Super kamiokande on the activities from 2000 to 2006 and future prospects
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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

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

Super-Kamiokande collaboration

33 institutes, 122 physicists

ICRR member:

Staff: 17

PD: 4

Students: 7

(faculty: 8, research assistant: 9)

Total 28


Super kamiokande on the activities from 2000 to 2006 and future prospects

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


Accident and partial reconstruction

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


Full reconstruction october 2005 april 2006

~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.


Atmospheric neutrinos

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)


Sk i ii atmospheric neutrino data

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.


N m n t 2 flavor analysis

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 > 0.93at 90% CL


Oscillation results 1998 vs sk i sk ii

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


L e analysis

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


Selection criteria

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


Sk i ii l e analysis and non oscillation models

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.


Oscillation to n t or n sterile

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


Testing n m n t vs n m n sterile

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


Limit on oscillations to n sterile

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


Search for cc n t events sk i

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


Likelihood neural net distributions

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


Super kamiokande on the activities from 2000 to 2006 and future prospects

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.


Future search for non zero q 13

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.


Future search for non zero q 131

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.


Summary of atmospheric neutrino analysis

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 > 0.93at 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.


Solar neutrinos

Solar neutrinos

Main Physics

High statistics measurement of 8B solar neutrinos to

(1) solve “solar neutrino problem”

(2) measure oscillation parameters (q12, Dm212)


Solar neutrino measurement in sk

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 informationvertex position

  • Ring patterndirection

  • Number of hit PMTsenergy

Ee = 9.1MeV

cosqsun = 0.95


Super kamiokande i solar neutrino data

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 )


Evidence for solar neutrino oscillation by sk and sno june 2001

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)

±


Super kamiokande on the activities from 2000 to 2006 and future prospects

Energy spectrum of SK-I

(tan2q, Dm2)

Energy correlated systematic error


Super kamiokande on the activities from 2000 to 2006 and future prospects

SK-I day/night difference

(Day-Night)

ADN=

(Day+Night)/2

Expected D/N asymmetry

ADN

-1%

-2%

-10%

-80%


Super kamiokande on the activities from 2000 to 2006 and future prospects

Excluded region by energy spectrum and day/night

Super-Kamiokande 1496 days

S.Fukuda et al., Phys. Lett. B 539 (2002) 179


Super kamiokande on the activities from 2000 to 2006 and future prospects

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


Super kamiokande on the activities from 2000 to 2006 and future prospects

Plot after KamLAND first result


Sk ii solar neutrino analysis

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.)


Super kamiokande on the activities from 2000 to 2006 and future prospects

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)


Super kamiokande on the activities from 2000 to 2006 and future prospects

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)


Summary of solar neutrino analysis

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.


Proton decay search

Proton decay search

Physics

Establish GUT

Quark+lepton


Proton decay search p e p 0

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


Proton decay search p n k

Proton decay search( pnK+)

m+ shape method

Prompt g method

K+p+p0 method

Combine those methods,

Lifetime: >2.3 x 1033 years


Sensitivity of future sk

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)


Supernova neutrinos

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.


Super kamiokande on the activities from 2000 to 2006 and future prospects

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.


Search for supernova relic neutrinos

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


Super kamiokande on the activities from 2000 to 2006 and future prospects

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 !


Future possibilities of n e tagging

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)


Possibility of srn detection

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)


Summary of proton decay

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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