PoS(ICHEP2012)007 http://pos.sissa.it/ Institute for Particle and Nuclear Studies, High Energy ∗ [email protected] Speaker. Status and results ofviewed. accelerator-based Future prospects long are baseline also discussed. oscillation experiments are re- ∗ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

36th International Conference on High Energy4-11 July 2012 Melbourne, Australia Takashi Kobayashi Accelerator Research Organization (KEK) E-mail: Long Baseline PoS(ICHEP2012)007 , , µ ]. ) 13 µ 2 ν 3 ] is θ ν , , the ] ex- e eV 12 . The 6 ( sin i 13 ν ,

θ 10 GeV m 23 2 i j 11 . Because θ ∼ , m 13 ∆ θ

sin 10 / . The existence 12 ) θ 13 Takashi Kobayashi θ GeV ( ] and ICARUS [ E 5 ∼ ) A experiment [ ]. The first accelerator-based km ν 2 ( beam is produced in the “con- L µ ν ]. In the three flavor mixing picture, the decides the feasibility of the future CP 8 , 7 13 ] and the OPERA [ θ 4 2 , appears always in the product with sin δ at which the first evidence of was found 2 eV 3 ∼− 2 − 10 GeV and several 100 km flight distance are optimized for measuring ]. The physics goals of the LBL experiments have been to understand ∼ 10 is the mass squared difference of the neutrino mass eigenvalues 1 [ j 2 | ∼ + m 2 ] in Japan started taking data in 2010 and the NO µ m − 9 are known to be large, the size of 2 i ∆ + | m µ 12 ν θ ≡ → 2 i j and m + ∆ π 23 In these proceedings, the present on-going experiments and future prospects are summarized. Soon after the discovery of neutrino oscillation by SK, the importance of the sub-leading In the last decades, great progress in understanding the nature of neutrinos has been made and it Accelerator based long baseline (LBL) neutrino oscillation experiments produce 1 θ as beam and detect it at several 100 km from the source. The beam is produced at KEK in Tsukuba-city and detected by Super-Kamiokande at 250 km [ ) changes its type during flight if the mass eigenstates of neutrino have different mass eigenval- µ µ µ τ [ being constructed to start data taking in 2013. oscillation with in atmospheric neutrino observation by Superk-Kamiokande (SK) [ violation search. With the goal to discover electron neutrino appearance and determine electron neutrino appearance channel was pointed out [ where LBL experiments with 1 LBL experiment was the started inν 1999 and finished in 2004 inThe Japan in experiment which confirmed the the existenceafter of 250 neutrino km oscillation by flight. observing Theperiments disappearance MINOS in of Europe experiment were in planned USby to [ SK. further confirm/establish the neutrino oscillation discovered and nature of neutrino, especially massments and of neutrino flavor oscillation. mixing Neutrino structure oscillation through is a the phenomena finding that and the type measure- of neutrino ( probability of electron neutrino appearance gives aof measure electron of neutrino the appearance mixing at angle thethe atmospheric CP oscillation length violating means observable, non-zero the phase is now established that the neutrino haveHowever still finite there mass are and many “surprisingly” unanswered large questions mixing suchpicture as unlike is whether quarks. the correct?, standard all 3x3 mixing three matrix from flavors the participate to quarks, the CP mixing?spectrum, is normal Why or violated?, inverted