getting the most in neutrino oscillation experiments hisakazu minakata tokyo metropolitan university

Getting the most in neutrino oscillation experiments

Hisakazu Minakata

Tokyo Metropolitan University

August 24-30, 2006 Nufact06@UC Irvine

In the last several years we have experienced the most

exciting era in physics


oscillation has been seen!

KamLANDKamLAND K2KK2K

SKSK

MINOSMINOS


Exploring the unknowns; 1-3 sector and mass hierarchy

<= solar + reactor

<= solar + reactor

Atm + accel =>

Atm + accel =>

=Ui i=Ui i

SK atmSK atm

solar+KamLANDsolar+KamLAND


Foreseeing the next 10-

20 years


Things changes at sin2213~0.01

• Conventional super beam works

• Known beam technology

• Background highly nontrivial

e beam contamination not negligible but tolerable

• beta beam / neutrino factory required

• Requires long-term R&D efforts

• Low background

• pure e beam () / well understood combination of e and beam (nufact)

Large 13 > 3oLarge 13 > 3o small 13 < 3osmall 13 < 3o


Superbeam; Two alternative strategies

• 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

Off axis narrow-band beamOff axis narrow-band beam On axis wide-band beamOn axis wide-band beam

multi-MW proton beam requiredmulti-MW proton beam required


Beta beam vs. 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

beta beambeta beam neutrino factoryneutrino factory


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 conventionalsuperbeam

• 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


T2KK; Tokai-to-Kamioka-Korea identical two-detector complex

2nd Korean detector WS was held @SNU, Seoul, in July 13-14

Ishitsuka et al. 05, Kajita-HM-Nakayama-Nunokawa, to appear

Ishitsuka et al. 05, Kajita-HM-Nakayama-Nunokawa, to appear

=>Okumura-san’s talk=>Okumura-san’s talk


Degeneracy; a notorious obstacle


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


23 octant degeneracy

Pe= sin2213 x s223

Pe= sin2213 x s223

Solar m2 on

Matter effect on

Solar m2 on

Matter effect on

OY Nufact03OY Nufact03

Altogether, 2 x 2 x 2 = 8-fold degeneracy

Altogether, 2 x 2 x 2 = 8-fold degeneracy


What’s good in T2KK?

(what about NOVA?)


T2KK vs. NOVA with 2nd detector (LOI)

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

NOVA 2nd phaseNOVA 2nd phase T2KKT2KK

In fact, they are similar; both uses off-axis narrow-band beam with similar values of L/E

= m2 L / 2E

In fact, they are similar; both uses off-axis narrow-band beam with similar values of L/E

= m2 L / 2E


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)


T2KK; the performance

• Analysis method (next slide); 4yr + 4yr anti-, fiducial0.27 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 !T2KK in situ solves 8-fold degeneracy !


2 definitione-like bins -like bins

systematicerror term

detector x beamcombination

f ij : fractional change in the predicted event rate in the i th bin

due to a variation of the parameter j

j : systematic error parameters, which are varied to minimize 2

for each chioce of the oscillation parameters

“ Pull Approach ” G.L.Fogli et al. PRD66 (2002) 053010

Nakayama-san’s slide @2nd Korean detector WSNakayama-san’s slide @2nd Korean detector WS


T2KK sensitivity; mass hierarchy

thick: 3, thin: 2thick: 3, thin: 2 Insensitive to 23Insensitive to 23


T2KK sensitivity; CP

thick: 3, thin: 2thick: 3, thin: 2 Insensitive to 23Insensitive to 23


Sensitivity to 23 octant (cont’d)si

n2

2 1

3

sin2 23 sin2 23

can determine 23 octantfor any by

> 32~3

If sin2 23<0.42 or >0.58(sin2 223= 0.974), 23 octantcan be determined by >2even at very small sin2 213 .


Sensitivity comparison with T2K+Reactor

T2K-II + phase II reactorT2KK=0 assumed

sin

2 2

13

sin2 23

sin

2 2

13

> 32~3

T2KK 2(rough)

T2KK has better sensitivityat sin2 213 < 0.06~0.07 .

hep-ph/0601258

Hiraide et al 06Hiraide et al 06


Why T2KK performance so good ?


Spectral information solves intrinsic degeneracy

from 1000 page Ishitsuka file

from 1000 page Ishitsuka file

SK momentum resolution ~30 MeV at 1 GeVSK momentum resolution ~30 MeV at 1 GeV

T2KT2K T2KKT2KK

2 detector method powerful!2 detector method powerful!


Sensitive to because energy dependence is far more dynamic in 2nd oscill

ation maximum


It is not quite only the matter effect

• 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 !

