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Sterile neutrinos at the Neutrino Factory

Sterile neutrinos at the Neutrino Factory. IDS-NF plenary meeting October 19-21, 2011 Arlington, VA, USA Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Motivation Steriles at near detectors Steriles at far detectors

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Sterile neutrinos at the Neutrino Factory

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  1. Sterile neutrinos at the Neutrino Factory IDS-NF plenary meeting October 19-21, 2011 Arlington, VA, USAWalter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  2. Contents • Motivation • Steriles at near detectors • Steriles at far detectors • Simulation and general constraints • Dependence on assumptions • Summary (mostly based on: Meloni, Tang, Winter, Phys.Rev. D82 (2010) 093008, arXiv:1007.2419)

  3. Motivation: eV2 sterile ns • LSND/MiniBooNE antineutrinos • Reactor anomaly • Global fits (arXiv:1007.1150) (B. Fleming, TAUP 2011) (Kopp, Maltoni, Schwetz, 1103.4570)

  4. Arbitrary sterile ns • Cosmology: upper bound O(1 eV) • However: sterile neutrinos even preferred, if light enough • Cannot excludethat light sterileneutrinos “hide“among the actives m3 m4 ? m2 m1 (Hamann et al, Phys.Rev.Lett. 105 (2010) 181301)

  5. Steriles at near detectors … focus on 3+1 framework in the following (for the sake of simplicity)

  6. Oscillation physics • Can be described independent of parameterization (with mixing matrix only) • Probabilities for short baseline limit: Observation:Appearance probabilitiesdepend on two mixing matrixentries, disappearanceprobabilities on one

  7. Choice of parameterization • Why do I need a parameterization? • Less parameters (unitarity assumed!) • Convenient if long-baseline included (matter effects) • Requirements for a parameterization: • Our parameterization: (Meloni, Tang, Winter, arXiv:1007.2419)

  8. Oscillation physics (2) • Parameterization dependent probabilities in short baseline limit: • For small mixing angles: qualitatively similar to param.-independent approach (Meloni, Tang, Winter, arXiv:1007.2419)

  9. Performance indicators • Discuss constraints for individual parameters (sensitivity limits for q14, q24, q34) • Requires marginalization over unknown other parameters • Renders appearance channels useless: always sensitive to a combination of mixing matrix elements/parameters • Main sensitivities: • q14: Pee (difficult at NuFact) • q24: Pmm (leading at NuFact) • q34: Ptt (currently impossible)

  10. Sterile at far detectors

  11. Oscillation physics • Peculiarity: NC matter effect (affects only active states) • Probabilities to 2nd order: q14 difficult at long baseline,q24 easiest, q34 by Pmt (discovery channel)?[but: high enough statisticscompared to h.o.t. in other channels?] (Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

  12. Hierarchy dependence • Characterized rel. to mass eigenstate 1: • Case |Dm412| ~ |Dm312|: • A+D: m3 and m4 on top of each other • B+C: m3 and m4 different (Dm412 = - Dm312) • Easier to identify because of matter effects?

  13. Simulation and general constraints

  14. Assumptions • IDS-NF baseline 1.0 (50 kt + 50 kt) • Near detectors: • At d=2 km with 32 t each (far detector limit) • Electron CID with 40% efficiency, 1% mis-ID • NB: May in fact needadditional near-near detectors to control systematics in disapp-earance channels  See my other talk(+ Giunti, Laveder, Winter, arXiv:0907.5487) • Also tested seperately: OPERA-inspired MECC at same distance, hadronic channels, 10 kt

  15. Generalized exclusion limits … without any constraints on Dm412 90% CL, 2 d.o.f. From nedisppearance From nmdisppearance From LBL-nmdisppearance(higher order effect) (Meloni, Tang, Winter, arXiv:1007.2419)

  16. Hierarchy dependence • A+D: Sensitivity at |Dm412| ~ |Dm312| destroyed (correlations) (Meloni, Tang, Winter, arXiv:1007.2419)

  17. Dependence on assumptions

  18. What special assumptions often made? • LSND-motivated Dm412 • Fast oscillation averaged out at long L • Special case Dm412 0 (MINOS, Adamson et al, arXiv:1003.0336) • Also no additional Dm412 • See Meloni, Tang, Winter, arXiv:1007.2419 • Two-flavor limits, e.g.(corresponds to same formula in our parameterization with Dm2 = Dm412 , q = q14)

  19. q24-q34 for LSND assump. • Now if fast oscillations average out, two-parameter combinations can be tested:(otherwise Dm412-marginalization would lead to vanishing sensitivity) • nt detection at longbaseline (Pmt) addsonly little if magicbaseline included(higher statistics in Pmm!) (Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

  20. Near detectors added • Impact of ND depends on assumptions: • Dm412 very large:Oscillations in ND averaged out • Dm412 ~ 1 eV2:ND sensitive to spectral signature Curvefrom lastslide (Meloni, Tang, Winter, arXiv:1007.2419)

  21. Comparison to MINOS • Also experimental collaborations use special assumptions, e.g. additional parameters fixed • Comparison to MINOS: Tremendous increase of sensitivity, especially for large q13 • Is 3+N a physics case for the Neutrino Factory, even if q13 large? (Meloni, Tang, Winter, arXiv:1007.2419; compared to MINOS, Adamson et al, arXiv:1003.0336)

  22. Summary and conclusions • Sterile neutrinos may have Dm412 ~ 1 eV2, but could also hide among the actives • Technically challenging, therefore hardly tested? • Neutrino factory can access some of the sterile parameters very well, even at the longer baselines Dm412 ~ 10-4 – 10-1 eV2 • Precision physics case even for large q13? • So far, no physics case for nt found;perhaps additional phases for steriles?

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