the hierarchy?, what mixing etc. looks isunraveling The neutrino so these the keeps different attracting mysteries absolute much could mass?, attention because particle provide why physics, breakthrough so physics to light?, at understand whatdominated high universe. fundamental is energy questions the scale in mass beyond the standard model and origin of matter Long Baseline Neutrinos 1. Introduction ν ues each other and the flavormass eigenstates. eigenstates The are typical expressed oscillation as length is a characterized linear by combinations of more than one ν ventional” method where pions producedν by hitting proton beam on a target decay in flight into PoS(ICHEP2012)007 µ × ν 6 . ] and for 5 20 GeV 20 ∼ i 10 ν × E h 4 . Takashi Kobayashi (right). The beam 1 and 3 20 10 decay by its decay topology × τ 7 . disappearance measurements as a µ ν emulsion cloud chamber (ECC) blocks, each 3 3 CC cross section). The black histogram is the spectrum ]. Main goal of the CNGS experiments is to detect 735km × 13 10 cm POT equivalent data. )[ POT in 2012. × 2 19 5 20 . 10 10 12 × 8 × × . 8 5 . . 1 appearance. The beam is produced by the 30 GeV ∼ e ν CC interactions (=flux µ ]. The neutrino beam is a 2-horn focused on-axis wide band beam with the ν 4 chambers with 476 ton total Liq. Argon mass. It has been taking data since 3 )[ 1 275 m ]. OPERA is an emulsion based detector which identify = POT by 2011 and 6 MINOS experiment. Left picture is the far detector in the Soudan mine. The right graphs are ex- 6 . 20 , respectively. 19 10 µ CERN neutrino to Gran Sasso (CNGS) is a high energy muon neutrino beam of The other detector is a Liquid Argon TPC detector, ICARUS, which consists of two 3 The T2K (Tokai to Kamioka) experiment is a long baseline experiment in Japan with the MINOS is a long baseline experiment with the precise ν × × appearance. There are two experiments now taking beam data from CNGS, OPERA [ 4 9 τ . . produced at CERN with the SPS 400-GeVSasso proton laboratory beam at and directed 732 to km the distance detectors (Fig. placed in Gran main physics goal, in whichMain muon Injector neutrino at beam FNAL and is detected produced byfrom by the FNAL the MINOS (Fig. detector 120 located GeV in proton the beam Soudan mine from at 735 km power of the Main Injectorat had near reached (980 at ton) 350 andfinished kW. far Magnetized on (5,400 tracking Apr. ton) calorimeters 30, site. are 2012 placed Physics with data the taking total had accumulated been POTs of started 10 in May 2005 and ICARUS [ (kink). The detector consists oftarget emulsion part based is active made target of part and 150,000 electronic 7 tracker part. The main goal of discovering 2.2 CNGS experiments ν of which is aof stack 1.25 of kt. 57 The emulsion1 OPERA sheets detector and started 56 to 1mm-thick take neutrino lead beam sheets, data with since the 2008 total and accumulated weight 2.3 T2K 2. Current experiments and their status 2.1 MINOS peak energy of around 3 GeV as seen in the expected neutrino spectrum in Fig. in the default MINOS running condition. and 3 Oct. 2010 and have accumulated 5 Figure 1: pected energy spectra of Long Baseline Neutrinos PoS(ICHEP2012)007 τ ν (3.1) flux is plotted (GeV) ν E µ ν Takashi Kobayashi CC cross section) as a τ ν ( × , f ar 6 10 ε × 0 0.5 1 1.5 2 2.5 3 3.5 1

