1. Institute for Advanced Study, Princeton
Geographical issues and physics applications of “very long” neutrino factory baselines
NuFact 05
June 23, 2005
Walter Winter
Institute for Advanced Study, Princeton

2. NuFact 05 - VLBL - Walter Winter
Contents
Introduction
What are “very long” baselines?
Applications of very long baselines
Detector sites for very long baselines
Summary
June 23, 2005
NuFact 05 - VLBL - Walter Winter

3. Picture of three-flavor oscillations
Atmospheric oscillation: Amplitude: q23 Frequency: Dm312
Solar oscillation: Amplitude: q12 Frequency: Dm212
Sub-leading effect: dCP
Coupling strength: q13
Magnitude of q13 is key to
“subleading” effects:
Mass hierarchy determination
CP violation
nm ne flavor transitions on
atmospheric oscillation scale
June 23, 2005
NuFact 05 - VLBL - Walter Winter

4. Appearance channels: nm ne
(Cervera et al. 2000; Freund, Huber, Lindner, 2000; Freund, 2001)
All interesting information there: q13, dCP, mass hier.
Complicated: Problems with correlations and degs
June 23, 2005
NuFact 05 - VLBL - Walter Winter

5. NuFact 05 - VLBL - Walter Winter
Neutrino factory
(from: CERN Yellow Report )
Ultimative “high precision” instrument!?
Muon decays in straight sections of storage ring
Decay ring naturally spans two baselines
Technical challenges: Target power, muon cooling, maybe steep decay tunnels
Timescale: 2025?
June 23, 2005
NuFact 05 - VLBL - Walter Winter

6. “Very long” (VL) baselines
Typical baseline: 3,000 km for 50 GeV neutrino factory (to measure CP violation)
Define “very long”: L >> 3,000 km
Challenge: Decay tunnel slopes!
Our benchmark neutrino factory: NuFact-II
Em = 50 GeV, L = 3,000 km (standard configuration)
Running time: 4 years in each polarity = 8 years
Detector: 50 kt magnetized iron calorimeter
1021 useful muon decays/ year (~ 4 MW target power)
10% prec. on solar params, 5% matter density uncertainty
Atmospheric parameters best measured by disapp. channel
(for details: Huber, Lindner, Winter, hep-ph/ )
June 23, 2005
NuFact 05 - VLBL - Walter Winter

7. Phenomenology of VL baselines (1)
Note:
Pure baseline effect! A 1: Matter resonance
Prop. To L2; compensated by flux prop. to 1/L2
(Factor 1)(Factor 2)
(Factor 1)2
(Factor 2)2
June 23, 2005
NuFact 05 - VLBL - Walter Winter

8. Phenomenology of VL baselines (2)
Factor 1: Depends on energy; can be matter enhanced for long L; however: the longer L, the stronger change off the resonance
Factor 2: Always suppressed for longer L; zero at “magic baseline” (indep. of E, osc. Params)
(Dm312 = , r=4.3 g/cm3, normal hierarchy)
Factor 2 always suppresses CP and solar terms for very long baselines; note that these terms include 1/L2-dep.!
June 23, 2005
NuFact 05 - VLBL - Walter Winter

9. Application 1: “Magic baseline”
Idea: Factor 2=0 independent of E, osc. Params
Purpose: “Clean” measurement of q13 and mass hierarchy
Drawback: No dCP measurement at magic baseline
combine with shorter baseline, such as L=3 000 km
q13-range: < sin22q13 < 10-2, where most problems with degeneracies are present
June 23, 2005
NuFact 05 - VLBL - Walter Winter

10. Magic baseline: q13 sensitivity
Use two-baseline space (L1,L2) with (25kt, 25kt) and compute q13 sensitivity including correlations and degeneracies:
No CP violation measurement there!
Animation in
q13-dCP-space:
Optimal performance for all quantities:
Unstable: Disappears for different parameter values
(Huber, Winter, PRD 68, 2003, , hep-ph/ )
June 23, 2005
NuFact 05 - VLBL - Walter Winter

11. CP coverage and “real synergies”
Range of all fit values which fit a chosen simulated value of dCP
Any “extra” gain beyond a simple addition of statistics
3 000 km km versus all detector mass at km (2L)
Magic baseline allows a risk-minimized measurement (unknown d)
“Staged neutrino factory”: Option to add magic baseline later if in “bad” quadrants?
(Huber, Lindner, Winter, JHEP, hep-ph/ )
One baseline enough
Two baselines necessary
June 23, 2005
NuFact 05 - VLBL - Walter Winter

