We propose the Hyper-Kamiokande (Hyper-K) detector as a next generation un- derground water Cherenkov detector. It will serve as a far detector of a long base- line neutrino oscillation experiment envisioned for the upgraded J-PARC beam, and as a detector capable of observing, far beyond the sensitivity of the Super-Kamiokande (Super-K) detector, proton decays, atmospheric neutrinos, and neutrinos from astro- physical origins. The current baseline design of Hyper-K is based on the highly suc- cessful Super-K detector, taking full advantage of a well-proven technology. Hyper-K consists of two cylindrical tanks lying side-by-side, the outer dimensions of each tank being 48(W) x54(H) x 250(L) m3. The total (fiducial) mass of the detector is 0.99 (0.56) million metric tons, which is about 20 (25) times larger than that of Super-K. This set of three one- page whitepapers prepared for the US Snowmass process describes the opportunities for future physics discoveries at the Hyper-K facility with beam, atmospheric and astrophysical neutrinos

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Hyper-Kamiokande Physics OpportunitiesSubmitted by the Hyper-Kamiokande Working Group ∗to the 2013 Snowmass ProcessAugust 31st 2013AbstractWe propose the Hyper-Kamiokande (Hyper-K) detector as a next generation un-derground water Cherenkov detector [1]. It will serve as a far detector of a long base-line neutrino oscillation experiment envisioned for the upgraded J-PARC beam, andas a detector capable of observing, far beyond the sensitivity of the Super-Kamiokande(Super-K) detector, proton decays, atmospheric neutrinos, and neutrinos from astro-physical origins. The current baseline design of Hyper-K is based on the highly suc-cessful Super-K detector, taking full advantage of a well-proven technology. Hyper-Kconsists of two cylindrical tanks lying side-by-side, the outer dimensions of each tankbeing 48(W )× 54(H)× 250(L) m3. The total (fiducial) mass of the detector is 0.99(0.56) million metric tons, which is about 20 (25) times larger than that of Super-K.A proposed location for Hyper-K is about 8 km south of Super-K (and 295 km awayfrom J-PARC) at an underground depth of 1,750 meters water equivalent (m.w.e.).The inner detector region of the Hyper-K detector is viewed by 99,000 20-inch PMTs,corresponding to the PMT density of 20% photo-cathode coverage (one half of thatof Super-K).The Hyper-K project is envisioned to be completely open to the internationalcommunity. The current working group contains members from Canada, Japan,Korea, Spain, Switzerland, Russia, the United Kingdom and the United States. TheUnited States physics community has a long history of making contributions to theneutrino physics program in Japan. In Kamiokande, Super-Kamiokande, K2K andT2K, US physicists have played important roles building and operating beams, neardetectors, and large underground water Cherenkov detectors. This set of three one-page whitepapers prepared for the US Snowmass process describes the opportunitiesfor future physics discoveries at the Hyper-K facility with beam, atmospheric andastrophysical neutrinos.