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Phenomenology of Sterile Neutrinos

Phenomenology of Sterile Neutrinos. YuFeng Li IHEP, Beijing 2012. 09. 16 2012 Shanghai Particle Physics and Cosmology Symposium. Three-Neutrino Mixing Paradigm. Still unknown parameters in ν physics: Neutrino Mass Hierarchy Lepton CP Violation Neutrino mass scale …….

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Phenomenology of Sterile Neutrinos

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  1. Phenomenology of Sterile Neutrinos YuFeng Li IHEP, Beijing 2012. 09. 16 2012 Shanghai Particle Physics and Cosmology Symposium

  2. Three-Neutrino Mixing Paradigm • Still unknown parameters in ν physics: • Neutrino Mass Hierarchy • Lepton CP Violation • Neutrino mass scale • …… G. L. Fogli et. al. arXiv:1205.5254v3

  3. Sterile neutrinos: Motivation (1) Oscillation mode with an anomalous (larger) mass-squared difference needs the fourth ν state (or more). (2) Z-boson width measurement only allows 3 light νs. (3) Sterile neutrinos  No standard model weak interaction. (4) Active neutrinos (νe , νμ,ντ) can oscillate into sterile neutrinos (νs). -- Disappearance of active neutrinos (NC deficit) -- Short base-line oscillations

  4. Sterile Neutrinos: Beyond SM Sterile νs exist in seesaw extensions of SM with RH νs. Being singlet under SM groups The mass scale is arbitrary. Sterile Neutrinos TeV Δm2~10-6 eV2 KeV GeV 1014 GeV eV Traditional seesaw Baryo-genesis via ν oscillation Testability in LHC Quasi-Dirac, Low-E solar νs Candidate for warm DM Anomalies in SBL ν oscillation • We will consider sterile νs with mass scale ∼ 1 eV in light of LSND, MiniBooNE, Reactor Anomaly, Gallium Anomaly.

  5. The 3+1 Scheme In the minimal case of one sterile ν, the 2+2 scheme is ruled out by the solar and atmospheric data. The 3+1 scheme: Perturbation of 3 ν mixingwith tiny A-S mixing

  6. SBL Oscillation in 3+1 Scheme • Only the interference terms of two comparable oscillation modes can have CP Violation. •  the 3+2 Scheme?

  7. SBL Oscillation in 3+2 Scheme

  8. SBL Anomalies

  9. LSND: the first anomaly The Motivation for the MiniBooNE Experiment

  10. MiniBooNE: the ν case νμ  νe channel with L~541m and 200MeV ≤ E ≤ 3GeV No νμ  νe signal excess corresponding to LSND νμ-bar νe-bar signal (E > 475MeV) Low-energy anomaly

  11. MiniBooNE: the ν-bar case (2010) 5.7e20 POT: agreement with LSND signal Similar L/E but different L and E  oscillations Discrepancy with the ν case Need CP Violation(3+2)?

  12. MiniBooNE: the ν-bar case (2012) Talk in Neutrino 2012 Higher stat ν-bar data is more consistent with the ν case (2009). Agreement with LSND signal is vanishing New MiniBooNE data arXiv:1207.4809

  13. MiniBooNE: low energy excess Fit of low-energy excess is marginal Non-oscillation physics ?

  14. ICARUS [arXiv:1209.0122]

  15. Reactor Electron ν-bar Anomaly New reactor νe-bar flux calculation: 6% deficit for SBL disappearance probability [Mueller et al, PRC 83 (2011) 054615; Huber, PRC 84 (2011) 024617; White Paper, arXiv:1204.5379]

  16. Gallium Anomaly: Gallium Radioactive Source Experiments Tests of the solar neutrino detectors GALLEX (Cr1, Cr2) and SAGE (Cr, Ar) Bahcall cross section

  17. Constraints

  18. νe and νe-bar Disappearance

  19. Fit of solar and KamLAND data Including all the solar and KamLAND data Obtained w/o Daya-Bay and RENO constraints of th13 With full parameter space scan (free th24 and th34)

  20. νμ and νμ -bar Disappearance

  21. The 3+1 Status With 2012 MiniBooNE data Missing the new ICARUS Constraint (see later) 3+1 status: Appearance-Disappearance tension. Tension remains in 3+2 [Giunti, Laveder, PRD 84 (2011) 073008] Tension reduced in 3+1+NSI [Akhmedov, Schwetz, JHEP 10 (2010) 115] No tension in 3+1+CPTV [Barger, Marfatia, Whisnant, PLB 576 (2003) 303] [Giunti, Laveder, PRD 82 (2010) 093016, PRD 83 (2011) 053006]

  22. Comments on the 3+2 Scheme 3+2 is preferred to 3+1 only if there is CP-violating difference of νμνe and νμ-barνe-bar transitions 2010 MiniBooNE antineutrino data indicated neutrino-antineutrino difference In 2010 it was reasonable and useful to consider 3+2 Neutrino-antineutrino difference almost disappeared with 2012 MiniBooNE antineutrino data

  23. 3+1 Global Fit without ICARUS

  24. 3+1 Global Fit with ICARUS

  25. Testable Implications

  26. Cosmology Ns = number of thermalized sterile neutrinos

  27. Conclusions SBL oscillation anomalies need sterile neutrinos. SBL νμ-barνe-bar Signal is not feeling well: (1) MB 2010 antineutrino data supports LSND and is different from neutrino data. (2) MB 2012 antineutrino data are more similar to neutrino data. (3) Probably there is no CP violation and no need of 3+2. (4) Agreement of MB-LSND is decreasing. SBL νe and νe-bar Disappearance is in good health: (5) Reactor νe-bar and Gallium νe anomalies are exciting. (6) Many promising projects to test SBL νe (νe-bar) disappearance with reactors and radioactive sources. (7) Independent tests through m4 effect in β-decay and ββ0ν-decay.

  28. Thank you!

  29. Overestimate the cross section?

  30. 3+2 Global Fit (2011)

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