Getting the most in neutrino oscillation experiments

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Getting the most in neutrino oscillation
experiments

• Hisakazu Minakata
• Tokyo Metropolitan University

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In the last several years we have experienced the
most exciting era in n physics
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n oscillation has been seen!
SK
MINOS
KamLAND
K2K
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Exploring the unknowns 1-3 sector and ? mass
hierarchy
naUai ni
Atm accel n gt
lt solar reactor n
SK atm
solarKamLAND
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Foreseeing the next 10-20 years
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Things changes at sin22?130.01
Large ?13 gt 3o
small ?13 lt 3o

• beta beam / neutrino factory required
• Requires long-term RD efforts
• Low background
• pure ?e beam (?) / well understood combination of
  ?e and ?? beam (nufact)

• Conventional super ???beam works
• Known beam technology
• Background highly nontrivial
• ?e beam contamination not negligible but
  tolerable

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Superbeam Two alternative strategies
Off axis narrow-band beam
On axis wide-band beam

• Pinpoint to the 1st oscillation maximum
• Relatively clean background at low energies
• elaborated ?0 rejection algorism
  developed

• Covers multiple oscillation maxima
• The issue of background becomes severer at high
  energies
• Dien Bien Phu of the BNL strategy

multi-MW proton beam required
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Beta beam vs. Neutrino factory
beta beam
neutrino factory

• pure ?e beam
• charged pion background seems tolerable
• e-? separation required but no charge ID required
• multi-MW proton beam NOT required

• well understood combination of ?e and ?? beam
  with precisely (10-5) known muon energy
• small background (how small?)
• muon charge ID required
• multi-MW proton beam required

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Getting the most in conventional??? superbeam

• To define the role of beta beam and/or neutrino
  factory precisely, it may be of help if superbeam
  reach is clearly marked
• Let me focus in on conventional?superbeam
  
• I will try to explain some basic facts and use
  two concrete examples
• T2KK (Tokai-to-Kamioka-Korea) \simeq extended
  NOVA
• Fermilab/BNL realization of BNL strategy

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T2KK Tokai-to-Kamioka-Korea identical
two-detector complex
Ishitsuka et al. 05, Kajita-HM-Nakayama-Nunokawa,
to appear

• 2nd Korean detector WS was held _at_SNU, Seoul, in
  July 13-14

gtOkumura-sans talk
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• Degeneracy a notorious obstacle

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Cause of the degeneracy easy to understand

• You can draw two ellipses from a point in P-Pbar
  space
• Intrinsic degeneracy
• Doubled by the unknown sign of ?m2
• 4-fold degeneracy

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?23 octant degeneracy
OY Nufact03
P?e sin22?13 x s223
Solar ?m2 on Matter effect on
Altogether, 2 x 2 x 2 8-fold degeneracy
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Whats good in T2KK? (what about NOVA?)
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T2KK vs. NOVA with 2nd detector (LOI)
In fact, they are similar both uses off-axis
narrow-band beam with similar values of L/E ?
?m2 L / 2E
NOVA 2nd phase
T2KK

• ?1st 0.8 ?
• ?2nd 1.8 ?
• (aL/?) 1st 0.17
• (aL/? )2nd 0.07

• ?1st ?
• ?2nd 3 ?
• (aL/?) 1st 0.05
• (aL/? )2nd 0.05

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T2KK the basic ideas

• Leptonic CP violation and mass hierarchy
  resolution highly nontrivial for
  conventional superbeam
• Try to do a reliable conservative estimate on its
  maximal (assuming 4MW total 1 Mton) performance
• Restrict to known background rejection
  technology by SK conservative estimate of the
  systematic errors (5) identical 2 detector
  setting
• T2KK (Tokai-to-Kamioka-Korea)

