# Presentation: 442974

## Neutrinos get under your skin!

- 30 April 2003

## Special thanks to

- Susan Kayser

- Gary Steigman

- Milly Strelzoff

- Alex Westmoreland

## We, and all everyday objects, are made of 3 kinds of tiny particles:

- These are bundled together to make Atoms:

- These atoms make up—

- Electrons

- Neutrons

- Protons

- Proton

- Neutron

- Electron

## Living Creatures—

## Buildings—

## Our home planet—

## Is The Whole Universe made of—

- Electrons

- Neutrons ?

- Protons

- NO!

- Electrons

- Neutrons

- Protons

- are rareties!

- For every one of them, the universe contains a billion neutrinos !
- To understand the universe, we must understand the neutrinos.

## {

- Inside:10,000,000neutrinos

- 1 ft

- 1 ft

- 1 ft

## {

- Inside:30,000,000neutrinos

## Passing through each person on earth every second:One hundred trillion neutrinos from the sun.

- The sun shines because of nuclear fusion in its core.
- This fusion produces—
-  Energy, including visible light
-  Neutrinos
-  The atoms more complicated than hydrogen
- We are made of stardust!

## 100,000,000,000,000s zip through each second.

- 100,000,000,000,000s zip through each second.

- Neutrinos–lots of them–get under your skin!

## Should we worry about all those neutrinos zipping through us?

- No. Neutrinos interact with other matter VERY FEEBLY.

- To a neutrino, we look like almost completely EMPTY SPACE.

## Our view

-  View

- Almost all neutrinos zipping through us do nothing at all.

- Typically, a solar neutrino would have to zip through 10,000,000,000,000,000,000 people before doing anything.

- The probability that a particular solar neutrino will interact as it zips through one of us is 1 / 10,000,000,000,000,000,000 .

## This same feebleness of interaction makes neutrinos hard to detect and study.

- They are ghostlike.

- Abundant but Elusive.

## Are Neutrinos Important to Our Lives?

- If there were no  s, the sun and stars would not shine.

-  No energy from the sun to keep us warm.
-  No atoms more complicated than hydrogen.
-    No carbon. No oxygen. No water.   No earth. No moon. No us.

- No  s is very BAD news.

## We depend on small amounts of heavy chemical elements like zinc and selenium.

- These heavy elements are produced only in Supernova Explosions.
- If there were no  s, there would be no supernova explosions. BAD news.

## Q:	How little are neutrinos?

- Q:	How little are neutrinos?
- A: Roughly 1/10,000,000,000,000,000 inch across. This is 1/1,000 the size of an atomic nucleus.

- Q:	How much do neutrinos weigh?
- A: Almost nothing. Years of experiments yielded no evidence that neutrinos have any mass at all.

## Q:	Could neutrinos be completely massless?Can a particle have no mass at all?

- A: A particle *can* be a bundle of pure energy, and have no mass at all.
- 	The photon—the particle of light—is like that.
- 	But we have recently discovered that neutrinos are *not* like that.
- 	Neutrinos weigh much less than electrons, protons, or neutrons, but they *do* have tiny nonzero masses.

## Q:	Are all neutrinos the same, or are there different kinds of neutrinos?

- A: Neutrinos come in three different flavors:
- 	The electron neutrino	e
- 	The muon neutrino	
- 	The tau neutrino	

- Q:	How do we know neutrinos have masses?
- A: We’ll explain that shortly.

- Vanilla
- Chocolate
- Strawberry

- The e and  were discovered many years ago.
- The  was discovered only recently.

## Q:	How do e, , and  differ from one another?

- A: All the particles of a given kind are identical.All electrons are absolutely identical.Electrons do not have birthmarks.
- 	But there are 3 kinds, or flavors, of electron-like particles:

- e, , and  are electrically charged, and are known as the charged leptons.

- Associated_Neutrino_
- e
- 
- 

## Neutrinos are created in a variety of physical processes.

- In nature or the laboratory, a neutrino is created together with a charged lepton.
- The neutrino and charged lepton always have the same flavor.

- 

- 

- or

- or

- Not

## When a neutrino collides with an atom in a neutrino detector, it creates a charged lepton.

- The charged lepton always has the same flavor as the neutrino.

- 

- 

- e

- e

- 

- 

- 

- or

- or

- Not

- Detector

- e

## 

- e

- e

- 

- Detector

- 

- 

- e

- e

- Source

- Flavors don’t mix.

- _Creation and Detection of a Neutrino_

## Neutrino Flavor Change and Neutrino Mass

- Neutrino masses, if nonzero, are still tiny compared to the masses of other particles.
- How can we detect such tiny masses?
- Suppose neutrinos do have nonzero masses...

