Getting the most in neutrino oscillation experiments Hisakazu Minakata Tokyo Metropolitan University

August 24-30, Irvine In the last several years we have experienced the most exciting era in physics

August 24-30, Irvine oscillation has been seen! KamLAND K2K SKSK SKSK MINOS

August 24-30, Irvine Exploring the unknowns; 1-3 sector and mass hierarchy <= solar + reactor Atm + accel  =>  =U  i i SK atm solar+KamLAND

August 24-30, Irvine Foreseeing the next years

August 24-30, Irvine Things changes at sin 2 2  13 ~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 > 3 o small  13 < 3 o

August 24-30, Irvine 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 beam On axis wide-band beam multi-MW proton beam required

August 24-30, Irvine 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 beam neutrino factory

August 24-30, Irvine 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

August 24-30, Irvine T2KK; Tokai-to-Kamioka-Korea identical two-detector complex 2nd Korean detector WS was Seoul, in July Ishitsuka et al. 05, Kajita-HM- Nakayama-Nunokawa, to appear =>Okumura-san’s talk

August 24-30, Irvine Degeneracy; a notorious obstacle

August 24-30, Irvine 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  m 2 4-fold degeneracy

August 24-30, Irvine  23 octant degeneracy P  e= sin 2 2  13 x s 2 23 Solar  m 2 on Matter effect on Solar  m 2 on Matter effect on OY Nufact03 Altogether, 2 x 2 x 2 = 8-fold degeneracy

August 24-30, Irvine What’s good in T2KK? (what about NOVA?)

August 24-30, Irvine 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 phase T2KK In fact, they are similar; both uses off-axis narrow-band beam with similar values of L/E  =  m 2 L / 2E In fact, they are similar; both uses off-axis narrow-band beam with similar values of L/E  =  m 2 L / 2E

August 24-30, Irvine 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)

August 24-30, Irvine T2KK; the performance Analysis method (next slide); 4yr + 4yr anti-, fiducial  0.27 Mton each Can resolve intrinsic and sign-  m 2 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 !

August 24-30, Irvine  2 definition e-like bins -like bins systematic error term detector x beam combination f i j : 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) Nakayama-san’s Korean detector WS

August 24-30, Irvine

August 24-30, Irvine T2KK sensitivity; mass hierarchy thick: 3 , thin: 2  Insensitive to  23

August 24-30, Irvine T2KK sensitivity; CP thick: 3 , thin: 2  Insensitive to  23

August 24-30, Irvine Sensitivity to  23 octant (cont’d) sin 2 2 13 sin 2  23 can determine  23 octant for any  by > 3 2~3 If sin 2  (sin 2 2 23 = 0.974),  23 octant can be determined by >2 even at very small sin 2 2 13.

August 24-30, Irvine Sensitivity comparison with T2K+Reactor T2K-II + phase II reactor T2KK =0 assumed sin 2 2 13 sin 2  23 sin 2 2 13 > 3 2~3 T2KK 2 (rough) T2KK has better sensitivity at sin 2 2 13 < 0.06~0.07. hep-ph/ Hiraide et al 06

August 24-30, Irvine Why T2KK performance so good ?

August 24-30, Irvine Spectral information solves intrinsic degeneracy from 1000 page Ishitsuka file SK momentum resolution ~30 MeV at 1 GeV T2K T2KK 2 detector method powerful!

August 24-30, Irvine Sensitive to  because energy dependence is far more dynamic in 2nd oscillation maximum

August 24-30, Irvine It is not quite only the matter effect With the same input parameter and Korean detector of 0.54 Mt the sign-  m 2 degeneracy is NOT completely resolved 2 identical detector method powerful ! T2KK Korea only

August 24-30, Irvine Solar and atm. terms differ in energy dependences All different in energy dependences !

