Atmospheric neutrino observationsin Super-Kamiokande I
M.Ishitsuka (ICRR)SK I における大気ニュートリノの観測（最終結果に近い段階の解析の現状）
石塚正基（東大宇宙線研）

Atmospheric neutrinop, He …

Downward（L=10~100 km）

θπ±, K±µ±νµe±
νµνe
Upward（L=up to 13000 km）

Up/Down SymmetryFlux(m-2sec-1sr-1GeV-1)

Zenith anglecosΘSuper-Kamiokande detector& atmospheric neutrino data
Water Cherenkov detector

Event classification

Fully Contained(Eν ~1GeV)Partially Contained(Eν ~10GeV)
 1000 m underground 50,000 ton (22,500 ton fid.) 11,146 20 inch PMTs
 1,885 anti-counter PMTs

Stopping µ (Eν ~10GeV)
Through-going µ (Eν ~100GeV)

Zenith angle distributions (FC+PC+up-µ)
No oscillation
Oscillation best fit (∆m2=2.0x10-3eV2, sin22θ=1.00)

100cosθ

0.501

Multi-GeV e-like

100-1-0.50cosθ

0.5

1Multi-GeV µ-like + PC

350

Multi-GeV µ-like+ PC
250
15060

10040-1-0.50cosθ

0.5

10-1-2 -1-130cosθ

0.5

Multi-ringMulti-GeV µ-like

8060
400-1-0.50cosθ

0.51Upward Stopping µ

1.2

Up Stop µ10.80.60.401205020-0.5

Multi-GeV Multi-ring

10030020080-1-2 -101.40.2-13-0.5

Number of Events-1Flux(10 cm s sr )200

Multi-ring
Sub-GeV µ-like
Sub-GeV Multi-ring

-1300

5045
4035302520151050

Flux(10 cm s sr )Number of Events

400

1200

Sub-GeV µ-like

500

Number of Events

Number of Events

Sub-GeV e-like

Multi-GeV e-like

140

Sub-GeV µ-like

Number of Events

Sub-GeV e-like

Number of Events

450
400
350
300
250
200
150
100500-1-0.50cosθ

0.5

14
3.5
32.5
2
1.5
10.5
0-1-0.8 -0.6 -0.4 -0.2

cosθ

0

Upward Through Going µ

Up Through µ-1-0.8 -0.6 -0.4 -0.2

cosθ

0

Allowed region (FC+PC+up-µ)νµ Jντ

νµQντ oscillations
Best fit(∆m2=2.0x10-3,sin22θ=1.0
χ2min=170.8/170 d.o.f)∆m2 = (1.3~3.0)x10-3eV2
sin22θ > 0.90 at 90%CL

Comparison with old result•Neutrino flux
(Honda 1995 Honda 2001)

Updated analysis
Old analysis•Neutrino interaction models(several improvements,agree with K2K near data)•Improved detector simulation•Improved event
reconstruction tools
Each changes slightly shifted
the allowed region to lower ∆m2

Flux changes

cosmic-ray proton flux
w/ Honda 2001

• Honda1D Æ Honda 3D– Absolute normalization lower– “3D” enhancement• At low energies• Near the horizon

Different flux in Super-Kamiokande Honda 2001 (3D) Honda 1995 (1D) Bartol 1996
¨ DataOther improvements
Neutrino interactions
Agree with K2K near data
Q.E.

MA=1.01.1Single π

MA=1.01.1Analysis tools
SK detector simulator
Light scattering parameters in water (laser measurement)
Outer detector PMT gain parameter (single p.e. distribution)
dE/dx in water Æ decrease 3% for µ (>300MeV/c)

Data reduction
Fully automated FC and PC data reductionEffect from each change

0.722

χ -χ min=4.6 for 90% C.L.

0.8

0.92

1

1.1

2

1.22

χ -χ min=4.6 for 90% C.L.

-3

100.7

0.8

0.9

Official ν interaction model
Old version

Neutrinointeraction model

-3

11.12

1.2

sin 2θ

sin 2θ

100.722χ -χ min=4.6 for 90% C.L.

0.8

0.9

1

1.1

1.2

sin22θ

90% C.L. allowed regions-210∆m2 (eV2)-3

New simulation/analysis tools
Old version

Detector simulation &Event reconstruction∆m2 (eV2)∆m2 (eV2)∆m2 (eV2)

Neutrino flux
Honda 2001 Flux
Honda 1995 Flux

90% C.L. allowed regions-2

1010101090% C.L. allowed regions-2

90% C.L. allowed regions-2

Official
Old version

miler
POld resultyrain

Each change
contributes to theshift in the allowed(∆m2) region.

Updated result-3

100.722χ -χ min=4.6 for 90% C.L.

0.80.911.11.2

sin22θ

Sub-sample consistency
Check the result using different types of dataÆ all allowed regions overlap best fit
1000FC νµFC νe
PC νµEvents / 1000 days

750
500
250
0150

Up-Stop νµ
Up-Thru νµ100
500 -2-1
101011010Eν (GeV)

210

3104105

Further improvement for SK I final result
9 Honda flux updated
Dipole approximation Æ Multi pole for geomagnetic field

9Upward going muon prediction
Analytical calculation Æ Monte Carlo method• Consider angular correlation ν Æ µ9 re-estimation of systematic errors
Æ more fundamental components withmathematical method• Check the sources clearly• Treat the correlations of errors correctly

re-estimate systematic uncertainties
Æ
estimate additional errors
SK I oscillation analysis will be finalized soon (with full paper)

-0.50cosθ

0.5

1

250
200
150
100

P<400MeV/cµ-like500-1-0.50cosθ

0.5

400
350
300
250
200
150
100
5001Updated
Honda flux(multi pole)

