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Super-Kamiokande (on the activities from 2000 to 2006 and future prospects)

Super-Kamiokande (on the activities from 2000 to 2006 and future prospects). M. Nakahata. Super-Kamiokande detector Atmospheric neutrinos Solar Neutrinos Proton decay search Supernova neutrinos. for Neutrino and astroparticle Division. Super-Kamiokande collaboration.

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Super-Kamiokande (on the activities from 2000 to 2006 and future prospects)

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  1. Super-Kamiokande(on the activities from 2000 to 2006 and future prospects) M. Nakahata • Super-Kamiokande detector • Atmospheric neutrinos • Solar Neutrinos • Proton decay search • Supernova neutrinos for Neutrino and astroparticle Division

  2. Super-Kamiokande collaboration 33 institutes, 122 physicists ICRR member: Staff: 17 PD: 4 Students: 7 (faculty: 8, research assistant: 9) Total 28

  3. History of Super-Kamiokande Detector Number of ID PMTs (photocoverage) Main results Start Evidence for Atmospheric n osc. 11,146 (40%) SK-I Tau n favor over sterile n in atm. osc. Evidence for Solar n osc. Accident LMA by solar n global analysis Partial Reconstruction 5,182 (19%) SK-II Atmospheric n L/E K2K final results Full reconstruction Atmospheric n tau appearance 11,129 (40%) SK-III

  4. Accident and partial reconstruction Accident on Nov.12, 2001. 6777 ID, 1100 OD PMTs were destroyed. Reconstructed using remaining 5182 ID PMTs. OD was fully reconstructed (April-September 2002). All PMTs were packed in acrylic and FRP cases to prevent shock-wave. ID: Inner detector OD: Outer detector

  5. ~6000 ID PMTs were produced from 2002 to 2005 and were mounted from Oct.2005 to Apr.2006. Full Reconstruction (October 2005 – April 2006) All those PMTs were packed in acryic and FRP cases. Mount PMTs on a floating floor. Pure water was supplied and SK-III data taking has been running since July 11, 2006.

  6. Atmospheric neutrinos Main Physics Study of muon-neutrinos oscillations Oscillation parameters (q23, Dm223, q13) Oscillation mode (nmnt ? nmnsterile ?) Oscillation signature (L/E dependence)

  7. SK-I: 92 kton・yr SK-II: 49 kton・yr Total: 141 kton・yr SK-I+II atmospheric neutrino data CC ne SK-I: hep-ex/0501064 + SK-II 804 days CC nm ＜ ＜ ＞ ＞ ＞ No osc. Osc.

  8. nm nt2 flavor analysis 1489 days (SK-1)+ 804 days (SK-II) Dc2 distributions Best Fit: Dm2 = 2.5 x 10-3 eV2 sin2 2q = 1.00 c2 = 839.7 / 755 dof (18%) Preliminary 1.9 x 10-3 eV2 < Dm2 < 3.1 x 10-3 eV2 sin2 2q > 0.93 at 90% CL

  9. 1 Dm2 (eV2) 10-4 1.0 0 90% CL of 1998 Oscillation results 1998 vs. (SK-I+SK-II) 1998 535days 90% CL 90 % CL

  10. Dm2L Pmm = 1 – sin22qsin2(1.27 ) m-like multi-GeV + PC En L m Pmm = (cos2q + sin2q ・ exp(– ))2 2t E L 1 Pmm = 1 – sin22q・ (1 – exp(–g0 )) 2 E L/E analysis SK collab. hep-ex/0404034 oscillation decoherence decay Should observe this dip! • Further evidence for oscillations • Better determination of oscillation parameters, especially Dm2

  11. FC single-ring m-like Full oscillation 1/2 oscillation D(L/E)=70% Selection criteria Select events with high L/E resolution (D(L/E) < 70%) Events are not used, if: ★horizontally going events ★low energy events Similar cut for: FC multi-ring m-like, OD stopping PC, and OD through-going PC

  12. decoherence decay SK-I+II (preliminary) Decoh. Decay Osc. SK-I+II L/E analysis and non-oscillation models c2(osc)=83.9/83dof c2(decay)=107.1/83dof c2(decoherence)=112.5/83dof Oscillation gives the best fit to the data. Decay and decoherence models disfavored by 4.8 and 5.3 s, resp.

