# Presentation: 035234

## Status of Neutrino Science

- Hitoshi Murayama
- LBNLnu
- April 11, 2003

## Two Main Directions

- Neutrino Properties
- Neutrino Masses
- Neutrino Mixings
- Nature of Neutrinos
- Neutrino as a Probe
- Parton Distribution Function
- Precision Electroweak Physics
- Neutrino Astrophysics

- LBNLnu Hitoshi Murayama

## Outline

- Introduction
- Current Status of Neutrino Oscillation
- Main Scientific Questions
- Majorana vs Dirac
- The last mixing angle and CP violation
- Conclusion

- LBNLnu Hitoshi Murayama

## Current Status of Neutrino Oscillation

## Rare Effects from High-Energies

*Rare Effects from High-Energies*

- Effects of physics beyond the SM as effective operators
- Can be classified systematically (Weinberg)

- LBNLnu Hitoshi Murayama

## Unique Role of Neutrino Mass

- Lowest order effect of physics at short distances
- Tiny effect (*m***/*E***)2~(eV/GeV)2=10–18!
- Interferometry (*i.e.*, Michaelson-Morley)!
- Need coherent source
- Need interference (*i.e.*, large mixing angles)
- Need long baseline
*Nature was kind to provide all of them!*
- “neutrino interferometry” (a.k.a. neutrino oscillation) a unique tool to study physics at very high scales

- LBNLnu Hitoshi Murayama

## MNS matrix	

- Standard parameterization of Maki-Nakagawa-Sakata matrix for 3 generations

- atmospheric

- ???

- solar

- LBNLnu Hitoshi Murayama

## What we learned in 2001–2

- Atmospheric **** is lost (>10), converted most likely to ****(>99%CL) (SK, MACRO, SOUDAN-II)
- Solar ***e* is converted to either **** or ****(>5) (SNO)
- Reactor anti-***e* are lost (99.95%CL) (KamLAND)
- Only the LMA solution left for solar neutrinos
- Tiny neutrino mass: the first evidence for *incompleteness of Minimal Standard Model*

- LBNLnu Hitoshi Murayama

## SNO Result

- Only ***e* produced in the Sun
- Wrong Neutrinos****** are coming from the Sun!
- Somehow some of ***e* were converted to ****** on their way from the Sun’s core to the detector
- 	 neutrino oscillation!

- LBNLnu Hitoshi Murayama

## KamLAND result

- First terrestrial expt relevant to solar neutrino problem
- KamLAND will exclude or verify LMA definitively

*Dec 2002*
- Expected #events:	86.8±5.6
- Background #events: 	0.95±0.99
- Observed #events:	54

- No oscillation hypothesis
- Excluded at 99.95%

- LBNLnu Hitoshi Murayama

## Summary of Neutrino Oscillation

- Before SNO and KamLAND

- Dec 2002
- with SNO
- and KamLAND

- LBNLnu Hitoshi Murayama

## Three-generation

- Solar, reactor & atmospheric ** oscillations easily accommodated within three generations
- sin22**23 near maximal, *m*2atm ~ 310–3eV2
- sin22**12 large, *m*2solar ~ 5–2010–5eV2
- sin22**13=|*U**e*3|2< 0.05 from CHOOZ, Palo Verde
- Because of small sin22**13, solar (reactor) & atmospheric ** oscillations almost decouple

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?

- LBNLnu Hitoshi Murayama

## Extended Standard Model

- Massive Neutrinos  Minimal SM incomplete
- How exactly do we extend it?
- Abandon either
- Minimality: introduce new unobserved light degrees of freedom (right-handed neutrinos)
- Lepton number: abandon distinction between neutrinos and anti-neutrinos and hence matter and anti-matter
- Dirac or Majorana neutrino
- Without knowing which, we don’t know how to extend the Standard Model

- LBNLnu Hitoshi Murayama

## Theoretical Bias:Seesaw Mechanism

- Why is neutrino mass so small?
- Need right-handed neutrinos to generate neutrino mass