0 ·

1.2 0.8 0.6 0.4 0.2 flux at SK is plotted in the right panel.

] MeV/cm POT/50 Flux[/10

21 2 µ f ar ν

732km σ · spectrum is optimized to maximize number of can be evaluated (and of course the statistical µ f ar ν f ar exp Φ · 4 N appearance probability) τ osc ν P are oscillation probability, neutrino flux, neutrino inter- ) = f ar ν ε E ( f ar exp and N f ar σ , f ar Φ , osc P in a far detector to the expected number of events with oscillation which can be ) ν T2K experiment. Expected energy spectrum of ). E from the beginning to June 9, 2012. ( f ar obs Cern Neutrino beam to Gran Sasso (CNGS). The expected energy spectrum of 20 f ar obs N 10 N × The basic method of the analyses in LBL experiments is to compare the observed number of Figure 3: 01 . in a simplified formula omittingphase to space, explicitly and write integration of,action for cross example, section final and state detection particle LBL experiment efficiency is at determined by the how far precisely error detector. of The precision or sensitivity of a events 3. Important issues in LBL experiments symbolically expressed as Main Ring (MR) of J-PARCSuper-Kamiokande (Japan detector at Proton 295 Accelerator km from Researchscheme J-PARC. Complex) In is order applied and to for detected maximize the the by firstoscillation sensitivity, time the off-axis maximum to have of intense narrow energystable 0.6 spectrum operation. GeV. peaked After T2K at one the year started expected of2011, data recovery work the taking from experiment in the resumed big Jan. data east3 Japan taking earthquake 2010 from on and March March 11, 2012 achieved and 200 total kW accumulated POT reached in the left panel (red histogram) overlaid with ( Figure 2: Long Baseline Neutrinos function of neutrino energy which demonstrate that the appearance events. PoS(ICHEP2012)007 /K, π (3.2) ], MIPP at FNAL Takashi Kobayashi ]. Example of such 16 , 19 , 15 , 18 , 14 16 near f ar ε ε · · ) and beam line geometry. Because θ f ar near σ σ · · f ar near Φ Φ · osc 5 P . These hadron production experiments have been 4 and polar angle · p obs near N ) = ν E ( f ar exp precisely, usually it is evaluated by extrapolating the measurement by N flux at near and far site (without oscillation) are not the same due to f ar exp µ N ν obs near ], NA61 at CERN-SPS for T2K and US experiments [ N 17 Example of results from hadron production measurements in NA61 for T2K for pion (left) and Beam flux (absolute normalization, spectrum shape andNeutrino near interaction to cross far section extrapolation) Detection efficiencies of far and near detectors law. However, by this extrapolation, partial cancellation of systematic errors associated with In order to predict As seen in these formula, important elements which determine the precision are The neutrino flux at near and far site and their relation are governed by parent hadron ( Dedicated measurements of hadron production for LBL experiments have been made in the 2 • • • R / providing critically important data for improving the precision of LBL experiments. for MINOS [ measurements from NA61 are plotted in Fig. a near detector Figure 4: Kaon (right) Long Baseline Neutrinos The energy spectra of geometrical difference relative to the neutrino productionciencies region are and usually also different the for cross near section1 and and effi- far detector, so this extrapolation does not follow simple absolute normalization, energy spectrumexpected. prediction, and neutrino interaction cross sections are For the beam flux and crosssurements section, have been as playing seen critical in roles the for following achieving examples, high in precision situ in or LBL supporting experiments. 3.1 mea- Understanding beam etc) distributions at production (momentum HARP experiment at CERN-PS for K2K and MiniBooNE experiments [ the geometory is underneutrino control, flux and precise extrapolation knowledge from the of flux hadron at near production site is to the essential one to at the predict far site precisely. PoS(ICHEP2012)007 , ]. 6 rec ν 27 E ] and 1) for ] have . 1 20 CC cross 25 µ ± ν 7 significance . σ POT data [ POT data taken 5 20 4 (10 Takashi Kobayashi . 20 , 4) Reconstructed 0 10 0 10 ± π × × 2 . 43 . Dominant background . beam at 2.5 01 . p µ ] and MiniBooNE [ ν + 24 − , e 23 → CCQE cross section measured by the µ n ν + e CCqe interactions by the near detector is ν ], T2K [ µ interactions in which one of electromagnetic appearance with 3 22 ν e , appearance should have only one electron-like 0 appearance in the ν e π e 21 ν 3 BG expectation with 1 ν . 