Future Experiments with Super Neutrino Beams

Transcription

1 1 Future Experiments with Super Neutrino Beams T. Nakaya a a Faculty of Science, Kyoto University, Sakyo-ku, Kyoto , JAPAN The recent status of future neutrino experiments with super neutrino beams is summarized in this paper. Physics motivations of the neutrino experiments are the discovery of ν µ ν e oscillation and the measurement of the mixing angle θ 13, the precise measurement of neutrino oscillation parameters, θ 23 and m 2 23, the determination of the sign of m 2 23, and the search for CP violation in neutrino oscillation as an ultimate goal. In order to achieve the physics goals, several neutrino experiments with super neutrino beams are proposed all over the world; the JHF-Kamioka project in Japan, several experiments in the United States, and the CERN SPL and the CERN SPL+β beam projects in Europe. The physics sensitivity of these experiments are typically θ , the precision of θ 23 at 1% level, the precision of m 2 23 at ev 2, and the sensitivity of the CP violation phase, δ, downto The experiments with the super beams have a great chance to discover new phenomena in neutrino oscillation within the next 10 years before the era of a neutrino factory. 1. Introduction The discovery of neutrino oscillation [1] is one of the most exciting news in physics during the last decade. The neutrino oscillation is physics beyond the standard model, and is evidence of a finite neutrino mass and lepton flavor violation. In addition, the large mixing in the neutrino sector is found to be much different from that in the quark sector. The neutrino oscillation opens a new window to study the symmetry between quarks and leptons through their mixing. The quarks and leptons may be unified at ultra-high energy in the Grand Unified Theory (GUT), and the very small neutrino mass can be explained by the See-Saw mechanism [2] in physics at the ultrahigh energy. The detailed physics background of neutrino oscillation is described in the papers of NEUTRINO After the discovery of neutrino oscillation, it is a natural way to study this new phenomenon with higher sensitivity and higher precision. An experiment with a super neutrino beam is a proposal of this high sensitive experiment. The neutrino oscillations are discovered in two phenomena; atmospheric neutrinos and solar neutrinos, which indicate the existence of two mass differences ( m) in three neutrinos. Since three neutrinos should have different masses, the scheme of three generation mixing in neutrino oscillation is a natural explanation with the Maki-Nakagawa- Sakata (MNS) matrix [3]. In MNS, there are three mixing angles and one CP violation phase. Two of mixing angles, θ 12 and θ 23,aremeasuredin atmospheric and solar neutrino oscillations, respectively. The third mixing angle (θ 13 )andthe phase (δ) are unknown yet. The discovery of the third mixing in ν µ ν e oscillation establishes the 3 generation mixing with the MNS matrix. In addition, a next generation experiment has a higher sensitivity to conduct the higher precision measurement of ν µ ν τ oscillation, which can probe the deviation of the mixing angle θ 23 from the bi-maximum (45 degrees), can measure the mass square difference m 2 precisely, and can determine the sign of m 2. The experiment can also search for the CP violation phenomena in neutrino oscillation, which determine the CP violation phase δ in the MNS matrix. The experiment is also sensitive to several non-standard scenarios in neutrino oscillation; such as an existence of a sterile neutrino, a neutrino decay or a flavor changing neutral current, and CPT violation, etc.. The next generation neutrino experiments with more intense neutrino beams are proposed all over the world. In this paper, the experiments with a high intensity conventional neutrino beam, so called super neutrino beam, are summarized.