  13. Oscillation to nt or nsterile ? m-like data show zenith-angle and energy dependent deficit of events, while e-like data show no such effect. nmnt or nmnsterile For sin22q=~1, matter effect suppresses oscillation at higher energy. nm→nt : No matter effect nm→ns : With matter effect Propagation nm→nt : With Neutral Current nm→ns : W/O Neutral Current Check upward-going NC events Interaction

  14. Testing nmnt vs. nmnsterile Neutral current Matter effect High E PC events (Evis>5GeV) Multi-ring e-like, with Evis >400MeV Up through muons nt nmnsterile nsterile nmnsterile nmnt nmnt (PRL85,3999 (2000)) Pure nmnsterile excluded

  15. Limit on oscillations to nsterile nm(sinx・nsterile+cosx・nt) If pure nmnt, sin2x=0 If pure nmnsterile, sin2x=1 SK-1 data Consistent with pure nmnt SK collab. draft in preparation

  16. Search for CC nt events (SK-I) CC ntMC CC nt events nt hadrons t nt hadrons Signature of CC nt events Only ～ 1.0 CC ntFC events/kton・yr (BG (other n events) ～ 130 ev./kton・yr) • Higher multiplicity of Cherenkov rings • More m→e decay signals • Spherical event pattern Likelihood and neural network analysis

  17. Up-going Zenith-angle Likelihood / neural-net distributions Pre-cuts: E(visible) >1.33GeV, most-energetic ring = e-like Down-going (no nt) Likelihood Neural-net

  18. Zenith angle dist. and fit results Hep-ex/0607059 Likelihood analysis NN analysis Data scaled t-MC Number of events nm, ne, & NC background cosqzenith cosqzenith Fitted # of t events Expected # of t events Zero tau neutrino interaction is disfavored at2.4s.

  19. Future: Search for Non-zero q13 Simulation (4.5 Mton·yr) 1+multi-ring, e-like, 2.5~5 GeV/c One mass scale dominance approx. Dm212 ~ 0 , Dm213 ~ Dm223 = Dm2 Electron appearance only 3 parameters P(nm  ne) at SK s213 ~ 0.04 s213 = 0.00 null oscillation cosqzenith Using finely binned data, look for enhancement at certain energies and angles due to electron neutrino resonance in earth.

  20. Future: Search for non-zero q13 Sensitivity of 20 years’ SK data s22q12=0.825 s2q23=0.4 ~ 0.6 s2q13=0.00~0.04 dcp=45o Dm212=8.3e-5 Dm223=2.5e-3 sin2 q23 = 0.60 0.55 0.50 0.45 0.40 CHOOZ exclude If q13 is close to CHOOZ limit, non-zero q13 can be observed by atmospheric neutrinos.

  21. Summary of Atmospheric neutrino analysis • Activities from 2000 to 2006 • Allowed parameter region was improved: • 1.9 x 10-3 eV2 < Dm2 < 3.1 x 10-3 eV2 • sin2 2q > 0.93 at 90% CL • L/E dependence of neutrino oscillation was observed. • nmnt favors over nmnsterile • Tau appearance with 2.4 s level. • Future prospects • Search for non-zero q13. If q13 is close to CHOOZ limit, it could be observed by atmospheric neutrinos.