6 0 ± 5 . CCqe interaction ]. Example of such results are quoted in Fig. e ν 26 1250 MeV. Eventually, 11 signal candidate are found. Their together with expected distributions. The expected observation at < 6 rec in the beam and (2) NC ν s is missed. The signal events are selected by requiring 1) 1 e-like ring w/ e E γ ]. ν ]. In T2K, signal event of 100 MeV, 2) No decay electron detected, 3) Force to find a 2nd ring although 20 ] and the right is preliminary results of 28 . Expected number of events in SK thus obtained are 3 > 6 23 ) . The significance of the excess beyond the background expectation is calculated ) event candidates beyond 1 vis 1 e E . ν 0 ( 0 Measurements of neutrino interaction cross sections. Left is the result of inclusive = A experiment[ ν appearance 13 e θ Another important element for the precision LBL experiments is understanding neutrino in- In 2011, T2K observed the first indication of ν 2 2 ˇ electron neutrino energy distribution is plotted in Fig. sin standard ring counting found onlyand 1 the ring, forced-found and reconstructed 2nd invariant ring mass be with the less original than ring 105 MeV to reject remaining Cerenkov ring which comes from visible energy ( At this conference, T2K released thenutil new June result 9th, of 2012 [ sources are (1) intrinsic showers from two decay- SK is predicted inMC principle simulation by validated extrapolating by the the neutrino hadron measurement production at data near actually site measured using by beam NA61. In Fig. section from T2KMINER [ oscillation experiments themselves such as K2K [ 4. Results 4.1 muon momentum distribution of events selected as 3.2 Understanding cross sections teraction cross sections. For that purpose, dedicated experiments such as MINERvA [ Figure 5: plotted. Absolute flux and spectrum shapeare of tuned neutrino beam to and reproduce neutrino this interactionwell observation. cross as sections The seen tuned in Fig. MC prediction reproduce the observation very Long Baseline Neutrinos been providing important results [ by detecting 6 PoS(ICHEP2012)007 1, . 0 ]. In , and is not δ = 30 , E 13 / θ 29 L 2 2 Takashi Kobayashi , the mixing angle 0 (sin 2 = eV appearance [ 13 2 e θ − 2 ν 2 10 & 2 m appearance candidate events. (Right) ∆ . Events with an electron from the e appearance although the 2 ν 0 is 0.08%. T2K detected an evidence e eV ν = . For 3 13 7 − θ . 0 and the normal (inverted) mass hierarchy a 10 POT in the neutrino-enhanced beam, MINOS CP CCQE reactions measured by the T2K near detec- = δ × 20 µ 3 7 δ ν 0, normal mass hierarchy). With an exposure of is obtained. 10 and is excluded. ∼ ) × = 2 13 − 6 θ . δ . For 093 2 . 7 2 0 1, ( . 0 region of = 051 . 2 backgrounds are 1.5 (1.1) and 19.2 (3.7) for all neutrino energy 0 13 m e ]. Observed number of events is 19 (4) while expected number of θ ν ∆ = 2 31 2 23 θ 2 0 (sin sin ) are shown in Figure = 13 θ 23 13 2 θ θ ( 2 20 GeV). The observations are consistent with background expectation. The distri- 2 2 2 events and beam < sin e POT in the antineutrino-enhanced beam, MINOS observed 20 signal candidate events ) or the probability to observe 11 events with ν (Left) Muon momentum distribution of rec ν region greater than a few times 10 13 . The exclusion contour is also plotted in Fig. σ 20 E θ 7 13 2 appearance for the first time which open a possibility to detect CP violation in the lepton 10 ( θ At CNGS, the OPERA experiment searches for the The MINOS experiment also has been making efforts to search for 0, normal mass hierarchy). The allowed regions as a function of the CP violating phase, 2 e 2 × ν 2 = 3 . δ 2sin while 17.5 (21.4) events are expected in the Far detector assuming sin 3 butions of the reconstructed neutrino energy forin the observed Fig. events and MC predictions are plotted Allowed region of oscillation parameters sin order to select electron neutrino2) candidate to events, events match are with required theor 1) expected a to beam be track in timing, extending fiducial 3)reject more volume, events not than with associated 15 a with muon, planes tracksthat 4) beyond longer of to the than a have end 24 5 minimum of contiguous planes duce ionizing planes a the particle, with reconstructed background, 5) an shower in to energy activitytechnique the have deposition is to at energy latest used. least from analysis, With half 1 a anobserved to exposure nearest-neighbor 152 of 8 electron “library 10 candidate GeV. event events In matching” in orderassuming the (LEM) Far to sin detector further while re- 127.7 (161.4) events are expected oscillated region ( sin tor. (Center) Reconstructed neutrino energy distribution of T2K to be 3.2 best fit of 2sin Figure 6: Long Baseline Neutrinos of sector. optimized to the atmospheric primary vertex are selected [ PoS(ICHEP2012)007 . 8 04 04 . . 0 0 and . In − + 23 2 23 96 θ . m 0 ∆ ) = and disappearance θ 2 µ 23 ( Takashi Kobayashi ν 2 ]. Using the data θ 33 by the MINOS appear- CC events while 3564 (GeV) 13 µ CP rec 2θ ν δ 2 ν and sin E sin , , , , , , , 2 5 is precisely known in LBL 42 71 28 100 and 108 103 107 106 L distribution of the fully recon- eV , 013012 , 171803 , 111301 , 191802 , 041801 13 86 ν 3 108 101 108 , 078 (2004). θ 107 − E 2 04 , 010001 (2012). 2 86 50 10 , 2369 (1978); S. P. disappearance [ , 493 (1969); Z. Maki, 17 , 051102R (2010). , 123 (2012). × 28 µ 82 12 ) ν , 172 (1958); V. N. Gribov and 09 10 . . ]. With the total neutrino-enhanced beam , -DESIGN-1998-01 34 , J. High En. Phys. (MINOS), Nucl. Inst. & Meth. A (MINOS), Phys. Rev. Lett. (MINOS), Phys. Rev. Lett. (MINOS), Phys. Rev. Lett. 0

