# Presentation: 281251

## Neutrinos at Fermilab and Beyond

- History of the Neutrino
- Neutrinos as probes of the Strong and Weak forces
- Neutrinos, mass, and flavor

**Notes:**
WHEN FINISHED WITH DRAFT, SCAN FOR JARGON AND OPPORTUNITY TO EXPLAIN IN EVERYDAY TERMS

## The historical path to neutrinos... Beta decay of atomic nuclei:

- The Invention of the Neutrino

*After*

*Electron** (e)*

*Before*

*Original Nucleus*

*Lighter *
*Nucleus*

-      Conservation of energy and momentum electron should have a fixed energy
-            (2 equations, 2 unknowns)

*Electron Energy*
*In the Decay*

*Number of Decays*
*at each Energy*

-  But, we actually see a wide range of energies...
*Since Energy and momentum*
*are conserved, there must be an unseen particle involved....*

## The Neutrino

*Before*

*After*

*Electron** (e)*

*Original Nucleus*

*Lighter *
*Nucleus*

*Neutrino** (****)*

- This must be a very different particle from the known ones:
-    Max electron energy is what we expect for 2 body* **(nearly) massless*
-    We don’t see it along with electron * **very weakly interacting*

*Pauli and Fermi*
*   **Early 1930’s*

- The neutrino:  “Little Neutral one” – massless, no electric charge,
-  new *Weak Force* Charge

## The Particle Zoo

- Also have anti-matter:
- Each particle type has a corresponding *anti-particle*

## Particles and Forces

- Particles of Matter (*Fermions* - *like electrons, muons, quarks, neutrinos*)
- interact by exchanging particles of Force (*Bosons* – *like photons,W,Z,g*)

- Strength of a force depends on
* **value of “coupling constant” – proportional to charge*
* **How easy it is to produce the *
*force carrier – “propagator”*

*muon*

*quark*

*photon*

*muon charge (e)*

- The more strongly a particle interacts with matter, the easier it is to stop and detect

*quark charge (1/3e or 2/3 e)*

## “4” Fundamental Forces

| Gravity (10-38):  
Felt by all 
particles, but 
very, very 
weak | Electromagnetic (0.007):
Felt by all particles 
with an electric 
Charge.  Carried 
by photons () |
| --- | --- |
| Strong Nuclear Force (1):
Felt only by “nuclear” particles (quarks, gluons)
Carried by the gluon (g) | Weak Nuclear Force (10-6):
Closely related to electromagnetism... really
one “electroweak force”
But very different in our lives |

**

***+***

***+***

***+***

***+***

******

******

******

**Notes:**
Add some scale of relative strength

## Neutrinos and the Weak Force

- Weak force carried by W and Z bosons
- W – “Charged current”     Z – “Neutral current”
- W and Z0 are very massive – ~ 80 and 91 GeV/c2 compare photon – massless
- “Weak charge” similar in size to electromagnetic charge

*neutrino (****)*

*neutrino*

*Z**0*

*W**+*

*neutrino (****)*

*electron*

## Neutrinos are Tough to Detect

- Neutrino interactions are extremely rare
- The weak force is... weak...
- Comparison:
- Electrons from beta decay can be stopped by aluminum foil
- X-rays (photons) are stopped by a thin piece of lead
- 5GeV Muons are stopped by meters of Iron
- Neutrinos from Sun can pass through
-    light-years of water...
- 	Good thing too! Trillions of neutrinos
-    pass through you every second!
- Why is the weak force so weak?

- Only about 1 in 1018 (a billion-billion) neutrinos passing through a proton will interact with it

**Notes:**
Mean free path???  See FNAL rad manuals for 

## Aside: Cross Sections

- Cross section  is an “effective area” presented by a particle in an interaction:
- Probability that a particle will interact passing through a thin piece of matter (atomic mass A, thickness d, density ) is *total effective area per unit area*
- Differential cross section can be defined for a specific outcome – e.g. d/d = effective area for scattering to an angle 

*d*

- Number of target particles in a unit area

## Neutrino Cross Sections 

-  (couplings)2 x (propagator)2 x  (details of participants)

*Similar for electromagnetic and weak force interactions*

*1/(Q**2**-M**B**2**)**2*

- At typical lab energies:
- M=0  1/Q4
- MW=80.1GeV  1/MW4

- Q is “momentum transfer” carried by boson

- For Q2GeV, EM/Wk ~ 2.5 million!

