Transcript Physics potential of very long neutrino factory baselines

Optimization of a neutrino factory
oscillation experiment
3rd ISS Meeting
Rutherford Appleton Laboratory, UK
April 25-27, 2006
Walter Winter
Institute for Advanced Study, Princeton
Contents
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Introduction
Optimization summary: L-Em
Improved detector summary
Channel requirements
See my talk(s) at KEK and
Patrick’s talk in Boston
– Some phenomenology: Why are other channels useful?
– Platinum
– Silver
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Where to concentrate the efforts? Synergies?
How does the optimal neutrino factory look like?
Comparison to beta beams
Summary
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Appearance channels
(Cervera et al. 2000; Freund, Huber, Lindner, 2000; Freund, 2001)
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Complicated, but all interesting information there:
q13, dCP, mass hierarchy (via A)
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Correlations and degeneracies
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Connected (green) or
disconnected (yellow)
degenerate solutions (at a
chosen CL) in parameter
space
Affect performance of
appearance measurements.
For example, q13 sensitivity
Discrete degeneracies: (also: Barger, Marfatia, Whisnant, 2001)
Intrinsic (d,q13)-degeneracy (Burguet-Castell et al, 2001)
sgn-degeneracy (Minakata, Nunokawa, 2001)
(q23,p/2-q23)-degeneracy (Fogli, Lisi, 1996)
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(Huber, Lindner, Winter, 2002)
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NF-Strategies to resolve degeneracies
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Combine with “silver channels” ne -> nt
(Donini, Meloni, Migliozzi, 2002; Autiero et al, 2004)
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Combine with “platinum channels” nm -> ne
(sin22q13 > 10-3 ? Depends on BG-level!)
(Boston workshop: Patrick’s talk)
Better detectors: Higher energy
resolution, higher efficiencies at
low energies (CID!) (discussed at KEK, Boston)
 Second NF baseline: “Magic baseline”
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How much
does
what help?
Where to
concentrate
the efforts?
(sin22q13 > 10-4)
(Lipari, 2000; Burguet-Castell et al, 2001; Barger, Mafatia, Whisnant, 2002; Huber,
Winter, 2003; others)
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Other possibilities?
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Optimization of a
neutrino factory
4 yr x 1.06 1021 m+ decays + 4 yr x 1.06 1021 m- decays
Detector: 50 kt magnetized iron calorimeter
ISS-values?
100 kt, 5+5 years running time = factor 2.36
luminosity increase for 1021 useful decays/year
Most of the following work
is done in collaboration with
P. Huber
M. Lindner
M. Rolinec
Optimization summary: L-Em
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Example: q13 sensitivity
relative to minimum in
each plot (5s – new!)
“Magic baseline” good
degeneracy resolver
L ~ 2000 – 4000 km
good for statistics
Em > 40 GeV
At 5s very robust to
– Threshold effects
– Dm312 larger
– Luminosity
April 25, 2006
(Huber, Lindner, Rolinec, Winter, to appear)
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CP violation and mass hierarchy
CP violation
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Mass hier.
L ~ 3000 – 5000 km good for CP violation (large q13 : 1500 – 6000)
L > 6000 km necessary for mass hierarchy (if small q13)
Use 4000 and 7500 km (“magic baseline”) as standard baselines
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Improved (golden) detector summary
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Better energy resolution?
Was: 0.15 x E (approximation)
Improve to:
?
Lower appearance threshold?
Was: 4 GeV, linearly
climbing to maximum at 20 GeV
Improve to: Max. already at 1 GeV?
(Fig. from Huber, Lindner, Winter, 2002;
CC/NC Backgrounds: Assume
Gray curve from Cervera et al, 2000)
-2
BG fraction b x E such that
~ 5 x 10-6 integrated over spectrum (b ~ 10-3)
 Background increases at low energies (Cervera et al, 2000)
 Even if CID improved, NC background limits performance!
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Improved detector: MH and CP violation
Blue shading:
Optimization
potential: Golden*
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Improved detector would be excellent degeneracy resolver!
