Transcript Where can neutrino physics lead us?

What is the case for nufact?
Hitoshi Murayama (UC Berkeley)
Intl Scoping Study Meeting of
Nufact and Superbeam
Boston University, March 8, 2006
The Question
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Neutrino physics has been full of surprises
We’ve learned a lot in the last ~8 years
We want to learn more
New projects are more and more expensive
Is it really worth it?
Especially worth ~B$, B€, 100B¥?
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Elevator Pitch
• If you happen to be on
an elevator with a
powerful senator, can
you explain why you
want to spend ~B$ on
your project in 30
seconds?
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What will NOT work
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For politicians and taxpayers, these arguments
wouldn’t be convincing and/or interesting enough
Measurements as precisely as we can
Push limits on 13 as much as we can
Verify the three-generation framework of neutrino
oscillation
Distinguish different flavor modles
Field needs another machine to sustain itself
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Quantum Universe Report
What are neutrinos telling us?
• Of all the known particles,
neutrinos are the most
mysterious. They played an
essential role in the
evolution of the universe,
and their tiny nonzero mass
may signal new physics at
very high energies.
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Quantum Universe Report
• Einstein’s Dream of Unified Forces
– Are there undiscovered principles of nature: new symmetries, new
physical laws?
– How can we solve the mystery of dark energy?
– Are there extra dimensions of space
– Do all the forces become one?
• The Particle World
– Why are there so many kinds of particles?
– What is dark matter? How can we make it in the laboratory?
– What are neutrinos telling us?
• The Birth of the Universe
– How did the universe come to be?
– What happened to the antimatter?
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Outline
• Why Neutrinos?
• A few scenarios
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sin2 213 ≪ 0.01
sin2 213 > 0.01
Mini-BooNE confirms LSND
LHC discovers new physics < TeV
• The Big Questions
– Scenario to “establish” seesaw/leptogenesis
• Conclusion
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Why Neutrinos?
Interest in Neutrino Mass
• So much activity on neutrino mass already.
Why are we doing this?
Window to (way) high energy scales
beyond the Standard Model!
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Why Beyond the Standard Model
• Standard Model is sooooo successful. But
none of us are satisfied with the SM. Why?
• Because it leaves so many great questions
unanswered
 Drive to go beyond the Standard Model
• Two ways:
– Go to high energies
– Study rare, tiny effects

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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!
• Inteferometry (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
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high scales
Ubiquitous Neutrinos
They must have played some
important role in the universe!
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The Data
de Gouvêa’s classification:
• “Indisputable”
– Atmospheric
– Solar
– Reactor
• “strong”
– Accelerator (K2K)
And we shouldn’t forget:
• “unconfirmed”
– Accelerator (LSND)
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Historic Era in Neutrino Physics
We learned:
• Atmospheric nms are lost. P=4.2 10–26 (SK) (1998)
• converted most likely to nt (2000)
• Solar ne is converted to either nm or nt (SNO) (2002)
• Only the LMA solution left for solar neutrinos
(Homestake+Gallium+SK+SNO) (2002)
• Reactor anti-ne disappear (2002) and reappear
(KamLAND) (2004)
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Neutrinos do oscillate!
Proper time t
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What we learned
• Lepton Flavor is not conserved
• Neutrinos have tiny mass, not very hierarchical
• Neutrinos mix a lot
the first evidence for
incompleteness of Minimal Standard Model
Very different from quarks
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Typical Theorists’ View ca. 1990
• Solar neutrino solution must be small angle
Wrong!
MSW solution because it’s cute
• Natural scale for Dm223 ~ 10–100 eV2
Wrong!
because it is cosmologically interesting
Wrong!
• Angle 23 must be ~ Vcb =0.04
• Atmospheric neutrino anomaly must go Wrong!
away because it needs a large angle
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The Invisibles
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The Big Questions
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What is the origin of neutrino mass?
Did neutrinos play a role in our existence?
Did neutrinos play a role in forming galaxies?
Did neutrinos play a role in birth of the universe?
Are neutrinos telling us something about
unification of matter and/or forces?
• Will neutrinos give us more surprises?
Big questions  tough questions to answer
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Immediate Questions
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Dirac or Majorana?