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T2KK the performance

• Analysis method (next slide) 4yr ? 4yr anti-?,
  fiducial?0.27 Mton each
• Can resolve intrinsic and sign-?m2 degeneracies
  to determine mass hierarchy and uncover CP
  violation
• see the next-next slides
• Can resolve ?23 octant degeneracy
• see the next-next-next slides

T2KK in situ solves 8-fold degeneracy !
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c2 definition
Nakayama-sans slide _at_2nd Korean detector WS
systematic error term
detector x beam combination
e-like bins
m-like bins

• f ij fractional change in the predicted event
  rate in the ith bin
• due to a variation of the parameter e j
• j systematic error parameters, which are varied
  to minimize c2
• for each chioce of the oscillation parameters

Pull Approach G.L.Fogli et al. PRD66
(2002) 053010
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(No Transcript)
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T2KK sensitivity mass hierarchy
thick 3?, thin 2?
Insensitive to ?23
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T2KK sensitivity CP
thick 3?, thin 2?
Insensitive to ?23
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Sensitivity to q23 octant (contd)
sin2 2q13
sin2 q23
sin2 q23
can determine q23 octant for any d by gt
3s 23s
If sin2 q23lt0.42 or gt0.58 (sin2 2q23 0.974), q23
octant can be determined by gt2s even at very
small sin2 2q13 .
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Sensitivity comparison with T2KReactor
Hiraide et al 06
d0 assumed
T2K-II phase II reactor
T2KK
sin2 2q13
T2KK 2s (rough)
gt 3s 23s
sin2 2q13
hep-ph/0601258
T2KK has better sensitivity at sin2 2q13 lt
0.060.07 .
sin2 q23
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Why T2KK performance so good ?
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Spectral information solves intrinsic degeneracy
from 1000 page Ishitsuka file
T2K
T2KK
2 detector method powerful!
SK momentum resolution 30 MeV at 1 GeV
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Sensitive to ? because energy dependence is far
more dynamic in 2nd oscillation maximum
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It is not quite only the matter effect
T2KK
Korea only

• With the same input parameter and Korean detector
  of 0.54 Mt the sign-?m2 degeneracy is NOT
  completely resolved

2 identical detector method powerful !
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Solar and atm. terms differ in energy dependences
All different in energy dependences !
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In a nutshell, 8 fold degeneracy can be resolved
by T2KK because ..

• intrinsic degeneracy is resolved by spectrum
  information
• sign-?m2 degeneracy is solved with matter effect
  2 identical detector comparison
• ?23 octant degeneracy is solved by identifying
  the solar oscillation effect in T2KK

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Can we resolve degeneracy one by one?
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Decoupling between degeneracies

• Suppose that you succeeded to solve the
  particular degeneracy, by forgetting about the
  remaining ones
• It does NOT necessarily mean that the problem is
  solved
• You have to verify that your treatment of
  degeneracy A is valid irrespective of the
  presence of degeneracy B
• One solution decoupling between the degeneracies
  

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?23 and sign-?m2 degeneracy decouple

• For example, one can show, to first order in
  matter effect, the followings
• ?P(octant) P(1st octant) - P(2nd) is invariant
  under the interchange of two sign-?m2 degenerate
  pair
• ?P(hierarchy) P(?m2 ) - P(?m2 -) is invariant
  under the interchange of two ?23 octant
  degenerate pair
• in T2K or T2KK setting, the intrinsic degeneracy
  is resolved by spectrum analysis
  decouple from the game

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More aggressive approaches?
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BNL strategy using wide-band beam to explore
multiple oscillation maxima
ltbackground ?
1 s
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Recent analysis incl. Fermilab version

• 1 MW beam from Fermilab/BNL
• ? 5 years anti-? 10 years
• Yanagisawas analysis assumed
• Aggressive assumptions for systematic errors
• signal norm. 1 background 10 no shape error

Barger et al. 06
CP fraction1
0.5
0
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BNL method vs. T2KK
BNL 1300 km
thin 3?
T2KK
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Problem of background
Fanny Dufour _at_2nd Korean detector WS
gt energy-dependent systematic errors
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Conclusion for conventional superbeam

