Super-Kamiokande

Introduction Contained events and upward mu

ons Updated results

Oscillation analysis with a 3D flux Multi-ring events 0/ ratio 3 decay Search for leptons s

Conclusion

Y.TotsukaKamioka

Super-Kamiokande collaboration

Super-Kamiokande detector

50,000 ton water Cherenkov detector (22.5 kton fiducial volume)

1000m underground (2700 m.w.e.)

11,146 20-inch PMTs for inner detector

1,885 8-inch PMTs for outer detector

Atmospheric neutrinos

p, He ...

, K

e

e

L=10-30 km

L=up to 13000 km

e e

= ~ 2

e e

@ low energy (EGeV)

@ high energy

Neutrino oscillations :

e e data MC1

Error in absolute flux~20%, but /e ratio~5%

e e

Atmospheric neutrino spectrum

Energy dependence of e ratio

<5% accuracy

ee

ee

(3-D)

(P.Lipari)

Primary cosmic ray flux

protons

He

From P.Lipari

Bartol and Honda fluxes

Zenith angle distribution(1D)

For E> a few GeV,Upward / downward = 1 (within a few %)

Up/Down asymmetry for neutrino oscillations

Calculated zenith angle distribution

E=0.5GeV E=3GeV E=20GeV

p

p

1D

p

p

3D

3D calculation by G.Battistoni et al. (hep-p

h/9907408)

10-3–0.2 GeV 0.2-0.5 GeV

0.5-1 GeV 1-5 GeV

horizontal vertical

3D neutrino flux calculation

Contained events

Interaction in the rock

Upward through-going muons

contained

through-going muonsstopping muons

Upward stopping muons

Initial neutrino energy spectrum

How to detect atmospheric neutrinos

Contained event analysis

e or

Fully Contained (FC) Partially Contained (PC)

No hit in Outer Detector One cluster in Outer Detector

Reduction

Automatic ring fitterParticle IDEnergy reconstruction

Fiducial volume (>2m from wall, 22 ktons) Evis > 30 MeV (FC), > 3000 p.e. (~350 MeV) (PC)

Final sample: FC: 8.2 ev./day, PC: 0.58 ev./day

Evis < 1.33 GeV : Sub-GeVEvis > 1.33 GeV : Multi-GeV

Total 754 1065.0

Data MC(Honda flux)1ring e-like 626 612.8 -like 558 838.3Multi ring 1318 1648.1Total 2502 3099.1

Sub-GeV (Fully Contained) Evis < 1.33 GeV, Pe > 100 MeV, P> 200 MeV

Data MC(Honda flux)1ring e-like 2864 2667.6 -like 2788 4072.8Multi ring 2159 2585.1Total 7811 9325.5

/e Data

/e MC

= 0.638 0.050

Multi-GeVFully Contained (Evis > 1.33 GeV)

Partially Contained (assigned as -like)

/e Data

/e MC

= 0.675 +0.034-0.032 0.080

(1289.4 d (79.3 kt .y))

0.017

Fully contained event summary

Zenith angle distribution

1289 days (79.3 kt . yrs)No oscillationBest fit (m2=2.4x10-3eV2, sin22=1.00)

2(best fit) = 132.4/137 d.o.f.

2(no osc.) = 299.3/139 d.o.f.2=167

(E<1.33 GeV)

(E>1.33 GeV)

Multi-ring event analysis

1289 days (79.3 kt . yrs)

No oscillationBest fit (m2=2.0x10-3eV2, sin22=1.00)

Sub-GeV muti-ring -like sample

Zenith angle distributions

Multi-GeV muti-ring -like sample

0.6 GeV < E < 1.33 GeV

E > 1.33 GeV

The zenith angle distortion is consistent with single-ring analysis.

preliminary

cos

cos

Upward through-going muons

horizontalvertical

No oscillation:

2(shape)=18.7 / 10 d.o.f.

(prob.=0.044)

Osc. best fit (m2=5.2x10-3eV2,sin22=0.86)

Upward stopping muons

No oscillation:(Bartol, GRV94)

Oscillation

(m2=3.2x10-3eV2,sin22=1.00)

stopping through ( )Data

stopping through ( )MC

=0..016 +0.013

- 0.011 0.368 +0.049

- 0.044

0...09

=

<< 1

1416 events / 1268 days

345 events / 1247 days

Zenith angle distributions of upward-going muons

79.3 kt . yrs

Best fit : m2=2.5x10-3eV2, sin22=1.00 (2=142.1 / 152 d.o.f.)

68% C.L.90% C.L.99% C.L.

SK combined result

m2 = (1.7~4)x10-3eV2

sin22 > 0.89 (90% C.L.)

Allowed region (FC + PC + UP-thru + UP-stop)

79.3 kt . yrsBest fit : m2=2.5x10-3eV2, sin22=1.00 (2=142.1 / 152 d.o.f.)

68% C.L.90% C.L.99% C.L.

