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Physics with a very long neutrino factory baseline

Physics with a very long neutrino factory baseline. IDS Meeting CERN March 30, 2007 Walter Winter Universität Würzburg. Contents. (mainly based on: Gandhi, Winter: “Physics with a very long neutrino factory baseline”, Phys. Rev. D75 (2007) 053002, hep-ph/0612158 ).

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Physics with a very long neutrino factory baseline

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  1. Physics with a very long neutrino factory baseline IDS Meeting CERN March 30, 2007Walter Winter Universität Würzburg

  2. Contents (mainly based on:Gandhi, Winter: “Physics with a very long neutrino factory baseline”, Phys. Rev. D75 (2007) 053002, hep-ph/0612158) • Introduction: Magic baseline • Open questions • A more realistic density model • Answers: e.g.: which detector locations? • More physics applications: • Matter density measurement • q13 precision measurement • Octant degeneracy • MSW effect sensitivity • Physics case for a very long baseline IDS CERN - Walter Winter

  3. Appearance channels: nmne Expansion in small sin 2q13 and a: • Information: q13, dCP, mass hierarchy (via A) (Cervera et al. 2000; Freund, Huber, Lindner, 2000; Akhmedov et al, 2004) IDS CERN - Walter Winter

  4. Idea of the “Magic baseline” • Idea:Yellow term = 0 independent of E, oscillation parameters • Purpose: “Clean” measurement of q13 and mass hierarchy • No dependence on E, osc. parameters • Drawback: No dCP measurement at magic baseline • combine with shorter baseline, such as L=3 000 km IDS CERN - Walter Winter

  5. Magic baseline: Quantified Use two-baseline space (L1,L2) with (25kt, 25kt) and compute q13 reach including correlations and degeneracies: (3s; red: measure for risk – in this case Dm212) Animation in q13-dCP-space: dCP sin22q13 (Huber, Winter, 2003) IDS CERN - Walter Winter

  6. Open questions Matter density uncertainties in 3D models ~ 5% (http://cfauvcs5.harvard.edu/lana/rem/mapview.htm) • Which density forcondition ?Not exactly known from geophysics! • Is the constant density approximation sufficient? • Is the expansion in a and q13 accurate enough? • What happens if my preferred detector location is not exactly on the “magic baseline”? • Is there a preferred detector site from geophysics? IDS CERN - Walter Winter

  7. A more realistic density profile model • PREM profile approximated by 7 profile steps between L~6000 km and 9000 km „Profile7“ • Efficient for computation • More realistic for model • Dashed: Often used baseline-averaged density (Gandhi, Winter, 2006) IDS CERN - Walter Winter

  8. Constant reference density rRef • Idea: Find constant dens. which best matches Profile7: rRef • Method: Minimize total Dc2 from all channels between Profile7 and rRef (simulate Profile7 and fit rRef for same osc. Params) • Least contribution of profile effect to statistical analysis (Gandhi, Winter, 2006) IDS CERN - Walter Winter

  9. Constant reference density • rRef = Mean density?Answer: ~ 5% offReason: long constant density layer dominates • Parameter dependence (q13, d) strongest for small q13, but there c2 function shallow(last slide) (see e.g. Akhmedov, 2000) (Gandhi, Winter, 2006) IDS CERN - Walter Winter

  10. How we address the main questions • What if the detector location is off the MB? • Show sensitivity as a function of baseline • Unknown matter density (geophysics):What if rRef wrong by ~5%? • Show results for 0.95 rRef and 1.05 rRef • Profile effects: How well does a constant density simulate the matter density profile?Is the actual sensitivity better or worse? • Show results for Profile7 and rRef IDS CERN - Walter Winter

  11. q13 sensitivity (Gandhi, Winter, 2006) • Strong impact for one baseline only • Exact detector location not so important for combination with shorter baseline (L ~ 7000 – 9000 km) IDS CERN - Walter Winter