August 24-30, Irvine In a nutshell, 8 fold degeneracy can be resolved by T2KK because.. intrinsic degeneracy is resolved by spectrum information sign-  m 2 degeneracy is solved with matter effect + 2 identical detector comparison  23 octant degeneracy is solved by identifying the solar oscillation effect in T2KK

August 24-30, Irvine Can we resolve degeneracy one by one?

August 24-30, Irvine 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

August 24-30, Irvine  23 and sign-  m 2 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-  m 2 degenerate pair  P(hierarchy) = P(  m 2 +) - P(  m 2 -) 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

August 24-30, Irvine More aggressive approaches ?

August 24-30, Irvine BNL strategy; using wide-band beam to explore multiple oscillation maxima <=background ? 1 

August 24-30, Irvine Recent analysis incl. Fermilab version 1 MW beam from Fermilab/BNL  5 years + anti- 10 years Yanagisawa’s analysis assumed Aggressive assumptions for systematic errors; signal norm. 1% background 10% + no shape error CP fraction= Barger et al. 06

August 24-30, Irvine BNL method vs. T2KK thin: 3  T2KK BNL 1300 km

August 24-30, Irvine Problem of background Fanny Korean detector WS => energy-dependent systematic errors

August 24-30, Irvine 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 1 degree OA Can resolve 8 fold parameter degeneracy in situ with consistency maintained by “decoupling” Caution; uncorrelated systematic errors (between 2 detectors) enter

August 24-30, Irvine Beta beam or neutrino factory?

August 24-30, Irvine BENE Report 06

August 24-30, Irvine Beta vs. T2KK CampagneCampagne et al. 06 CampagneCampagne et al. 06

August 24-30, Irvine 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 Powerful, but expensive! ~1000 Million Euro/degeneracy

August 24-30, Irvine 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 sin 2 2  13 ~ 0.01 A strategy of solving 8-fold parameter degeneracy developed by one-by-one manner with ‘‘decoupling’’

August 24-30, Irvine 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

August 24-30, Irvine Supplementary slides

August 24-30, Irvine 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/cm 3 Korea : 0.27 Mton fid., L = 1050 km,  = 2.8 g/cm 3 –  m 2 12 = 8.0 x (eV 2 ) |  m 2 23 |= 2.5 x (eV 2 ) sin 2  12 = 0.31 Oscillation parameter space (unknown parameters) –sin 2  23 : 0.35 ~ 0.65 [ 31 bins ] –sin 2 2  13 : ~ 0.15 [ 98 bins on log scale ] –  CP : 0 ~ 2  [ 100 bins ] –mass hierarchy: normal or inverted [2 bins ]  4 dimensional analysis using no external information on these parameters Nakayama-san’s Korean detector WS

August 24-30, Irvine Sensitivity study (cont’d) Binning –e-like: 5 energy bins ( , , , , GeV ) –  -like: 20 energy bins ( GeV ) –(Kamioka, Korea) x ( beam, beam)  (5+20) x 4 = 100 bins in total Systematic errors –e-like bins (1)BG normalization5 % (2)BG spectrum shape5 % (i-3)/2(i=1…5 ene bin) (3)signal normalization5 % –  -like bins (4)BG normalization20 % (5)spectrum shape5 % E (GeV)-0.8 / 0.8 (6)signal normalization5 % –both bins (7)spectrum distortion in Koreashape diff. btw Kam. and Korea  1 

August 24-30, Irvine Effect of the solar term m 2 12 = 8.0 x (eV 2 ) m 2 23 = 2.5 x (eV 2 ) sin 2  12 = 0.31 sin 2 2 23 = 0.96 = 3/4  normal mass hierarchy Kamioka 0.27Mton ( 4MW, 4yr + 4yr ) Korea 0.27Mton ( 4MW, 4yr + 4yr ) sin 2  23 = 0.4, sin 2 2 13 = 0.01 sin 2  23 = 0.6, sin 2 2 13 = Solar term is negligibly small due to shorter baseline in Kamioka. Number of signal events (BG not included) Solar term can be seen in low E region in Korea.