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The Neutrino Scene

The Neutrino Scene. Boris Kayser Fermilab June 3, 2004. Evidence For Flavor Change. Neutrinos Solar Reactor (L ~ 180 km) Atmospheric Accelerator (L = 250 km) Stopped m + Decay LSND L  30 m. Evidence of Flavor Change Compelling Very Strong Compelling Interesting Unconfirmed.

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The Neutrino Scene

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  1. The Neutrino Scene Boris Kayser Fermilab June 3, 2004

  2. Evidence For Flavor Change • Neutrinos • Solar • Reactor(L ~ 180 km) • Atmospheric • Accelerator(L = 250 km) • Stopped m+ Decay LSND L  30 m • Evidence of Flavor Change • Compelling • Very Strong • Compelling • Interesting • Unconfirmed ) (

  3. Solar Neutrinos • Nuclear reactions in the core of the sun produce ne. Only ne. • Sudbury Neutrino Observatory (SNO) measures, for the high-energy part of the solar neutrino flux: • nsol d  e p p  fne • nsol d  n n p  fne+ fnm+ fnt From the two reactions, fne fne+ fnm+ fnt ——————— = 0.306 ± 0.026 (stat) ±0.024 (syst) Clearly, fnm+ fnt ≠ 0 . Neutrinos do changeflavor.

  4. There is some spectrum of 3 or more neutrino mass eigenstates ni: n4 n3 (Mass)2 n2 n1 Mass (ni)  mi ne,nm,and nt are mixtures of these mass eigenstates.

  5. la(le e, lmm, ltt) Uai ni Detector U is the Leptonic Mixing Matrix.

  6. What Have We Learned? • If LSND is confirmed, there are at least 4 neutrino species. • If LSND is not confirmed, nature may contain only 3 neutrinos. • Then, from the existing data, the neutrino spectrum looks like —

  7. { sin2q13Bounded by reactor exps. with L ~ 1 km From max. atm. mixing, { From nm(Up) oscillate but nm(Down) don’t { In LMA–MSW, Psol(nene) = ne fraction of n2 From distortion of ne(solar) and ne(reactor) spectra { From max. atm. mixing, n1+n2 includes (nm–nt)/√2 n3 Dm2atm (Mass)2 n2 } Dm2sol n1 nt [|Uti|2] nm [|Umi|2] ne [|Uei|2]

  8. The Mixing Matrix The flavor content picture shows the |Uai|2, but not the signs or phases of the Uai. Solar Atmospheric Cross-Mixing cij cos qijsij sin qij Majorana CP phases q12 ≈ qsol ≈ 32°,q23 ≈ qatm ≈ 35-55°, q13 < 15° d would lead to P(na nb) ≠ P(na nb).CP But note the crucial role of s13 sin q13. ~

  9. — The Future —What We Would Like to Find Out • How many different kinds of neutrinos are there? • What are the masses of the neutrinos? • What implications do neutrinos and solar-physics/astrophysics/cosmology have for each other? • Are neutrinos their own antiparticles?

  10. How extensive is the mixing of different types of neutrinos? • Do neutrino interactions violate CP? • Are there surprises, such as large electromagnetic interactions from extra dimensions? • What can neutrinos tell us about physics at the grand unification scale? • Are neutrinos responsible for the matter-antimatter asymmetry of the universe?

  11. The American Physical Society Divisions of — • Particles and Fields • Nuclear Physics • Astrophysics • Physics of Beams • are sponsoring a year-long study, aimed at laying the groundwork for a sensible future program to answer the open questions. To quote the Charge— “The Study will lay scientific groundwork for the choices that must be made during the next few years.”