120
100

P>400MeV/ce-like-1-0.50cosθ

0.58060

Multi-GeV
e-like40
2001-1-0.50cosθ

0.51350

Number of Events

Number of Events

300

140

Number of Events

P<400MeV/ce-like
-1

200
180
160
140
120
100
80
60
40200

Number of Events

Number of Events

250
225
200
175
150
125
100
75
50
250

Number of Events

Updated Honda flux

300
250
200
150

P>400MeV/cµ-like-1-0.50cosθ

0.5

Multi-GeVµ-like + PC

100
50

10-1

The difference is small-0.50cosθ

0.51Old Hondaflux (dipole)

Upward-going µ Monte Carlo
number of event

2500
2000

Neutrino direction

1500
1000

0Muon direction

Upward stopping µ500
-1-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.1
cosΘ0

Analytical calculation

number of event

6000
5000
4000

MC

3000

ν

2000

Upward through-going µ10000-1-0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.2 -0.10cosΘµ Æ fitter

The difference is small in upward stopping µ 5 bin analysis
Æ becomes large in 10 bin analysis

Calculation methods, basic idea
(based on Fogli et al., hep-ph/0206162) nnnk  N obs − N exp (1 + ∑ f k ⋅ ε ) k =1χ2 = ∑ 2σn =1nK

Definition of χ22

 εk + ∑  k =1 σ k 2Knn
N obs: observed , N exp: expected , ε k : systematics

In our current analysis, minimum χ2 is obtained by
optimizing εj (j = 1,2,..) for each (sin22θ,Δm2) point.

But, mathematically,χ2 is minimum ⇔Minimizing χ2∂ χ2= 0∂εj⇔

for any j .

Solving nsys linear equation.

Re-estimation of systematic errors
Sub-GeVReduction
Neutrino flux
E-γ
PID
Ring counting
Vertex position
Energy calibration
Non-ν BG
flashercosmic mneutron BG
Neutrino interaction
CCNC
Hadron simulator
FC/PC separation

Error in µ/e ratio

Multi-GeV<<1<50.6
2
3
0.6
1.0

3
<5
1.6
36
2.4
4.1

<0.5
<0.1
<0.1

<0.1
<0.2
<0.2

3.5
3
0.5
<0.1

4.3
4
1.0
0.5

7.8% 11.8%

Treat as independent
error term andre-estimate the values

List of updated systematic errors(A) Neutrino flux
① flux absolute normalization② νe/νµ ratio③ anti-neutrino/neutrino ratio④ geomagnetic effect(up-down ratio)⑤ horizontal-vertical ratio (3D effect)⑥ horizontal-vertical ratio (K/pi)⑦ Neutrino flight length (production height)⑧ Energy spectrum⑨ Sample-by-sample normalization(B) Neutrino cross section & kinematics
①②③
④
⑤
⑥
⑦
⑧Quasi elastic scattering
low energy neutrino scattering in QE
single-pion production
multi-pion production
Bodek correction in DIS
coherent pion
NC/CC rationeutrino-lepton angular correlation(D) Event selection① FC reduction② PC reduction③ Up-µ detection efficiency④ 1.6 GeV cut ( Æ 2% energy calibration)⑤ Through-going/stopping µ separation(E) Event reconstruction① 1-ring/multi-ring separation② Particle ID③ Energy calibration④ Up-down asymmetry of energy calibration(F) Other sources①②③④m/e ratio
up/down ratio
FC/PC relative normalization
τ from oscillation

SK-II is working
Super-Kamiokande
Run20941Event2717
201-1
2 -1
1 :0
1 :49 :47Inenr: 34
0 5 i
h ts, 72Ouet

r:1 85ih ts,

823 pE306 pE (in-time)

Tri g er ID:0 x0bD law:1 690 .0 cm

Full y-Co tn ain
e dCharge(pe)>26.
723.3-26.
7
20.2-23.3
17.3-20.2
14.7-17.3
12.2
-14.7
10.0-12.2
8.0-10.0
6.2-8.0
4.7- 6.
2
3.3-4.7
2.2-3.3
1.3- 2.
2
0.7-1.3
0.2-0.7
< 0.2
710
568
426
284
142
00500

1000

1500

2000

Times (ns)SK-II Cosmic ray muon sample

20inch PMT withAcrylic + FRP vesselWith about half of original ID PMTs
– 20-inch PMTs in acrylic shells toprevent future chain implosions– OD at full complement (1885) of 8inch PMTs

Number of EventsFirst report from SK-II
Number of Events / Event rate in SK-II
60

SK-II
149 days

SK-I
1489 days

Fully-contained
events1245(8.33±0.24)

12180(8.18±0.07)

Partially-contained
events80(0.54±0.06)

911(0.62±0.02)

50

40

30

20

100-1

-0.8

-0.6

-0.4

-0.2

00.2

0.4

0.6

0.8

1cosθ

zenith angle, Multi-GeV FC+PC

The event rate is consistent with SK-I

SK-II zenith angle forMulti-GeV µ-like + PC

Clear deficit in upward-going events

Summary¾ νµQντ 2 flavor oscillations¾ Updated result–Best fit value is (∆m2 = 2.0x10-3 eV2, sin2(2θ) = 1.0)
–1.3 < ∆m2 < 3.0x10-3 eV2, sin2(2θ) > 0.90 @ 90% C.L.
–Each change contributes to the shift of allowed region¾ final SK-I result–To be published soon with SK-I paper after modifications
z updated Honda flux calculationz prediction of upward-going µ by Monte Carlo methodz re-estimated systematic errors¾Status of SK-II¾SK-II analysis has started– Event rate is consistent with SK-I
– deficit in upward-going event in Multi-GeV µ-like + PC sample