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

Transcription

1 Super-Kamiokande (on the activities from 2000 to 2006 and future prospects) M. Nakahata for Neutr ino and astr opar ticle Division Super-Kamiokande detector Atmospheric neutrinos Solar Neutrinos Proton decay search Supernova neutrinos

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

3 History of Super-Kamiokande Detector 1996 Start SK-I Accident Partial Reconstruction SK-II Full reconstruction SK-III Number of ID PMTs (photocoverage) 11,146 (40%) 5,182 (19%) 11,129 (40%) Main results Evidence for Atmospheric osc. Tau favor over sterile in atm. osc. Evidence for Solar osc. LMA by solar global analysis Atmospheric L/E K2K final results Atmospheric tau appearance

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

5 Full Reconstruction (October 2005 April 2006) ~6000 ID PMTs were produced from 2002 to 2005 and were mounted from Oct.2005 to Apr 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 ( 23, m 2 23, 13 ) Oscillation mode (? sterile?) Oscillation signature (L/E dependence)

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

8 2 flavor analysis 1489 days (SK-1)+ 804 days (SK-II) Best Fit: m 2 = 2.5 x 10-3 ev 2 sin 2 2 = = / 755 dof (18%) 2 distributions P reliminary x ev ev 2 2 < m m 2 2 < x ev ev 2 2 sin sin > at at 90% 90% CL CL

9 Oscillation results 1998 vs. (SK-I+SK-II) days 90% CL m 2 (ev 2 ) 90 % CL % CL of 1998

10 L/E analysis SK collab. hep-ex/ oscillation P = 1 sin 2 2 sin 2 m ( L ) E decoherence 1 L P = 1 2 sin 2 2 (1 exp( )) E decay P = (cos 2 sin 2 exp( m L )) 2 2 E -likemulti-gev +PC Should observe this dip! Further evidence for oscillations Better determination of oscillation parameters, especially m 2

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

12 SK-I+II L/E analysis and non- oscillation models decoherence decay SK-I+II (preliminary) Decoh. Decay 2 (osc)=83.9/83dof 2 (decay)=107.1/83dof 2 (decoherence)=112.5/83dof Osc. Oscillation gives the the best best fit fit to to the the data. Decay Decay and and decoherence models models disfavored by by and and ,, resp. resp.

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

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

15 Limit on oscillations to sterile (sin sterile +cos ) If pure, sin 2 =0 If pure sterile, sin 2 =1 SK-1 data Consistent with pure SK collab. draft in preparation

16 Search for CC events (SK-I) CC events hadrons CC MC hadrons Signature of CC events Higher multiplicity of Cherenkov rings More e decay signals Spherical event pattern Likelihood and neural network analysis Only ~ 1.0 CC FC events/kton yr yr (BG (other events) ~ 130 ev./kton yr) yr)

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

18 Zenith angle dist. and fit results Likelihood analysis NN analysis Hep-ex/ scaled MC Data Number of events, e, & NC background Fitted # of events Expected # of events cos zenith 138±48(stat) +15 / -32(syst) 78±26(syst) 78±27 (syst) cos zenith 134±48(stat) +16 / -27(syst) Zero tau neutrino interaction is disfavored at 2.4.

19 Future: Search for Non-zero 13 Simulation (4.5 Mton yr) One mass scale dominance approx. m 2 12 ~ 0, m2 13 ~ m2 23 = 1+multi-ring, e-like, 2.5~5 GeV/c m2 m L P 27 Electron appearance ( 2 e) sin 23 sin 2 13 sin E only 3 parameters P( e ) at SK s 2 13 ~ 0.04 s 2 13 = 0.00 null oscillation cos zenith 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 13 s =0.825 s 2 23=0.4 ~ 0.6 s 2 13=0.00~0.04 cp=45 o m 2 12=8.3e-5 m 2 23=2.5e-3 Sensitivity of 20 years SK data CHOOZ exclude sin 2 23 = If 13 is close to CHOOZ limit, non-zero 13 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 ev 2 < m 2 < 3.1 x 10-3 ev 2 sin 2 2 > 0.93 at 90% CL L/E dependence of neutrino oscillation was observed. favors over sterile Tau appearance with 2.4 level. Future prospects Search for non-zero 13. If 13 is close to CHOOZ limit, it could be observed by atmospheric neutrinos.