Absolute mass scale?
How small is 13?
CP Violation?
Mass hierarchy?
Is 13 maximal?
LSND? Sterile neutrino(s)? CPT violation?
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Tools
• Available tools now:
– SuperK, SNO, KamLAND, Borexino, Mini-BooNE,
MINOS, Cuoricino, NEMO, SDSS, …
• Available soon (?):
– Opera, Double-Chooz, T2K, MINERnA, SciBooNE,
NOnA, reactor 13 expts, KATRIN, PLANCK, new
photometric surveys, more 0n expts, …
Do we really need more?
What do we need?
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Do we really need more?
What do we need?
• The answer depends on
what we will find in the
near future
• Talk about a few scenarios
– sin2 213 ≪ 0.01
– sin2 213 > 0.01
– Mini-BooNE confirms
LSND
– LHC discovers new physics
< TeV
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sin2 213≪0.01
Obvious case?
• Superbeams will not address 13, mass
hierarchy, or CP violation
• A clear case for neutrino factory and/or beam
• de Gouvêa: Will we get the funds to get a
neutrino factory even if all previous
investments end up “unsuccessful”?
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sin2 213>0.01
sin2 213>0.01
• Reactor/T2K/NOnA finds sin2 213
This is my prejudice
• Upgrades (4MW J-PARC to HyperK,
Proton Driver+NOnA 2nd detector, etc)
– Measures sin2 213 precisely
– Determines mass hierarchy
– Discovers CP violation
What’s left then?
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The source of CP violation
• Having seen
does not tell us what is causing it (in particular in
the presence of “matter effect background”)
• Is it due to the Dirac phase in the MNS matrix?
• Exactly the same question being addressed by Bfactories
– i.e., K can be explained by the KM phase, but is it?
– Cross check in a different system, e.g., B  Yes!
– Is there new interaction (e.g. SUSY loop)?  future
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Testing MNS hypothesis
• One way I know is to use tau modes
• Consequence of CPT and three flavors
• Can they be studied at neutrino factory?
– I know it is tough even for a neutrino factory,
but other facilities will clearly not do it
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Testing MNS hypothesis
• A simulation like this will make the case
with new neutrino interaction
(mt)
(mt)
w/o new neutrino interaction
(em)
(em)
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Mini-BooNE confirms LSND
The hell breaks loose
• In this case, it is hard to understand what is
going on, because there is currently no
simple way to accommodate LSND result
with other neutrino data
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Multiple sterile neutrinos?
Sterile neutrino and CPT violation?
Mass varying neutrinos?
Something even more wild and wacky?
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What it takes
• We will need neutrino “oscillation” experiments
with multiple baselines, multiple modes
– E~10 GeV, L~10km, looking for t appearance
– Redo CDHSW (nm disappearance experiment with
L=130 & 885m, E=19.2GeV)
– E~1 GeV, L~1 km, looking for oscillatory behavior and
CP violation in nenm, or better, nmne
– Some in the air, some in the earth
– Probably more
– Muon source would help greatly
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LHC discovers new physics <TeV
TeV new physics
• Whatever it is,
– SUSY, large extra dimensions, warped extra dimension,
technicolor, Higgsless, little Higgs
it is hard to avoid the TeV-scale physics to
contribute to flavor-changing effects in general
• Renewed strong case for, e.g., super-B
• Very strong case for lepton flavor violation, gm2
– Hence, for a muon storage ring
• Obvious competition with ILC and beyond
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For example, SUSY
• High-energy data (LHC/ILC) will provide masses
of superparticles
– But most likely not their mixings
• Low-energy LFV experiments (e.g., me,
mAeA) provide rates (T-odd asymmetry if lucky)
– Combination of virtual particles in the loop and their
mixing
• Put them together
– Resolve the mixing
– Constrain models of flavor
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What about the Big Questions?
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What is the origin of neutrino mass?
Did neutrinos play a role in our existence?
Did neutrinos play a role in forming galaxies?
Did neutrinos play a role in birth of the universe?
Are neutrinos telling us something about
unification of matter and/or forces?
• Will neutrinos give us more surprises?
