Transcript Physics potential of very long neutrino factory baselines

Optimization of a neutrino
factory for large q13
Golden 07
IFIC, Valencia
June 28, 2007
Walter Winter
Universität Würzburg
Contents
Introduction
 Challenges for large q13
 Optimization of a high-energy neutrino factory
 Alternative: Low-energy neutrino factory?
 … combined with superbeam?
 Comparison to “competitors”: WBB, BB etc.
 Summary and conclusions

June 28, 2007
Golden 07 - Walter Winter
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The setting


What are „large q13“?
Assume:
Decision for future program
after T2K, Double Chooz, etc.
Choose: sin22q13 > 0.01
GLoBES 2005
Which performance indicators
are relevant?
(FNAL Proton Driver study)
– sin22q13 discovered (by assumption) 
– Mass hierarchy not a problem (for sin22q13 > 0.01, at
least for beta beam and NF with reasonably long L) 
– Sensitivity to CP violation?
Or: For what fraction of all possible (true) dCP can
CP violation be discovered by a given experiment?
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Golden 07 - Walter Winter
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The „competitors“
… and how to make a selection?





Wide band beam (WBB)
NOvA-like off-axis beam
T2KK-like two detector setup
Beta beam (different configs)
Neutrino factory?
Possible optimization goals:
1.
Physics potential optimal, effort ignored
2.
Effort x Physics potential optimal
3.
Robustness (systematics, Dm312, exposure, …)
4.
…
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Golden 07 - Walter Winter
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Straightforward comparison
… for sensitivity to CP violation
g=350 beta beam
Burguet-Castell et al, 2005
Neutrino factory
3000 +7500 km
50 kt + 50 kt
NuMI beam
to 100kt LArTPC
FNAL - DUSEL
100kt LArTPC
270kt+270kt
WC detector
(Barger, Huber, Marfatia, Winter, hep-ph/0703029)


Superbeam upgrades can easily outperform a „straightforward“ NF
How can one optimize a neutrino factory for large q13?
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Golden 07 - Walter Winter
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Neutrino factory challenges (1)

Designed as a discovery instrument:
Flux ~ Em2, cross sections ~ En
 As high Em as possible to obtain high event rates

First oscillation maximum at
En, max [GeV] ~ 2 x 10-3 x L [km]
(in vacuum, Dm312 = 0.0025 eV2)
L = 3000 km : En, max = 6 GeV
L = 1000 km : En, max = 2 GeV
 For high Em, event peak is off the osc. max.

Charge ID difficult for low En
if optimized for low backgrounds
(Fig. from Huber, Lindner, Winter, 2002;
Gray curve from Cervera et al, 2000)
 Overall design for small q13, i.e., low backgrounds
 How can that be optimized for large q13?
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Neutrino factory challenges (2)


(from: Ohlsson, Winter, 2003)
(from: Huber, Lindner, Winter, 2002)
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sin22q13=0.01, dCP = p/4

Matter density
uncertainties <= 5%
relevant for large q13
Reason: long L, high En
(unlike superbeams with
En << Eres)
r and
energy
threshold
main
impact
factors for
large q13
Optimization options for large q13
Opt. goal 1: Physics potential optimal, effort ignored






Magic baseline (MB)
Better detector:
Golden*
Platinum channel:
Plat*
Instead of platinum:
Combination with
superbeam?
Better known
matter density?
…
(from: Huber, Lindner, Rolinec, Winter, 2006)
June 28, 2007
Golden 07 - Walter Winter
Em ~ 20 – 50 GeV
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Impact of matter density uncertainties?
The more
information added,
the less important …
 In fact: at L >> 6000
km, one can measure
the matter density at
the level of 0.5%

Dashed: 2%
Solid: 5%
(Winter, hep-ph/0502097;
Minakata, Uchinami, hep-ph/0612002;
Gandhi, Winter, hep-ph/0612158)
(from: Huber, Lindner, Rolinec, Winter, 2006)
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Magic baseline

Idea:
Yellow term = 0 independent
of E, oscillation parameters
(Huber, Winter, 2003)


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

Effect for large q13: Reduces correlation q13-dCP-r3000
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Platinum channel, superbeams

Compare to antineutrinos:
 Antineutrino channel without matter effect suppression/enhancement
 Supports information on dCP for large q13

Main challenge for platinum:
Requires CID, but electrons are showering for high energies
 So far, Plat* with 40% eff. and no upper threshold purely speculative!
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Combination: NF plus superbeam?