2 2 The detailed theoretical motivation and the notation in neutrino oscillation is reported in a paper by Dr. Lindner [4]. The recent status of off-axis neutrino beams at NUMI and CNGS is reported in a paper by Dr. Dydak [5]. This paper concentrates to summarize the status of experiments with super neutrino beams. In Section 2, a Super Neutrino Beam together with the corresponding accelerator is introduced. In Section 3, an experiment with the super neutrino beam is summarized. In Section 4, the physics sensitivity of the experiments is presented. 2. Super Neutrino Beams A Super Neutrino Beam is a very intense neutrino beam produced by a high intensity proton accelerator of an order of MW beam power. A super neutrino beam is recently proposed in Japan, the United States, and Europe. The neutrino beam is produced with a conventional method using horn focusing. The intensity of the super beam is typically two orders of magnitude higher than the world s first long-baseline neutrino experiment, K2K [6]. In consequence, a two-orders of magnitude higher sensitive search and more precise measurements can be conducted as compared with K2K. The proton accelerators for a neutrino beam are summarized in Table 1. In Table 1, the proton accelerators for super neutrino beams are under construction or at the stage of an idea. With the accelerators shown in Table 1, the existing or proposed (super) neutrino beams are summarized in Table 2. The experimental sensitivity is proportional to the product of the # CC events in Table 2 and the size of a detector. A standard of the quality of a neutrino beam is L/L osci. since non-oscillated neutrinos only generate background events for a measurement. Some of the proposed neutrino beams are designed to conduct the experiment with the baseline of oscillation maximum to suppress the background events. A ν e contamination in the beam, f(ν e ), is also an intrinsic background in ν µ ν e search. The typical ν e contamination is 0.5 % which sets a limit on the sensitivity of ν µ ν e search with a super neutrino beam. 3. Experiments with Super Neutrino Beams Experiments using a super neutrino beam are currently proposed in Japan, the United States, and Europe. In Japan, the JHF-Kamioka neutrino project is proposed to start in 2007 [7]. In the United States, several experiments are taken into consideration. In Europe, CERN SPL and SPL+β beam proposals [8] are taken into consideration. The experiments in the United States and Europe have no defined schedule by the present stage. These experiments are summarized in this section for the experimental setup, the beam-line, and the detector. The physics sensitivity is presented in the next section The JHF-Kamioka Neutrino Project in Japan The JHF-Kamioka neutrino project is proposed as an experiment in the Japan Hadron Facility (JHF). The experiment uses a high-intensity narrow-band neutrino beam produced by the 50 GeV proton synchrotron (PS) in JHF. The JHF accelerator is under construction and is planed to start operation in The far detector at the beginning is Super-Kamiokande (SK), a50ktwaterčerenkov detector. The baseline length of the experiment is 295 km, as shown in Figure 1. Several features of the JHF-Kamioka Super Kamiokande 295km Tokyo KEK JAERI (Tokai) Figure 1. Baseline of the JHF-Kamioka neutrino experiment

3 3 Table 1 High Intensity Proton Accelerators for a neutrino beam. The accelerators listed below JHF are used for a super neutrino beam. Accelerator Operation Beam Power Energy Intensity Reputation rate (MW) (GeV) (10 12 ppp 1 ) (Hz) KEK-PS running BNL-AGS running FNAL-Main Injector running CERN-SPS running JHF construction BNL Super-AGS idea FNAL New Proton Driver idea CERN SPL idea JHF-upgrade idea : Protons per pulse. neutrino experiment are A narrow-band neutrino beam with the energy tuned to the oscillation maximum. JHF, the angle is adjusted between 2 and 3 degrees to produce neutrinos below 1 GeV. The expected neutrino spectra are shown in Figure 2. The energy of the neutrino beam is below 1 GeV to suit the characteristics of the water Čerenkov detector. A quasi-elastic (QE) interaction is used to reconstruct the neutrino energy. The energy resolution is 100 MeV dominated by Fermi motion. These features make the experiment very unique to perform precision physics in the neutrino sector. A neutrino beam is produced by a proton beam. The proton beam is extracted in a single turn and transported to a production target passing through a superconductivity magnet beam line. The secondary pions produced in the target are focused by dual electromagnetic horns [9], and decay in a 130 m long decay pipe. The narrow-band neutrino beam is produced with an off-axis technique [10], in which the beam direction is intentionally displaced by a few degrees from the far detector direction. With the finite decay angle, the characteristics of the Lorentz boost makes the neutrino energy almost independent of the parent pion momentum, which results in a narrow spectrum. The peak neutrino energy can be adjusted by the off-axis angle. In ν µ N CC (/100MeV/22.5kt/yr) > E ν (GeV) Figure 2. Neutrino energy spectra of charged current interactions with the JHF Off-Axis neutrino beam. The spectra with the off-axis angle of 1 degree (solid line), 2 degrees (dashed line) and 3 degrees (dotted line) are shown. The standard wide-band beam at 0 degree is also shown by a thin line for reference.

