# Presentation: 170373

## Big World of Small Neutrinos

- Hitoshi Murayama
- QuarkNet
- July 1, 2002

## Neutrinos are Everywhere

- QuarkNet

## “Wimpy and Abundant”Neutrinos are Everywhere

- They come from the Big Bang:
- When the Universe was hot, neutrinos were created equally with any other particles
- They are still left over: ~300 neutrinos per cm3
- They come from the Sun:
- Trillions of neutrinos going through your body every second
- They are shy:
- If you want to stop them, you need to stack up lead shield up to three light-years

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## Outline

- Introduction
- Neutrinos in the Standard Model
- Evidence for Neutrino Mass
- Solar Neutrinos
- Implications of Neutrino Mass
- Why do we exist?
- Conclusions
- (LSND)

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## Neutrinos in the Standard Model

## Puzzle with Beta Spectrum

- Three-types of radioactivity: ******
- Both ****discrete spectrum because
*	**	**E******= E**i **– E**f*
- But ** spectrum continuous

- F. A. Scott, *Phys. Rev.* **48**, 391 (1935)

- Bohr: *At the present stage of atomic theory, however, we may say that we have no argument, either empirical or theoretical, for upholding the energy principle in the case of ****-ray disintegrations*

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## Desperate Idea of Pauli

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## Three Kinds of Neutrinos

- There are three

- And no more

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## Neutrinos are Left-handed

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## Neutrinos must be Massless

- All neutrinos left-handed  massless
- If they have mass, can’t go at speed of light.

- Now neutrino right-handed??
- 		 contradiction  can’t be massive

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## Anti-Neutrinos are Right-handed

- CPT theorem in quantum field theory
- C: interchange particles & anti-particles
- P: parity
- T: time-reversal
- State obtained by CPT from ***L* must exist: ***R*

- _

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## Other Particles?

- What about other particles?  Electron, muon, up-quark, down-quark, etc
- We say “weak interaction acts only on left-handed particles” yet they are massive.
- 		*Isn’t this also a contradiction?*
- 	No, because of the Higgs condensate.

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## Universe is filled with Higgs

- Empty looking space is filled with Higgs
- Particles bump on it, but not photon because Higgs neutral.
- Can’t go at speed of light (massive), and right-handed and left-handed particles mix  no contradiction

- But neutrinos can’t bump because there isn’t a right-handed one  stays massless

- 0.511 MeV/*c*2

- 105 MeV/*c*2

- 176,000 MeV/*c*2

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## Standard Model

- Therefore, neutrinos are strictly massless in the Standard Model of particle physics
- 	*Finite mass of neutrinos imply the Standard Model is incomplete!*
- Not just incomplete but probably a lot more profound

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## Lot of effort since ‘60s

- Finally convincing evidence for “neutrino oscillation”
*Neutrinos appear to have **tiny** but **finite** mass*

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## Evidence for Neutrino Mass

## Super-Kamiokande (SuperK)

- Kamioka Mine in central Japan
- ~1000m underground
- 50kt water
- Inner Detector
- 11,200 PMTs
- Outer Detector
- 2,000 PMTs

- Michael Smy

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## SuperKamiokaNDENucleon Decay Experiment

*p**e*+**0, *K*+**, etc
- So far not seen
- Atmospheric neutrino main background

- Cosmic rays isotropic
- Atmospheric neutrino up-down symmetric

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## A half of  lost!

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## Neutrino’s clock

- Time-dilation: the clock goes slower
- At speed of light *v*=*c*, clock stops
- But something seems to happen to neutrinos *on their own*

- Neutrinos’ clock is going
- Neutrinos must be slower than speed of light
- Neutrinos must have a mass

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## The Hamiltonian

- The Hamiltonian of a freely-propagating particle is simply
- Therefore, time evolution of a momentum eigenstate is just the phase factor

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## Mass Matrix

- But wait!  A set of particles can have a mass *matrix* if they have the same quantum numbers.
- In case of (*u,c,t*) quarks, (*d,s,b*) quarks, and (***e**,******,*****) neutrinos, their masses are 33 mass matrices.
- Correspondingly, the Hamiltonian is also a 33 matrix:

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## 22 Mass Matrix

- Discuss 22 mass matrix for simplicity
- Without a loss of generality, parameterize:
- Eigenstates:
- Eigenvalues:

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## Two-Neutrino Oscillation

- When produced *(e.g*., **+**+****), neutrino is a particular type
- After time evolution:
- No longer 100% ****, partly ****!

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## Survival Probability

- Probability for **** to be still **** after *t*

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## Survival Probability

- Half of the up-going ones get lost

*p*=1 GeV*/c,* sin2 2**=1 *m*2=310–3(eV/*c*2)2

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## Slide 27

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## More cross checks

- Multi-ring events can be used to provide useful cross checks (Hall, HM)

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## More to come

- 818 events if no oscillation
- 56 events observed
- MINOS (IL  MN) 2005

- 250km

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## Public Interest in Neutrinos

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## Slide 31

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## Solar Neutrinos

## How the Sun burns

- The Sun emits light because nuclear fusion produces a lot of energy

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## Slide 34

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## We don’t get enough

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## Neutrino oscillation?