  22. Solar neutrinos Main Physics High statistics measurement of 8B solar neutrinos to (1) solve “solar neutrino problem” (2) measure oscillation parameters (q12, Dm212)

  23. Solar neutrino measurement in SK • 8B neutrino measurement byn + e-→n + e- • Sensitive tone, nm, nts(nm(t)+e-) =~0.15×s(ne+e-) • High statistics ~15ev./day with Ee > 5MeV • Real time measurement. Studies on time variations. • Studies on energy spectrum. • Precise energy calibration by LINAC and 16N. Typical event • Timing information vertex position • Ring pattern direction • Number of hit PMTs energy Ee = 9.1MeV cosqsun = 0.95

  24. Super-Kamiokande-I solar neutrino data May 31, 1996 – July 13, 2001 (1496 days ) n + e- n + e- 22400230 solar n events (14.5 events/day) 8B flux : 2.35  0.02  0.08 [x 106 /cm2/sec] Data +0.014 = 0.406 0.004 -0.013 SSM(BP2004) ( Data/SSM(BP2000) = 0.465 0.005 +0.016/-0.015 )

  25. Evidence for solar neutrino oscillation by SK and SNO (June 2001) ES =e +0.15, SK ES = 2.320.03+0.08/-0.07 [x106/cm2/s] CC =e SNO CC = 1.750.07+0.12/-0.11 (cf. SSM(BP2000)= 5.05+1.0/-0.8) Obtained total flux: exp= 5.5±1.4 SK SNO CC Data as of June 2001 SK: 1258 days of SK-I SNO: 241 days of pure D2O (CC only) ±

  26. Energy spectrum of SK-I (tan2q, Dm2) Energy correlated systematic error

  27. SK-I day/night difference (Day-Night) ADN= (Day+Night)/2 Expected D/N asymmetry ADN -1% -2% -10% -80%

  28. Excluded region by energy spectrum and day/night Super-Kamiokande 1496 days S.Fukuda et al., Phys. Lett. B 539 (2002) 179

  29. Allowed region combined with all solar neutrino data • Rates: Homestake (Cl), GALLEX (Ga), SAGE (Ga), SK (H2O), SNO CC+NC (D2O) • Zenith spectra from SK: energy spectra of electrons at 7 zenith angle bins (day + 6 nights) LMA is favored with 99 % CL. Plot as of May 2002 S.Fukuda et al., Phys. Lett. B 539 (2002) 179

  30. Plot after KamLAND first result

  31. SK-II solar neutrino analysis +154 signal = 7239 (stat.) -152 Energy spectrum Event direction SK-II 791 days 7-20MeV Consistent with SK-I flux = 2.38 ±0.05 (stat.) +0.16/-0.15(sys.) x106/cm2/sec SK-I result: 2.35 +/-0.02(stat.) +/-0.08(syst.)

  32. Future prospects: precise spectrum measurement Is there spectrum distortion ? ne survival probability Recoil electron spectrum ~10% spectrum distortion expected from LMA But, SK-I spectrum is almost flat. Data: SK-I P(ne → ne) sys. error Dm2 (eV2) 6.3 x 10-5 4.8 x 10-5 7.2 x 10-5 10.0 x 10-5 7.2 x 10-5 sin2(q) 0.35 0.28 0.28 0.28 0.22 En (MeV)

  33. Future propsects: expected sensitivity of SK-III Statistical significance Expected spectrum in SK-III sin2(q) 0.22 0.28 0.28 0.28 0.35 Dm2 (eV2) 7.2 x 10-5 10 x 10-5 7.2 x 10-5 4.8 x 10-5 6.3 x 10-5 5 years data assumed Energy correlated systematic error Significance ( s ) 3s level Solar+KamLAND best fit Live time (years) Assumption: Correlated systematic error: x 0.5 4.0-5.5MeV background : x 0.3 of SK-I (> 5.5MeV is same as SK-I)

  34. Summary of Solar neutrino analysis • Activities from 2000 to 2006 • Evidence for solar neutrino oscillation by comparing SK and SNO data in 2001. • The flat energy spectrum and small day/night value of SK favored LMA solution. • LMA solution was obtained by solar global analysis (SK, SNO, radiochemical) with 99% CL. • SK-II data is consistent with SK-I data. • Future prospects • Precise measurement of energy spectrum. ~10% distortion is expected for the LMA solution. By lowering background in lower energy region, it should be observed in 5-7 years.