4 4 Table 2 (Super) Neutrino Beams. The energy is the mean neutrino energy. The distance is the baseline between the accelerator and the detector. # CC events is the number of neutrino events with charged current interaction. L osci. is the oscillation length 1. f(ν e ) is a fraction of ν e flux relative to ν µ. Neutrino Beam Status Energy Distance (L) # CC events L/L osci. f(ν e ) (GeV) (km) (/kton/year) at peak K2K running NUMI (high-e) start NUMI (low-e) start CNGS start JHFν proposed NUMI off-axis under study Super-AGS under study JHFν upgrade idea SPL idea SPL β beam 2 idea : The definition of neutrino oscillation length is L osci. = π 2 <E ν > 1.27 m 2 for m 2 = ev 2. 2 : 6 He beam with γ = 150 for ν e In order to perform a CP violation search, a new far detector with a mass of Mton is a crucial element together with an upgrade of the JHF accelerator to 4 MW. The Mton water Čerenkov detector, Hyper-Kamiokande, is under design and R&D [11] for this propose. The schematic picture of Hyper-Kamiokande is shown in Figure 3. Figure 3. A schematic picture of Hyper- Kamiokande detector In a CP violation search, an anti-neutrino beam is produced in the JHF by reversing the polarity of the magnetic field of the horns. The antineutrino flux is estimated to be 15% lower than the neutrino flux, and the total number of antineutrino events results in one third of the neutrino events because of the smaller cross section Super-beam proposals in the United States In the United States, an upgrade of the AGS (Super-AGS) at BNL, a construction of a new proton driver at FNAL, and an upgrade of the Main Injector at FNAL are taken into consideration for a super neutrino beam. The performance of these accelerators is summarized in Table 1 and Table 2 except for the FNAL Main Injector upgrade. By the present stage, the LOI of Super- AGS is submitted, and other proposals are under consideration. For an experiment with the super neutrino beam, two neutrino detectors are proposed. One is a 500 kton Water Čerenkov detector (UNO) similar as Super-Kamiokande, and the other is a magnetized liquid argon TPC with a mass of 100 kton (LANNDD). There are several candidate places of an experimental site with the detectors, and there are three accelerators for a super neutrino beam. The baseline of the experiment is not decided yet, and there are several proposals as shown in Figure 4.

5 5 A unique feature of the United States proposal is ν/100m 2 /20 mev ν µ ν e ν µ bar ν e bar Energy (GeV) Figure 4. Baselines of super neutrino beam experiments under consideration in the United States. the longer baseline than other projects in Japan and Europe. The baseline of the proposed experiment from BNL to Soudan is 1711 km. This is a unique feature to study a matter effect in neutrino oscillation to determine the sign of m CERN SPL and SPL+β beam proposal in Europe The Super-Proton-Linac, SPL, with 4 MW beam power is designed at CERN as the first stage of an accelerator complex of a neutrino factory [12]. The SPL has very high beam power, and it is an ideal source of neutrinos before a neutrino factory starts. The SPL is planned to recycle LEP super-conducting RF cavities for saving. The SPL beam energy is 2.2 GeV, and it produces a low energy neutrino beam of 250 MeV by horn focusing. The spectra of neutrinos are shown in Figure 5. The low energy neutrino beam can suppress a fake ν e background by neutral current π 0 production. The baseline of the experiment is 130 km from CERN to Frejus. The low energy neutrinos maximumly oscillate at the distance. The proposed detector is the UNO detector, a 500 kton Water Čerenkov detector sitting in the Frejus tunnel [8]. Another unique proposal at CERN is a SPL β beam project, which makes a beam of radioactive ions produced by using SPL. Possible candi- Figure 5. Neutrino beam spectra by SPL with horn focusing. The fluxes are computed at 50 km from the target, then scaled to the relevant distances. dates of the radioactive ion are 6 He for ν e and 18 Ne for ν e. Since the typical beam energy of ions is one GeV and the Q value of the β decay is MeV, a very forward focused electron neutrino beam can be produced. This is one of the novel ideas to make an electron neutrino beam. The SPL neutrino beam and the β beam can be operated simultaneously, and the far detector measures both ν µ and ν e at the same time. The measurements of ν µ ν e and ν e ν µ oscillations provide a test of Time symmetry in neutrino oscillation. 4. Physics Sensitivity The proposed experiments with a super neutrino beam have similar sensitivity for physics, which is determined by the product of the beam power and the size of a detector by first approximation. In this paper, the physics sensitivity in the JHF-Kamioka project is presented in detail for reference. Other experiments are sometimes introduced for comparison ν µ ν e search The first physics goal of the experiment with a super neutrino beam is discovery of ν µ ν e os-

6 6 cillation to provide information on θ 13,oneofthe unknown parameters in neutrino oscillation. The JHF-Kamioka neutrino experiment is conducted with Super-Kamiokande (SK) at the beginning. As a beam exposure, a five year operation (1 year = 130 days) with full intensity is assumed in this study. An off-axis beam of 2 degrees is assumed to optimize m 2 = ev 2, for which the current best knowledge of m 2 is between ( ) 10 3 ev 2 at 90% C.L. by Super- Kamiokande [13] and K2K [14]. The signal of ν µ ν e oscillation is an appearance of ν e events in SK. The background processes are an intrinsic ν e contamination in the beam, ν µ events accompanying a π 0 which can fake an electron, and ν µ events with the muon being mis-identified as an electron. The largest background contribution comes from events with a π 0. The expected signal events and the background events are shown in Figure Expected Signal+BG Total BG BG from ν µ Reconstructed Eν(GeV) Figure 6. Reconstructed neutrino energy distributions of signal+background (BG), total BG, and BG from ν µ interactions. The ν e oscillation signal is calculated for m 2 = ev 2 and sin 2 2θ µe 1 2 sin2 2θ 13 =0.05. A clear peak by the ν µ ν e oscillation is seen at the expected neutrino energy constrained by the narrow-band beam. By assuming a 10% uncertainty of π 0 background yield, the sensitivity of the ν µ ν e search is shown in Figure 7. The achievable sensitivity of sin 2 2θ 13 can reach down to at 90% C.L. The JHF upgrade with Hyper-Kamiokande can m 2 (ev 2 ) % C.L. sensitivities JHF 5year WBB OAB 2deg. NBB 2GeVπ CHOOZ excluded sin 2 2θ µe Figure 7. The 90% C.L. sensitivity contours for the ν µ ν e search. The mixing angle sin 2 2θ eµ in this figure is an effective mixing angle between ν µ and ν e and sin 2 2θ eµ 1 2 sin2 2θ 13. For reference, the standard wide-band beam (WBB), the momentum selected narrow-band beam with a dipole magnet (NBB), and the 90% C.L. excluded region of CHOOZ are overlaid. improve the sensitivity of θ 13 down to below the 10 3 level, for which an understanding of the background is very important. A similar study is done for the SPL-UNO project, and results in a sensitivity of θ 13 down to the 10 4 level. The sensitivity of an experiment with a super beam is limited by an understanding of the background at the 10 3 level or below. In order to improve the estimation of the background, the JHF-Kamioka project proposes to build a similar Water Čerenkov detector as the SK at an intermediate distance of 2km from the target Precision measurement of sin 2 2θ and m 2 The neutrino oscillation parameters, sin 2 2θ 23 and m 2 23, can be determined by measuring the distortion of the energy spectrum in ν µ ν µ oscillation. The basic event selection in the JHF-

7 7 Kamioka experiment is requiring a fully contained single-ring muon-like event in a fiducial volume of 22.5 kt similar to that of the atmospheric neutrino analysis [1]. The expected neutrino energy spectra at SK are shown in Figure 8 in both cases of oscillation and no oscillation. After subtracting the background from non quasi-elastic events, the energy distortion is observed clearly in the ratio of the spectra with and without oscillation as shown in Figure 8. The oscillation parameters extracted in the figure are ( m 23, sin 2 2θ µτ ) = ((2.96 ± 0.04) 10 3 ev 2, 1.0 ± 0.01) from the input of ( ev 2, 1.00). The sensitivity is δm 2 23 x L=130 90% CL, syst=1% 3σ, syst=1% 3σ, syst=2% sin 2 1 (2θ 23 ) 90% CL and 3 σ contour plots Figure 9. Determination accuracy of sin 2 2θ 23 and m 2 withasplsuperbeamanda40ktonwater Čerenkov detector for a five years exposure. The crossing sign shows the initial value of the parameters. Figure 8. (Left-top) Reconstructed neutrino energy spectrum at SK for oscillation with ( m 23, sin 2 2θ 23 )=( ev 2, 1.00). The contribution of non-qe interactions is overlaid by a shaded (blue) histogram. (Left-bottom) The reconstructed neutrino energy spectra after subtracting the non-qe contribution. The histogram is for no oscillation, and the dots are for oscillation. (Right) The ratio of the reconstructed spectra with and without oscillation. The fit result of the oscillation is overlaid. expected to be 1% of precision to sin 2 2θ 23 and better than ev 2 to m 23. The sensitivity on m 2 is limited at ev 2 by uncertainties of the energy scale and neutrino flux estimation. A similar study is done for the SPL super beam with a 40 kton Water Čerenkov detector as shown in Figure Confirmation of ν µ ν τ oscillation and a limit on a sterile neutrino Though neutrino oscillation has been established in atmospheric neutrinos and ν µ ν τ is the most favored channel, the confirmation of ν µ ν τ in an accelerator experiment is important. For this purpose, the OPERA and ICARUS experiments are under construction at CERN [15]. A super beam experiment is also sensitive to confirm ν µ ν τ oscillation, and the measurement is used to set a limit to the existence of a sterile neutrino (ν s ). The ν µ ν τ channel is detected with neutral current (NC) interactions, which are insensitive to neutrino flavors. The number of NC events is the sum N(ν e )+N(ν µ )+N(ν τ ), where N(ν l )isthenumber of ν µ ν l NC events. N(ν e )andn(ν µ )are well measured through charged current (CC) interactions. In addition, N(ν µ ) is small owing to a narrow band-beam tuned at the oscillation max-