- Can explain the data
- Two major solutions:
- LMA
- LOW/Quasi-Vacuum
- 		(Friedland)
- Biggest systematics is the solar neutrino flux calculations
*Problem with the solar model?*

- LMA

- LOW

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## Josh Klein, Lepton Photon 2001

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## SNO comes to the rescue

- Charged Current:***e*
- Neutral Current: ***e*+****+****
- 5.3 difference
-  ****** are coming from the Sun!

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## Wrong Neutrinos

- 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!

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## Dark Side of Neutrino Oscillation

- Traditional parameterization of  neutrino oscillation in terms of (*m*2, sin22**) covers only a *half* of the parameter space
- 	(de Gouvêa, Friedland, HM)
- Convention: **2 heavier than **1
- Vary ** from 0 ̊ to 90 ̊
- sin22** covers 0 ̊ to 45 ̊
- Light side (0 to 45 ̊) and Dark Side (45 ̊ to 90 ̊ )
- To cover 0 **  90 use tan2 **

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## March 2002

- April 2002 with SNO

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## What Next?

- Can we convincingly verify oscillation with man-made neutrinos?
- Hard for low *m*2
- To probe LMA, need L~100km, 1kt
- Need low *E***, high ****
- Use neutrinos from nuclear reactors

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## Location, Location, Location

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## KamLAND sensitivity on LMA

- First terrestrial expt relevant to solar neutrino problem
- KamLAND will exclude or verify LMA definitively
*Data taking since Nov 2001*

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## KamLAND first neutrino event

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## Measurements at KamLAND

- Can see the dip when *m*2>210–5eV2
- 		(Pierce, HM)

- Can measure mass & mixing parameters

- Data/theory

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## Implications of Neutrino Mass

## Mass Spectrum

- What do we do now?

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## Two ways to go

- (1) Dirac Neutrinos:
- There are new particles, right-handed neutrinos, after all
- Why haven’t we seen them?
- Right-handed neutrino must be *very very weakly coupled*
- Why?

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## Extra Dimensions

- All charged particles are on a 3-brane
- Right-handed neutrinos SM gauge singlet
- 	 Can propagate in the “bulk”
- Makes neutrino mass small
- 	(Arkani-Hamed, Dimopoulos, Dvali, March-Russell;
- 	Dienes, Dudas, Gherghetta; Grossman, Neubert)
*m*** ~ 1/*R* if one extra dim  *R*~10**m
- An infinite tower of sterile neutrinos
- Or anomaly mediated SUSY breaking
- 	(Arkani-Hamed, Kaplan, HM, Nomura)

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## Two ways to go

- (2) Majorana Neutrinos:
- There are no new light particles
- What if I pass a neutrino and look back?
- Must be right-handed *anti*-neutrinos
- No fundamental distinction between neutrinos and anti-neutrinos!

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## 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!)

- , but ***R* SM neutral

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## Grand Unification

*Grand Unification*

- electromagnetic, weak, and strong forces have very different strengths
- But their strengths become the same at 1016 GeV if supersymmetry
- To obtain
*	**m*3~(*m*2atm)1/2, *m**D*~*m**t*
- 		 *M*3~1015GeV!

- Neutrino mass may be probing unification:
*Einstein’s dream*

*M*3

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## Why do we exist?Matter Anti-matter Asymmetry

## Slide 55

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## Matter and Anti-MatterEarly Universe

- They basically have all annihilated away except a tiny difference between them

- 10,000,000,001

- 10,000,000,000

- Matter

- Anti-matter

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## Matter and Anti-MatterCurrent Universe

- They basically have all annihilated away except a tiny difference between them
- The Great Annihilation

- 1

- us

- Matter

- Anti-matter

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## Sakharov’s Conditionsfor Creating Matter Excess

*Necessary* requirements for creating excess matter to survive The Great Annihilation:
- Non-conservation of Matter
- 	(matter conversion to anti-matter etc)
- CP violation
- 	(subtle fundamental difference between matter and anti-matter)
- Non-equilibrium
- (*M*>0) > (*M*<0)

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## Majorana NeutrinoTo The Rescue

- Majorana neutrino: no fundamental distinction between matter and anti-matter
-  There are processes that can change the balance between matter and anti-matter
- Produce ***R *in the Early Universe
- Their decay can preferentially produce matter over anti-matter
*Leptogenesis*

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## Conclusions

- Neutrinos are *weird*
- Strong evidence for neutrino mass
- Small but finite neutrino mass:
- Need drastic ideas to understand it
- If Majorana, *neutrino mass may be responsible for our existence*
- A lot more to learn in the next few years

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