Idea: combine
superbeam with
neutrino factory
Superbeam peaks at
much lower energies
LSB ~130 km,
En ~ 0.25 GeV
For large q13:
LNF ~ 730 km sufficient
(Em = 50 GeV)
L/E+matter effect
complementary!
Matter effect + high statistics
from NuFact versus
operation close to vacuum
osc. maximum at superbeam
June 28, 2007
Golden 07 - Walter Winter
(Burguet-Castell et al, 2002)
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Better detector: Golden*

?
Lower appearance threshold
CC/NC Backgrounds: Assume
BG fraction b x E-2 such that
~ 5 x 10-6 integrated over spectrum (b ~ 10-3)
 Background increases at low energies
Possibly for large q13: (not included yet!)
Use different cuts to increase efficiency
(CID error at the level of ~1% OK!?)
 Better energy resolution
Was: 0.15 x E (approximation)
Improve to:
?

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Effort matters! Low-E neutrino factory?
Opt. goal 2: Effort x physics potential optimal

Effort

Lower threshold allows for
lower Em - but how low?
For example:
Em = 4.12 GeV, L=1280 km:
Fraction of dCP for CPV
(Geer, Mena, Pascoli, 2007)
(WW @ KEK talk, Jan. 2006)

June 28, 2007
How does that compare to the
other competing options?
Golden 07 - Walter Winter
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Neutrino factory superbeam (NF-SB)
(arXiv:0706.2862 [hep-ph])
Idea:
Use on-axis superbeam from secondary pion/kaon beam in
addition to NF beam (same accelerator facility!)
p p, K
nm + m
ne
SB appearance
nm
ne





ne
nm
NF Platinum
NF Golden
4 MW superbeam basically coming for free?
Same detector might be used at same baseline
(if out-of-phase bunches from SB and NF)
Compared to platinum channel, no CID is required; higher
efficiencies possible
Correlated matter effect between NF and superbeam if same L
Can be combined with low-E neutrino factory idea
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NF-SB schematics
Target station/decay pipe(s):
How can this be done?
(Huber, Winter, 2007)


Drawback: Target station challenging
Conservative assumption:
only half the muons go in NF channel (recycler?)
Degrees of freedom: Ep, Em, L
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Golden 07 - Walter Winter
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NF-SB requirements
(high-Z target; Zisman @ IDS CERN, March 2007)

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Ep window

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

Ep: Tested MiniBOONE-like
(Ep=8 GeV) and AGS-like
(Ep=28 GeV) WBB for the
superbeam
Ep ~ 28 GeV better choice
June 28, 2007

Em, L varied
Assume: Ptarget ~ 4 MW leading
to 0.5 1021 useful muon
decays/year
(50% of „standard-NF“)
Detektor: 50 kt Golden*
5 yr running time in each
polarity = 10 yr total
80% electron detection
efficiency (without CID!)
5% systematics (except for
normalization errors 2.5%) – as
usual
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Comparison of appearance rates
NF Golden-SB appearance-NF Platinum
Golden


Ep chosen such that SB peaks at lower E
Platinum peaks at higher E (spectrum!)
June 28, 2007
Golden 07 - Walter Winter
(Huber, Winter, 2007)
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2.5 1021 useful muon decays
Em=5 GeV
L=1250 km
Synergy: NF – Superbeam?

