# Presentation: 247780

## um... neutrinos?

- an introduction

**Paul Nienaber**
**Fermilab**

## begin with the end in mind...

- what’s our current picture of “the particle zoo?”
- how do neutrinos fit into that picture?
- how do you generate/detect neutrinos?
- what do you mean, “neutrinos ‘oscillate’?”
- what’s the MiniBooNE neutrino experiment?

## what’s in the world?

**What do particle physicists do?**
- investigate the fundamental structure of matter, space, and time
**How do we do that?**
- one approach: analyze – that is, examine differences, make distinctions – at root, take things apart
-  **What have we found out?**
- fundamental simplicity: small number of basic constitutive components

## particles, particles, particles...

- identify/classify particles by mass (energy)
- identify/classify particles by charge
-        (+ / – / 0 )
- ordinary matter is made of atoms
- most everyday experience of electric charge comes from negatively charged electrons
- dense, positively charged core: nucleus
- nucleus composite, too!
-      contains protons (+) and neutrons (0)
-            -- which raises another question...

## if protons are [+], and squeezed into the tiny nucleus, why don’t they electrically repel? 
ADDITIONAL FORCE: only operates at very short distances: called the STRONG force
are the three constituents of atoms – protons, neutrons, and electrons – all “equivalently fundamental”?
NO: protons and neutrons are composite; electrons are not
protons and neutrons are built from constituents called QUARKS

- ADDITIONAL FORCE: only operates at very short distances: called the STRONG force
- are the three constituents of atoms – protons, neutrons, and electrons – all “equivalently fundamental”?
- NO: protons and neutrons are composite; electrons are not
- protons and neutrons are built from constituents called **QUARKS**

**particles, particles, particles...**

## before quarks:
after quarks:

quarks feel the STRONG force

electrons and their two heavier cousins do not

is this the whole zoo?
                      ... no ...

- after quarks:
- quarks feel the STRONG force
- electrons and their two heavier cousins do not
- is this the whole zoo?
-                       ... no ...

**particles, particles, particles...**

## certain radioactive decays revealed the existence of additional, elusive denizens of the particle zoo

**particles, particles, particles...**

- they have NO electric charge
- these new particles hardly interact with other particles at all (no strong, no charge)
- if they have a mass, it’s very, very tiny
- these are the neutrinos (“little neutrals”)
- each pairs with an electrically [ – ] partner

## headline nus...

- neutrinos abound in the universe – in every gallon of space, there are a million neutrinos
- they come from stars, from the sun, and are leftover relics from the Big Bang
- they pass through matter essentially without a trace – they are very difficult to detect
- still, neutrinos matter! they are a crucial part of our understanding the workings of matter
- Two of the 2002 Physics Nobel Prize winners were neutrino physicists
- Ray Davis: neutrinos from the Sun
- Masatoshi Koshiba: supernova neutrinos

## intermission

## vellcome to ze laborratory

- so... how do you do a neutrino experiment?
- three ingredients:
- BEAM
- TARGET
- DETECTOR
- since neutrinos interact so rarely, need LOTS of beam and LOTS AND LOTS of target/detector

## eye of neut, toe of frog?

- need a source or beam of neutrinos – recipe?
- neutrinos come from...
- reactions inside the atomic nucleus
- fusion (inside stars and the Sun)
- fission (nuclear power plants)
- decay of certain subatomic particles
- these “neutrino parent” particles are produced when fast-moving protons smack into matter
- in the upper atmosphere (atmospheric neutrinos)
- in a particle physics laboratory near you (accelerator neutrinos)

- ... requires making particles which decay into neutrinos ...

- Making neutrinos...

- ...which you accomplish by slamming protons into a chunk of matter, ...

- ...letting the “parents” decay ...

- (... and perhaps filtering out the leftovers).

## catch me if you can

- now you have a pitcher – need a catcher
- “catching” a particle only works if the particle is electrically charged
- “see” a neutrino ONLY if it hits something and knocks out or produces a charged particle
- one way a neutrino can interact: run into something and change into its own charged partner :
-                            “tagger” reaction

******e **** +**

**X**

**+ X ́**

****

**e****-**

********** **** ****+**

**X**

**+ X ́**

****

******-**

********** **** ****+**

**X**

**+ X ́**

****

******-**

## catch me if you can

**need LOTS of detector material**
**can’t sacrifice sensitivity**
**must consider COST**
**one popular method: Čerenkov detector**

**if a charged particle moves through a liquid at a speed faster than the speed of light in the liquid, the liquid will give off a  “shock wave” burst of light**
**called Čerenkov light**
**light pulses are very dim – need exquisitely sensitive light detectors and VERY clear liquid**

## catch me if you can

**catch me if you can**

- Čerenkov light comes out at a specific angle, and maps out a cone as it moves away from the track
- different kinds of particles make different tracks and therefore make different kinds of rings

**light sensor array**

- short track

- sharp-edged, open ring

- track direction

- short, scattering track (electron)

- “fuzzy” ring

## neutrinos “oscillate” ?!

- if I make a beam entirely of (e.g.) muon neutrinos, and place my detector immediately downstream, I detect 100% muon neutrinos

- BUT if I move the detector a distance away, a small fraction of the muon neutrinos can change into electron neutrinos...

- ...and then back again!

**neutrin**
**-o-**
**taker**

**(100-x)% **********
**[?!!]**

**    ****x% ********e**

## this astonishing behavior is actually not unusual in the weird and counter-intuitive world of quantum physics

particles behave like: ________

wave frequency depends on energy (mass)

neutrino oscillation demonstrates that, contrary to what we once thought, neutrinos have mass

- particles behave like: ________
- wave frequency depends on energy (mass)
- neutrino oscillation demonstrates that, contrary to what we once thought, neutrinos have mass

**neutrinos “oscillate” ?!**

**WAVES**

**E = mc****2**** !**

## MiniBooNE experiment

**Booster: start with protons**

**protons strike beryllium**** **

**Magnetic focuser: “horn****”**

**Decay region**

**Absorber: filter out all but neutrinos**

**450 m earth: ************→********e****?**

**MiniBooNE detector**

**↞  ****decay pipe  ****↠**

## MiniBooNE detector

- 12 m diameter tank
- 800 tons ultra-pure mineral oil
- 1500 8” light sensors (photo-multiplier tubes)

## MiniBooNE’s goal is to test a previous experiment performed at Los Alamos

if that result is confirmed, our picture of the “particle zoo” will have to change

MiniBooNE started running in August 2002, and will run for at least three years

we’ve collected more than 200,000 neutrino events so far

**if that result is confirmed, our picture of the “particle zoo” will have to change**
**MiniBooNE started running in August 2002, and will run for at least three years**
**we’ve collected more than 200,000 neutrino events so far**

**eye spy. . .**

**some new kind of nu?**

**a typical MiniBooNE event**

## we’ve made a lot of progress in understanding the fundamental structure of matter, and work at Fermilab has been a big part of that progress

neutrino physics, and particularly oscillations are one of the current exciting avenues of investigation

stay tuned!  the voyage of exploration continues...

**neutrino physics, and particularly oscillations are one of the current exciting avenues of investigation**
**stay tuned!  the voyage of exploration continues...**

**solving future puzzles...**

- . . . . . . thanks!