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Resolving neutrino parameter degeneracy

Resolving neutrino parameter degeneracy. Sin Kyu Kang Seoul National University of Technology. 3rd International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam Sep. 30 and Oct. 1 2007, Univ. of Tokyo, Hongo. Determination of q 13.

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Resolving neutrino parameter degeneracy

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  1. Resolving neutrino parameter degeneracy Sin Kyu Kang Seoul National University of Technology 3rd International Workshop on a Far Detector in Korea for the J-PARC Neutrino Beam Sep. 30 and Oct. 1 2007, Univ. of Tokyo, Hongo

  2. Determination ofq13 • Relatively largeq13opens the possibility to observe generic 3-flavor effects including CP violation and mass hierarchy. • q13 << 1hint for some flavor symmetry Why is it so interesting ? the key parameter for next generation of neutrino oscillation experiments.

  3. How to measure13 • Reactors: Disappearance (nenx) • Negligible for • Use reactors as a source of e (<E>~3.5 MeV) with a detector 1-2 kms away • and look for non-1/r2 behavior of the e rate sin2(2q13) sin2(2q12) Dm213 Dm212 Reactor experiments provide the only clean measurement of sin22: no matter effects, no CP violation, no correlation with other parameters.

  4. Accelerators: Appearance (nmne) • Use fairly pure, accelerator produced beam with a detector • traveling a long distance from the source and look for • the appearance of e events T2K: <E> = 0.7 GeV, L = 295 km NOA:<E> = 2.3 GeV, L = 810 km • But, the probability P depends on several parameters which • may be correlated withq13

  5. T2K experiment • JPARC : 40 GeV PS • 0.75 MW for phase I • 4 MW for phase II • ~2.5° off axis with respect to SK • Peak energy : ~700 MeV • ~2,200 nm interactions/yr at SK for OA 2.5° GOALS : (i)measure q13 (neappearance) (ii) q23 & Dm²23 (nmdisappearance)

  6. To achieve the goals • High statistics by a high intense n beam • Tune En at the oscillation maximum • Narrow band beam to reduce BG • Sub-GeV n beam for Water Cherenkov Off-Axis n beam 4MW Super JHF 0.75MW JHF 50GeV-PS Hyper-Kamiokande Super-Kamiokande

  7. T2K Sensitivity Reach Hayato, n2004

  8. But, measuring by appearance channel suffers from degeneracies • Intrinsic (d, q13)-degeneracy : (Burguet-Castell et al, 2001) (also: Barger, Marfatia, Whisnant, 2001) • sgn(Dm213)-degeneracy : (Minakata, Nunokawa, 2001) • (q23, p/2-q23)-degeneracy : (Fogli, Lisi, 1996)

  9. Intrinsic (d, q13)-degeneracy The parameters (d, q13) can give the same probabilities as another pair of parameters (d*, q*13) for fixed values of the other parameters Ambiguity reduces to (d, p-d)

  10. sgn(Dm213)-degeneracy There are also parameters(d*, q*13)with that give the same probabilities (P & P)with Dm213 <0 Dm213 >0

  11. (q23, p/2-q23)-degeneracy It is sin2 2 q23determined by nm survival measurement, So q23 can not distinguished from p/2-q23 Yasuda 03

  12. Altogether 8-fold degeneracy

  13. Breaking of degeneracies • several possibilities to resolve the degeneracies are known: • combining information from detectors at different • baselines • using additional oscillation chanels (ne nt ) • spectral information (wideband beam) • adding information on q13 from a reactor experiment • adding information from atmospheric neutrino • experiments

  14. Breaking neutrino parameter degeneracy at T2KK

  15. There are two merits of measuring T2K beam in Korea(Hagiwara et al.) (a) The contribution from become large. It is useful to determine the sign of (b) The correlation between CP phase and q13 in Korea is different from SK.