∗Project contact: Tsuyoshi Nakaya <t.nakaya@scphys.kyoto-u.ac.jp>arXiv:1309.0184v1  [hep-ex]  1 Sep 2013The Hyper-Kamiokande Working GroupBoston University (USA): E. Kearns, J.L. StoneChonnam National University (Korea): K.K. JooDuke University (USA): T. Akiri, A. Himmel, K. Scholberg, C.W. WalterEarthquake Research Institute, The University of Tokyo (Japan): A. Taketa, H.K.M.TanakaETH Zurich (Switzerland): A. RubbiaInstitute for Nuclear Research (Russia): A. Izmaylov, M. Khabibullin, Y. KudenkoImperial College London (UK): M. Malek, Y. Uchida, M.O. WasckoIowa State University (USA): I. Anghel, G. Davies, M.C. Sanchez, T. XinKamioka Observatory, ICRR, The University of Tokyo (Japan): K. Abe, Y. Haga, Y.Hayato, J. Kameda, Y. Kishimoto, M. Miura, S. Moriyama, M. Nakahata, S. Nakayama, H.Sekiya, M. Shiozawa, Y. Suzuki, A. Takeda, H. Tanaka, T. Tomura, R. WendellKavli IPMU, The University of Tokyo (Japan): M. Hartz, L. Marti, K.Nakamura, M.R.VaginsKEK (Japan): M. Friend, T. Ishida, T. Kobayashi, Y. OyamaKobe University (Japan): A. T. Suzuki, Y. TakeuchiKyoto University (Japan): S. Hirota, K. Huang, A. K. Ichikawa, M. Ikeda, A. Minamino, T.Nakaya, K. TateishiLancaster University (UK): A. Finch, L.L. Kormos, J. Nowak, H.M. O’Keeffe, P.N. RatoffLos Alamos National Laboratory (USA): G. SinnisLouisiana State University (USA): F.d.M. Blaszczyk, J. Insler, T. Kutter, O. Perevozchikov,M. TzanovMiyagi University of Education (Japan): Y.FukudaNagoya University (Japan): K.Choi, T. Iijima, Y. ItowOkayama University (Japan): H. Ishino, Y. Koshio, T. Mori, M. Sakuda, T. YanoOsaka City University (Japan): Y. Seiya, K. YamamotoPontif́ıcia Universidade Católica do Rio de Janeiro (Brazil): H. Minakata, H. NunokawaQueen Mary, University of London (UK): F. Di Lodovico, T. Katori, R. Sacco, B. Still, R.Terri, J.R. WilsonSeoul National University (Korea): S. B. KimState University of New York at Stony Brook (USA): J. Adam, J. Imber, C. K. Jung, C.McGrew, J.L. Palomino, C. YanagisawaSTFC Rutherford Appleton Laboratory (UK): D. Wark, A. WeberSungkyunkwan University (Korea): C. RottThe California State University Dominguez Hills (USA): K. Ganezer, B. Hartfiel, J. HillThe University of Tokyo (Japan): H. Aihara, Y. Suda, M. YokoyamaTohoku University (Japan): K. Inoue, M. Koga, I. ShimizuResearch Center for Cosmic Neutrinos, ICRR, The University of Tokyo (Japan): T.Irvine, T. Kajita, I. Kametani, Y. Nishimura, K. Okumura, E. RichardTokyo Institute of Technology (Japan): M. Ishitsuka, M. Kuze, Y. OkajimaTRIUMF (Canada): P. Gumplinger, A. Konaka, T. Lindner, K. Mahn, J.-M. Poutissou, F.Retiere, M. Scott, M.J. WilkingUniversity Autonoma Madrid (Spain): L. LabargaUniversity of British Columbia (Canada): S.M. Oser, H.A. TanakaUniversity of Geneva (Switzerland):A. Blondel, A. Bravar, F. Dufour, Y. Karadhzov, A.Korzenev, E. Noah, M. Ravonel, M. Rayner, R. Asfandiyarov, A. Haesler, C. Martin, E. Scant-amburloUniversity of Hawaii (USA): J.G. LearnedUniversity of Regina (Canada): M. BarbiUniversity of Toronto (Canada): J.F. MartinUniversity of California, Davis (USA): M. Askins, M.Bergevin, R. SvobodaUniversity of California, Irvine (USA): G. Carminati, S. Horiuchi, W.R. Kropp, S. Mine,M.B. Smy, H.W. SobelUniversity of Liverpool (UK): N. McCauley, C. TouramanisUniversity of Oxford (UK): G. Barr, D. Wark, A. WeberUniversity of Pittsburgh (USA): V. PaoloneUniversity of Sheffield (UK): J.D. Perkin, L.F. ThompsonUniversity of Washington (USA): J. Detwiler, N. Tolich, R. J. WilkesUniversity of Warwick (UK): G.J. Barker, S. Boyd, D.R. Hadley, M.D. HaighUniversity of Winnipeg (Canada): B. JamiesonVirginia Tech (USA): S. M. Manecki, C. Mariani, S. D. Rountree, R. B. VogelaarYork