1. 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: AAAAA A A A

2. 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. 3 Motivation: eV 2 sterile s  LSND/MiniBooNE antineutrinos  Reactor anomaly  Global fits (arXiv:1007.1150) (B. Fleming, TAUP 2011) (Kopp, Maltoni, Schwetz, 1103.4570)

4. 4 Arbitrary sterile s  Cosmology: upper bound O(1 eV)  However: sterile neutrinos even preferred, if light enough  Cannot exclude that light sterile neutrinos “hide“ among the actives (Hamann et al, Phys.Rev.Lett. 105 (2010) 181301) m1m1 m2m2 m3m3 m 4 ?

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

6. 6 Oscillation physics  Can be described independent of parameterization (with mixing matrix only)  Probabilities for short baseline limit: Observation: Appearance probabilities depend on two mixing matrix entries, disappearance probabilities on one

7. 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. 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. 9 Performance indicators  Discuss constraints for individual parameters (sensitivity limits for  14,  24,  34 )  Requires marginalization over unknown other parameters  Renders appearance channels useless: always sensitive to a combination of mixing matrix elements/parameters  Main sensitivities:   14 : P ee (difficult at NuFact)   24 : P  (leading at NuFact)   34 : P  (currently impossible)

10. Sterile at far detectors

11. 11 Oscillation physics  Peculiarity: NC matter effect (affects only active states)  Probabilities to 2 nd order:  14 difficult at long baseline,  24 easiest,  34 by P  (discovery channel)? [but: high enough statistics compared to h.o.t. in other channels?] (Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

12. 12 Hierarchy dependence  Characterized rel. to mass eigenstate 1:  Case |  m 41 2 | ~ |  m 31 2 |:  A+D: m 3 and m 4 on top of each other  B+C: m 3 and m 4 different (  m 41 2 = -  m 31 2 )  Easier to identify because of matter effects?

13. Simulation and general constraints

14. 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 need additional 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. 15 Generalized exclusion limits … without any constraints on  m 41 2 (Meloni, Tang, Winter, arXiv:1007.2419) From e disppearance From  disppearance From LBL-  disppearance (higher order effect) 90% CL, 2 d.o.f.

16. 16 Hierarchy dependence  A+D: Sensitivity at |  m 41 2 | ~ |  m 31 2 | destroyed (correlations) (Meloni, Tang, Winter, arXiv:1007.2419)

17. Dependence on assumptions

18. 18 What special assumptions often made?  LSND-motivated  m 41 2  Fast oscillation averaged out at long L  Special case  m 41 2  0 (MINOS, Adamson et al, arXiv:1003.0336)  Also no additional  m 41 2  See Meloni, Tang, Winter, arXiv:1007.2419  Two-flavor limits, e.g. (corresponds to same formula in our parameterization with  m 2 =  m 41 2,  =  14 )

19. 19  24 -  34 for LSND assump.  Now if fast oscillations average out, two- parameter combinations can be tested: (otherwise  m 41 2 -marginalization would lead to vanishing sensitivity)   detection at long baseline (P  ) adds only little if magic baseline included (higher statistics in P   ) (Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)

20. 20 Near detectors added  Impact of ND depends on assumptions:   m 41 2 very large: Oscillations in ND averaged out   m 41 2 ~ 1 eV 2 : ND sensitive to spectral signature (Meloni, Tang, Winter, arXiv:1007.2419) Curve from last slide

21. 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  13  Is 3+N a physics case for the Neutrino Factory, even if  13 large? (Meloni, Tang, Winter, arXiv:1007.2419; compared to MINOS, Adamson et al, arXiv:1003.0336)

22. 22 Summary and conclusions  Sterile neutrinos may have  m 41 2 ~ 1 eV 2, 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  m 41 2 ~ 10 -4 – 10 -1 eV 2  Precision physics case even for large  13 ?  So far, no physics case for  found; perhaps additional phases for steriles?