Sterile neutrinos at the Neutrino Factory IDS-NF plenary meeting October 19-21, 2011 Arlington, VA, USA Walter Winter Universitt Wrzburg TexPoint fonts used in EMF: AAAAA A A A 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) , arXiv: ) 3 Motivation: eV 2 sterile s LSND/MiniBooNE antineutrinos Reactor anomaly Global fits (arXiv: ) (B. Fleming, TAUP 2011) (Kopp, Maltoni, Schwetz, ) 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) ) m1m1 m2m2 m3m3 m 4 ? 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 probabilities depend on two mixing matrix entries, disappearance probabilities 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: ) 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: ) 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) Sterile at far detectors 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: ; Discovery channel: Donini et al., arXiv: ) 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? 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 need additional near-near detectors to control systematics in disapp- earance channels See my other talk (+ Giunti, Laveder, Winter, arXiv: ) Also tested seperately: OPERA-inspired MECC at same distance, hadronic channels, 10 kt 15 Generalized exclusion limits without any constraints on m 41 2 (Meloni, Tang, Winter, arXiv: ) From e disppearance From disppearance From LBL- disppearance (higher order effect) 90% CL, 2 d.o.f. 16 Hierarchy dependence A+D: Sensitivity at | m 41 2 | ~ | m 31 2 | destroyed (correlations) (Meloni, Tang, Winter, arXiv: ) Dependence on assumptions 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: ) Also no additional m 41 2 See Meloni, Tang, Winter, arXiv: Two-flavor limits, e.g. (corresponds to same formula in our parameterization with m 2 = m 41 2, = 14 ) 19 24 - 34 for LSND assump. Now if fast oscillations average out, two- parameter combinations can be tested: (otherwise m 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: ; Discovery channel: Donini et al., arXiv: ) 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: ) Curve from last slide 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: ; compared to MINOS, Adamson et al, arXiv: ) 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 ~ eV 2 Precision physics case even for large 13 ? So far, no physics case for found; perhaps additional phases for steriles?