## 

- 

- Detector

- 

- 

- Source

- Long Journey

- Then, if you give a neutrino enough time, it can change from one flavor to another!

- The neutrino oscillates between two flavors:

- Born 

- Maybe Maybe 

- Pure 

- Maybe Maybe 

- Pure 

- Time, or Distance Traveled

## Neutrino Oscillation

## The world of the tiny particles is governed byQUANTUM MECHANICS.

- An object can be maybe here and maybe there. It can be maybe this and maybe that.It can be maybe a  and maybe a .

- Quantum mechanics involves *uncertainty* at its core.
- (Copenhagen )

## A proton is a proton is a proton.It does not morph into something else.

- How does a  morph into a  ?
- Answer: A  is not a particle to begin with.
- There *are* neutrino particles:

## e, , and  are different MIXTURES of 1, 2, and 3.

- In each of—

- e, , and  are different soups, all made from the same ingredients: 1, 2, and 3.

- 

- 

- 

- 

- the emitted neutrino is actually a 1, 2, or 3.

- e is:

- maybe 1 maybe 2 maybe 3

## 

- 

- 

- 

- Long Journey

- _Voyage of a Neutrino_

- Original 1, 2, 3Soup

- New, different 1, 2, 3Soup

- 1, 2, 3 parts of soup travel at different speeds because they have different masses.

- The  mixture of 1, 2, 3 has turned into the  mixture. But only because 1, 2, 3 have different masses.
- Neutrino flavor change implies neutrino mass!

## Neutrino flavor change

-  (“neutrino flavor oscillation”)
-  can make even *tiny *neutrino masses visible if we let the neutrinos travel far enough.

## The Evidence for Neutrino Flavor Change

- In the core of the sun

- Nuclear
- Reactions

- Solar neutrinos are all born as e , not  or  .

- e

- e

## Protons and heavier particles are raining down on earth’s atmosphere from outer space.

- These incoming particles are called cosmic rays.
- In a neutrino detector, cosmic ray “events” can imitate neutrino events.
- To eliminate the cosmic ray events, we put the detector deep underground, where the cosmic rays will not reach it.

- To detect the solar neutrinos arriving at the earth,
-  we go deep underground.

## Photo courtesy of SNO

- In the Creighton nickel mine, 6800 feet below Sudbury, Canada,
- is the Sudbury Neutrino Observatory (SNO).

##     The SNO detector. 

-     The SNO detector.
- The central sphere is 40 feet across, and is filled
-      with heavy water.

- Photo courtesy of SNO

## SNO detects solar neutrinos in several different ways.

- One way counts

- Number (e) .

- Another counts

- Number (e) + Number () + Number () .

- SNO finds

- Number (e)

- Number (e) + Number () + Number ()

** ****=  **1/3 .

## All the solar neutrinos are born as e .

- But 2/3 of them morph into  or 

- Neutrinos do change flavor.

- Therefore, neutrinos do have non-zero masses.

- before they reach earth.

## Sun

- takes place within the sun.

- Neutrinos interact with solar material

- like light with clear glass.

- This doesn’t stop the light or the neutrinos.

- But it increases the number of neutrinos that change flavor

- Core

- Earth

- e

- 

- 

- or

## The Neutrino Disappearing Act

- When vanilla neutrinos change flavor, an experiment that can detect
- only vanilla neutrinos
- will think they have disappeared.

- The original solar neutrino experiment,
-  performed by **Ray Davis** and coworkers,
- could detect only e .

- This experiment saw only 1/3 the expected number of neutrinos.

## Two-thirds had changed into invisible

- (to **Ray Davis**)  or  .

- In 2002: Nobel Prize to **Ray Davis**

- Nuclear power reactors produce e .

- Detectors of reactor e cannot see  or  .

- The observed solar neutrino flavor changing

- implies that many reactor e disappear into  or  by

- the time they have traveled 100 miles.

## In the Kamioka zinc mine in Japan,  110 miles

- from some big reactors, is the  Kamland e detector.

- Kamland finds that 40% of the e emitted

- by the reactors have disappeared.

- Cosmic rays colliding with atoms in the

- atmosphere make  .

- Half  these atmospheric  disappear while transiting the earth

## Earth

- Detector placed by
-  **Masatoshi Koshiba** et al.
- in the Kamioka zinc mine.

- Number ( Up)

- 

- 

- 

- Number ( Down)

-  =  1/2

## 2002: Nobel Prize to Masatoshi Koshiba

**All the neutrino disappearing acts are**
**beautifully described, in detail,**
**as changes of ****f****l****a****v****o****r****.**

## Open Questions

- Q:

- Do neutrinos come in more than 3 flavors?