- 

- W

- Z0

**

**

**

**

**

**

## The Discovery of the Neutrino

- Direct detection of the neutrino had to wait more than 20 years after its “invention”!

*1**st** idea – nuclear bomb blast...*

*2**nd** idea – nuclear reactor *

*50 gal water with some Cd to detect neutrons*

*Trillions of neutrinos per*
*square inch per second*

*Inverse* beta decay

*(anti-)*
*neutrino*

*proton*

*Cd*

*Reines and Cowen - 1956*
*Savannah River Plant *

*neutron*

*photons*

*electron*

*positron*

- A few neutrinos per hour were detected!
- 6x10-44cm2

## Neutrino Flavor

- We’ve already seen

- 

- e

- W

*But we also have*

- 

- 

- W

- 

- 

- W

*and*

*(Muon)*

*(Tau)*

*Are there different flavors of neutrinos, for electrons, *
*                    **muons, and taus...?*

## The Muon Neutrino

*Lederman (Leon), Schwartz, and Steinberger at Brookhaven (1962):*

- Do neutrinos produced along with muons make
- electrons when they interact, or only muons?

- 

- 

*Steel*
*Shielding*

**

- 

- There are distinct *muon* and *electron* neutrinos
- (Won the Nobel Prize in 1988)

*10 tons of Aluminum*

*100 trillion neutrinos *
*51 interactions seen!*

**Notes:**
How many events? Verify year

## Tau Neutrino

*Is there a neutrino that only makes tau (****) leptons?*

- DONUT (E872) at Fermilab -1997....

- 4 tau neutrino
- interactions observed!

- Iron

- Iron

- Emulsion

- 1mm

- Kink is  signature

## What Can You do with a Neutrino?

-  (couplings)2 x (propagator)2 x  (details of participants)

- By studying neutrino interactions, you can learn about

- Electroweak force:
-  unification of electromagnetic and weak forces

- Structure of protons and neutrons  details of the Strong Nuclear Force (QCD)

- And – you can learn about the nature of mass, and possibly get insight into Grand Unification of EW and QCD!

- W and Z bosons

## Scattering

- Elastic and inelastic scattering

- Elastic scattering: particles interact without changing each other

- Conservation of energy and momentum  cross section can only be a function of one variable

- Inelastic scattering: particles change each other

- More degrees of freedom  cross section can be a function of two variables

## Neutrino Scattering as a Probe

- Deep inelastic scattering of neutrinos on nucleon (proton/neutron)

- At low momentum transfers, nucleon is a “blob”.  Quarks are “confined” by QCD.

- At higher transfers, quarks become resolvable and scattering appears to be *elastic* off “free” quarks

- Deep inelastic limit

- Cross section gives us quark (and anti-quark) structure of nucleon

- 

- 

## Neutrino Scattering as a Probe, II

- If you look closely, QCD comes into play

- E.g., gluon splits into quark, anti-quark pair

- g

- q

- q

- g

- W

- Higher momentum transfer Q2  shorter wavelength of Boson “probe”  higher resolution

- Quark structure depends on how hard you hit the proton

- 

- 

## Sample of Scattering Results

- Evolution of quark structure vs. Q2 agrees well with QCD theory

- Much newer results exists, but are still preliminary

- CCFR experiment – took data at Fermilab in 1980s and early 90’s.

## Electroweak Studies

- Unification of electromagnetic and weak forces leads to an interesting prediction for relative coupling of W’s and Z’s:

*Z**0*

*W**+*

- 

- 

- N

- N

- 

- 

## NuTeV 

- Neutrinos at the TeVatron – successor to CCFR

* *

## NuTeV Analysis

- NuTeV distinguishes charged current () from neutral current () by “event length”

## NuTeV Charged Current

- Muons traverse meters of steel – easy signature for charged current interaction

## NuTeV sin2W Result

- Measured:
- sin2W=0.22773
-              0.00135
-              0.00093

- Expected:
- sin2W=0.2227
-              0.00037

- “3 ” deviation:
- 1 in 400 chance of  being just a fluctuation

- sin2W Interpreted as MW measurement

## Interpretation

-  Z boson interacts 1% weaker
-  Bigger QCD effects than anticipated?
-  Unlikely, based on analysis of possible effects.
-  Could it be destructive interference with another boson of mass ~1.2 TeV?
-  Great example of lower energy experiments having possible impact on very high energy physics.