Also: Em = 20 GeV possible (while 50 GeV do not harm)
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Improved detector: Systematics
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CP violation
measurement very
robust with respect
to systematics
(signal normalization
error) and
BG level as long as
b << 10-2
Note that 20% BG
uncertainty assumed
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Standard
“improved”
detector
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Systematics: Leading atm. parameters
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For Dm312 systematics somewhat
important
Dashed:
10% error on
solar params
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Energy resolution important for leading atm. parameters
Systematics somewhat important for Dm312,
but impact of solar input much larger
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Channel requirements: Phenomenology
Assume specific hierarchy
 Antineutrinos:
 Magic
baseline:
 Silver:
 Platinum:
(Akhmedov, Johansson, Lindner, Ohlsson, Schwetz, 2004)
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Platinum channel
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Changes sign of CP-odd term
Compare to antineutrinos:
Antineutrino channel without matter effect
suppression/enhancement (dep. on hierarchy)
Support information on dCP for large q13?
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Platinum channel: Assumptions
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Electron detection properties are MINOS-like
(NuMI note NuMI-L-714)
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2.5 GeV threshold
40% efficiency
Energy resolution 0.15 x E
1% BG from all neutral current events
1% BG from charge identification
Limits the q13
for which this
channel is useful!
Fiducial detector mass: same as “golden” mass
Matter density uncertainty:
Correlated with golden channel
If platinum is possible, use it in all “golden” detectors,
such as for NuFact+NuFact@MB at both places!
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Platinum channel: Results
Golden+Platinum
Golden+Platinum
Golden
Golden
BG-dominated
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Good degeneracy resolver; especially for large q13!
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Silver channel
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Changes sign of CP-even and CP-odd terms
Here: we only test maximal mixing
Interesting for matter density correlation:
2nd and 3rd terms fully correlated/anticorrelated with
matter density uncertainty from 1st term
(if same matter profile as golden channel)
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Silver channel: Assumptions
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Emulsion cloud chamber a la OPERA
(Autiero et al, 2004)
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Threshold starting at 2.5 GeV (Fig. 7, Autiero et al, 2004)
Energy resolution 0.20 x E (optimistic?)
10 kt fiducial mass
Only neutrinos detected
Matter density uncertainty:
Correlated with golden channel if at same baseline
Also: Test improved Silver* with 5 x Signal, 3 x BG
(if all leptonic and hadronic t decay channels could be
measured?) (Migliozzi, private communication)
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Silver channel: Options
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Which baseline?
– Same as golden channel + correlated matter effect
– Different from golden channel + uncorrelated matter
effect (e.g., L=732 km)
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Main results (qualitatively):
– Muon energies should probably not be too low
(higher tau production threshold!)
– Silver channel hardly affects golden channel opt.
– Correlated matter effect helps and makes
4000 + 4000 km attractive
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Silver channel: Results and comparison
Effect of
correlated
matter effect
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Matter density correlation helps
Silver without upgrades not competitive to platinum
Silver* at “golden” baseline complementary to platinum
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Better detector vs. new channels
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Better detector = increase reach by improved statistics/energy info
Different channel = resolve degs by complementary information
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Overall picture: Comparison matrix
Baselines
Detector effort
1
One baseline
Two baselines
Golden
n/a
(Golden)MB
Beta beam (g=350, L=730 km)
(Burguet-Castell et al, 2005)
2
3
4
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(Golden)2L
Golden*
Golden+Silver
Golden+Platinum
Golden+(Golden)MB
Golden+Silver+Platinum
Golden*+(Golden*)MB
Golden+(Golden)MB+Platinum
Golden+(Silver)732
Golden*+(Golden*)MB+Platinum
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Comparison matrix: Explanations
Detector degree of freedom
Synergies:
Comparable
statistics
Direct
comparison of
options at same
baseline
Accelerator degree of freedom
Overall effort
Optimized detector, additional channel, or increased luminosity increase “detector effort” by one
Baseline: 4000 km, unless different one in index (MB=“Magic baseline”). Muon energy: 50 GeV
Stars: Improved golden detector; in any star option the muon energy is 20 GeV
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“Simple” options
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No surprises: L=4000 km good for CP violation,
L=7500 km good for mass hierarchy
Beta beam very good for CP violation, but cannot measure mass
hierarchy for small q13
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Synergies for detector effort “two”
Compare with
each other: If
similar impact,
concentrate on
better one?
(Thick curves: two baselines)
Compare to
(Golden)2L:
If better in some
region, real
synergy effect!
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Synergies and optimal performance in “competing regions” for Golden*,
Golden+Platinum, Golden+(Golden)MB
NEW: Magic baseline helps for large q13!
