The Neutrino World

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APS Multi-Divisional Neutrino Study
Boris Kayser Wine Cheese February 4, 2005
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(No Transcript)
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The last seven years
Compelling evidence that neutrinos have mass and
mix
Open questions about the neutrino world
Need for a coherent strategy for getting answers
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A year-long study of the future of neutrino
physics, sponsored by the American Physical
Society Divisions of
Nuclear Physics Particles and Fields Astrophysics
Physics of Beams
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WHO really triggered this study???
One data point HEPAP felt that, in view of the
discoveries in neutrino physics, the roadmap for
the particle physics future needs to have a
neutrino component.
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What Have We Learned?
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We do not know how many neutrino mass eigenstates
there are. If the Liquid Scintillator Neutrino
Detector (LSND) experiment is confirmed, there
are more than 3. Confirmation of LSND would show
that our usual assumptions about the neutrino
spectrum and neutrino mixing are wrong. If LSND
is not confirmed, nature may contain only 3
neutrinos. Then, from the existing data, the
neutrino spectrum looks like
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Normal
Inverted
or
(Mass)2
?m2atm


?m2sol 7.9 x 105 eV2, ?m2atm
2.4 x 103 eV2
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Generically, grand unified models (GUTS) favor
GUTS relate the Leptons to the Quarks.

is un-quark-like, and would probably
involve a lepton symmetry with no quark analogue.
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The Unitary Leptonic Mixing Matrix U
l? (le ? e, l?? ?? l? ? ?)
U?i
?i
Detector
The component of ?i that creates l? is called ??,
the neutrino of flavor ?.
The ?? fraction of ?i is U?i2.
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From hep-ex/ 0406035
Solar ?m2 and mixing angle from KamLAND analysis
of KamLAND and solar neutrino data
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From Ed Kearns
From L/E
Atmospheric ?m2 and mixing angle from
SuperKamiokande L/E analysis and full data set
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The spectrum, showing its approximate flavor
content, is
?3
?2

?m2sol
?1
?m2atm
or

(Mass)2
?m2atm
?2

?m2sol
?1
?3
?? U?i2
??U? i2
?e Uei2
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The Mixing Matrix
Solar
Atmospheric
Cross-Mixing
cij ? cos ?ijsij ? sin ?ij
Majorana CP phases
?12 ?sol 32, ?23 ?atm 36-54, ?13 lt
15 ? would lead to P(??? ??) ? P(??? ??).
CP But note the crucial role of s13 ? sin ?13.

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Observing Oscillations
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The Neutrino Study
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• To quote the Charge
• The Study will lay scientific groundwork for the
  choices that must be made during the next few
  years.
• A grassroots study like this, co-sponsored by
  several APS Divisions, is unprecedented.
• It aimed at consensus, which was not a trivial
  goal. But consensus on key recommendations was
  achieved!

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The Structure of the Study

• Over 200 Participants
• Seven Working Groups

• Solar and Atmospheric Neutrino Experiments
• John Bahcall, Josh Klein
• Reactor Neutrino Experiments
• Gabriela Barenboim, Ed Blucher
• Superbeam Experiments and Development
• Bill Marciano, Doug Michael

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• Neutrino Factory and Beta Beam Experiments and
  Development
• Stephen Geer, Michael Zisman
• Neutrinoless Double Beta Decay and Direct
  Searches for Neutrino Mass
• Steve Elliott, Petr Vogel
• What Cosmology/Astrophysics and Neutrino Physics
  can Teach Each Other
• Steve Barwick, John Beacom
• Theory Discussion Group
• Rabi Mohapatra

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• Writing Committee Hamish Robertson (Chair),
  Janet Conrad, Andre de Gouvea, Steve Elliott,
• Stuart Freedman, Maury Goodman, Boris Kayser,
• Josh Klein, Doug Michael

• Organizing Committee Janet Conrad, Guido
  Drexlin, Belen Gavela, Takaaki Kajita, Paul
  Langacker, Keith Olive, Bob Palmer, Georg
  Raffelt, Hamish Robertson, Stan Wojcicki, Lincoln
  Wolfenstein
• Co-Chairpersons Stuart Freedman, Boris Kayser

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Our Main Report, The Neutrino Matrix, and the
reports of the Working Groups, may be found at
www.aps.org/neutrino
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• Briefings have been given for
• DOE
• NSF
• HEPAP
• NSAC
• P5
• FERMILAB PAC
• OSTP
• EPP 2010 (National Academy Committee)

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The Open Questions
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Neutrinos and the New Paradigm

• What are the masses of the neutrinos?
• What is the pattern of mixing among the different
  types of neutrinos?
• Are neutrinos their own antiparticles?
• Do neutrinos violate the symmetry CP?