  12. Working Groups — The Central Element • Each working group is defined by an experimental approach. • The groups and their leaders — • Solar and Atmospheric Neutrino Experiments • John Bahcall <jnb@ias.edu>, Josh Klein <jrk@physics.utexas.edu> Reactor Neutrino Experiments • Gabriela Barenboim <gabriela@fnal.gov>, Ed Blucher <blucher@hep.uchicago.edu> Superbeam Experiments and Development • Bill Marciano <marciano@bnl.gov>, Doug Michael <michael@hep.caltech.edu>

  13. Neutrino Factory and Beta Beam Experiments and Development Stephen Geer <sgeer@fnal.gov>, Michael Zisman <mszisman@lbl.gov> • Neutrinoless Double Beta Decay and Direct Searches for Neutrino Mass Steve Elliott <elliotts@lanl.gov>, Petr Vogel <pxv@caltech.edu> • What Cosmology/Astrophysics and Neutrino Physics can Teach Each Other Steve Barwick <barwick@HEP.ps.uci.edu>, John Beacom <beacom@fnal.gov> • Theory Discussion Group Rabi Mohapatra <rmohapat@physics.umd.edu>

  14. Conclusions and recommendations in a report to be completed by end of August. Final General Meeting — Snowmass, June 28-30 See www.interactions.org/neutrinostudy All are welcome!

  15. Dm2atm (Mass)2 n2 Dm2sol n1 Methods and Payoffs • Emphasis on questions whose answers will come from accelerator and reactor experiments. • Assume first that there are only 3 neutrino mass eigenstates. • What is the neutrino mass spectral pattern? • Today: 1.9  10-3 < Dm2atm < 3.0  10-3 eV2 (90% SuperK) • Tomorrow: ? < Dm2atm < ? (MINOS)

  16. Is the spectral pattern or ? Generically, SO(10) grand unified models predict . is un-quark-like, and would probably involve a lepton symmetry with no quark analogue. n behavior in earth matter can distinguish between and . ( — )

  17. n2 n3 } Dm2sol n1 Dm2atm or (Mass)2 Dm2atm n2 } Dm2sol n3 n1 nt [|Uti|2] nm [|Umi|2] ne [|Uei|2]

  18. E 12 GeV Sign[m2( ) - m2( )] In matter, at superbeam energies, Dm2atm Dm2eff ≈ Dm2atm [1 - S ] •  Larger E is better • But want L/E to correspond to ~ peak of oscillation •  Larger E should be matched by larger L

  19. Determining whether the spectrum is like or like could be a unique contribution of NOnA or its proton-driver-enhanced successor, or of a Brookhaven Long Base Line program. At NOnA, with a 2nd detector, the determination would be possible for sin2 2q13 almost down to 0.01. (The NOnA collaboration)

  20. What is q13 ? • sin2q13 = |Ue3|2 is the small ne piece of n3. n3 is at one end of Dm2atm. • We need an experiment with L/E sensitive to Dm2atm, and involving ne. Possibilities Reactor ne disappearance while traveling L ~ 1 km. Acceleratornm ne or ne nmwhile traveling L > Several hundred km.

  21. Accelerator LBL measurements depend on q13, qatm, Sign (Dm2atm), andd. They can probe all of these quantities. Reactor experiments depend only on q13. Thus, they can measure q13 cleanly.

  22. Sensitivity: Experiment sin2 2q13 Present CHOOZ bound 0.2 Double CHOOZ 0.03 Future US experiment 0.01(Detectors at ~200 m and ~ 1.5 km) Sensitivity needed as part of the overall program: ~ 0.01 Other measurements: Neutrino magnetic moment, the anomalous Weinberg angle

  23. Do neutrino interactions violate CP? • Look for — • P(nm ne) ≠ P(nm ne) (Superbeam)orP(ne nm) ≠ P(ne nm) ( n Factory) • Must separate CP violation from matter effects. • Can establish CP if Facility sin2 2q13 exceeds • Superbeam from proton driver10-2 • n factory10-4

  24. We can exist only because Matter>>antimatter in the universe. CP in n oscillation would be evidence that theMatter>>antimatterasymmetry arose from Leptonic — not Quark or Squark — CP in the early universe.

  25. Are theremore than 3neutrino mass eigenstates? • MiniBooNE can confirm or refute LSND. • If MiniBooNE running with n sees no signal, it will not have tested LSND unless it runs with n. • If MiniBooNE (n and/or n) sees a signal — • How many additional neutrinos are there? • What are the splittings Dm2? • How should reactor and LBL experiments be interpreted? • Are there new, Short-Base-Line CP effects? • An additional detector would be called for.

  26. Conclusion • Neutrino physics presents us with exciting opportunities. • Fermilab could play a leading role in the neutrino program of the future.

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