Sterile neutrinos at the Neutrino Factory
IDS-NF plenary meetingOctober 19-21, 2011Arlington, VA, USA
Walter WinterUniversität Würzburg
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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)
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Motivation: eV2 sterile s
LSND/MiniBooNE antineutrinos Reactor anomaly
Global fits(a
rXiv
:100
7.11
50)
(B. F
lemin
g, TA
UP
2011)
(Kopp, Maltoni, Schwetz, 1103.4570)
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Arbitrary sterile s
Cosmology: upper bound O(1 eV) However: sterile neutrinos even preferred,
if light enough Cannot exclude
that light sterileneutrinos “hide“among the actives
(Hamann et al, Phys.Rev.Lett. 105 (2010) 181301)m1
m2
m3
m4 ?
Steriles at near detectors
… focus on 3+1 framework in the following (for the sake of simplicity)
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Oscillation physics
Can be described independent of parameterization (with mixing matrix only)
Probabilities for short baseline limit:
Observation:Appearance probabilities
depend on two mixing matrixentries, disappearance
probabilities on one
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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, T
ang, W
inter, arXiv:1007.2419)
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Oscillation physics (2)
Parameterization dependent probabilities in short baseline limit:
For small mixing angles: qualitatively similar to param.-independent approach
(Melon
i, Tan
g, Win
ter, arXiv:1007.2419)
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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: Pee (difficult at NuFact)
24: P (leading at NuFact)
34: P (currently impossible)
Sterile at far detectors
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Oscillation physics
Peculiarity: NC matter effect (affects only active states)
Probabilities to 2nd 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)
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Hierarchy dependence
Characterized rel. to mass eigenstate 1:
Case |m412| ~ |m31
2|: A+D: m3 and m4 on top of each other B+C: m3 and m4 different (m41
2 = - m312)
Easier to identify because of matter effects?
Simulation and general constraints
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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
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Generalized exclusion limits
… without any constraints on m412
(Meloni, Tang, Winter, arXiv:1007.2419)
From e
disppearanceFrom
disppearanceFrom LBL-
disppearance(higher order effect)
90% CL, 2 d.o.f.
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Hierarchy dependence
A+D: Sensitivity at |m41
2| ~ |m312|
destroyed (correlations)
(Meloni, Tang, Winter, arXiv:1007.2419)
Dependence on assumptions
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What special assumptions often made?
LSND-motivated m412
Fast oscillation averaged out at long L Special case m41
2 0 (MINOS, Adamson et al, arXiv:1003.0336)
Also no additional m412
See Meloni, Tang, Winter, arXiv:1007.2419
Two-flavor limits, e.g.
(corresponds to same formula in our parameterization with m2 = m41
2 , = 14)
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24-34 for LSND assump.
Now if fast oscillations average out, two-parameter combinations can be tested:(otherwise m41
2-marginalization would lead to vanishing sensitivity)
detection at longbaseline (P) addsonly little if magicbaseline included(higher statistics in P)
(Meloni, Tang, Winter, arXiv:1007.2419; Discovery channel: Donini et al., arXiv:0812.3703)
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Near detectors added
Impact of ND depends on assumptions: m41
2 very large:Oscillations in ND averaged out
m412 ~ 1 eV2:
ND sensitive to spectral signature
(Meloni, Tang, Winter, arXiv:1007.2419)
Curvefrom last
slide
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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)
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Summary and conclusions
Sterile neutrinos may have m412 ~ 1 eV2, but
could also hide among the activesTechnically challenging, therefore hardly
tested?
Neutrino factory can access some of the sterile parameters very well, even at the longer baselines m41
2 ~ 10-4 – 10-1 eV2
Precision physics case even for large 13?
So far, no physics case for found;perhaps additional phases for steriles?