  12. CP violation measurement (Gandhi, Winter, 2006) • Very long baseline clearly helps • Optimal L ~ 7700 km +- 500 km • Very long baseline helps for L ~ 7000 km to 9000 km, but small absolute impact • Profile effect enhances perform. • No clear preference of a very long baseline (poor statistics dominated) IDS CERN - Walter Winter

  13. Consequences for detector locations • Mass hier.: L ~ 6000 - 9000 km good for sin22q13 > 10-4 • Choose, e.g., L ~ 7000 – 9000 km: IDS CERN - Walter Winter

  14. Some answers • Magic baseline is a very accurate description for one baseline only • Very long baselines between ~ 7000 km and 9000 km OK if second detector at shorter L • In this case, little impact from profile effects and poor geophysics information • Mean density is not a good choice for a constant reference density • Use rRef further on, which reproduces profile very well • Profile effects improve absolute sensitivity somewhat compared to constant density IDS CERN - Walter Winter

  15. Further applications of avery long neutrino factory baseline

  16. Matter density measurement Lower mantle density • Idea: Treat r as yet another oscillation parameter to be measured; marginalize oscillation parameters! • Comes „for free“ from very long baseline!? • Two different models: • Measure rRef • Measure rLM(lower mantle density) (Winter, 2005; Minakata, Uchinami, 2006; Gandhi, Winter, 2006) IDS CERN - Walter Winter

  17. Matter density: Geophysical use? • Example:Plume hypothesis • A precisionmeasurement << 1%could discriminatedifferent geophysicalmodels • Possible selectorof detectorlocations? (Courtillot et al., 2003; see talk from B. Romanowicz, Neutrino geophysics 2005) IDS CERN - Walter Winter

  18. Results for one-parameter measurement • Assume that only one parameter measured • For large q13, < 1% precision at 3s • Indep. confirmed byMinakata, Uchinami(for one baseline) (Gandhi, Winter, 2006) IDS CERN - Walter Winter

  19. A more sophisticated model • Assume that upper mantle density (rUM)only known with certain precision: (Gandhi, Winter, 2006) IDS CERN - Walter Winter

  20. Reduction of matter density uncertainty (dashed: 2%, solid: 5% matter density uncertainty) • Use of very long baseline reduces the impact of matter density uncertainties as well • No need for extra geophysics effort if two baselines used (Huber, Lindner, Rolinec, Winter, 2006) IDS CERN - Walter Winter

  21. q13 precision measurement • Example: sin22q13 = 0.001: (Gandhi, Winter, 2006) • Bands: dependence on d (worst case, median, best case) IDS CERN - Walter Winter

  22. Resolving the q23 degeneracy (Gandhi, Winter, 2006) • 4000 km alone: Problems with degs for intermediate q13 • 7200 km alone: No sensitivity for small q13 • 4000 km + 7200 km: Good for all q13 IDS CERN - Walter Winter

  23. MSW effect sensitivity for q13=0 • Null result if solar effectsneglected: • But solar term:Note thati.e., effect increases with baseline! 5s (Freund et al, 1999) (Winter, 2004) IDS CERN - Walter Winter

  24. Physics case for a very long NF baseline 10-1 sin22q13 • Reduced impact of matter density uncertainty • Better CP violation performance • Precise matter density measurement • Helps for the q23 measurement • Helps for octant degeneracy resolution • Improves q13 precision measurement „Large“ 10-2 • Guaranteed mass hierarchy sensitivity • Correlation and degeneracy resolution • Improved precision measurement of dCP • Information on the matter density „Medium“ (see: Gandhi, Winter, 2006) 10-3 • Maximized q13 and mass hier. sens. reach • Correlation and degeneracy resolution • Improved precision measurement of dCP „Small“ 10-4 • MSW effect sensitivity • Potentially future mass hier. sensitivity „Zero“ IDS CERN - Walter Winter

  25. Summary • Magic baseline description holds for all practical applications, but use rRef instead of mean density • Two baseline setup rather insensitive to very long baseline length (but: VL baseline clearly helps) • Geophysics spin-off may prefer specific detector locations; needs more investigation • Physics case for very long baseline no matter how big q13 is (if neutrino factory is built) IDS CERN - Walter Winter

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