0 0

6 4 2

e (SNO), Phys. Rev. Lett.

13 Indentified Indentified ν shows the

) (eV (to be published). m (to be published).

∆ + − 2 2 2 32 et al. (RENO), Phys. Rev. Lett. (PDG), Phys. Rev. D et al. (T2K), Phys. Rev. Lett. (Super-Kamiokande), Phys. Rev. D et al. (Double ), Phys. Rev. Lett. 8 (Daya Bay), Phys. Rev. Lett. et al. et al. et al. , Proceedings of the XXV International Con- et al. 39 Proceedings of the XXV International Con- et al. et al. appearance search. Top plot is the neutrino energy . et al. et al. et al. et al. 29 2 e 8 ν , 190 (2008). 200 MeV/c and found 31 events against an expec- = ( ference on NeutrinoJapan, June Physics 2012 and Astrophysics, Kyoto, A. Palazzo, and A. M.(2012). Rotunno, Phys. Rev. D and Thomas Schwetz, JHEP ference on NeutrinoJapan, June Physics 2012 and Astrophysics, Kyoto, 131801 (2012). (2012). (2012). (2011). 261802 (2009); Phys. Rev. D 181802 (2011). Mikheyev and A.913 Yu. (1985). Smirnov, Sov. J. Nucl. Phys. 596 (1998). nology, FERMILAB-THESIS-2009-44 (2009). FERMILAB-THESIS-2011-53 (2011). Campinas, FERMILAB-THESIS-2012-23 (2012). FERMILAB-THESIS-2008-04 (2008). 181801 (2011). 112005 (2005). (2008). B. Pontecorvo, Phys. Lett. B M. Nakagawa, and870 S. (1962). Sakata, Prog. Theor. Phys. | [5] G. L. Fogli, E.[6] Lisi, M. C. A. Gonzalez-Garcia, Michele Marrone, Maltoni, Jordi Salvado, D. Montanino, [8] Y. Abe [9] F. P. An [4] R. Nichol, in [7] Y. Itow, in [3] Y. Ashie [1] B. Pontecorvo, JETP [2] B. Aharmim [10] J. K. Ahn [11] K. Abe [12] P. Adamson [13] P. Adamson [14] J. Beringer [15] L. Wolfenstein, Phys. Rev. D [16] E. K. Akhmedov [17] D. G. Michael [18] K. Anderson [19] J. P. Ochoa, Ph.D. Thesis, California[20] Institute R. of Tech- Toner, Ph.D.[21] J. Thesis, A. B. Coelho, University Ph.D. Thesis, of Universidade[22] Estadual R. de Cambridge, Ospanov, Ph.D. Thesis, University of Texas at[23] Austin, P. Adamson STFC; the USnesota; NSF; the the University StateFAPESP, of CNPq, and Athens, University and Greece; ofMinnesota CAPES. DNR, Min- and We the Brazil’s areLaboratory, crew grateful and of the to personnel thetributions the of Soudan to Fermilab this Underground for effort. their Weputing con- thank Texas Center Advanced Com- at Thethe University provision of of computing Texas resources. at Austin for > 2 m µ 22 p 0.4 ∆ 0.4 /4 /4 | π π < > . 23 23 . The allowed region given by T2K is overlaid in the Fig. θ θ -mode -mode 8 /4 /4 for the two ν ν π π δ MINOS 8 < < 0.3 0.3 1.51.5 23 23 θ θ POT) and atmospheric (anti-)neutrinos (37.9 kiloton-years). The POT POT 23 θ > 0 20 20 < 0 2 2 2 10 10 m 20 m × × POT taken before the long shutdown due to the earthquake, T2K )) )sin ∆ ∆ ππ 13 11 MINOS Best Fit MINOS Best Fit 68% C.L. 90% C.L. (( 0.2 /4 /4 /4 /4 0.2 θ MINOS 10.6 3.3 δδ event candidates together with MC expectations of signal (red) and back- π π π π 10 -mode -mode (2 ν ν 2 20 4. > < > <