  35. Proton decay search Physics Establish GUT Quark+lepton

  36. Proton decay search（ pe+p0) SK-I (1489days） SK-II (804days） Total momentum (MeV/c) Total mass (MeV/c2) No candidate was observed. Expected signal region. Life time limit (pe+p0)：>8.4 x 1033 years

  37. Proton decay search（ pnK+) m+ shape method Prompt g method K+p+p0 method Combine those methods, Lifetime: >2.3 x 1033 years

  38. Sensitivity of future SK pgnK+ pge+p0 SK×20 yrs  450ktyr BG=1~2events τ/B  4 × 1033 yrs (SK 20yrs, 90%CL) τ/B  2 × 1034 yrs (SK 20yrs, 90%CL)

  39. Supernova neutrinos Physics • High statistics supernova events at neutrino burst (~8000 events at 10kpc) to investigate detailed mechanism of supernova burst. • Supernova relic neutrinos (SRN) to study star formation in the universe.

  40. Supernova burst search (online) Data Acquisition system Online host computer A few minutes later Supernova watch computer Offline computer • Selection criteria: • ≥ 25 ev. within 10 sec. • Rmean > 7.5m If a candidate is found ALARM Rmean: averaged distance between event vertices. This cut reject spallation and flasher backgrounds. Notify to shift person Send signal to SNEWS SNEWS: (SuperNova Early Warning System) Check vertex distribution and event pattern Current members: SK, SNO, AMANDA/Ice Cube, LVD Alarm rate was about once per ~10 days. (specification of SNEWS). They were due to PMT flashers and multiple spallation events. No real galactic supernova was found during SK-I and SK-II.

  41. Search for supernova relic neutrinos Reactor n Solar 8B Solar hep SRN predictions Atmospheric n Population synthesis (Totani et al., 1996) Constant SN rate (Totani et al., 1996) Cosmic gas infall (Malaney, 1997) Cosmic chemical evolution (Hartmann et al., 1997) Heavy metal abundance (Kaplinghat et al., 2000) LMA noscillation (Ando et al., 2002) Spallation B.G. below ~18 MeV

  42. Search for supernova relic neutrinos in SK-I n Energy spectrum (>18MeV) 1496 days (SK-I) Total background Atm. nm → invisible m → e Atm. ne SK-I flux limit: < 1.2 /cm2/sec 90% CL limit of SRN SK limit is close to the model predictions !

  43. ne could be identified by delayed coincidence. Future: Possibilities of ne tagging n g ne p Possibility 1 p n+p→d + g 2.2MeV g-ray DT = ~ 200 msec Gd e+ g Number of hit PMT is about 6 in SK-III Possibility 2 Positron and gamma ray vertices are within ~50cm. n+Gd →~8MeV g DT = several 10th msec Add 0.2% GdCl3 in water (ref. Vagins and Beacom)

  44. Possibility of SRN detection Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with flux revise in NNN05. No B.G. reduction B.G. reduction by neutron tagging Spallation SK10 years (e=47%) SK10 years (e=80%) Hard to distinguish Statistically <1s excess (10yrs, Evis =18-30 MeV) ~1.2s for SK20yrs Assuming 90% of invisible muon B.G. can be reduced by neutron tagging. Assuming 80% detection efficiency. Signal: 22.7, B.G. 13.1(Evis =15-30 MeV) Signal: 44.8, B.G. 14.7(Evis =10-30 MeV)

  45. Summary of proton decay • Activities from 2000 to 2006 • Lifetime lower limit was obtained: • pe+p0：>8.4 x 1033 yrs • pnK+: >2.3 x 1033 yrs • Future prospects • pe+p0：>2 x 1034 yrs, pnK+: >4 x 1033 yrs for 20 yrs data Summary of supernova neutrinos • Activities from 2000 to 2006 • Supernova burst search has in online and offline analyses. No candidate was found. • SRN Flux limit: < 1.2 /cm2/sec for E>18 MeV by SK-I data. It is close to theoretical predictions. • Future prospects • Improved search for SRN neutrinos by neutron tagging.

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