- To obtain *m*3~(*m*2atm)1/2, *m**D*~*m**t*, *M*3~1015GeV (GUT!) Majorana Neutrinos

- , but ***R* SM neutral

- LBNLnu Hitoshi Murayama

## Neutrinoless Double-beta Decay

- The only known practical approach to discriminate Majorana vs Dirac neutrinos
- 		0**: *nn ** ppe*–*e*– with no neutrinos
- Matrix element  <*m****e*>=*i**m****i**U**ei*2
- Current limit |<*m****e*>| ≤ about 1eV
*m*3~(*m*223)1/2≈0.05eV looks a promising goal
- However, *m*3*U**e*32<<*m*3 and we can ignore *m*3* *
- Fortunately, *U**e*12 and *U**e*22 cannot cancel exactly because the maximal angle excluded by SNO: *U**e*12–*U**e*22=cos2212>0.07 (1)

- LBNLnu Hitoshi Murayama

## Three Types of Mass Spectrum

- Degenerate
- All three around >0.1eV with small splittings
- Possible even after WMAP+2dF: *m*<0.23eV
- May be confirmed by KATRIN, cosmology
- |<*m****e*>|=|*i**m****i**U**ei*2|>*m* cos2212>0.07*m*
- Inverted
*m*3~0, *m*1~*m*2~(*m*223)1/2≈0.05eV
- May be confirmed by long-baseline experiment with matter effect
- |<*m****e*>|=|*i**m****i**U**ei*2|>(*m*223)1/2 cos2212>0.0035eV
- Normal
*m*1~*m*2~0, *m*3~(*m*223)1/2≈0.05eV
- |<*m****e*>|=|*i**m****i**U**ei*2| may be zero even if Majorana

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?

- LBNLnu Hitoshi Murayama

## Now that LMA is confirmed...

- Dream case for neutrino oscillation physics!
-  *m*2solar within reach of long-baseline expts
- Even CP violation may be probable
- neutrino superbeam
- muon-storage ring neutrino factory
- Possible only if:
-  *m*122, *s*12 large enough (LMA)
-  **13 large enough

- LBNLnu Hitoshi Murayama

## Shootout (Lindner)

- LBNLnu Hitoshi Murayama

## Slide 22

- LBNLnu Hitoshi Murayama

## Slide 23

- LBNLnu Hitoshi Murayama

## 13 decides the future

- The value of **13 crucial for the future of neutrino oscillation physics
- Determines the required facility/parameters/baseline/energy
- Two paths to determine **13
- Long-baseline accelerator neutrino oscillation
- Reactor neutrino experiment with two detectors

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?

- LBNLnu Hitoshi Murayama

## Verify Oscillation

- Even atmospheric neutrino data do not show “oscillation” yet
- 	 MINOS, J-PARC
- 	 *m*223, **23, mass hierarchy and **13
- KamLAND data is consistent with overall suppression
- 	 continued running
- 	 *m*212

- LBNLnu Hitoshi Murayama

## Low-Energy Solar Neutrinos

- Solar neutrino data suggest energy-dependent survival probability
- 	 tests MSW effect
- 	**12
- 	 Helps interpretation of CP violation, double beta decay data

- 7%

- 1%

- 20%

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?

- LBNLnu Hitoshi Murayama

## If LSND right,All hell breaks loose

- Sterile neutrinos are strongly constrained by the combination of all existing data and WMAP+2dF
- CPT violation is strongly constrained by SNO+KamLAND
- If LSND correct, all previous measurements need to be re-examined by a collection of short-, medium- and long-baseline experiments.  Possibly mini-muon-storage ring.

- LBNLnu Hitoshi Murayama

## Seven Questions

- Dirac or Majorana?
- Absolute mass scale?
- How small is **13?
- CP Violation?
- Mass hierarchy?
- Verify Oscillation?
- LSND? Sterile neutrino(s)? CPT violation?
- Specific recommendations to attack these questions in the context of LBNL

- LBNLnu Hitoshi Murayama