• T2KK (2 detector) BNL method (multiple OM) are
  reaching optimal sensitivities achievable by
  conventional ?? superbeam
• These two method can be combined e.g., Korean
  detector _at_ 1 degree OA
• Can resolve 8 fold parameter degeneracy in situ
  with consistency maintained by decoupling

Caution uncorrelated systematic errors (between
2 detectors) enter
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Beta beam or neutrino factory?
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BENE Report 06
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Beta vs. T2KK
Campagne et al. 06
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n factory as ultimate degeneracy solver
Typical everything at once method

• By combining at 3 detectors at 130, 730, and 2810
  km, it was claimed that neutrino factory can
  resolve all the 8-fold degeneracy if q13 gt 1
  (Donini, NuFACT03)

Powerful, but expensive! 1000 Million
Euro/degeneracy
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Conclusion

• To clearly define the role of nufact/? the better
  idea for superbeam reach required
• I tried to give it by using two concrete
  settings T2KK (2 detector) BNL method
  (multiple OM)
• their performance is quite good (compared
  to what was thought in 10 years ago!) and the
  sensitivities to CP mass hierarchy may go down
  to sin22?13 0.01
• A strategy of solving 8-fold parameter degeneracy
  developed by one-by-one manner with
  decoupling

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Conclusion (continued)

• However, a caution needed BNL analysis needs
  better understanding of energy dependent
  background (at low energies)
• Sensitivities of T2KK could be enhanced by near
  on-axis Korean detector
• If successful, they are competitive to ??beam

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Supplementary slides
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Sensitivity study
Nakayama-sans slide _at_2nd Korean detector WS

• Assumption
• 2.5 o off-axis T2K 4MW beam
• 4 years n beam 4 years n beam
• Kamioka 0.27 Mton fid., L 295 km, r 2.3
  g/cm3Korea 0.27 Mton fid., L 1050 km, r
  2.8 g/cm3
• Dm212 8.0 x 10-5 (eV2)Dm223 2.5 x 10-3
  (eV2)sin2 q12 0.31
• Oscillation parameter space (unknown parameters)
• sin2 q23 0.35 0.65 31 bins
• sin2 2q13 0.0015 0.15 98 bins on log
  scale
• dCP 0 2p 100 bins
• mass hierarchy normal or inverted 2 bins
• ? 4 dimensional analysis
• using no external information on these parameters

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Sensitivity study (contd)

• Binning
• e-like 5 energy bins (0.4-0.5, 0.5-0.6,
  0.6-0.7, 0.7-0.8, 0.8-1.2 GeV)
• m-like 20 energy bins (0.2-1.2 GeV)
• (Kamioka, Korea) x (n beam, n beam)
• ? (520) x 4 100 bins in total
• Systematic errors
• e-like bins
• BG normalization 5
• BG spectrum shape 5 (i-3)/2 (i15 ene bin)
• signal normalization 5
• m-like bins
• BG normalization 20
• spectrum shape 5 En(GeV)-0.8 / 0.8
• signal normalization 5
• both bins
• (7) spectrum distortion in Korea shape diff. btw
  Kam. and Korea ? 1s

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Effect of the solar term
Dm212 8.0 x 10-5 (eV2) Dm223 2.5 x 10-3
(eV2) sin2 q12 0.31 sin22q23 0.96 d 3/4
p normal mass hierarchy
sin2 q23 0.4, sin2 2q13 0.01 sin2 q23 0.6,
sin2 2q13 0.0067
Kamioka 0.27Mton ( 4MW, 4yr n 4yr n )
Korea 0.27Mton ( 4MW, 4yr n 4yr n )
Number of signal events (BG not included)
Solar term is negligibly small due to shorter
baseline in Kamioka.
Solar term can be seen in low En region in Korea.