Optimization for disappearance searches at the VLENF (Very Low Energy Neutrino Factory)

IDS-NF plenary meetingApril 18-20, 2012Univ. of Glasgow, UK

Walter WinterUniversität Würzburg

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Contents

Motivation, phenomenology Concept Geometry and systematics implementation Two-baseline optimization e disappearance

disappearance

Summary

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Motivation: anomalies?

Gallium experiments:electron neutrino disappearance?(Acero, Giunti, Laveder, 2007)

Reactor fluxes, revisited:electron antineutrino disappearance?(Mention et al, 2011; Huber, 2011)

LSND/MiniBOONE:electron antineutrino appearance?(LSND, 2001; MiniBooNE, 2010)

Hints for sterile neutrinos with m2 ~ 1 eV2

To be tested in different channels; electron neutrino/antineutrino disappearance one of the key channels!

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Phenomenology

Typically used by experiments: two-flavor picture:

But what does that mean?

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Example: 3+1 framework Oscillation probabilities:

Well known tension between appearance and disapp. data (appearance disapp. in both channels)

e and disappearance described by different parameters

Since disappearance data ~ |U4|2, app. ~ |U4|4,disappearance (in principle) more sensitive!

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VLENF: Concept/geometry

E ~ 2 – 4 GeV, no muon acceleration VLENF concept (Tunnell, Cobb, Bross, 2011)

Lesson from reactor experiments:Identical near detector to measure flux x cross sections (Giunti, Laveder, Winter, 2009)

E=2 GeV

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Geometry implementation

Near detector will experience geometry effects of beam divergence and extension of straight (assume that divergence muon decay kinematics limited)

Effectof beam

geometry

Effectof straight

(Tang, Winter, 2009; Giunti, Laveder, Winter, 2009)

GLoBESbuilt-in

(point source)

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Systematics implementation

Cross section x efficiencies (shape error)Uncorrelated among bins, fully correlated between near and far detectors; 10%

Fiducial volume errorUncorrelated between detectors, fully correlated among bins; 0.6% (reactor exp.!)

Energy calibration error 0.5% Background uncertainties 35%

[NC backgrounds, mis-ID 10-4; charge mis-ID undefined in two flavor framework!]

Energy resolution 10% sqrt(E) e, or 5% sqrt(E)

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Difference app. – disapp.

Appearance:Background-limited (NC, charge mis-ID)

Disappearance:Limited by signal uncertainty (cross sections, efficiencies, fiducial volume)

Need to rely on a near detector!

Challenge: Oscillations in near detector for m2 >> 10 eV2

Cannot derive an effective systematical error from near detector, need combined fit!

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Impact of geometry

(WW, arXiv:1204.2671)

E=2 GeV,1019 useful

muon decays;e disapp.ND

FD

d=20 + 500 m Large

m2 > 30 eV2 sensitivity destroyed by extension of straight and detector

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Impact of systematics

Shape error (cross sec. x efficiency) limits large m2 > 10 eV2 sensitivity

“Low systematics“: Shape 2%Fid. volume 0.1%, BG 10%Calib 0.1%

Systematics limit 10% error

(WW, arXiv:1204.2671)

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Two-baseline optimization

Optimization depends on m2, somewhat on E Use setup A in the following (good compromise)

E=2 GeV,1019 useful

muon decays

(WW, arXiv:1204.2671)

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e disappearance

Need either E=4 GeV or 1019 useful muon decays/polarity to cover best-fit

Highly competitive compared to alternatives (Sterile neutrino white paper)

Can one improve on “systematics limit“?

(WW, arXiv:1204.2671)

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disappearance

Goes beyond SciBooNE + MiniBooNE by about an order of magnitude

Slightly better than e disappearance (beam spectrum!)

Setup A again good compromise

E=2 GeV,1019 useful

muon decays

(WW, arXiv:1204.2671)

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Different polarities

(WW, arXiv:1204.2671)

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Summary and conclusions VLENF requirements for disappearance:

1019 useful muon decays/polarity or E=4 GeV Far detector, distance ~ 500m – 800m (rather 500m);

consistent with appearance requirements (Tunnell, Cobb, Bross, 2011)

Near detector, identical, as close as possible to source With that: comparison to alternatives:

VLENF can do both e and disappearance, in both polarities VLENF can cover e disappearance best-fit VLENF outperforms basically any alternative setup

( Sterile neutrino white paper)

Open issues: Systematics limit for large m2? Perhaps even shorter decay straight possible?