8 8 imum, and N(ν e ) is also small due to the small value of θ 13. As a result, the measurement of NC events is predominantly sensitive to N(ν τ ). We expect to observe 700 NC events in JHF- Kamioka. Observing a deficit of NC events is evidence of ν µ ν s oscillation. Though the sensitivity to ν µ ν s oscillation is under study, the limit on the fraction of ν µ ν s to ν µ ν τ oscillation is estimated to be O(10 20)% [7]. A CP = P (ν µ ν e ) P ( ν µ ν e ) P (ν µ ν e )+P( ν µ ν e ) = m2 12 L sin 2θ 12 sin δ. (1) 4E ν sin θ 13 In Equation 1, the recent discovery of solar neutrino oscillation with the LMA solution encourages to search for CP violation since both parameters m 12 and sin 2θ 12 in solar neutrino oscillation are large enough to make A CP measurable. The CP asymmetry is enhanced with a lowenergy neutrino beam, and it is independent of the value of θ 13 unless background exists 1. The A CP is estimated to be as large as 25%, while the fake asymmetry by a matter effect is only at the 5 10% level. Figure 10 shows the number of ν e and ν e events for 2 years of ν µ and 6 years of ν µ beam exposure. The measurement of A CP 4.4. Determination of the sign of m 2 Only the program in the United States is sensitive to determine the sign of m 2, though more studies will be done with a neutrino factory. A search for matter enhanced ν µ ν e oscillation with a distance of 9300 km from FNAL to Kamioka is studied [16]. An amplification of the oscillation signal by a factor of 20 is expected with a proper parameter set. In the JHF beam, a very long baseline experiment from Japan to Korea or China is also studied for this purpose [17]. Typically the neutrino beam energy with a super beam is lower and the baseline is shorter than for a neutrino factory experiment, the experiment is not so sensitive to the measurement. More studies have to be done in this area to fully investigate the potential of the super beam CP Violation Search The ultimate goal of experiments with a super neutrino beam is to measure CP violation in the lepton sector through neutrino oscillation. In the JHF-Kamioka project, an upgrade of JHF and the construction of Hyper-Kamiokande are assumed for a CP violation search. The CP asymmetry, A CP, is measured by comparing the ν µ ν e oscillation probability with that for the ν µ ν e oscillation. A CP is expressed as: Figure 10. The numbers of ν e and ν e appearance events in JHF-Kamioka. The two circles indicate the 3σ contour (blue) and the 90% confidence level (red) contours as a function of the parameter δ with the unit of a degree. depends on the estimated accuracy of the background events. Taking the background estimation into account, the sensitivity of δ extracted from A CP is studied in Figure 11 without considering the uncertainty of the other neutrino oscillation parameters; θ 13, θ 12,and m 12.A3σdis- covery is possible for δ > 14 if we understand 1 Please note that A CP is inversely proportional to θ 13, and the statistics of the number of events is proportional to θ 13. Both effects are canceled without background.