2 identical detector method powerful !

T2KKT2KK Korea onlyKorea only


Solar and atm. terms differ in energy dependences

All different in energy dependences !

All different in energy dependences !


In a nutshell, 8 fold degeneracy can be resolved by T2KK because

..• intrinsic degeneracy is resolved by spectru

m 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


Can we resolve

degeneracy one by one?


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


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


More aggressiv

e approach

es?


BNL strategy; using wide-band beam to explore multiple oscillation maxima

<=background ?

<=background ?

1 1


Recent analysis incl. Fermilab version• 1 MW beam from F

ermilab/BNL 5 years + anti- 1

0 years• Yanagisawa’s analy

sis assumed• Aggressive assumpt

ions for systematic errors;

• signal norm. 1% background 10% + no shape error

CP fraction=1CP fraction=1

000.50.5

Barger et al. 06Barger et al. 06


BNL method vs. T2KK

thin: 3thin: 3 T2KKT2KK

BNL 1300 km

BNL 1300 km


Problem of backgroundFanny Dufour @2nd Korean detector WS

Fanny Dufour @2nd Korean detector WS

=> energy-dependent systematic errors=> energy-dependent systematic errors


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 @ 1 degree OA

• Can resolve 8 fold parameter degeneracy in situ with consistency maintained by “decoupling”

Caution; uncorrelated systematic errors (between 2 detectors) enter

Caution; uncorrelated systematic errors (between 2 detectors) enter


Beta beam or neutrino f

actory?


BENE Report 06BENE Report 06


Beta vs. T2KK

Campagne et al. 06Campagne et al. 06

http://www.slac.stanford.edu/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Campagne,J.E.%22

http://www.slac.stanford.edu/spires/find/wwwhepau/wwwscan?rawcmd=fin+%22Campagne,J.E.%22


factory as ultimate degeneracy solver

• 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 13 > 1° (Donini, NuFACT03)

Typical ‘‘everything at once’’ method Typical ‘‘everything at once’’ method

Powerful, but expensive! ~1000 Million Euro/degeneracyPowerful, but expensive! ~1000 Million Euro/degeneracy


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; T2K

K (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 sin2213 ~ 0.01

• A strategy of solving 8-fold parameter degeneracy developed by one-by-one manner with ‘‘decoupling’’


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


Supplementary slides


Sensitivity study• Assumption

– 2.5 o off-axis T2K 4MW beam– 4 years beam + 4 years beam– Kamioka : 0.27 Mton fid., L = 295 km, = 2.3 g/cm3

Korea : 0.27 Mton fid., L = 1050 km, = 2.8 g/cm3

m212 = 8.0 x 10-5 (eV2)

|m223| = 2.5 x 10-3 (eV2)

sin2 12 = 0.31

• Oscillation parameter space (unknown parameters)– sin2 23 : 0.35 ~ 0.65 [ 31 bins ]– sin2 213 : 0.0015 ~ 0.15 [ 98 bins on log scale ] CP : 0 ~ 2 [ 100 bins ]– mass hierarchy : normal or inverted [2 bins ]

4 dimensional analysisusing no external information on these parameters

Nakayama-san’s slide @2nd Korean detector WS

Nakayama-san’s slide @2nd Korean detector WS


Sensitivity study (cont’d)• 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) -like : 20 energy bins (0.2-1.2 GeV)– (Kamioka, Korea) x ( beam, beam)

(5+20) x 4 = 100 bins in total

• Systematic errors– e-like bins

BG normalization 5 % BG spectrum shape 5 % (i-3)/2 (i=1…5 ene bin) signal normalization 5 %

-like bins BG normalization 20 % spectrum shape 5 % E(GeV)-0.8 / 0.8 signal normalization 5 %

– both bins(7) spectrum distortion in Korea shape diff. btw Kam. and Korea 1


Effect of the solar termm2

12 = 8.0 x 10-5 (eV2)m2

23 = 2.5 x 10-3 (eV2)sin2 12 = 0.31sin2223 = 0.96 = 3/4 normal mass hierarchy

Kamioka 0.27Mton

( 4MW, 4yr + 4yr )

Korea 0.27Mton

( 4MW, 4yr + 4yr )

sin2 23 = 0.4, sin2 213 = 0.01

sin2 23 = 0.6, sin2 213 = 0.0067

Solar term is negligibly smalldue to shorter baseline in Kamioka.

Num

ber

of

signal events

(BG

not

incl

uded

)

Solar term can be seenin low E region in Korea.

getting the most in neutrino oscillation experiments hisakazu minakata tokyo metropolitan university

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