Where can neutrino physics lead us

1
Where can neutrino physics lead us?

• Hitoshi Murayama (UC Berkeley)
• 2nd Intl Scoping Study Meeting of
• Nufact and Superbeam
• KEK, Tsukuba, Jan 23, 2006

2
The Question

• Neutrino physics has been full of surprises
• Weve 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?

3
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?

4
Outline

• Introduction
• A few scenarios
• sin2 2?13 0.01
• sin2 2?13 gt 0.01
• Mini-BooNE confirms LSND
• LHC discovers new physics lt TeV
• Scenario to establish seesaw/leptogenesis
• Conclusion

5
Introduction
6
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!

7
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

?
8
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!
• 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 high scales

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Ubiquitous Neutrinos
They must have played some important role in the
universe!
11
The Data

• de Gouvêas classification
• Indisputable
• Atmospheric
• Solar
• Reactor
• strong
• Accelerator (K2K)
• And we shouldnt forget
• unconfirmed
• Accelerator (LSND)

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Historic Era in Neutrino Physics

• We learned
• Atmospheric nms are lost. P4.2 1026 (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
  (HomestakeGalliumSKSNO) (2002)
• Reactor anti-ne disappear (2002) and reappear
  (KamLAND) (2004)

13
Neutrinos do oscillate!
?Proper time ?
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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 MSW
  solution because its cute
• Natural scale for Dm223 10100 eV2 because it
  is cosmologically interesting
• Angle q23 must be Vcb 0.04
• Atmospheric neutrino anomaly must go away because
  it needs a large angle

Wrong!
Wrong!
Wrong!
Wrong!
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The Big Questions

• 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

• Dirac or Majorana?
• Absolute mass scale?
• How small is q13?
• CP Violation?
• Mass hierarchy?
• Is q13 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, MINER?A, SciBooNE,
  NO?A, reactor ?13 expts, KATRIN, PLANCK, new
  photometric surveys, more 0??? 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 gt 0.01
• Mini-BooNE confirms LSND
• LHC discovers new physics lt TeV

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sin2 2?130.01
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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?13gt0.01
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sin2 2?13gt0.01

• Reactor/T2K/NO?A finds sin2 2?13
• This is my prejudice
• Upgrades (4MW J-PARC to HyperK, Proton
  DriverNO?A 2nd detector, etc)
• Measures sin2 2?13 precisely
• Determines mass hierarchy
• Discovers CP violation
• Whats 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
  B-factories
• 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

• The only 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

26
Testing MNS hypothesis

• A simulation like this will make the case

w/o new neutrino interaction
with new neutrino interaction
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Mini-BooNE confirms LSND
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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
• 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
• E10 GeV, L10km, looking for ? appearance
• Redo CDHSW (?? disappearance experiment with
  L130 885m, E19.2GeV)
• E1 GeV, L1 km, looking for oscillatory behavior
  and CP violation in ?e???, or better, ????e
• Some in the air, some in the earth
• Probably more
• Muon source would help greatly

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LHC discovers new physics ltTeV
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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
• 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., ??e?, ?A?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?

• 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

34
Origin of Neutrino Mass,our existence, even our
universe
35
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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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
• mn 1/R if one extra dim ? R10mm
• An infinite tower of sterile neutrinos
• Or anomaly mediated SUSY breaking

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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
  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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Leptogenesis

• You generate Lepton Asymmetry first. (Fukugita,
  Yanagida)
• 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
• Despite detailed information on neutrino masses,
  it still works (e.g., Bari, Buchmüller, Plümacher)

42
Origin of Universe

?R

• Maybe an even bigger role 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)
• Decay products supersymmetry and hence dark
  matter
• Neutrino is mother of the Universe?

amplitude
size of the universe
43
Origin of the Universe

• Right-handed scalar neutrino Vm2f2
• ns0.96
• r0.16
• 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

• 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

48
A scenario to establish seesaw

• Next generation experiments discover neutrinoless
  double beta decay
• Say, ?m??ee0.1eV (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

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High precision even for ILC
Preliminary
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 (??e conversion, ????)
  seen at the reasonable level expected in SUSY
  seesaw (even though I dont believe mSUGRA)
• Bd?? 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

• 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
• Big questions can be answered only based on
  collection of experiments, not oscillation alone
• Whats the elevator pitch?

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The I?visibles
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