Transcript Document 7312083

The Big World of Little Neutrinos
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Hitoshi Murayama (Berkeley)
June 6, 2007
Aspen Center for Physics Colloquium
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“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
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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
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, can’t go at speed of light.
• Now neutrino right-handed??
 contradiction  can’t have a mass
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Anti-Neutrinos are Right-handed
• CPT theorem in
quantum field theory
– C: interchange
particles & antiparticles
– 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 lefthanded particles” yet they are massive.
Isn’t 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.
• Can’t go at speed of light (massive), and right-handed and
left-handed particles mix  no contradiction
0.511 MeV/c2
105 MeV/c2
176,000 MeV/c2
But neutrinos can’t
bump because there
isn’t a right-handed
one  stays massless
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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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Neutrinos
from 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
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+p0, K+n, 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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Neutrino’s clock
• Time-dilation: the
clock goes slower
v2
  t 1  2
c
• 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
massive neutrino is simply
H
2
m
p2  m 2  p 
2p
• But in quantum mechanics, mass is a matrix
in general. 22 case:
2
2
2

m
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2
M  2
 m 21
m 212 

2
m 22 
M 1  m1 1
M 2 2  m22 2
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Two-Neutrino Oscillation
• When produced (e.g., p+m+nm), neutrino is
of a particular type
n m ,,tt  1 cos  e
im12 t /| 4 p
 2 sin  e
im222t / 4 p
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Two-Neutrino Oscillation
• When produced (e.g., p+m+nm), neutrino is
of a particular type
n m ,,tt  1 cos  e
im12 t /| 4 p
 2 sin  e
im222t / 4 p
• No longer 100% nm, partly n!
• “Survival probability” for nm after t
P  n m nm ,t
2
2 4

m
c GeV ct 
2
2

 1  sin 2 sin 1.27
2 c p km
eV


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Survival Probability
p=1 GeV/c, sin2 2=1
m2=310–3(eV/c2)2
Half of the up-going
ones get lost
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Excellent Fit
2/dof=839.7/755 (18%)
m2=2.510-3 eV2
sin22=1
Downwards nm’s don’t disappear
1/2 of upwards nm’s do disappear
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Cross check with man-made n’s
Veto Shield
Coil
Fermilab
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Good consistency!
• MINOS result 2006
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Public Interest in Neutrinos
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Solar Neutrinos
How the Sun burns
• The Sun emits light because nuclear fusion
produces a lot of energy
2 Lsun
1
10
1
2
n 

7
10
sec
cm
25MeV 4p (1AU) 2
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We don’t get enough
• Neutrino
oscillation?
• Something
wrong with our
understanding of
the Sun?
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SNO comes to the rescue
• Charged Current:ne
• Neutral Current: ne+nm+n
• 7.6s difference
 nm, are coming from the Sun!
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Wrong Neutrinos
• Only ne produced in the
Sun
• Wrong Neutrinos nm, are
coming from the Sun!
• Somehow some of ne were
converted to nm, on their
way from the Sun’s core
to the detector
 neutrino oscillation!
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Terrestrial “Solar Neutrino”
• Can we convincingly
verify oscillation with
man-made neutrinos?
Psurv
KamLAND

m 2 c 4 GeV L 


 1  sin 2 sin 1.27
2
E
km
eV


n
2
2
• Hard for low m2
• To probe LMA, need
L~100km, 1kt
• Need low En, high n
• Use neutrinos from
nuclear reactors
1kt
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Location, Location, Location
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KamLAND
Reactor neutrinos do oscillate!
Proper time 
L0=180 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
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)2=10–20!
• 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. Can’t 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 haven’t 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)

4 S*
d M
(LH u N )
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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 antineutrinos!
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Seesaw Mechanism
• Why is neutrino mass so small?
• Need right-handed neutrinos to generate
neutrino mass , but nR SM neutral
n L

n R 
 mD
mD   n L 
 
M  n R
2
mD
mn 
 mD
M
To obtain m3~(m2atm)1/2, mD~mt, M3~1015GeV (GUT!)
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Grand Unification
• electromagnetic, weak,
and strong forces have
very different strengths
• But their strengths
become the same at 1016
GeV if supersymmetry
• To obtain
m3~(m2atm)1/2, mD~mt
 M3~1015GeV!
M3
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-Matter
Early Universe
1,000,000,001
1,000,000,000
Matter
Anti-matter
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Matter and Anti-Matter
Current Universe
us
1
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(B>0) > G(B<0)
• 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 >
200GeV), W is massless
and fluctuate in W
plasma
– Energy levels for lefthanded quarks/leptons
fluctuate correspondingly
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decompressor
are needed to see this picture.
QuickTime™ and a
decompressor
are needed to see this picture.
L=Q=Q=Q=B=1  B–L)=0
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Leptogenesis
• You generate Lepton Asymmetry first.
• Generate L from the direct CP violation in righthanded neutrino decay
* *
G(N1  n i H)  G(N1  n i H)  Im(h1j h1k hlk hlj )
• 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()
QuickTime™ and a
• Maybe an even bigger role
• Microscopically small Universe at
Big Bang got stretched by an
exponential expansion (inflation)
• Need a spinless field that
Cinepak decompressor
QuickTime™
a
are needed
to see thisand
picture.
Cinepak decompressor
are needed to see this picture.
– slowly rolls down the potential
– oscillates around it minimum
– decays to produce a thermal bath
(HM, Suzuki, Yanagida, Yokoyama)
log R
• The superpartner of right-handed
neutrino fits the bill
• When it decays, it produces the
lepton asymmetry at the same time

Neutrino is mother of the Universe?
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t
Origin of the Universe
• Right-handed scalar
neutrino: V=m22
• ns~0.96
• r~0.16
• Need m~1013GeV
• Still consistent with latest
WMAP
• But V=4 is excluded
• Verification possible in the
near future
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

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Future
Remaining angle 13
NOnA
NOnA
MINOS
19kt
L=810km
32-plane
block
Admirer
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Daya Bay
Far site
1600 m from Ling Ao
2000 m from Daya
Overburden: 350 m
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
Mid site
~1000 m from Daya
Overburden: 208 m
Ling Ao-ll NPP
(under const.)
230 m
290 m
Entrance
portal
Ling Ao
NPP
Daya Bay Near
360 m from Daya Bay
Overburden: 97 m
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 can’t be
new particles < 1014GeV except
for gauge-singlets
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Plausible scenario
• Lepton flavor violation
• 0nbb found
limits (meg, me
• LHC discovers SUSY
conversion, mg etc)
• ILC shows unification of
improve
gaugino and scalar masses
• Tevatron and EDM (e and
• Dark matter concordance
n) exclude Electroweak
between collider,
Baryogenesis
cosmology, direct
• CMB B-mode polarization
detection
gives tensor mode r=0.16
• CP in n-oscillation found
If this happens, we will be led to believe
seesaw+leptogenesis (Buckley, HM)
67
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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n
69
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