- An experiment at Los Alamos, using man-made
-  neutrinos, suggests the answer is yes.

- But this is a big surprise, since we only
-  know of 3 electron-like particles:

-     e,  ,  and   .

- An experiment is currently in progress at Fermilab
-  to confirm or refute the Los Alamos one.

## Q:

- How much do the neutrino particles
-   1, 2, and 3 weigh?

- Neutrino oscillation data tell us that

- Mass of  3 (the heaviest one) is **bigger than**

-  {Mass of electron}/10,000,000.

- The lumpiness of the  universe (clusters of galaxies,
-  voids) appears to tell us that

- Mass of  3 (the heaviest one) is **smaller than**

- 5 x {Mass of electron}/10,000,000.

## Neutrinos are abundant in the universe

- and they do help to shape it.

- Why are the neutrinos so much lighter than

- the other particles?

- Knowing the answer might shed light on the

- origin of all particle masses.

- At this point there is only speculation.........

- Q:

## Q:

- Are neutrinos the reason the universe contains

- matter but almost no antimatter?

- For every particle , there is a corresponding antiparticle.

- _Matter_

- _Antimatter_

- Electron

- Proton

- Neutron

- Neutrino 

- Positron

- Antiproton

- Antineutron

- Antineutrino 

## Matter

- Antimatter

- Good thing for us there is no antimatter around!!

- The development of a universe containing matter

- but no antimatter requires that

- matter and antimatter behave differently.

##  MATTER - antimatter lopsided universe.

- that is way too small to explain the universe.

- If neutrinos behave differently from antineutrinos,

- the physics of these particles might lead to an

- explanation of our

-  MATTER - antimatter lopsided universe.

- Future experiments will look for that difference

- between   and   behavior.

## R Summary S

- Neutrinos are abundant, but elusive.
- They have tiny, but nonzero, masses.
- They can do amazing things, like change from chocolate- to strawberry-flavored.
- Without them, we wouldn’t be here.
- They are under our skin—always.

- rrrrRSssss

## Distance Traveled

- Pure 

- Pure 

- 0

- 0

- 1

- 1

- Pure 

- Pure 

- Probability It Is 

- Probability It Is 

- Prob. of 

- Prob. of 

## Atmospheric Neutrinos

- SK studies Atmospheric Neutrinos— e and  created in the earth’s atmosphere by cosmic rays colliding with atoms in the air. The cosmic rays do not make .

- _Atmospheric Neutrinos_

## Slide 53

## In SK—

- Atmospheric neutrino makes a charged particle.
- The charged particle, moving through the water, emits light.
- Electric eyes covering the inside walls of SK detect the light.
- From the light pattern, SK can tell an e from a .

- e makes e ”     

## Slide 55

## Slide 56

## SK finds—

- Only *half* as many atmospheric  coming up from far side of earth as are coming down from nearby.
- Half the  made far away disappear during their long journey.
- Are they oscillating into neutrinos of another flavor???
- The hypothesis that  oscillate into  fits a wealth of data from SK and other detectors beautifully.
- This includes a weak signal in SK for , even though cosmic rays don’t make .

## Solar Neutrinos

- The nuclear processes that power the sun produce gazillions of neutrinos. These processes make only e, not  or .
- Underground solar neutrino detectors find that half or more of the e expected to arrive every day from the sun are missing.
- Are they oscillating into neutrinos of another flavor???

## The SNO measurement counts only e.  and  are not seen.

- Meanwhile, SK counts neutrinos from the sun using electrons in ordinary water:

-  from sun

- This counts e,  and .

## Just seeing the electron get struck by a neutrino doesn’t tell us whether the neutrino was a e,  or .

- But comparing the SNO count (e only) to the SK count (e, and  and ), we can count the number of  and .
- The result—
- e, made by the sun, oscillate into  and/or .

## Man-Made Neutrinos

- Beams of neutrinos can be made using particle accelerators like those at Fermilab.
- Oscillation of neutrinos made by an accelerator at Los Alamos has been reported.
- If this oscillation is genuine, nature contains a new kind of neutrino that interacts with matter even more feebly than the other neutrinos.
- To confirm or disprove the Los Alamos oscillation, the MiniBooNE experiment will soon be done at Fermilab.

## To Confirm the Atmospheric Neutrino Oscillation

- Send a man-made beam of neutrinos a long distance, to give the  s time to oscillate.
- See if man-made  dis-appear in the same way that atmospheric  do.
- Try to confirm that the probability that a  is still a  actually *oscillates* down and up, and down and up, and...