Physics with a very long neutrino factory baseline

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Physics with a very long neutrino factory baseline

• IDS Meeting
• CERN
• March 30, 2007Walter Winter
• Universität Würzburg

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Contents
(mainly based onGandhi, 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

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Appearance channels nm ne
Expansion in small sin 2q13 and a
(Cervera et al. 2000 Freund, Huber, Lindner,
2000 Akhmedov et al, 2004)

• Information q13, dCP, mass hierarchy (via A)

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Idea of the Magic baseline

• IdeaYellow 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 L3 000 km

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Magic baseline Quantified

• Use two-baseline space (L1,L2) with (25kt, 25kt)
  and compute q13 reach including correlations and
  degeneracies

Animation in q13-dCP-space
(3s red measure for risk in this case Dm212)
dCP
sin22q13
(Huber, Winter, 2003)
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Open questions

• 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?

Matter density uncertainties in 3D models
5 (http//cfauvcs5.harvard.edu/lana/rem/mapvi
ew.htm)
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A more realistic density profile model

• PREM profile approximated by 7 profile steps
  between L6000 km and 9000 km Profile7
• Efficient for computation
• More realistic for model
• Dashed Often used baseline-averaged density

(Gandhi, Winter, 2006)
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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)
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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)
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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

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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)

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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)

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Consequences for detector locations

• Mass hier. L 6000 - 9000 km good for sin22q13
  gt 10-4
• Choose, e.g., L 7000 9000 km

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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

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Further applications of avery long neutrino
factory baseline
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Matter density measurement

• 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)

Lower mantle density
(Winter, 2005 Minakata, Uchinami, 2006
Gandhi, Winter, 2006)
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Matter density Geophysical use?

• ExamplePlume hypothesis
• A precisionmeasurement ltlt 1could
  discriminatedifferent geophysicalmodels
• Possible selectorof detectorlocations?

(Courtillot et al., 2003 see talk from B.
Romanowicz, Neutrino geophysics 2005)
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Results for one-parameter measurement

• Assume that only one parameter measured
• For large q13, lt 1 precision at 3s
• Indep. confirmed byMinakata, Uchinami(for one
  baseline)

(Gandhi, Winter, 2006)
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A more sophisticated model

• Assume that upper mantle density (rUM)only known
  with certain precision

(Gandhi, Winter, 2006)
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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)
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q13 precision measurement

• Example sin22q13 0.001

(Gandhi, Winter, 2006)

• Bands dependence on d (worst case, median, best
  case)

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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

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MSW effect sensitivity for q130

• Null result if solar effectsneglected
• But solar termNote thati.e., effect
  increases with baseline!

5s
(Freund et al, 1999)
(Winter, 2004)
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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
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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)