Big questions  tough questions to answer
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Origin of Neutrino Mass,
our existence, even our universe
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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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
mn ~ 1/R if one extra dim  R~10mm
• An infinite tower of sterile neutrinos
• Or anomaly mediated SUSY breaking
4
1
d
 (LH u N )
M 
Pl
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Two ways to go
(2) Majorana Neutrinos:
– There are no new light
particles
– Why 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~(Dm2atm)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~(Dm2atm)1/2, mD~mt
 M3~1015GeV!
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M3
Neutrino mass may be
probing unification:
Einstein’s dream
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Leptogenesis
• You generate Lepton Asymmetry first. (Fukugita, Yanagida)
• Generate L from the direct CP violation in right-handed
neutrino decay
* *
(N1  n i H)  (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”
• Despite detailed information on neutrino masses, it still
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works (e.g., Bari, Buchmüller,
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n~R
Origin of Universe
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
– 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)
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Decay products: supersymmetry and
hence dark matter
Neutrino is mother of the Universe?
size of the universe amplitude
• Maybe an even bigger role: inflation
• Need a spinless field that
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QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
QuickTime™ and a
Cinepak decompressor
are needed to see this picture.
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Origin of the Universe
• Right-handed scalar
neutrino: V=m2f2
• ns=0.96
• r=0.16
• Detection possible in
the near future
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Can we prove it experimentally?
• Unfortunately, no: it is
difficult to reconstruct
relevant CP-violating
phases from neutrino
data
• But: we will probably
believe it if the
following scenario
happens
Archeological evidences
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A scenario to “establish” seesaw
• We find CP violation in neutrino oscillation
– At least proves that CP is violated in the lepton
sector
• Ue3 is not too small
– At least makes it plausible that CP asymmetry
in right-handed neutrino decay is not
unnaturally suppressed
• But this is not all
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A scenario to “establish” seesaw
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LHC finds SUSY, LC establishes SUSY
no more particles beyond the MSSM at TeV scale
Gaugino masses unify (two more coincidences)
Scalar masses unify for 1st, 2nd generations (two
for 10, one for 5*, times two)
 strong hint that there are no additional particles
beyond the MSSM below MGUT except for gauge
singlets.
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Gaugino and scalars
• Gaugino masses test unification
itself independent of
intermediate scales and extra
complete SU(5) multiplets
• Scalar masses test beta
functions at all scales, depend
on the particle content
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A scenario to “establish” seesaw
• Next generation experiments
discover neutrinoless double beta
decay
• Say, mnee~0.1eV (quasi-degenerate)
• There must be new physics below
~1014GeV that generates the
Majorana neutrino mass
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A scenario to “establish” seesaw
• It leaves the possibility for R-parity violation
• Consistency between cosmology, dark matter
detection, and LHC/ILC will remove the concern
M
0.756(n 1)x n1
3s0
 2 /(TeV)2
f
 1/ 2

 ann
g  ann MPl3 8H02
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High precision even for ILC
= 1014GeV
seesaw Modified
Type-I
New particles
31
324
(mQ2-mU2)/M12
1
1.283
Type-II
seesaw
15+15*
1.078
(mQ2-mE2)/M12
1
1.084
1.026
(mD2-mL2)/M12
1
1.040
1.014
Matt Buckley
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A scenario to “establish” seesaw
• B-mode fluctuation in
CMB is detected, with
a reasonable
inflationary scale
 strong hint that the
cosmology has been
‘normal’ since
inflation (no extra D
etc)
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A scenario to “establish” seesaw
Possible additional archeological evidence, e.g.,:
• lepton-flavor violation (me conversion, tm)
seen at the “reasonable” level expected in SUSY
seesaw (even though I don’t believe mSUGRA)
• Bdf KS shows deviation from the SM consistent
with large bR-sR mixing above MGUT
• Isocurvature fluctuation seen suggestive of N1
coherent oscillation, avoiding the gravitino
problem
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Conclusions
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Revolutions in neutrino physics
Neutrino mass probes rare/subtle/high-energy physics
There is a very good chance for further big progress
Most likely, we will need superbeam, and also neutrino
factory and/or beta beam
• Neutrino physics is within the context of particle physics,
astrophysics and cosmology
• Big questions can be answered only based on collection of
experiments, not oscillation alone
What’s the elevator pitch?
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