 2

⎛

⎝ ⎜

⎞

⎠ ⎟

Turns out to be a good assumption!

q = arbitrarymixing angle

Probability to be detected nm:

Probability to be detected ne:

Dm2 = (mn1 - mn2)2

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Going a little deeper

ne “disappearance”:

nm “appearance”:

simple harmonic oscillator!

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Going a little deeper

ne “disappearance”:

nm “appearance”:

simple harmonic oscillator!

Nature: q oscillation amplitude; Dm2 oscillation frequency

Experiment: E n energy, L distance n travels

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Going a little deeper

Prob. detected ne

Prob. detected nm

~Dm2, osc. frequency

n created as ne

~q,osc. amplitude

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Going a little deeper

Prob. detected ne

Prob. detected nm

~Dm2, osc. frequency

n created as ne

~q,osc. amplitude

Experimental game: nature has chosen oscillation parameters q, Dm2,

we choose n E, propagation distance L, look for

appearance or disappearance!

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Where do neutrinos come from?

Roughly 100 trillion neutrinos from the sun pass through your body every second! on average, only 2 will interact

in your lifetime

Nuclear Fusion

Around 99% of thermal energy released in core-collapse supernovae carried away by n!

Incredible when you consider how “bright” they are from the ~ 1% of energy that goes to photons

High-energy cosmic particles (from supernova?) collide with atmospheric atoms to produce particle showers, including those that decay to n

Neutrinos created in neutron decay as a by-product of nuclear fission

n beam created by smashing protons into nuclear material safe to stand in!

Everything we know about n’s made possible by these sources

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Other n sources

Bananas a single banana emits about

1 million n’s per day from naturally-occurring radioactive potassium

The big bang! Still around! Big bang so strong and n’s so

weakly interacting that ~50 big bang n’s pass through your thumb per second!

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Available n energies

Luckily, even the natural n sources span a wide energy range!

Gives us the E in the quantity L/E we use to probe n oscillations. Next up, L but first…

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All about collecting the tiniest signals of light (photons)

“Photomultiplier” tube exploits Einstein’s photoelectric effect

e.g., Super Kamiokande, a gigantic detector houses ~11,000 tubes in 50,000 tons of ultra pure H20!

Modern n detection

light can behave like a particle and a wave!

ejected electrons(signal)

incomingphotons

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How do n’s lead to photons?

Light travels slower in detector medium (water, oil, lead, ice) than in vacuum vacuum: light travels at c; medium: light travels at c/n,

n the index of refraction Particles can have v > c/n! Just like a sonic boom

from a jet: when traveling faster than speed of sound, a sonic shock wave follows. n detectors see “light booms”! “Cherenkov light”

creates ring of light

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Modern n detection

n flavor determined by charged partner production

difference in ring due to mass: mm ~200 * me

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n detectors around the world

ANTARES - at the bottom

of the Mediterranean sea!

350m

SNO - buried in a Canadian mine

MiniBooNEobserves accelerator

n’s

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n detectors around the world

The biggest detector in the world: “IceCube” at south pole

Use 1 cubic km of ice as a neutrino detector!

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Last experimental issue:n travel distance L

Natural n sources:

Artificial sources: n travel distance

limited by diameter of Earth!

solar

atmospheric ~40 km or 13,000

km

MINOS experiment:shoots n’s from IL to MN

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n oscillation parameters found!

Fortunately, both natural n sources (solar, atmospheric) provide n oscillations we’re sensitive to on Earth!

Both oscillation modes confirmed by man-made n sources with different n E, travel distance L, but same ratio L/E

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n oscillation parameters found!

Fortunately, both natural n sources (solar, atmospheric) provide n oscillations we’re sensitive to on Earth!

Both oscillation modes confirmed by man-made n sources with different n E, travel distance L, but same ratio L/E

KamLAND nuclear reactor expt confirms solar osc. parameters

MINOS accelerator exptconfirms atmospheric n oscillations

(confirmed by other experiments too!)

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n oscillation parameters found!

Confirmation with Super-K, K2K and MINOS data

Confirmation with SNO, Kamland data

oscillation parameters:

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So what do we know?

Only remaining pieces: q13, d

q13: “how much flavor state ne is in the mass state n3?”

d: do neutrinos and anti-neutrinos oscillate differently?

From only these two sets of oscillation parameters, we know almost the entire mixing matrix U

c = coss = sin

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Exciting times for n’s!

d only meaningful if q13 is non-zero sin(0) = 0

March 7: Daya Bay (China) reactor experiment announces discovery of q13!

April 3 (two days ago!!): RENO (Korea) reactor experiment announces independent confirmation! “During preparation of this paper, Daya Bay

reported observation of a non-zero value for q13”

s13 = sin q13

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d: are n’s responsible for our universe?

Our universe clearly dominated by matter, yet we’ve no idea why

In the lab, if we create/destroy matter we always create/destroy antimatter in equal quantities - should be true for big bang too

Where did all the antimatter go??

n’s could be responsible. Because n’s so prolific in early universe, even a small difference between neutrino, anti-neutrino oscillations could’ve tipped the balance in favor of matter domination

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Other outstanding issues

What is the absolute n mass? we only know square of mass

state differences KATRIN experiment hopes

to measure it

Are there more than three n mass states? many hints, nothing conclusive yet

What’s the ordering of the mass states?

Are neutrinos their own antiparticle?

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Summary

n physics is a young field, but incredible progress is being made n oscillations one of the very few concrete results

not predicted by the hallowed standard model

Along the way, we are constructing the biggest particle detectors in history

In the near future (decades?) we may know everything about n’s, including whether or not they’re responsible for the formation of our universe

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Thanks for listening!

jgrange@alum.ups.edu

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backup

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Going a little deeper

Explicitly,

Say the sun created a ne:

Multiply by QM time propagator:

Simplifying assumptions: n’s travel near speed of light n mass is small compared to it’s energy

only two propagation states contribute to oscillations

70cm

30cm

it only takes ~1/10 A to stop a heart… we run 174 kA through the horn,around 106 times more!

Beryllium “slugs” - our target!

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protons

5 × 1012 protons, 5 times a second!For current flowing along a long, straight wire,

(Ampere’s Law)

I

B

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protons

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protons

However, focusing is NOT perfect.

Not all get defocused, mostly due to low angle production and higher energies

opposite charged particles will not get swept away if they don’t “notice” the magnetic field

This leads to beam, hence data, contamination Contamination varies based on energy of

incoming protons,

current, horn/target geometry, and horn polarity48