## Neutrinos and Mass

- We know neutrinos must be very light –
- Lighter than we can detect in beta decay
- This makes neutrinos very different from other particles.  *What can it tell us about how particles get mass?*  Higgs mechanism...

*Electron neutrino has at most 1/100000 the mass of the electron*

*Compare to quarks: top quark is “only” about 50 times more massive than its partner, the b-quark*

**Notes:**
What are direct mass limits on 3 neutrinos?

## What is the Mass of Each  Flavor?

- Neutrinos can have several masses at once!
- Quantum mechanics allows particles to be in several “states” simultaneously... *superposition principle*
- If states of definite mass aren’t states of definite flavor...
- Define 1, 2, 3 – neutrino mass states
-             e, ,  – neutrino flavor states
- Mixing of masses in each flavor:
-                            e=Ve11+Ve22+Ve33
-                            =V11+V22+V33
-                            =V11+V22+V33

**Notes:**
Why can’t electrons oscillate

## Neutrino Flavor Oscillations

- Different masses in each neutrino flavor allow flavors to change among each other
*How?*
- Quantum mechanics – particles have wavelike nature...
- Oscillation frequency depends on the energy (and therefore the mass) of the particle

- Original neutrino flavor: equal contributions from both masses

*Neutrino *

- New neutrino flavor: equal but opposite contributions from both masses

- Back to original flavor

## Oscillation Probability

*Mass difference: *the bigger the mass difference, the faster the flavor oscillation

- Probability of seeing a neutrino flavor change, at a given energy and distance, depends on:

*Mixing: *how different the original neutrino is from a single mass

*Wave peaks are different, but the overall effect on flavor is small*

**Notes:**
Oscillation probability

## Simple 2 Flavor Mixing

- Imagine only two neutrino flavors mix

- =cos()1sin()2
- =sin()1+cos()2

- 

- 

- 

- 

*Neutrino state is a vector in this plane*

- 

- Oscillation probability of neutrino with energy E
-           (GeV) travelling a distance L (km), m22-m12m2 in eV2
-          P(vab) = sin2(2)sin(1.27m2 L/E)

- Larger sin2(2  Larger mixing  Larger oscillation probability

- Larger m2  Faster oscillation
- (*no mass **** no ****m**2 **** no oscillation*)

## Evidence for Neutrino Oscillations

- Solar neutrinos – sun only produces electron neutrinos

*At solar energies, only electron is light enough for this process to actually happen*

*electron*

*electron neutrino*

- Detecting the neutrinos on earth:

- Only about 1⁄2 of expected (electron) neutrinos seen

- About the correct expected total number of neutrinos is seen

- The electron neutrinos are changing flavor between being created in the sun, and reaching earth  Evidence of neutrino mass...

- e.g., SNO experiment in Sudbury, Ontario

**Notes:**
What exactly did SNO do again?

## Atmospheric Neutrinos

- Look for neutrinos produced by cosmic rays in atmosphere –
- probe different mass-difference scales than solar neutrinos

*proton*

*pion (******)*

*muon (******)*

*electron*

****

***e*

****

*Underground *
*Detector*

- Expect about twice as many muon neutrinos as electron neutrinos

- Can make reasonably solid predictions
- for distribution of neutrino angles

*If no oscillations....*

## Super Kamiokande

- Kamioka mine in Japan  - 3300 feet underground!
- 12000 + very sensitive light detectors
- Look for particles going faster than speed of light ! (speed of light in water....)
-  Cerenkov light: Similar to “Sonic Boom”

- Muon and its decay electron

- Pattern of light hitting detectors gives type and energy

## Super-K Oscillation Evidence

- Neutrinos from above come from near by – no time to oscillate

- Neutrinos from below come from far away– lots of time to oscillate

- Earth

- Strong evidence of oscillations between muon and tau neutrinos: m2~0.003eV2, sin2(2)~1

## LSND

- Atmospheric and Solar neutrino oscillation evidence are both *disappearance*
- Too few of the expected neutrino types are seen
- One experiment claims *appearance* of unexpected neutrinos – Liquid Scintillator Neutrino Detector at Los Alamos
- See 1 in 300 very low energy muon neutrinos turn into electron neutrinos
- Very short distance – possibly “large” mass difference
- Very important to verify or refute.

