# Presentation: 578687

## The Neutrino Scene

- Boris Kayser
- Fermilab
- June 3, 2004

## (

- _Neutrinos_
- Solar
- Reactor(L ~ 180 km)
- Atmospheric
- Accelerator(L = 250 km)
- Stopped  Decay LSND L  30 m

- _Evidence of Flavor Change_
- Compelling
- Very Strong
- Compelling
- Interesting
- Unconfirmed

- )

## Solar Neutrinos

- Nuclear reactions in the core of the sun produce e. Only e.
- Sudbury Neutrino Observatory (SNO) measures, for the high-energy part of the solar neutrino flux:
- sol d  e p p   e
- sol d  n p   e + + 
- From the two reactions,

- Clearly, +  ≠  0 .   Neutrinos do change flavor.

- e
- e + + 

- ———————  =  0.306 ± 0.026 (stat) ±0.024 (syst)

## There is some spectrum of 3 or more neutrino mass eigenstates i:

- (Mass)2

- 1

- 2

- 3

- 4

- Mass ()  mi

- e,, and  are mixtures of these mass eigenstates.

## i

- l  (le e, l , l )

- Detector

- Ui

- U is the Leptonic Mixing Matrix.

## What Have We Learned?

- If LSND is confirmed, there are at least 4 neutrino species.
- If LSND is not confirmed, nature may contain only 3 neutrinos.
- Then, from the existing data, the neutrino spectrum looks like —

## }

- m2atm

- e [|Uei|2]

- [|Ui|2]

- [|Ui|2]

- 

- 

- 

- (Mass)2

- m2sol

## The Mixing Matrix

- The flavor content picture shows the |Ui|2, but not the signs or phases of the Ui.

- 12 ≈ sol ≈ 32°,  23 ≈ atm ≈ 35-55°,  13 < 15°
-  would lead to P() ≠ P().   CP
- But note the crucial role of s13  sin 13.

- cij  cos ijsij  sin ij

- Atmospheric

- Cross-Mixing

- Solar

- Majorana CP phases

- ~

## — The Future —What We Would Like to Find Out

- How many different kinds of neutrinos are there?
- What are the masses of the neutrinos?
- What implications do neutrinos and solar-physics/astrophysics/cosmology have for each other?
- Are neutrinos their own antiparticles?

## How extensive is the mixing of different types of neutrinos?

- Do neutrino interactions violate CP?
- Are there surprises, such as large electromagnetic interactions from extra dimensions?
- What can neutrinos tell us about physics at the grand unification scale?
- Are neutrinos responsible for the matter-antimatter asymmetry of the universe?

## are sponsoring a year-long study, aimed at laying the groundwork for a sensible future program to answer the open questions.

-  Particles and Fields
-  Nuclear Physics
-  Astrophysics
-  Physics of Beams

- To quote the Charge—
- “The Study will lay scientific groundwork for the choices that must be made during the next few years.”

## Working Groups — The Central Element

- Each working group is defined by an experimental approach.
- The groups and their leaders —
- Solar and Atmospheric Neutrino Experiments
- John Bahcall <jnb@ias.edu>, Josh Klein <jrk@physics.utexas.edu>
- 				Reactor Neutrino Experiments
- Gabriela Barenboim <gabriela@fnal.gov>, Ed Blucher <blucher@hep.uchicago.edu>
- Superbeam Experiments and Development
- Bill Marciano <marciano@bnl.gov>, Doug Michael <michael@hep.caltech.edu>

## Neutrino Factory and Beta Beam Experiments and Development
Stephen Geer <sgeer@fnal.gov>, Michael Zisman <mszisman@lbl.gov>

Neutrinoless Double Beta Decay and Direct Searches for Neutrino Mass
Steve Elliott <elliotts@lanl.gov>, Petr Vogel <pxv@caltech.edu>

What Cosmology/Astrophysics and Neutrino Physics can Teach Each Other
Steve Barwick <barwick@HEP.ps.uci.edu>, John Beacom <beacom@fnal.gov>