9 9 δ Figure 11. The sensitivity of the CP violation parameter δ as a function of sin 2 2θ 13 in the JHF-Kamioka neutrino project with background events. The sensitivity depends on the estimated accuracy of the background level. In the figure, the uncertainty of the background level is assumed to be 10, 5, 2,1 and 0%. The values m 2 12 = ev 2 and θ 12 = π/4 areassumed. the background level at 2% of accuracy. In order to estimate the background at this accuracy, the similar Water Čerenkov detector at 2km from JHF plays a crucial role. A similar study is done for the SPL super beam with the UNO detector. The sensitivity of δ and θ 13 is shown in Figure 12. The SPL β beam experiment can also probe the Time asymmetry in neutrino oscillation, and provide information on the CP violation phase δ in the MNS matrix Other Physics In order to achieve the physics goal in the long baseline neutrino experiment with a super beam, the far to near neutrino flux ratio must be well estimated. For this purpose, a pion production measurement at CERN(HARP) and FNAL(E907) experiments is valuable. Those experiments have to be conducted for a future super neutrino beam. With a very intense neutrino beam at the near site, non-oscillation neutrino experiments with Figure 12. Determination accuracy (one sigma, 90% and 99% contour) of θ 13 and δ with a SPL super beam and the UNO detector for 2 years of ν µ and 10 years of ν µ beam exposure. The stars show the initial values of the parameters. much higher statistics are possible. The physics motivations of the experiments are A study of the LSND effect unless the Mini- Boone experiment rejected the possibility or if Mini-Boone discovered the signature. A study of neutrino interactions; such as a measurement of quasi-elastic interactions and the kinematics, etc.. A probe of the neutrino magnetic moment by studying the ν µ e elastic scattering at low Q 2. There are coming more other proposals for such a high intensity neutrino beam. 5. Summary and Conclusion In the next five years, several long baseline neutrino experiments (MINOS, OPERA, and θ

10 10 ICARUS) will start operation and provide more information on neutrino oscillation. An experiment with a super neutrino beam will follow the trend, and further explore the physics to build a complete scheme of neutrino oscillation with a determination of the MNS matrix. The JHF- Kamioka project is one of the proposals and is planning to start the experiment in 2007 at the earliest. The typical physics sensitivity with a super neutrino beam is The sensitivity on sin 2 2θ 13 is The accuracy of the sin 2 2θ 23 measurement is 1%. The accuracy of m 23 is ev 2. The sensitivity on the CP violation phase δ is down to 15 degree assuming a proper set of oscillation parameters. Confirmation of ν µ ν τ oscillation and a limit to ν µ ν s oscillation. 6. Acknowledgments The author thanks the JHF-SK Neutrino working group members, K2K collaborators, and Super-Kamiokande collaborators to complete this work. The author also thanks many colleagues working for a super neutrino beam in Japan, the United State and Europe, who gave many valuable comments for this work. The author could attend the conference with the support by the Kyoto University Foundation. REFERENCES 1. Super-Kamiokande collaboration, Phys. Rev. Lett. 81, 1562 (1998). 2. T. Yanagida, in Proc. of Workshop on the Unified theory and Baryon Number in the Universe, ed. by O. Sawada and A. Sugamoto (KEK report 79-18, 1979). M. Gell-Mann, P. Ramond and R. Slansky, in Supergravity, ed. by P. van Nieuwenhuizen andd.z.freedman(northholland,amsterdam, 1979), p Z. Maki, M. Nakagawa, S.Sakata, Prog. Theor. Phys. 28,870 (1962). 4. M. Lindner, a proceeding in NEUTRINO 2002 in Munich 2002, The Physics Potential of Future Long Baseline Experiments, May, F. Dydak, a proceeding in NEUTRINO 2002 in Munich 2002, Detector and Experiments at Future Neutrino Facilities, May, S.H. Ahn, et al. (K2K Collaboration), Phys. Lett. B511, 178 (2001). 7. Y. Itow, et. al., The JHF-Kamioka neutrino project, hep-ex/ , June J. J. Gomez-Cadenas, et. al., Physics Potential of Very Intense Conventional Neutrino Beams, hep-ph/ , May For example, Yamanoi Y. et al., KEK Preprint , November D. Beavis, A. Carroll, I. Chiang, et al., Proposal of BNL AGS E-889 (1995). 11. M. Koshiba, Phys. Rep. 220, 229 (1992) K. Nakamura, Neutrino Oscillations and Their Origin, (Universal Academy Press, Tokyo, 2000), p S. Geer, a proceeding in NEUTRINO 2002 in Munich 2002, Neutrino Factory Designs and R&D, May, M. Shiozawa, a proceeding in NEUTRINO 2002 in Munich 2002, Superkamiokande, May, K. Nishikawa, a proceeding in NEUTRINO 2002 in Munich 2002, K2K Results, May, S. Katsanevas, a proceeding in NEUTRINO 2002 in Munich 2002, CNGS, May, F. DeJongh, hep-ex/ , Long Baseline Neutrino Physics: From Fermilab to Kamioka May M. Aoki, et al., hep-ph/ , Prospect of Very Long Base-line Neutrino Oscillation Experiments with the KEK-JAERI High Intensity Accelerator. Dec