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Neutrinos and the Unexpected

• Are there sterile neutrinos?
• Do neutrinos have unexpected or exotic
  properties?
• What can neutrinos tell us about the models of
  new physics beyond the Standard Model?

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Neutrinos and the Cosmos

• What is the role of neutrinos in shaping the
  universe?
• Is CP violation by neutrinos the key to
  understanding the matter antimatter asymmetry
  of the universe?
• What can neutrinos reveal about the deep interior
  of the earth and sun, and about supernovae and
  other ultra high energy astrophysical phenomena?

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Recommendations for Future Experiments
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• We recommend, as a high priority, a comprehensive
  U.S. program to
• Complete our understanding of neutrino mixing
• Determine the character of the neutrino mass
  spectrum
• Search for CP violation among neutrinos

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Components of this Program

1. An expeditiously deployed reactor experiment
   with sensitivity down to sin22?13 0.01
2. A timely accelerator experiment with comparable
   ?13 sensitivity, and sensitivity to the mass
   hierarchy through matter effects
3. A megawatt-class proton driver and neutrino
   superbeam with an appropriate very large detector
   capable of observing CP violation

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In Pursuit of ?13

• Both CP violation and our ability to tell
  whether the spectrum is normal or inverted depend
  on ?13.

If sin22?13 lt 0.01, a neutrino factory will be
needed to study both of these issues.
How may ?13 be measured?
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sin2?13
?3
?m2atm
(Mass)2
?2

?m2sol
?1

• sin2?13 ?Ue3?2 is the small ?e piece of ?3.
• ?3 is at one end of ?m2atm.
• ?We need an experiment with L/E sensitive to
  ?m2atm, and involving ?e.

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Possibilities
Reactor ?e disappearance while traveling L 1.5
km. L/E 500 km/GeV. This process depends on ?13
alone. Accelerator ?? ? ?e while traveling L gt
Several hundred km. L/E 400 km/GeV. This
process depends on ?13, ?23, the CP phase ?, and
on whether the spectrum is normal or inverted.
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sin2?13
?3
?m2atm
(Mass)2
?2

?m2sol
?1
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1. The Reactor Experiment
A relatively modest-scale reactor experiment can
cleanly determine whether sin22?13 gt 0.01,
measure it if it is, and help break the ?23
90º ?23 degeneracy.
Sensitivity Experiment sin2 2?13 Present
CHOOZ bound 0.2 Double CHOOZ 0.03 (In
2011) Future US experiment 0.01(Detectors at
200 m and 1.5 km)
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2. The Accelerator Experiment

• An accelerator ? experiment can probe several
  neutrino properties
• ?13
• ?23
• Whether the spectrum is normal or inverted
• CP violation
• Only the U.S. can have baselines long enough to
  probe whether the spectrum is normal or inverted.
  

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Why are long baselines needed? At superbeam
energies, matter effects ? sin2 2?M sin2 2?13
1 S . Signm2( ) - m2(
) At oscillation maximum, P(??? ?e) gt1
P(??? ?e) lt1 30 E 2 GeV
(NO?A) 10 E 0.7 GeV (T2K)

()
()


The effect is
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Larger E is better. But want L/E to correspond
roughly to the peak of the oscillation. Therefore,
larger E should be matched by larger L. Using
larger L to determine whether the spectrum is
normal or inverted could be a unique contribution
of the U.S. program.
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3. The Proton Driver and Large Detector
These facilities are needed if we are to be able
to determine whether the spectrum is normal or
inverted, and to observe CP violation, for any
sin22?13 gt (0.01 0.02).
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Why would CP in ? oscillation be interesting?
The most popular theory of why neutrinos are so
light is the See-Saw Mechanism

Familiar light neutrino
?

