Super- -Kamiokande Kamiokande’ ’s s Solar Neutrino results Solar Neutrino results Super M. Nakahata Kamioka observatory, ICRR, Univ. of Tokyo for Super-Kamiokande collaboration � Super-Kamiokande(SK) detector � Day/night and energy spectrum in SK-I � Oscillation analysis � Preliminary results from SK-II � Future prospects
Super- -Kamiokande detector Kamiokande detector Super 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 SK-I SK-II SK-III accident SK full 50kton total, reconstruction 22kton fiducial (plan) volume 1000m underground Water Cherenkov detector 11,146 Number of ID (*) PMTs 5,182 40% Photocathod coverage 19% ~6 p.e./MeV Cherenkov light yield ~2.8 p.e./MeV Acrylic+FRP cases (*) Inner Detector Number of ID PMTs will be back to 11,146 in SK-III.
Solar neutrino measurement in SK � 8 B neutrino measurement by ν + e - → ν + e - � Sensitive to ν e , ν µ , ν τ σ(ν µ(τ) + e - ) =~0.15 × σ(ν e + e - ) � High statistics ~15ev./day with E e > 5MeV � Real time measurement. Studies on time variations. � Studies on energy spectrum. � Precise energy calibration by LINAC and 16 N. Expected spectrum distortion Expected day/night (at LMA region) tan 2 ( θ ) ∆ m 2 (eV 2 ) asymmetry 6.3 x 10 -5 0.55 4.8 x 10 -5 0.38 Data/SSM 0.38 7.2 x 10 -5 0.38 10.0 x 10 -5 7.2 x 10 -5 0.28 ~10% Recoil electron energy (MeV)
Super- -Kamiokande Kamiokande- -I solar neutrino data I solar neutrino data Super May 31, 1996 – July 13, 2001 (1496 days ) ν + e - � ν + e - 22400 ± 230 solar ν events (14.5 events/day) [x 10 6 /cm 2 /sec] 8 B flux : 2.35 ± 0.02 ± 0.08 Data +0.014 ± 0.004 = 0.406 -0.013 SSM(BP2004) ( Data/SSM(BP2000) = 0.465 ± 0.005 +0.016/-0.015 )
SK-I day/night difference A DN = (Day-Night) (Day+Night)/2
Un- -binned day/night analysis binned day/night analysis Un Z Day Energy and zenith angle dependence of SK event rate variation. core Example for ∆ m 2 =6.3x10 -5 eV 2 , tan 2 θ =0.55 mantle θ z
Un-binned time variation method # Backgrounds # Signal Event Event Likelihood for solar # Backgrounds # Signal in each energy bins Events Energy “Time” neutrino extraction in each energy bins Events ( ) ∑ N n ( ) ∏∏ − + bin i B S = ⋅ + ⋅ × i L e B u ( c ) m S p ( c , E ) z ( t ) i ν ν ν ν i i i i = ν = 1 i 1 21 Energy bins 21 Energy bins MC = i m ∑ i MC j j Background Shape Background Shape ν Flux Solar ν Flux Solar n Variatio n Time- -Variatio Time Solar Signal Shape Solar Signal Shape
Day/night asymmetry LMA best fit tan 2 θ =0.55 (Assuming BP2000 flux and error) ∆ m 2 =6.3x10 -5 eV 2 tan 2 θ =0.55 A DN =-1.8 ± 1.6 +1.3 % SK data( ± 1 σ) -1.2 expected ∆ m 2 =6.3x10 -5 eV 2 SK data( ± 1 σ)
Energy spectrum of SK-I Best fit solar+KamLAND (as of before ν 2004) (tan 2 θ , ∆ m 2 ) Energy correlated systematic error
Energy spectrum of SK-I ∆ m 2 =7.2x10 -5 eV 2 , tan 2 θ =0.38 Best fit solar+KamLAND (before ν 2004) Best fit 8 B flux: 5.21 x 10 6 /cm 2 /sec ∆ m 2 =6.3x10 -5 eV 2 , tan 2 θ =0.55 SK only with BP2000 flux and error constraint Best fit 8 B flux: 4.84 x 10 6 /cm 2 /sec Energy correlated systematic error
Oscillation analysis ( ) − ρ δ δ δ bin d 2 = ∑ N 2 2 2 L χ + + + − ∆ 2 i i B S R 2 log σ σ σ σ timevar 2 2 2 2 = i 1 i B S R Energy correlated Spectrum Time variation systematic error β + η Data b h = ρ = i i i d , + i i 8 SSM SSM B hep f i i i ( ) ( ) ∆ θ ∆ θ 8 osc 2 2 osc 2 2 B m , tan hep m , tan = = i i b , h + + i i 8 SSM SSM 8 SSM SSM B hep B hep i i i i ( ) ( ) ( ) ( ) δ δ δ = δ × δ × δ B S R f , , f f f Β Β i S R i i S i R 8 B spec. energy energy shape scale resolution Function for energy correlated systematic errors
Flux independent excluded region
assuming fixed Allowed region 5.05x10 6 /cm 2 s total 8 B Flux: BP2000 8 B flux
BP2000 total 8 B Flux: 5.05x10 6 /cm 2 s BP2004 total 8 B Flux: 5.79x10 6 /cm 2 s
BP2000 total 8 B Flux: BP2004 5.05x10 6 /cm 2 s total 8 B Flux: 5.79x10 6 /cm 2 s BP2004 BP2000 total 8 B Flux: total 8 B Flux: 5.79x10 6 /cm 2 s 5.05x10 6 /cm 2 s Michael Smy, UC Irvine
Analysis of lower energy region in SK-I Vertex position distribution of background (4.5 – 5.0 MeV) Wall Z after previous cuts R Events Events Rn before cuts Center after previous cuts Water is supplied from bottom (same method as above 5.0MeV) Bottom Z(cm) Top R²(cm²) � Apply tighter cuts to reduce external background. � Use improved vertex reconstruction program. � Remove high radon periods. � Select period when trigger eff. for 4.5-5.0MeV is >95%. (466days, Sep.1999-July 2001)
Analysis of lower energy region in SK-I Direction to the sun Solar neutrino energy spectrum 1496 days 629 +128 -126(sta.) signals 68016+-262 bg events 4.5 – 5.0 MeV data 466 days Flux: 3.13 ± 0.63(sta.) ± 0.16(sys.) /cm 2 /sec 4.5-5.0 MeV data is consistent with previous results.
