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

Optimization for disappearance searches at the VLENF (Very Low Energy Neutrino Factory). IDS-NF plenary meeting April 18-20, 2012 Univ. of Glasgow, UK Walter Winter Universität Würzburg. TexPoint fonts used in EMF: A A A A A A A A. Contents. Motivation, phenomenology Concept

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

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  1. Optimization for disappearance searches at the VLENF (Very Low Energy Neutrino Factory) IDS-NF plenary meeting April 18-20, 2012 Univ. of Glasgow, UKWalter Winter Universität Würzburg TexPoint fonts used in EMF: AAAAAAAA

  2. Contents • Motivation, phenomenology • Concept • Geometry and systematics implementation • Two-baseline optimization • ne disappearance • nm disappearance • Summary

  3. 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 Dm2 ~ 1 eV2 • To be tested in different channels; electron neutrino/antineutrino disappearance one of the key channels!

  4. Phenomenology • Typically used by experiments: two-flavor picture: • But what does that mean?

  5. Example: 3+1 framework • Oscillation probabilities: • Well known tension between appearance and disapp. data (appearance  disapp. in both channels) • ne and nm disappearance described by different parameters • Since disappearance data ~ |Ua4|2, app. ~ |Ua4|4,disappearance (in principle) more sensitive!

  6. VLENF: Concept/geometry • Em ~ 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) Em=2 GeV

  7. Geometry implementation • Near detector will experience geometry effects of beam divergence and extension of straight (assume that divergence muon decay kinematics limited) GLoBESbuilt-in(point source) Effectof beamgeometry Effectof straight (Tang, Winter, 2009;Giunti, Laveder, Winter, 2009)

  8. 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) ne, or 5% sqrt(E) nm

  9. 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 Dm2 >> 10 eV2  Cannot derive an effective systematical error from near detector, need combined fit!

  10. Impact of geometry • d=20 + 500 m • Large Dm2 > 30 eV2 sensitivity destroyed by extension of straight and detector Em=2 GeV,1019 useful muon decays;ne disapp. ND FD (WW, arXiv:1204.2671)

  11. Impact of systematics • Shape error (cross sec. x efficiency) limits large Dm2 > 10 eV2 sensitivity • “Low systematics“: Shape 2%Fid. volume 0.1%, BG 10%Calib 0.1% Systematics limit  10% error (WW, arXiv:1204.2671)

  12. Two-baseline optimization Em=2 GeV,1019 useful muon decays • Optimization depends on Dm2, somewhat on Em • Use setup A in the following (good compromise) (WW, arXiv:1204.2671)

  13. ne disappearance • Need either Em=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)

  14. nm disappearance • Goes beyond SciBooNE + MiniBooNE by about an order of magnitude • Slightly better than ne disappearance (beam spectrum!) • Setup A again good compromise Em=2 GeV,1019 useful muon decays (WW, arXiv:1204.2671)

  15. Different polarities (WW, arXiv:1204.2671)

  16. Summary and conclusions • VLENF requirements for disappearance: • 1019 useful muon decays/polarity or Em=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 ne and nm disappearance, in both polarities • VLENF can cover ne disappearance best-fit • VLENF outperforms basically any alternative setup( Sterile neutrino white paper) • Open issues: • Systematics limit for large Dm2? • Perhaps even shorter decay straight possible?

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