Very heavy neutrino
N
The heavy neutrinos N would have been made in the
hot Big Bang.
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If neutrino oscillation violates CP, then quite
likely so does N decay. Then, in the early
universe, we would have had different rates for
the CP-mirror-image decays N ? l
and N ? l This would have led to
unequal numbers of leptons and antileptons
(Leptogenesis). Perhaps this was the original
source of the present preponderance of Matter
over Antimatter in the universe.
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The Difference a Proton Driver Can Make
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The spectral hierarchy without a proton driver
(Feldman)
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The spectral hierarchy with a proton driver
(Feldman)
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CP violation without a proton driver
one cannot demonstrate CP violation for any
delta without a proton driver.
(Feldman) Without a proton driver,
one cannot make a 3 sigma CP discovery.
(Shaevitz)
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CP violation with a proton driver
90 CL contours for 5 yr ? 5 yr ? running
(BNL)
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We recommend, as a high priority, that a phased
program of increasingly sensitive searches for
neutrinoless nuclear double beta decay (0???) be
initiated as soon as possible.
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• Observation of 0??? would establish that
• Lepton number L is not conserved
• Neutrinos are Majorana particles ( ? ? )
• Nature (but not the Standard Model) contains
  Majorana neutrino masses. These involve physics
  different from that which gives masses to the
  charged leptons, quarks, nucleons, humans, the
  earth, and galaxies.

Then neutrinos and their masses are very
distinctive.
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The Quest for the Origin of Mass
Neutrino experiments and the search for the Higgs
boson both probe the origin of mass. The see-saw
mechanism suggests that the physics behind
neutrino mass resides at 1015 GeV, near where
Grand Unified Theories say all the forces of
nature, save gravity, become one.
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We recommend the development of a solar neutrino
experiment capable of measuring the energy
spectrum of neutrinos from the primary pp fusion
process in the sun.

• Confirm the Mikheyev-Smirnov-Wolfenstein
  explanation of solar neutrino behavior
• Test, at last, whether the pp fusion chain is the
  only source of solar energy

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The Context
Our recommendations for a strong future program
are predicated on fully capitalizing on our
investments in the current program

• Accelerator ? experiments within the U.S.
• American participation in experiments in
  Antarctica, Argentina, Canada, Germany, Italy,
  and Japan

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The current/near-future program should include

• Determination of the 7Be solar neutrino flux to
  5.
• Clear-cut confirmation or refutation of LSND.
• RD on techniques for detecting astrophysical
  neutrinos above 1015 eV.
• Measurements of neutrino cross sections needed
  for the interpretation of neutrino experiments.

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An Important Observation
Future experiments that we feel are particularly
important rely on suitable underground
facilities. Having these facilities will be
crucial.
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Looking Ahead

• A neutrino factory (or beta beam) is the ultimate
  tool in neutrino physics. It may be the only way
  to study CP violation and other issues.
  Substantial neutrino factory RD is needed if
  this facility is to be possible in the long term.
  

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Conclusion
We have a very rich opportunity to do exciting
physics.
Fermilab could play a major role.
Neutrino physics has connections to Cosmology,
astrophysics, nuclear physics, the origin of
mass, the relation between matter and antimatter,
the symmetries of nature, physics at energies
where the forces of nature become unified,
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We hope our study, and its report, will help the
community chart a sensible, fruitful, future
course.
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Backup Slides
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Green lt 10M/yr Blue
10M - 40M/yr Orange 40M -100M/yr Red
gt 100M/yr
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New Experiments
04 05 06 07 08 09 10 11 12 13 14 15
16 17 18 19 20
Running
Construction
RD
200 kg ??
No Signal?
Constr.
Running
RD
1 ton ??
New Experiments
RD
Construction
Running
pp Solar
RD
Constr.
Running
Reactor
RD
Construction
Running
Long Baseline
Construction/Running
Cross Sections
Green lt 10M/yr Blue
10M - 40M/yr Orange 40M -100M/yr Red
gt 100M/yr
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Facilities
04 05 06 07 08 09 10 11 12 13 14 15
16 17 18 19 20
Proton driver
RD
Construction
Running
Multipurpose Detector
Facilities
Construction
RD
Const.
RD
Construction
Running
UG Lab
Running
RD
RD
? Factory
Green lt 10M/yr Blue
10M - 40M/yr Orange 40M -100M/yr Red
gt 100M/yr
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POSSIBILITIES
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Some of the key experiments have studied
non-accelerator neutrinos made in the earths
atmosphere, in the sun, or in nuclear power
reactors.
Accelerator neutrino experiments will play an
increasing role as we move to answer the
questions raised by the discovery of neutrino
mass.