University (Canada): S. BhadraExploring CP violation with the upgraded J-PARC Beam01δ [π]0 0.05 0.1 0.15sin22θ13-12σ1σ3σ7.5MWyearHyper-KFigure 1: Allowed regions in the space of sin2 2θ13and δ near the known value of sin2 2θ13. Blue,green, and red lines represent 1, 2, 3 σ allowedregions in with the hierarchy known to be normal.In 2011, the T2K [2], MINOS [3],and Double Chooz [4] experimentsshowed the first indications of full three-flavor oscillations. In 2012 the DayaBay [5] and RENO [6] experiments re-ported the first precision measurementsof the θ13 mixing angle which drivesthree-flavor oscillation. This unexpect-edly large value of θ13 guarantees theability to measure the CP violatingphase δ. The Hyper-K projects buildson the proven success of the waterCherenkov technique with an upgradedJ-PARC beam plus a megaton-scale de-tector.The J-PARC to Hyper-K experimentwill use a proton beam with a ∼ 1MWof power to produce both neutrinos andanti-neutrinos with a horn focusing sys-tem. The beam is directed 2.5◦ off-axisto the 560 kton fiducial volume Hyper-K detector 295 km away. The neutrinos are measurednear the production site and then again at the far detector. CP violation will manifestitself in a difference between the measured rate of νµ → νe and ν̄µ → ν̄e transformationsas well as in spectral distortions. The high event rate in the far detector will also allowfor precise measurements of neutrino mixing parameters that will continue the worldwideeffort to constrain the 3× 3 PMNS matrix.02040601σ error of δ (degree)δ=90oδ=0o0 1 2 3 4 5 6 7 8 9 10sin22θ13=0.1Integrated beam power (MW∙year)Figure 2: 1σ uncertainty of δ as a func-tion of integrated beam power. The ra-tio of ν and ν̄ running time is fixed to3:7.In 10 years of running, split 3:7 between neutrinosand antineutrinos respectively, we expect to collectapproximately 2000 to 4000 signal events in eachmode. Assuming the mass hierarchy is determinedby other means, and that the total systematic er-ror managed to the 5% level, then the CP phasemay be distinguished from δ = 0 at 3σ for 74% ofthe entire range in δ. Figure 1 shows example 1σcontours using the current range of sin2 2θ13. Fig-ure 2 demonstrates the expected uncertainty in δas a function of integrated beam power for two val-ues of δ. After 7.5 MW·years, δ will be measuredwith an accuracy between 7 and 15 degrees.Exploring Neutrino Properties with Atmospheric NeutrinosIn the late nineties, atmospheric neutrinos measured in the Super-Kamiokande detectorprovided the first definitive evidence that neutrinos had mass and that the mass statesmixed to make the well known flavor states [7]. Atmospheric neutrinos remain an importantprobe of neutrino oscillations, and the large statistics sample from the one-half megatonHyper-K will offer an unprecedented opportunity to study them in detail. Atmosphericneutrinos exist in both neutrino and anti-neutrino varieties in both muon and electronflavors. Approximately 1,000,000 events are expected to be collected in a 10 year period.The large value of θ13, along with the neutrino versus anti-neutrino dependent matterresonance effect in the earth opens up the study of oscillation driven electron neutrinoappearance. The oscillation effect in the electron neutrino flux have been analyticallycalculated [8] as:Φ(νe)Φ0(νe)− 1 ≈ P2 · (r · cos2 θ23 − 1)−r · sin θ̃13 · cos2 θ̃13 · sin 2θ23 · (cos δ ·R2 − sin δ · I2)+2 sin2 θ̃13 · (r · sin2 θ23 − 1) (1)Figure 3: The sensitivity to themass hierarchy as a function ofθ23 with θ13 fixed at sin2 2θ13 =0.098 (NH case).where we call the first, second, and third terms the “so-lar term”, “interference term”, and “θ13 resonance term”,respectively. P2 is the two neutrino transition probabilityof νe → νµ,τ which is driven by the solar neutrino massdifference ∆m221. R2 and I2 represent oscillation ampli-tudes for CP even and odd terms. For anti-neutrinos, thesign of the δ should be changed. Additionally, the mod-ified probabilities for P2, R2, I2 are obtained by replacingthe matter potential V → −V (see [8] for details). Theelectron appearance effect along with precision measure-ments of muon disappearance [9] and tau appearance [10]will allow Hyper-K to probe the octant of θ23 oscillation,the mass hierarchy and CP violation phase.A full Monte Carlo and reconstruction study usingSuper-Kamiokande tools has determined that the ex-pected significance for the mass hierarchy determinationis more than 3σ provided sin2 θ23 > 0.4. We expect to beable to discriminate between sin2 θ23 < 0.5 (first octant)and > 0.5 (second octant) at the 3σ level if sin2 2θ23 is less than 0.99. For all values of δ,40% of the δ range can be excluded at three sigma assuming that sin2 θ23 > 0.4. All of theseresults are obtained using atmospheric neutrinos alone. In combination with the JPARCbeam they can be even more tightly constrained. As an example, figure 3 demonstratesthe sensitivity to the mass hierarchy as a function of θ23 with θ13 fixed at sin2 2θ13 = 0.098for the case of the normal hierarchy.Low-Energy Neutrino Physics and Astrophysics with Hyper-KHyper-K represents the next generation of highly-successful water Cherenkov technology forobservation of low-energy (less than ∼50 MeV) neutrinos, including solar neutrinos [11, 12,13], core-collapse supernova neutrinos [14, 15, 16], and potentially dark matter annihilationneutrinos [17].Solar Neutrinos: Assuming sufficient depth to overcome cosmic-muon-induced spallationbackground, Hyper-K will observe ∼115,000 elastic solar 8B neutrino-electron scatters peryear (above its energy threshold and after event selection efficiency, assuming a livetimeof 90%), an unprecedentedly large solar neutrino rate. With tight control of systematicuncertainties, Hyper-K will be very sensitive to the solar day/night effect, i.e. the regener-ation of νe flavor of solar neutrinos passing through the Earth. Within five years, Hyper-Kwill determine the solar zenith angle variation amplitude to ∼0.5%– expressed here as aday/night asymmetry, defined as (day − night)/(0.5(day + night))– measuring ∆m221 witha precision comparable to that of current reactor antineutrino experiments, and establish-ing (or refuting) the presence of matter effects on neutrino oscillations with a significanceexceeding 4σ [18].11010 210 310 410 510 610 710 810 910 1010-11 10 102103! –e +p!e + 16O! –e + 16O!