SK combined result

m2 = (1.7~4)x10-3eV2

sin22 > 0.89 (90% C.L.)

m2 (

eV

2)

sin22

unphysical region

Allowed region - II(FC + PC + UP-thru + UP-stop)

No oscillationBest fit (m2=2.5x10-3eV2, sin22=1.00)

Zenith angle distributions for the best fit

Allowed region (grand global fit)(FC + PC + UP-thru + UP-stop + multi-rings)

79.3 kt . yrs

Within physical region; x2min = 157.5/170 dofat sin22 = 1.0, m2 = 2.510-3 eV2

With unphysical region;x2min = 157.4/170 dofat sin22 = 1.01, m2 = 2.510-3 eV2

Zenith angle distributions for the best fit(grand global fit)

No oscillationBest fit (m2=2.5x10-3eV2, sin22=1.00)

Zenith angle distributions for the best fit (cont)(grand global fit)

No oscillationBest fit (m2=2.5x10-3eV2, sin22=1.00)

Systematics in the 1D fit

sterile (0 method)

(/)Data

(/)MC

> 1 for

1 for s

Data 355.2 events (BG subt.)

MC 323.2 events

(/)Data

(/)MC = 1.49 0.08(stat.) 0.11(sys.)

{

Experimental only

0 info from K2K-1kt

0

FC-( )data= 0.99 0.03 0.1

PRELIMINARY 0

FC-( )MC

(0/)data vs (0/)MC-no-osc

PRELIMINARY

Using matter effect and enriched NC sample

: No matter effect

s : With matter effectNeutrino oscillation in matter:

( ) = ( cosm

s

sinm- sinm cosm ) 1

2( )sin22m

sin22=

(cos2sin22= 2 GFnnE / m2

For sin22= 1

sin22m1

~ + 1

And for E = 30~100 GeV 1 and

sin22m1Suppression !

Strategy:

Obtain allowed region using lower energy events (Fully contained sample)

Then,

Test zenith angle of NC enriched events, high energy PC and through-going muon events.

sterile (matter in earth)

Allowed region using only FC events

Zenith angle of upward-going muon

m2 = 3 x10-3eV2

sin22 = 1

m2 = 3 x10-3eV2

sin22 = 1

s

> 45000 p.e.(E> ~ 5 GeV)<E>=~25 GeVs

Zenith angle of high energy PC events

s

Criteria> 400 MeV visible energyMulti-ring evente-like ring is the most energetic ringContentsNC : 29 %e CC : 46 % CC : 25 %

m2 = 3 x10-3eV2

sin22 = 1

Zenith angle of NC enriched events

s

sin22 = 1

s

s

Up/Down ( cos ) ratio of NC enriched multi-ring

Up/Down (cos) ratio of High Energy PC Vertical/Horizontal ratio (co

s -0.4) of up muons

Data

DataData

10-3 10-2 eV2 10-3 10-2 eV2

Ratios vs. m2

><

> 0.4<-0.4

<-0.4> 0.4

combine NC enriched, high E PC and up muons

s is excluded with 99 % C.L.

excluded

excluded

excluded

Allowed vs. excluded regions

Neutrino CC cross sections

CC

Signature of appearance:

+ N + N’ + +

CC

Expected events

Higher multiplicity of Cherenkov rings More e decay signals More spherical event pattern

ehadrons(

Search for appearance (3 methods) :(1) Energy flow and event shape analysis(2) Likelihood method using # of rings, e, max p.e.

ring and etc.(3) Neural network method

Each method is optimized using only downward going events and then looks at upward going events.(I.e. blind method to disable systematic bias.)

All

cos<-0.2

cos>0.2

~20ev./yr for 3x10-3 eV2

sin22 = 1

E(GeV) m2(eV2)

Search for leptons

Multi-ring samples: atm + e w/o : CC

All methods show ~2 excess of -like events.The result is consistent with oscillations.

MC with MC without

Likelihood method

Observed # of : 27+9-8

m2=3x10-3eV2, sin22=1.00

(expected # of : 74 events)

Efficiency for : 43.5 %

# of production: 62 -18+39

Energy flow method

+14-13

Efficiency for : 32 %# of production: 79 -40

Observed # of : 25.5

cos

Neural network method

Observed # of : 42 19 +13-13

# of production: 92 35.3 -0

+44

+14Efficiency for : 45 %

+17-16

-27+21

Zenith-angle distribution

Test oscillation with :

P()=sin22sin2(LEn) (n : parameters)

Use FC, PC, Up-through, and Up-stop data

n=-1 is the standard neutrino oscillation

index n

2

-2 -1 0 1Magnified view

n = -1.06 0.14

Probability of exotic oscillation models

Neutrino decay

Let neutrinos oscillate and decay 3 X(invis);

P( ) = sin4 + cos4 exp( )

+ sin2 exp( ) cos( )

Consider two cases;

dcy>>osc, and dcy<<osc,

wheredcy = , osc =

m3 L3 E

m3 L23 E

m2 L 2E

3E m3

4E m2

dcy >>osc

For m2 , 2

min = 221.2/153 dof

Bad fit !

dcy << osc

For m2 0, 2

min = 147.1/153 dof at (sin2, m3/3) = (0.68, 0.01 (GeV/km)

) Good fit !

Up/down of NC enriched events (short dcy)

FC, Nring>1, Evis>400MeV, Brightest ring = e-like

Allowed from FC+PC+Upmu

Excluded from NC

The case of dcy

<<osc

is disfavored

Conclusions on atmospheric neutrinos

Oscillation parameters for : m2 = 1.7 ~ 4 x 10-3 eV2, sin22 > 0.89(90%CL)

3D flux does not change the conclusion but more precise 3D calculations are needed

s is strongly disfavored 0/ ratio is consistent with Excess from leptons ~ 2 Decay senario is disfavored with > 2

for dcy>>osc and dcy<<osc