## New Oscillation Experiments

- Use accelerator based neutrino beams
- Allows physicists to have control of neutrino source
- MiniBooNE – Fermilab
- Confirm or refute LSND experiment at Los Alamos
- K2K
- Send a neutrino beam to SK from 250 km (155 miles) away – major setback with photodetector implosion
- NUMI/MINOS
- Send muon neutrinos to a new detector in Northern Minnesota – 735 km (460 miles)

## NeUtrinos at the Main Injector/Main Injector Neutrino Oscillation Search
Good match to the Super-Kamiokande Atmospheric neutrino oscillation evidence
Create muon neutrinos at Fermilab, look for them	 in Minnesota

Study neutrino beam before oscillations have a chance to happen 
Compare neutral and charged currents in Near and Far detectors

- NeUtrinos at the Main Injector/Main Injector Neutrino Oscillation Search
- Good match to the Super-Kamiokande Atmospheric neutrino oscillation evidence
- Create muon neutrinos at Fermilab, look for them	 in Minnesota
- Study neutrino beam before oscillations have a chance to happen
- Compare neutral and charged currents in Near and Far detectors

- NUMI/MINOS

- 735km

- Fermilab

- Tower, MN

## The NUMI Neutrino Beam

*(Not to scale)*

- Hadron absorber (stops strongly interacting particles made of quarks)

- Near Detector- tens of neutrino interactions per burst

- 10’s of trillions of protons hit target every other second in very short burst
- Special “horn” magnet focuses pions and kaons towards detectors

- Main injector: 120 GeV protons

- Earth stops muons

- Pions and kaons decay, creating neutrinos

*340 ‘*

*3300 ‘*

## MINOS Detectors

- 1-inch thick
- Steel plates

- 1 cm thick Plastic Scintillator (gives off UV light when charged particles pass through)

- neutrino

- muon

- photomultipliers

- 4 cm wide scintillator strips

- Distinguish charged from neutral current by outgoing muon
- Detector Mass
- Near: 980 tons
- Far: 5400 tons

*(not to scale)*

- 8 meters

- Side view

- Front view

- Wavelength Shifting Fibers capture UV light, and emit green light.

- Duty factor: 10s live per 1.9s greatly reduces backgrounds from cosmic rays

## MINOS Far Detector

-  2300 feet underground in Soudan mine
-  5,400 tons
-  A little over 1⁄2 finished

## MINOS Program

- Near Detector construction starts in 2003
- Start taking data in 2004
- Verify muon neutrino oscillations (disapperance) in controlled environment
- Make precise
-      measurements of
-      neutrino mass
-      differences
- Set limit or measure
- e

## MINOS Sensitivity

- Sensitivity to oscillation parameters in 2 years of data taking

## MiniBooNE

- Booster Neutrino Experiment
- LSND signal: hints at large mass difference – fast oscillations
- Choose a relatively low energy to just produce just enough extra particles to identify interaction
- Use Booster beam (8GeV)
- 550 m distance (1800 feet)

- 250,000 gallons of mineral oil
- 1400 photodetectors
- Look for Cerenkov light and *scintillation* light

## MiniBooNe Sensitivity

- Should be taking data very soon – conclusive answer on LSND oscillations to follow
- Muon neutrino electron neutrino

## The Future in Neutrinos

- Mini-BooNE
- May become BooNE if a signal is observed
- NuMI
- Search for e (e appearance) –expected to be a small effect – with a new detector miles from the current one
- New near detector optimized for scattering studies
- Much higher rate  better precision on many topics
- Neutrino factory?
- Let muons decay in a “storage ring” – very clean beams
- Great technological challenge.

## Conclusions

- Neutrinos are a very, very odd kind of particle
- Very weakly interacting – originally detected indirectly
- Very, very light
- Neutrinos a great probe of the nature of matter
- No Electromagnetic interactions – great for studying weak forces
- Unique abilities to probe structure of proton and neutron
- What makes them so light?
- What can mixing and oscillations tell us about particle flavor? – W*hat is flavor*???
- Exciting time in neutrino physics
- Fermilab – recent results from DONUT, NuTev
- Upcoming MINOS/MiniBooNE
- More great experiments around the world

**Notes:**
Why can’t electrons oscillate