  16. T2KK solves 8-fold degeneracy (Kajita et al., 06)

  17. Impact of astrophysical neutrinos

  18. Detection of astrophysical neutrinos telescope • Icecube O(km) long muon tracks

  19. IceCube will distinguish nm,ne, ntbased on the event • characteristics: • nm → m produce long muon tracks Good angular resolution, but limited energy resolution • ne → eproduce EM showers Good energy resolution, poor angular momentum • nt → t → ntproduce double-bang’ events at high energy. One shower when t is produced, another when it decays: n spectra in AGN range ( 1013 - 1016 eV)

  20. p, p, L=10 L=10 - - 30 30 He ... He ... km km p p ± ± ± ± , K , K ± ± e e n n n n n n m m m m e e L=up to 13000 L=up to 13000 km km pmnm enmne Flavor composition of astrophysical neutrino sources • Flavor ratio: ( Fe : Fm : Ft ) • Neutron beam source:(1:0:0) ~ TeV. HE proton be converted to a HE neutron (p + g → n + p+). Neutrinos are produced from the neutron decays. (1:0.4:0.4) at telescope • Pion beam source:(1:2:0) ~ PeV (p+ → … → e+ + nm+ ne+ nm). • The four leptons share equally the energy of • the pion.(1:1:1) at telescope • Muon damped source:(0:1:0) from pion decays with muon absorption. dN/dE ~E-2, eg., from GRB, ~ GeV

  21. Oscillating probabilityover a very long travel: P( a →b, x) = ∑|Uam|2|Ubm|2 +m  m’∑ Re(UamUam’Ubm’Ubm) cos(Dm2 x/2p) +m  m’∑ Im(UamUam’Ubm’Ubm) sin(Dm2 x/2p) = dab- 2 m<m’∑ Re(UamUam’Ubm’Ubm) • The predicted flavor composition at the earth depends on the mixing parameters including CP phase and CP-even part of the mixng only. • No dependence onDm2 • Use R ≡Fm/(Fe+Ft)for astrophysical sources Averaged out !

  22. Rneutron beam= Pem/ (Pee+Pet) ~ 0.26 + 0.30 q13 cos dCP, (to the first order in q13 ) • R muon damped = Pmm / (Pme+Pmt) ~ 0.66 - 0.52 q13 cos dCP W. Winter, 2006

  23. R pion beam = (2Pmm +Pem) / (2Pme+Pee+2Pmt+Pet) ~ 0.50 - 0.14 q13 cos dCP • Pme~ 2q132 ± 0.09 q13 sin dCP :terr. neutrino beam

  24. Can we obtain useful information on oscilaltion parameters from measuring R ? Very difficult due to low statistics and no spectral information But, complementary to the one of Reactor exp. and neutrino beams. (Winter,06) Best-fit

  25. Combining reactor experiment with astrophysical neutrios Assume that reactor exp. (double chooz) measures Sin22q13 and astrophys. source is able to provide the information on a similar time scale as the reactor exp. (Winter,06)

  26. Impact on mass hierarchy • Astrophysical source may help mass hierarchy measurement at superbeam: 20% prec. good thanks to the fact that mass hierarchy sensitivity is affected by the correlations withdcp and sin22q13

  27. Impact on (q23, p/2-q23)-degeneracy Astrophysical source may help to resolve it

  28. Summary • T2K is next generation neutrino LBL experiment and will measureq13through appearance nm nechannel • Measuringq13will suffer from parameter degeneracy (8-fold) • Astrophysical neutrinos with high energy are complementary to resolve degeneracy.

  29. Appearance channels: nmne (Cervera et al. 2000; Freund, Huber, Lindner, 2000; Freund, 2001) • Complicated, but all interesting information there: q13, dCP, mass hierarchy (via A)

  30. Astrophysical sources • Astrophysical neutrino sources producecertain flavor ratios of neutrinos (ne:nm:nt):Neutron decays: (1:0:0)Muon damped sources: (0:1:0)Pion decays: (1:2:0) • These ratios are changed through averaged neutrino oscillations:Only CP-conserving effects remaining ~ cos dCP • Measure muon track to shower ratio at neutrino telescope: R = fm/(fe+ft)(conservative, since in future also flavors!?)

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