Theory Discussion Group
Rabi Mohapatra <rmohapat@physics.umd.edu>

- Stephen Geer <sgeer@fnal.gov>, Michael Zisman <mszisman@lbl.gov>
- Neutrinoless Double Beta Decay and Direct Searches for Neutrino Mass
- Steve Elliott <elliotts@lanl.gov>, Petr Vogel <pxv@caltech.edu>
- What Cosmology/Astrophysics and Neutrino Physics can Teach Each Other
- Steve Barwick <barwick@HEP.ps.uci.edu>, John Beacom <beacom@fnal.gov>
- Theory Discussion Group
- Rabi Mohapatra <rmohapat@physics.umd.edu>

## Final General Meeting —

- Snowmass, June 28-30
- See www.interactions.org/neutrinostudy
- All are welcome!

## Methods and Payoffs

- Emphasis on questions whose answers will come from accelerator and reactor experiments.
- Assume first that there are only 3 neutrino mass eigenstates.
- What is the neutrino mass spectral pattern?
- Today: 1.9  10-3 < m2atm < 3.0  10-3 eV2 	    (90% SuperK)
- Tomorrow:	?   < m2atm < 	     ?		    (MINOS)

## Is the spectral pattern           or          ?

- Generically, SO(10) grand unified models predict       .
-       is un-quark-like, and would probably involve a lepton symmetry with no quark analogue.
-  behavior in earth matter can distinguish between        and       .

**( ****—**** )**

## }

- m2atm

- e [|Uei|2]

- [|Ui|2]

- [|Ui|2]

- 

- 

- 

- (Mass)2

- m2sol

- 

- m2atm

- 

- 

- m2sol

- or

## m2atm m2eff ≈ m2atm  [1 - S              ]

- m2atm m2eff ≈ m2atm  [1 - S              ]

-  Larger E is better
- But want L/E to correspond to ~ peak of oscillation
-  Larger E should be matched by larger L

## Determining whether the spectrum is like        or like      	could be a unique contribution of NOA or its proton-driver-enhanced successor, or of a Brookhaven Long Base Line program. 

- At NOA, with a 2nd detector, the determination would be possible for sin2 213 almost down to 0.01.
- (The NOA collaboration)

## What is 13 ?

- sin2 13 = |Ue3|2 is the small e piece of 3. 3 is at one end of m2atm.
- We need an experiment with L/E sensitive to m2atm, and involving e.

- Possibilities

- Reactor e disappearance while traveling L ~ 1 km.
- Accelerator e or ewhile traveling L > Several hundred km.

## Accelerator LBL measurements depend on 13, atm, Sign (m2atm), and .

- They can probe all of these quantities.
- Reactor experiments depend only on 13. Thus, they can measure 13 cleanly.

## Sensitivity:

- 	Experiment			sin2 213
- Present CHOOZ bound		   0.2
- Double CHOOZ			   0.03
- Future US experiment		   0.01(Detectors at ~200 m   and ~ 1.5 km)
- Sensitivity needed as part of the overall program:			~ 0.01
- Other measurements: Neutrino magnetic moment, the 			    anomalous Weinberg angle

## Do neutrino interactions violate CP?

- Look for —
- 	P(e) ≠ P(e)		(Superbeam)or	P(e ) ≠ P(e )		(  Factory)
- Must separate CP violation from matter effects.
- 					Can establish CP if	     Facility			sin2 213 exceeds
- Superbeam from proton driver		10-2
- 	    factory				10-4

##  Matter   >>  antimatter

-  Matter   >>  antimatter
- 					in the universe.
- CP in  oscillation would be evidence that the Matter  >>  antimatter asymmetry arose from
- 	Leptonic — not Quark or Squark —
- CP in the early universe.

## Are there more than 3 neutrino mass eigenstates?

- MiniBooNE can confirm or refute LSND.
- If MiniBooNE running with  sees no signal, it will not have tested LSND unless it runs with .
- If MiniBooNE ( and/or ) sees a signal —
- How many additional neutrinos are there?
- What are the splittings m2?
- How should reactor and LBL experiments be interpreted?
- Are there new, Short-Base-Line CP effects?
- An additional detector would be called for.

## Conclusion

- Neutrino physics presents us with exciting opportunities.
- Fermilab could play a leading role in the neutrino program of the future.