+e -BetelgeuseAntaresGalacticcenterLMCM31distance(kpc)events/0.74Mega-tonFigure 4: Expected numbers ofSN burst events in HK for eachinteraction as a function of thedistance to the SN [1].Supernova Neutrinos: Hyper-K is sensitive to neu-trinos from Galactic core-collapse supernovae (∼250,000interactions in ∼10 s at the Galactic center a fewtimes/century), nearby supernovae (∼25 interactions atAndromeda; 1/2 interactions for distances < 4 MPc with∼ 60%/25% probability every few years) and distant su-pernovae (∼100 interactions/year, up to z ∼ 1). WithGd salt doping [19], Hyper-K could also separate ν̄e in-verse beta reactions from other interactions. A large-statistics Galactic burst offers many unique opportuni-ties (e.g. [20, 21] and references therein). From the time,flavor and energy profile of the neutrinos, we can learnabout the neutronization burst, shock wave effects, ex-plosion temperatures, and black hole formation. We maygain information on neutrino parameters, in particularmass hierarchy. Spectral swaps between neutrino flavorswill enable the study of ν− ν interactions. In addition toan early alert for even quite distant supernovae, Hyper-Kcould also achieve precision pointing to a nearby super-nova’s direction. Even a few neutrinos from nearby ex-tragalactic supernovae will determine the nature of nearby transients whose mechanismis uncertain [22]. The rate and spectrum of distant supernova neutrinos characterize theproperties of typical supernova explosions (luminosity and explosion temperature). Fordistant supernovae, Gd doping is essential to tag ν̄e between 10 and 30 MeV and therebydistinguish supernova neutrinos from atmospheric neutrino backgrounds.References[1] K. Abe, T. Abe, H. Aihara, Y. Fukuda, Y. Hayato, et al. (2011), 1109.3262.[2] K. Abe et al. (T2K Collaboration), Phys.Rev.Lett. 107, 041801 (2011), 1106.2822.[3] P. Adamson et al. (MINOS Collaboration), Phys.Rev.Lett. 107, 181802 (2011), 1108.0015.[4] Y. Abe et al. (DOUBLE-CHOOZ Collaboration), Phys.Rev.Lett. 108, 131801 (2012),1112.6353.[5] F. An et al. (DAYA-BAY Collaboration), Phys.Rev.Lett. 108, 171803 (2012), 1203.1669.[6] J. Ahn et al. (RENO Collaboration), Phys.Rev.Lett. 108, 191802 (2012), 1204.0626.[7] Y. Fukuda et al. (Super-Kamiokande Collaboration), Phys.Rev.Lett. 81, 1562 (1998),hep-ex/9807003.[8] O. Peres and A. Y. Smirnov, Nucl.Phys. B680, 479 (2004), hep-ph/0309312.[9] Y. Ashie et al. (Super-Kamiokande Collaboration), Phys.Rev. D71, 112005 (2005),hep-ex/0501064.[10] K. Abe et al. (Super-Kamiokande Collaboration) (2012), 1206.0328.[11] J. Hosaka et al. (Super-Kamiokande Collaboration), Phys.Rev. D73, 112001 (2006),hep-ex/0508053.[12] J. Cravens et al. (Super-Kamiokande Collaboration), Phys.Rev. D78, 032002 (2008),0803.4312.[13] K. Abe et al. (Super-Kamiokande Collaboration), Phys.Rev. D83, 052010 (2011),1010.0118.[14] K. Hirata et al., Phys. Rev. Lett. 58, 1490 (1987).[15] M. Ikeda et al. (Super-Kamiokande Collaboration), Astrophys.J. 669, 519 (2007),0706.2283.[16] K. Bays et al. (Super-Kamiokande Collaboration), Phys.Rev. D85, 052007 (2012),1111.5031.[17] C. Rott, J. Siegal-Gaskins, and J. F. Beacom (2012), 1208.0827.[18] M. Smy on behalf of the Super-K collaboration, Proceedings of the XXV InternationalConference on Neutrino Physics and Astrophysics, Kyoto 2012 (2012).[19] J. F. Beacom and M. R. Vagins, Phys.Rev.Lett. 93, 171101 (2004), hep-ph/0309300.[20] A. Dighe, J.Phys.Conf.Ser. 136, 022041 (2008), 0809.2977.[21] K. Scholberg, Ann.Rev.Nucl.Part.Sci. 62, 81 (2012), 1205.6003.[22] T. A. Thompson, J. L. Prieto, K. Stanek, M. D. Kistler, J. F. Beacom, et al., Astro-phys.J. 705, 1364 (2009), 0809.0510.

Hyper-Kamiokande Physics Opportunities

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Hyper-Kamiokande Physics Opportunities

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