) as a function of e 23 23 23 23 disappearance determine the oscillation parameters π/ θ θ θ θ × 23 ν θ POT POT 2sin − ( 10 20 20 2 µ 23 > 0, > 0, < 0, < 0, 10 10 POT, MINOS observed 2894 fully reconstructed 2 2 2 2 0.1 θ 0.1 0.50.5 × × 36 )sin m m m m ν × to our data using constraints from reactor . ∆ ∆ ∆ ∆ 3.3 13 δ 10.6 θ 20 (2 2 43 . 10

00 0 0

11 33 22 00

ln(L) -2 -2 0.0 2.0 1.5 1.0 0.5 0.0 ln(L) 2.0 1.5 1.0 0.5

∆

∆ ×

) ( ) ( δ π δ π 14(syst) without neutrino oscillations. The observed and expected reconstructed 7 . mass hierarchies. FIG. 4: Thehood resulting from values a of fit of twice the negative log likeli- FIG. 3:values The for 68% 2sin and 90% confidence intervals of allowed experiments [8–10], assuming variousarchy values and of the the mass sign hier- of ± CCqe events by requiring fully-contained in fiducial volume, single muon-like ring µ (Left 2 plots)Allowed regions of oscillation parameters sin ν disappearance from the neutrino energy distribution. µ MINOS experiment has been providing the most precise measurements of Measurements of T2K also started to contribute the measurement of ν distributions are plotted in Fig. 2 23 m ν and allowed region is plotted in Fig. beside the Super-Kamiokande atmospheric neutrino measurement.preliminary Recently results MINOS using released new the complete data set [ contrast to the atmospheric neutrinoexperiments. measurements, Therefore, flight precise measurements distance are∆ possible for the oscillation parameters structed events where the distortion ofseen. the energy spectrum In expected addition, by in oscillationsenhanced can beam the be data latest clearly (3 analysis,best two fit additional point data with sets all are these included: sample are the antineutrino- tation of 104 4.2 distribution of the detected ground(blue). Bottom plot isregions excluded of region other by experiments. OPERA (upper right of the blue curve) with the allowed with 0 or 1 decay electron associated, E ance search. (Right 2 plots) Results from OPERA corresponding to 1 selected Latest preliminary SK results areexperiments also are consistent drawn with in each the other. same figure and all the results from different exposure of 10 Figure 7: Long Baseline Neutrinos events are predicted assuming no oscillation. Figure PoS(ICHEP2012)007 . ) CP 13 ap- δ θ syst e ( yrs or ν · 2 8 . . provided 15 17 − + appearance and sin 13 ) interactions θ τ while the ap- τ 23 ν A which could ν θ stat 13 ν ( Takashi Kobayashi measurements by 3 m . ∆ , sin 13 44 θ 12 ]. Systematic error on θ ± and 8 31 . POT data taken in 2010- 13 θ 19 disappearance with more than 10 e × ν ]. Discovery of large 88 35 . [ appearance search. The 13 events at far detectors in MINOS (Left) and θ τ µ ν ν ]. 34 9 interaction with the fine tracking capability of ECC. τ ν appearance by positively identifying the CC interactions e candidate event was found in the data taken in 2008-2009 ν from precision measurements of the appearance probability, τ appearance [ ν τ CP ν from CC δ τ POT. OPERA is analyzing 8 19 10 and/or mass hierarchy by combining with the precise × evidence of CP appearance and background events are 2.1 and 0.2 [ 30 . δ σ τ signal excess over the background is found to be 170 8 ν . τ . Threrefore, in the near term future, it is very important to improve the precision of ν 2 23 disappearance is now getting more important. The CP violating term in the m ∆ µ Reconstructed neutrino energy distributions of enhanced sample of atmospheric neutrinos. With the 2806 days of data (=173 kt ν days), · τ appearance search ν significance and provide precise measurements of τ Reactor disappearance measurements primarily depend only on Although it is not accelerator based LBL experiment, SK has been searching for T2K found the first evidence of The The main goal of the OPERA experiment is the ν σ events which is 3 are identified by decay kink of OPERA reported in 2010 thatcorresponding one to 5 2011 and another candidateagainst event expected is found so far. In total 2 candidate eventsin has the been found great opportunities to understand the unknownhierarchy. nature of neutrinos, such as CP symmetry and mass the expectation is being estimated. 