12. Magic baseline: Detector sites?
“Hot spots”: Interesting for many labs
Pyhaesalmi mine, Finland: MB from JHF
Gran Sasso, Italy: MB from Fermilab
China, India: MB from CERN? (
June 23, 2005
NuFact 05 - VLBL - Walter Winter

13. Appl. 2: Matter effect sensitivity for q13=0
Idea: For q13=0 only “solar term” survives. Factor 2 is suppressed in matter vs. vacuum :
Purpose: Verify MSW effect at high CL even for q13=0
Drawback: No mass hierarchy measurement (this term)
q13-range: Interesting for sin22q13 < 10-3
Note: No 1/L2 suppression of solar term in vacuum!
June 23, 2005
NuFact 05 - VLBL - Walter Winter

14. MSW sensitivity: q13-L-dependence
(dCP=0)
For sin22q13 >> a2 ~ 10-3: Depending on sin22q13, L=3 000 km might be sufficient
For sin22q13 << a2 ~ 10-3: Independent of sin22q13, even works for sin22q13=0: L > km required!
No sensitivity here
(Winter, PLB 613, 2005, 73, hep-ph/ )
June 23, 2005
NuFact 05 - VLBL - Walter Winter

15. MSW effect vs. mass hierarchy
(5s, dashed curve: no correlations )
Both qualitatively similar for large q13, but: matter effect sens. harder (Difference vacuum-matter < difference normal-inverted)
Small q13: No mass hierarchy sensitivity whatsoever
Some dependence on dCP, but L > km safe
(Winter, PLB 613, 2005, 73, hep-ph/ )
June 23, 2005
NuFact 05 - VLBL - Walter Winter

16. Application 3: Measurement of the Earth’s core density
Idea: Factor 1 does not drop prop. 1/L2 close to resonance
But: The longer L, the sharper the change off the resonance Very sensitive to matter density especially for large L
q13 large, A~1 (resonance)
Purpose: Measure the absolute density of the Earth’s core
Drawbacks: Not possible to measure dCP; “vertical” decay tunnel sophisticated
q13-range: sin22q13 >> 10-3
June 23, 2005
NuFact 05 - VLBL - Walter Winter

17. Core density measurement: Principles
Most direct information on the matter density from Earth’s mass and rotational inertia, but:
Least sensitive to the innermost parts
Seismic waves: s-waves mainly reflected on core boundaries
Least information on inner core
No “direct” matter density measurement; depends on EOS
No “absolute” densities: mainly sensitive to density jumps
Neutrinos: Measure Baseline- averaged density:
Equal contribution of innermost parts. Measure least known innermost density!
June 23, 2005
NuFact 05 - VLBL - Walter Winter

18. Core density measurement: Results
(Winter, hep-ph/ )
First: consider “ideal” geographical setup: Measure rIC (inner core) with L=2 RE
Combine with L=3000 km to measure oscillation parameters
Key question: Does this measurement survive the correlations with the unknown oscillation parameters?
For sin22q13 > 0.01 a precision at the per cent level is realistic
For < sin22q13 < 0.01: Correlations much worse without 3000 km baseline
(1s, 2s, 3s, dCP=0, Dashed: no correlations)
June 23, 2005
NuFact 05 - VLBL - Walter Winter

19. Density measurement: Geography
Something else than water in “core shadow”?
Inner core shadow
Outer core shadow
June 23, 2005
NuFact 05 - VLBL - Walter Winter

20. “Realistic geography”
… and sin22q13=0.01. Examples for rIC:
There are potential detector locations!
Per cent level precision not unrealistic
JHF
BNL
CERN
(Winter, hep-ph/ )
Inner core shadow
June 23, 2005
NuFact 05 - VLBL - Walter Winter

21. Summary: VL baseline applications
Excluded
10-1
10-2
10-3
10-4
10-5
10-6
sin22q13
Pur-pose
Measure density of the Earth’s core
Magic baseline: Resolve correlations/ degeneracies
Verify Earth matter effects at high CL L
L> km
(outer core)
L ~ km
L > km
Major challenge: Decay ring/decay tunnel slope
Open question: Simultaneous or subsequent operation of VL baseline? Feasiblity study for storage ring configurations needed!
June 23, 2005
NuFact 05 - VLBL - Walter Winter