SK-II data
Detector calibration in SK- -II II Detector calibration in SK • PMT relative gain calibration by using Ni(n, γ )Ni source and an uniform light source (Xe-scintillation ball). • Timing calibration by N 2 -DYE laser ball. Energy distributions LINAC calibration data were taken at 6 positions. Tail due to 2 electrons
SK- -II detector performance II detector performance SK （ ） （ LINAC calibration ） LINAC calibration Energy resolution Vertex resolution ~20% at 10 MeV ~100cm at 10 MeV Angular resolution Absolute energy calibration ± 2% ~28deg. at 10 MeV MC tuning is in progress.
N calibration 16 N calibration 16 Energy spectrum (a) (b) (c) w/o trigger E =14.2 MeV n 16 16 O(n,p) N 2 m n n n 16 n N n n with trigger correction DT generator n+ 16 O → p+ 16 N D+T → He+n Zenith angle dependence of energy scale (14.2 MeV) ± 0.5%
SK- -II Trigger II Trigger SK LE trigger: Number of hit PMTs within 200nsec: N 200ns > 14 SLE trigger: N 200ns > 10 (added after July 15, 2003) Online vertex reconstruction and fiducial volume cut are applied to SLE events. SLE LE Trigger rate: LE: ~70 Hz SLE: ~1100 Hz E > 6.5 MeV for SLE trigger 100% efficient for E > 8.0 MeV for LE trigger
SK- -II preliminary results II preliminary results SK Dec.24,2002 – March 25, 2004 Direction to the sun 325 days 8 – 20 MeV +82 Solar ν signal = 2161 (stat.) events -80 Flux= 2.38 ± 0.09 (stat.) (Systematic error (x10 6 /cm 2 /s) under study) (cf. SK-I result: 2.35 ± 0.02(stat.) ± 0.08(sys.))
SK- -II: Day II: Day- -Night difference Night difference SK 325 days (Dec.24,2002 – March 25, 2004) Events/day/kton/bin Events/day/kton/bin Day Night Flux= 2.34 ± 0.13 (stat.) Flux= 2.40 ± 0.12 (stat.) cos θ sun cos θ sun (D-N) = - 0.025 ± 0.075 (stat.) A DN = (D+N)/2 (Systematic error under study)
SK- -II energy spectrum II energy spectrum SK SK-I average Consistent with SK-I
Time variation Time variation
Future prospects towards SK-III Possibility of detecting spectrum distortion ν e survival probability Recoil electron spectrum 0.55 ~10% upturn Data/SSM(BP2004) should be seen Lower threshold 0.5 reduce stat. error P( ν e → ν e ) reduce sys. error sys. error 0.45 tan 2 ( θ ) ∆ m 2 (eV 2 ) 6.3 x 10 -5 0.55 0.4 0.38 4.8 x 10 -5 0.38 7.2 x 10 -5 10.0 x 10 -5 0.38 0.28 7.2 x 10 -5 0.35 5 7.5 10 12.5 20 E ν (MeV) Energy(MeV)
Future prospects towards SK-III Significance of spectrum distortion tan 2 ( θ ) ∆ m 2 (eV 2 ) Current breakdown of correlated 0.28 7.2 x 10 -5 systematic errors 0.38 10 x 10 -5 7.2 x 10 -5 0.38 4.8 x 10 -5 0.38 0.55 6.3 x 10 -5 Significance ( σ ) 3 σ level Solar+KamLAND best fit Live time (years) � Better Energy scale calibration Assumptions: (~ ± 0.4%) is needed. Correlated systematic error: x 0.5 � Better 8 B spectrum shape from 4.0-5.5MeV background: x 0.3 nuclear physics is needed. (same BG as SK-I above 5.5MeV)
Conclusion Conclusion � High statistics solar neutrino data has been taken at Super- Kamiokade. � Day/night asymmetry is obtained by unbinned method : A DN = -1.8 ± 1.6 +1.3/-1.2 %. � Energy spectrum: SK prefers smaller ∆ m 2 and larger tan 2 θ compared with global best fit parameters. � Assuming 8 B total flux of the SSM predictions, LMA solution is preferred. � Solar neutrino signal in 4.5 – 5.0 MeV (total energy) bin was newly obtained. � Preliminary results from SK-II are consistent with SK-I. � Hope to see definite energy spectrum distortion in SK-III, if it should be there.
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