Synergy ~ Improvement of physical potential beyond a
simple addition of statistics (hep-ph/0211300)

Comparison neutrino factory versus NF-SB:
Use double luminosity in neutrino factory, because both polarities
may be used simultaneously
= 1021 useful muon decays/year for NF alone
= 0.5 1021 useful muon decays/year for NF-SB alone
~ similar effort assumption
Comparison WBB versus NF-SB:
more difficult since detector effort versus accelerator effort
Use WBB with Ep=28 GeV and 500 kt WC detector for comparison
Open questions:


– What option has the better absolute performance?
– L-Em Optimization?
– What if two baselines used for the NF-SB? (similar to Burguet-Castell et al)
June 28, 2007
Golden 07 - Walter Winter
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L-Em Optimization: CPV discovery
CP fraction for discovery (3s) , sin22q13=0.1



(Huber, Winter, 2007)
Geer et al. choices are sufficiently close to optimum
NF-SB synergistic, better performance than NF alone
Our choices : L = 900 km, Em = 5 GeV and L=1250 km, Em=5 GeV
(given the low energy ~ minimum effort ~ constraint)
June 28, 2007
Golden 07 - Walter Winter
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Use two baselines?


Same baseline close to
optimal!
In addition: correlated
matter effect helps: ~
2% improvement in CP
fraction
0.8

Our choice
0.82

What happens
if NF and SB have two
detectors (50 kt each)
at LNF and LSB?
Matter effect
uncorrelated between
LNF and LSB
Em = 5 GeV
(Huber, Winter, 2007)
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Golden 07 - Walter Winter
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Comparison to competitors
Ep=28 GeV
500 kt WC
(Huber, Winter, 2007)


NF-SB can outperform any of the
discussed setups except from beta beam
But: Luminosity choice for beta beam arbitrary in this context!
Parameters: g=350, L=712 km, 5 yr x 5.8 1018 useful 6He decays/yr, 5 yr x
2.2 1018 useful 18Ne decays/yr (Burguet-Castell et al, 2005)
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What does it take to outperform any setup?
(… neglecting „effort“)



Additional platinum channel: small effect
Additional MB or higher Em~10 GeV:
especially useful for small sin22q13 ~ 0.01
Additional large (500 kt) WC detector at same site:
largest effect for large q13
 Luminosity matters to outperform beta beam!
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Golden 07 - Walter Winter
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Potential further improvements
Better golden efficiency
(possibly traded in for higher
backgrounds)
 Muon recycling from SB decay pipe?
 Further Ep optimization/SB horn
 Larger detector? Detector hybrid?
 Optimization of „magnetization fraction“
(part of the detector to be magnetized)
 Staged concepts?

Such as 1. WBBGolden*, 2. NF-SB, 3. NF-SBGolden*+WC
June 28, 2007
Golden 07 - Walter Winter
Up to
~ 4 x NF
luminosity
Maximum
synergy?
Optimized
NF-SB
statistics
Optimized
funding?
24
A short note on the
Mass hierarchy measurement
Requirement: Determine mass hierarchy for all
possible values of dCP (Fraction of dCP=1) @ 3s
 Results:

– Low-E NF: L > 800 km, almost indep. of Em
– NF-SB: L > 500 km sufficient
TALK THIS
AFTERNOON
Reason: Schwetz-effect (hep-ph/0703279)

Since we find L > 900 km for CPV, any of these
requirements is fulfilled!
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Golden 07 - Walter Winter
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Summary

Optimization goals:
– Cost x Physics potential optimal: NF-SB?
– Physics potential optimal: Beta beam? NF-SBWC? High-E NF?

Discovery machine (sin22q13<0.01) versus precision
instrument (sin22q13>0.01) : Different requirements for
– Machine: Target station, muon energies, baseline(s)
– Detector: Optimization for high effs versus low backgrounds
But: Better low-energy threshold useful for both!
(though no prerequisite for high-E NuFact)

Optimize for two different NuFacts until T2K, Double
Chooz, NOvA etc. finished?
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Golden 07 - Walter Winter
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