22 Solar neutrinos Main Physics High statistics measurement of 8 B solar neutrinos to (1) solve solar neutrino problem (2) measure oscillation parameters ( 12, m 2 12 )

23 Solar neutrino measurement in SK 8 B neutrino measurement by + e - + e - Sensitive to e e - =~0.15 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. Typical event Ee = 9.1MeV cos sun = 0.95 Timing information vertex position Ring pattern direction Number of hit PMTs energy

24 Super-Kamiokande Kamiokande-I I solar neutrino data May 31, 1996 July 13, 2001 (1496 days ) + e - + e solar events (14.5 events/day) 8 B flux : [x 10 6 /cm 2 /sec] Data SSM(BP2004) = ( Data/SSM(BP2000) = / )

25 Evidence for solar neutrino oscillation by SK and SNO (June 2001) SK ES = /-0.07 [x10 6 /cm 2 /s] SNO CC = /-0.11 Obtained total flux: exp = 5.5±1.4 ES = e +0.15, CC = e (cf. SSM(BP2000) = /-0.8) 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 (tan 2, m 2 ) Energy correlated systematic error

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

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 Event direction SK-II 791 days 7-20MeV Energy spectrum signal = (stat.) flux = 2.38 ±0.05 (stat.) +0.16/-0.15(sys.) x10 6 /cm 2 /sec Consistent with SK-I SK-I result: /-0.02(stat.) +/-0.08(syst.)

32 Future prospects: precise spectrum measurement Is there spectrum distortion? e survival probability Recoil electron spectrum ~10% spectrum distortion expected from LMA P( e e ) But, SK-I spectrum is almost flat. Data: SK-I sys. error sin 2 ( ) m 2 (ev 2 ) 6.3 x x x x x 10-5 E (MeV)

33 Future propsects: expected sensitivity of SK-III Expected spectrum in SK-III 5 years data assumed Energy correlated systematic error Significance ( ) Statistical significance sin 2 ( ) level m 2 (ev 2 ) 7.2 x x x x x 10-5 Solar+KamLAND best fit Assumption: Correlated systematic error: x MeV background : x 0.3 of SK-I (> 5.5MeV is same as SK-I) Live time (years)

34 Summary of Solar neutrino analysis Activities from 2000 to 2006 Evidence for solar neutrino oscillation by comparing SK and SNO data in 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 Physics Proton decay search Grand Unification G SU (2) U (1) SU (3) Quark+lepton Establish GUT

36 Proton decay search(p e + 0 ) SK-I (1489days) SK-II (804days) Total momentum (MeV/c) No candidate was observed. Total mass (MeV/c 2 ) Life time limit (p e + 0 ):>8.4 x years Expected signal region.

37 Proton decay search(p K + ) + shape method Prompt method K + method Combine those methods, Lifetime: >2.3 x years

38 Sensitivity of future SK p e + 0 p + SK 20 yrs 450ktyr BG=1~2events τ/b yrs (SK 20yrs, 90%CL) τ/b 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 Offline computer ALARM Supernova watch computer If a candidate is found Selection criteria: 25 ev. within 10 sec. Rmean > 7.5m Notify to shift person Check vertex distribution and event pattern Send signal to SNEWS SNEWS: (SuperNova Early Warning System) Current members: SK, SNO, AMANDA/Ice Cube, LVD Rmean: averaged distance between event vertices. This cut reject spallation and flasher backgrounds. 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 Solar 8 B Solar hep 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 oscillation (Ando et al., 2002) SRN pr edictions Atmospheric Spallation B.G. below ~18 MeV

42 Search for supernova relic neutrinos in SK-I Energy spectrum (>18MeV) 1496 days (SK-I) Total background Atm. invisible e Atm. e SK-I flux limit: < 1.2 /cm 2 /sec 90% CL limit of SRN SK limit is close to the model predictions!

43 Future: Possibilities of e tagging e p e + n Possibility 1 Gd p n+p d + 2.2MeV -ray T = ~ 200 sec Number of hit PMT is about 6 in SK-III Positron and gamma ray vertices are within ~50cm. Possibility 2 n+gd ~8MeV T = several 10th sec Add 0.2% GdCl 3 in water (ref. Vagins and Beacom) e could be identified by delayed coincidence.

44 Possibility of SRN detection Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003) with flux revise in NNN05. Spallation No B.G. reduction SK10 years ( =47%) B.G. reduction by neutron tagging SK10 years ( =80%) Hard to distinguish Statistically <1 excess (10yrs, E vis =18-30 MeV) ~1.2 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(E vis =15-30 MeV) Signal: 44.8, B.G. 14.7(E vis =10-30 MeV)

45 Summary of proton decay Activities from 2000 to 2006 Lifetime lower limit was obtained: p e + 0 :>8.4 x yrs p K + : >2.3 x yrs Future prospects p e + 0 :>2 x yrs, p K + : >4 x 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 /cm 2 /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.