The Big World of Little Neutrinos

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The Big World of Little Neutrinos

• Hitoshi Murayama (Berkeley)
• June 6, 2007
• Aspen Center for Physics Colloquium

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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?
• Future
• Conclusions

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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 have a mass

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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 force acts only on left-handed
  particles yet they are massive.
• Isnt this also a contradiction?
• No, because we are swimming in a
• Bose-Einstein condensate in Universe

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Universe is filled with Higgs

• Empty space filled with a BEC cosmic
  superconductor
• Particles bump on it, but not photon because it
  is 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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Neutrinosfrom backstage to center stage

• Pauli bet a case of champagne that noone would
  discover neutrinos
• Finally discovered by Cowan and Reines using a
  nuclear reactor in 1958
• Massless Neutrinos in the Standard Model (60s)
• Evidence for neutrino mass from SuperK (1998) and
  SNO (2002)

• First evidence that the minimal Standard Model of
  particle physics is incomplete!
• 2002 Nobel to pioneers Davis and Koshiba

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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 massive
  neutrino is simply
• But in quantum mechanics, mass is a matrix in
  general. 2?2 case

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Two-Neutrino Oscillation

• When produced (e.g., p?mnm), neutrino is of a
  particular type

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Two-Neutrino Oscillation

• When produced (e.g., p?mnm), neutrino is of a
  particular type
• No longer 100 nm, partly nt!
• Survival probability for 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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Excellent Fit
Downwards ??s dont disappear
1/2 of upwards ??s do disappear
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Cross check with man-made ?s
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Good consistency!

• MINOS result 2006

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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

• Neutrino oscillation?
• Something wrong with our understanding of the Sun?

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SNO comes to the rescue

• Charged Currentne
• Neutral Current nenmnt
• 7.6s 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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Terrestrial Solar Neutrino

• 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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KamLANDReactor neutrinos do oscillate!
?Proper time ?
L0180 km
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Progress in 2002 on the Solar Neutrino Problem
March 2002
April 2002 with SNO
Dec 2002 with KamLAND
June 2004 with KamLAND
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Implications of Neutrino Mass
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Mass Spectrum
What do we do now?
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Rare Effects from High-Energies

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

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Unique Role of Neutrino Mass

• Lowest order effect of physics at short distances
• Tiny effect (mn/En)2(0.1eV/GeV)21020!
• 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

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Neutrinos have mass

• They have mass. Cant go at speed of light.

• What is this right-handed particle?
• New particle right-handed neutrino (Dirac)
• Old anti-particle right-handed anti-neutrino
  (Majorana)

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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 Dimension

• 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
• Barbieri, Strumia)
• Or SUSY breaking
• (Arkani-Hamed, Hall, HM, Smith, Weiner
• 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!

EM
weak
strong
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
1,000,000,001
1,000,000,000
Matter
Anti-matter
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Matter and Anti-MatterCurrent Universe
us
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Matter
Anti-matter
The Great Annihilation
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Baryogenesis

• What created this tiny excess matter?
• Necessary conditions for baryogenesis (Sakharov)
• Baryon number non-conservation
• CP violation
• (subtle difference between matter and
  anti-matter)
• Non-equilibrium
• ? G(DBgt0) gt G(DBlt0)
• It looks like neutrinos have no role in this

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Electroweak Anomaly

• Actually, SM converts L (n) to B (quarks).
• In Early Universe (T gt 200GeV), W is massless and
  fluctuate in W plasma
• Energy levels for left-handed quarks/leptons
  fluctuate correspon-dingly

• DLDQDQDQDB1 ? D(BL)0

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Leptogenesis

• You generate Lepton Asymmetry first.
• Generate L from the direct CP violation in
  right-handed neutrino decay
• L gets converted to B via EW anomaly
• ? More matter than anti-matter ? We have
  survived The Great Annihilation

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Origin of Universe
V(?)

• Maybe an even bigger role
• Microscopically small Universe at Big Bang got
  stretched by an exponential expansion (inflation)
• Need a spinless field that
• slowly rolls down the potential
• oscillates around it minimum
• decays to produce a thermal bath
• The superpartner of right-handed neutrino fits
  the bill
• When it decays, it produces the lepton asymmetry
  at the same time
• (HM, Suzuki, Yanagida, Yokoyama)
• Neutrino is mother of the Universe?

?
log R
t
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Origin of the Universe

• Right-handed scalar neutrino Vm2f2
• ns0.96
• r0.16
• Need m1013GeV
• Still consistent with latest WMAP
• But V?f4 is excluded
• Verification possible in the near future

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?
?
?
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Future
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Remaining angle ?13NO?A
19kt
NOnA
MINOS
L810km
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Daya Bay
Empty detectors moved to underground halls
through access tunnel. Filled detectors swapped
between underground halls via horizontal tunnels.
Ling Ao Near 500 m from Ling Ao Overburden 98 m
Ling Ao-ll NPP (under const.)
Ling Ao NPP
Entrance portal
Daya Bay NPP
Total tunnel length 2700 m
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Very Long Baseline Experiment
Do neutrinos and anti-neutrinos oscillate
differently? (CP violation)
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LHC/ILC may help

• LHC finds SUSY
• ILC measures masses precisely

• If both gaugino and sfermion masses unify, there
  cant be new particles lt 1014GeV except for
  gauge-singlets

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Plausible scenario

• 0??? found
• LHC discovers SUSY
• ILC shows unification of gaugino and scalar
  masses
• Dark matter concordance between collider,
  cosmology, direct detection
• CP in ?-oscillation found

• Lepton flavor violation limits (??e?, ??e
  conversion, ???? etc) improve
• Tevatron and EDM (e and n) exclude Electroweak
  Baryogenesis
• CMB B-mode polarization gives tensor mode r0.16

If this happens, we will be led to
believe seesawleptogenesis (Buckley, HM)
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Conclusions

• Neutrinos are weird
• Strong evidence for neutrino mass
• Small but finite neutrino mass
• Need drastic ideas to understand it
• Neutrino mass may be responsible for our
  existence (or even the universe itself)
• A lot more to learn in the next few years

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