63.1 Mt of the appeared flavor.7.7 Reactor experiments clearly observed pearance probability depends not only onand them sign of but also on variousthe other appearance parameters probability including as much asenable possible to by constrain LBL experiments T2K and NO Therefore, in order to constrain 5. Future reactor experiments. pearance probability is symmetrically proportional to all mixing angles sin Figure 8: 4.3 Long Baseline Neutrinos T2K (Center) experiments. Points with errorand bars without are data disappearance. and (Right) the histograms Allowedexperiments. are parameter expected regions distributions by with disappearance measurements by various PoS(ICHEP2012)007 σ ]. . In (4% 39 2 13 θ eV ˇ ˇ ] and the Cerenkov Cerenkov 3 − 38 10 off-axis [ disappearance. appearance and ◦ × µ Takashi Kobayashi through precision e ν 09 11 . . . ν 0 0 23 + − off axis [ θ ◦ 39 . measurement from reactor 13 ]. In Europe, EoI of the LBNO θ 300 kton class Water × 36 (2007) 101–159 95 (90%CL) . . 0 level appearance signal. The OPERA 439 ∼ σ 93 . 0 , “Evidence for oscillation of atmospheric > Phys.Rept. which can be measured by the 23 . θ et al. 10 300 km from J-PARC, 2.5 23 2 θ 2 ∼ significance in the atmospheric neutrino observation. σ opened the possibility to find CP violation and determine ]. The primary option of the project is to produce neutrino 13 θ 37 , “Measurement of Neutrino Oscillation by the K2K Experiment,” is now most constrained by MINOS as 2 . (1998) 1562–1567 et al. appearance using fine tracking detector with emulsion technique. 2 23 81 τ m observation as sin ν ∆ ν appearance at 3.8 Collaboration, Y. Fukuda τ ν disappearance for coming years. (2006) 072003 µ ν Phys.Rev.Lett. appearance is reported by T2K experiment. It opened possibility of CP violation by SK atm A experiments are expected to play important role to constrain D74 e ν ν , now least known mixing angle is 23 candidate events are detected while the expected appearance signal and the background disappearance, θ 13 Collaboration, M. Ahn τ µ θ ν ν neutrinos,” K2K Super-Kamiokande Phys.Rev. For the longer term future, efforts to formulate experiments to attack the CP violation and mass Present status and results , and future prospects of LBL experiments are reported. The 3.2 The discovery of finite and large disappearance in LBL experiments combined with precision µ [3] [2] [1] S. E. Kopp, “Accelerator-based neutrino beams,” hierarchy are being made in the world taking into account the new knowledge of the large T2K and NO measurement of the US, the proposed LBNE project, inby which a the 34 neutrino kton beam Liq. is produceda Argon at phased TPC FNAL approach in and starting the detected with Homestake a mineproject 10 at is kt 1300km submitted detector from to on FNAL, CERN surface is SPSCbeam first reconfigured [ [ using into new facility atFinland. CERN In SPS the first and phase, direct 20phase, to kton possibilities LAr a TPC of detector is 100 placed used kton to at class determine 2300km the LAr from mass TPC hierarchy. CERN at In in 2300km the and second 2 and mass hierarchy determination. MINOS also reported 2 Long Baseline Neutrinos high precision of similar level forments all of three angles are necessary. Thanks to the precision measure- detector at 130 km (Frejus) withtwo 4MW options beam for from future high LBL power experiments SPL are are being being discussed; discussed. One In isother Japan, a is 1-Mt 100 class kt class Water LAr TPC in Okinoshima island at 658 km from6. J-PARC, 0.78 Summary evidence of experiment is looking for So far 2 expectation are 2.1 and 0.2, respectively. AlthoughKamiokande it observed is not accelerator LBL experiment,For the the Super- meas) and detector, Hyper-Kamiokande in Kamioka at ν mass hierarchy in the future. Inexperiments the can near start constraining term, CP violation precision andoptimized mass for measurements hierarchy. CPV Future of and large Mass scale experiments hierarchy are being discussed and proposed in theReferences world. PoS(ICHEP2012)007 . τ ν → µ ν . (2011) . (2008) (2012) . D83 (2011) 106–135 D78 Takashi Kobayashi (2012) , . A659 (2012) 035210 Phys.Rev. (2007) 29–53 CERN-98-02, Phys.Rev. . 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