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Physics case: Large sin22q13
Discovery reaches for:
CP violation (3s)
Mass hierarchy (3s)
sin22q13 (5s)
For large q13,
only CP violation
an issue
 Beta beam best
option even after
optimization
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Physics case: Interm. sin22q13
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ISS RAL NuFact - Walter Winter
“Typical” physics
case for a neutrino
factory!?
Improved detector
and magic baseline
sufficient to make
physics case
against beta beam
for any
performance
indicator used here
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Physics case: Small sin22q13
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ISS RAL NuFact - Walter Winter
Clear physics case
for neutrino
factory even with
“moderate”
improvements
Optimal reach for
improved detector
and magic baseline
Beta beam cannot
determine mass
hierarchy
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Where to concentrate the efforts?
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Optimized NuFact: Measure mass hierarchy and CP violation
almost down to sin22q13 = 10-5!
(including all degeneracies, for maximal mixing, 3s)
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Comparison to beta beams
Assumptions:
 2.9 1018 6He decays/year
1.1 1018 18Ne decays/year at
simultaneous operation for eight years
(or double ion decays/year)
 g=350, L=730 km, 500 kt WC
Maximum at CERN?
(Burguet-Castell et al, 2005)
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g=1000, L=1300 km, 50 kt TASD
High end. Optimal for CP violation
(Huber, Lindner, Rolinec, Winter, 2005)
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g=1000, L=2600 km, 50 kt TASD
High end. Optimal for mass hierarchy
(Huber, Lindner, Rolinec, Winter, 2005)
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g=1000, L=1300 km + 2600 km
Why not two baselines similar to
NuFact?
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Comparison to beta beams (2)
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NF good for q13 discovery, MH discovery and dCP for small q13
Beta beam competitive for CP violation (large q13); But: Extreme
effort to measure MH if q13 small could make physics case difficult!
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Summary
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Physics case for neutrino factory for small/intermediate
sin22q13 established; no clear physics case for large q13 yet
(baseline reopt. and reduced matter density uncertainties help somewhat …)
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The optimal neutrino factory has (at least)
– Two baselines with golden channel detectors
– A golden detector as optimized as possible
– Electron neutrino detection in all golden detectors
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The silver channel could be interesting if
– Improved efficiencies (more tau decay channels)
– Correlated matter effects (put detector to golden baseline)
– Specific physics case (non-maximal mixing, unitarity test etc.)
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(Our) plans
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Refine systematics/BG impact study
Check what one has to do for improved leading
atm. parameter measurements
Re-check silver channel baseline optimization:
732 km? Both at same baseline? Change of
optimization? Muon energies?
Test impact of matter density uncertainties
after (correlated) platinum/silver channels
Possibly some work on large q13 case
Finish this analysis (writeup as paper)
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Additional slides
MINOS: Larger value of Dm312?
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No qualitative changes in L-E-optimization,
but improved absolute reaches!
Physics case for magic baseline even stronger
April 25, 2006
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ISS RAL NuFact - Walter Winter
Example: 0.003 eV2
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Better detector: q13 sensitivity
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High CL chosen (4s):
avoid threshold effects
(q13,dCP)-degeneracy
affects sensitivity limit
at L ~ 1500-5000 km
Better detector threshold:
L=2000-3000 km most
attractive q13-baseline
April 25, 2006
ISS RAL NuFact - Walter Winter
“Magic
baseline”
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No dCP at Lmagic!
Better detector: Large q13
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Both better Eres and threshold useful
Both better detector and smaller matter density uncertainty useful
Either or combination sufficient to compete with the superbeam upgrades (prel.)
Large Dr+better detector prefers shorter baselines (1000-2000km); Em small OK
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Better detector in L-E-space: q13 sens.
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3s sensitivity to sin22q13
Better Eres
Better threshold
Better Eres+thresh.
(Huber, Lindner, Rolinec, Winter, to appear)
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Better detector in L-E-space: Large q13
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CP fraction for CP
violation (3s):
“Standard”
“Optimal
appearance”
L=1000 km/Em=20 GeV
possible alternative?
(Huber, Lindner, Rolinec, Winter, to appear)
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Silver channel: Optimal baseline?
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Correlated matter effect with LECC=4000 km better than any other
baseline (except q13 sensitivity for L ~ 1500 km)
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