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The Big World of Little Neutrinos
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Hitoshi Murayama (Berkeley)
June 6, 2007
Aspen Center for Physics Colloquium
2
“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
3
Outline
•
•
•
•
•
•
•
•
Introduction
Neutrinos in the Standard Model
Evidence for Neutrino Mass
Solar Neutrinos
Implications of Neutrino Mass
Why do we exist?
Future
Conclusions
4
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
6
Desperate Idea of Pauli
7
Three Kinds of Neutrinos
• There are three
• And no more
8
Neutrinos are Left-handed
9
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
10
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
11
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
12
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
13
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
14
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
15
Lot of effort since ‘60s
Finally convincing
evidence for “neutrino
oscillation”
Neutrinos appear to
have tiny but finite mass
16
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
18
SuperKamiokaNDE
Nucleon Decay Experiment
• pe+p0, K+n, etc
– So far not seen
– Atmospheric neutrino
main background
• Cosmic rays isotropic
– Atmospheric neutrino
up-down symmetric
19
A half of nm lost!
20
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
21
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. 22 case:
2
2
2
m
11
2
M 2
m 21
m 212
2
m 22
M 1 m1 1
M 2 2 m22 2
22
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
23
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
24
Survival Probability
p=1 GeV/c, sin2 2=1
m2=310–3(eV/c2)2
Half of the up-going
ones get lost
25
Excellent Fit
2/dof=839.7/755 (18%)
m2=2.510-3 eV2
sin22=1
Downwards nm’s don’t disappear
1/2 of upwards nm’s do disappear
26
Cross check with man-made n’s
Veto Shield
Coil
Fermilab
27
Good consistency!
• MINOS result 2006
28
Public Interest in Neutrinos
29
30
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
32
33
We don’t get enough
• Neutrino
oscillation?
• Something
wrong with our
understanding of
the Sun?
34
35
SNO comes to the rescue
• Charged Current:ne
• Neutral Current: ne+nm+n
• 7.6s difference
nm, are coming from the Sun!
36
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!
37
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
38
Location, Location, Location
39
KamLAND
Reactor neutrinos do oscillate!
Proper time
L0=180 km
40
Progress in 2002
on the Solar Neutrino Problem
March 2002
April 2002
with SNO
Dec 2002
with KamLAND
June 2004
with KamLAND
41
Implications of Neutrino Mass
Mass Spectrum
What do we do now?
43
Rare Effects from High-Energies
• Effects of physics beyond the SM as
effective operators
• Can be classified systematically (Weinberg)
44
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
45
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)
46
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?
47
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 )
48
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!
49
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!)
50
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
51
Why do we exist?
Matter Anti-matter Asymmetry
53
Matter and Anti-Matter
Early Universe
1,000,000,001
1,000,000,000
Matter
Anti-matter
54
Matter and Anti-Matter
Current Universe
us
1
Matter
Anti-matter
The Great Annihilation
55
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…
56
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
QuickTime™ and a
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
57
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”
58
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?
59
t
Origin of the Universe
• Right-handed scalar
neutrino: V=m22
• 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
60
61
Future
Remaining angle 13
NOnA
NOnA
MINOS
19kt
L=810km
32-plane
block
Admirer
63
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
64
Very Long Baseline Experiment
Do neutrinos and anti-neutrinos
oscillate differently? (CP violation)
65
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
66
Plausible scenario
• Lepton flavor violation
• 0nbb found
limits (meg, me
• 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
68
n
69
70