Big%20World%20of%20Small%20Neutrinos

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Big World of Small Neutrinos

• Hitoshi Murayama
• QuarkNet
• July 1, 2002

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Neutrinos are Everywhere
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Wimpy and AbundantNeutrinos 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
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Puzzle with Beta Spectrum

• Three-types of radioactivity a, b, g
• Both a, g discrete spectrum because
• Ea, g Ei Ef
• But b 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 b-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, cant go at speed of light.

• Now neutrino right-handed??
• ? contradiction ? cant 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 nL must exist nR

_
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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.
• Isnt 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.
• Cant go at speed of light (massive), and
  right-handed and left-handed particles mix ? no
  contradiction

But neutrinos cant bump because there isnt a
right-handed one ? stays massless
0.511 MeV/c2
105 MeV/c2
176,000 MeV/c2
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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
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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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SuperKamiokaNDENucleon Decay Experiment

• p?ep0, Kn, etc
• So far not seen
• Atmospheric neutrino main background

• Cosmic rays isotropic
• Atmospheric neutrino up-down symmetric

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A half of nm lost!
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Neutrinos clock

• Time-dilation the clock goes slower
• At speed of light vc, 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
  (ne,nm,nt) 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., p?mnm), neutrino is a
  particular type
• After time evolution
• No longer 100 nm, partly nt!

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Survival Probability

• Probability for nm to be still nm after t

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Survival Probability
p1 GeV/c, sin2 2q1 Dm23?103(eV/c2)2
Half of the up-going ones get lost
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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
250km

• 81?8 events if no oscillation
• 56 events observed
• MINOS (IL ? MN) 2005

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Public Interest in Neutrinos
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Solar Neutrinos
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How the Sun burns

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

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We dont 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 Currentne
• Neutral Current nenmnt
• 5.3s difference
• ? nm,t are coming from the Sun!

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Wrong Neutrinos

• Only ne produced in the Sun
• Wrong Neutrinos nm,t are coming from the Sun!
• Somehow some of ne were converted to nm,t on
  their way from the Suns core to the detector
• ? neutrino oscillation!

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Dark Side of Neutrino Oscillation

• Traditional parameterization of neutrino
  oscillation in terms of (Dm2, sin22q) covers only
  a half of the parameter space
• (de Gouvêa, Friedland, HM)
• Convention n2 heavier than n1
• Vary q from 0 to 90
• sin22q covers 0 to 45
• Light side (0 to 45) and Dark Side (45 to 90 )
• To cover 0?? q ? 90?? use tan2 q

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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 Dm2
• To probe LMA, need L100km, 1kt
• Need low En, high Fn
• 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 Dm2gt2?105eV2
• (Pierce, HM)

• Can measure mass mixing parameters

Data/theory
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Implications of Neutrino Mass
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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 havent 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)
• mn 1/R if one extra dim ? R10mm
• 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

, but nR SM neutral
To obtain m3(Dm2atm)1/2, mDmt, M31015GeV (GUT!)
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Grand Unification
M3

• electromagnetic, weak, and strong forces have
  very different strengths
• But their strengths become the same at 1016 GeV
  if supersymmetry
• To obtain
• m3(Dm2atm)1/2, mDmt
• ? M31015GeV!

Neutrino mass may be probing unification Einstein
s dream
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Why do we exist?Matter Anti-matter Asymmetry
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Matter and Anti-MatterEarly Universe
10,000,000,001
10,000,000,000
Matter
Anti-matter
They basically have all annihilated away except a
tiny difference between them
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Matter and Anti-MatterCurrent Universe
us
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Matter
Anti-matter
They basically have all annihilated away except a
tiny difference between them The Great
Annihilation
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Sakharovs Conditionsfor 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
• ? G(DMgt0) gt G(DMlt0)

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Majorana NeutrinoTo 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 nR 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