Super-Kamiokande

1
Super-Kamiokande
Y.Totsuka Kamioka

• Introduction
• Contained events and upward muons
• Updated results
• Oscillation analysis with a 3D flux
• Multi-ring events
• p0/m ratio
• n3 decay
• Search for t leptons
• nm?ns
• Conclusion

2
Super-Kamiokande collaboration

3
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
4
Atmospheric neutrinos
p, He ...
L10-30 km
p ?, K?
e?
nm
nm
ne
Lup to 13000 km
_at_ low energy (En lt 1 GeV)




2
n

n
m
m
_at_ high energy
n

n
e
e
Error in absolute flux20, but nm/ne ratio5
Neutrino oscillations
?1
d
a
t
a
M
C
5
Atmospheric neutrino spectrum
(P.Lipari)
(3-D)
Energy dependence of nm/ne ratio
lt5 accuracy
6
Primary cosmic ray flux
protons
He
From P.Lipari
7
Bartol and Honda fluxes
8
Zenith angle distribution(1D)
Calculated zenith angle distribution
En0.5GeV
En3GeV
En20GeV
For En gt a few GeV, Upward / downward 1
(within a few )
Up/Down asymmetry for neutrino oscillations
9
3D neutrino flux calculation
p
p
1D
3D
p
p
n
n
n
n
3D calculation by G.Battistoni et al.
(hep-ph/9907408)
nm
10-30.2 GeV
0.2-0.5 GeV
0.5-1 GeV
1-5 GeV
horizontal
vertical
10
How to detect atmospheric neutrinos
Contained events
Upward through-going muons
Upward stopping muons
Interaction in the rock
Initial neutrino energy spectrum
contained
stopping muons
through-going muons
11
Contained event analysis
Fully Contained (FC)
Partially Contained (PC)
m
e or m
No hit in Outer Detector
One cluster in Outer Detector
Reduction
Automatic ring fitter Particle ID Energy
reconstruction
Fiducial volume (gt2m from wall, 22 ktons) Evis gt
30 MeV (FC), gt 3000 p.e. (350 MeV) (PC)
Final sample FC 8.2 ev./day, PC 0.58 ev./day
Evis lt 1.33 GeV Sub-GeV Evis gt 1.33 GeV
Multi-GeV
12
Fully contained event summary
(1289.4 d (79.3 kt . y))
Sub-GeV (Fully Contained)
Evis lt 1.33 GeV, Pe gt 100 MeV, Pm gt 200 MeV
Data
MC(Honda flux) 1ring e-like 2864
2667.6 m-like
2788 4072.8 Multi ring
2159 2585.1 Total
7811 9325.5
m
/
e
0.638
D
a
t
a
? 0.017
?0.050
m
/
e
M
C
Multi-GeV
Fully Contained (Evis gt 1.33 GeV)
Data
MC(Honda flux) 1ring e-like 626
612.8 m-like
558 838.3 Multi ring
1318 1648.1 Total
2502 3099.1
Partially Contained (assigned as m-like)
Total 754
1065.0
m
/
e
0.034
0.675
D
a
t
a
? 0.080
-0.032
m
/
e
M
C
13
Zenith angle distribution
1289 days (79.3 kt . yrs)
No oscillation
Best fit (Dm22.4x10-3eV2, sin22q1.00)
(Elt1.33 GeV)
(Egt1.33 GeV)
c2(best fit) 132.4/137 d.o.f. c2(no osc.)
299.3/139 d.o.f.
Dc2167
14
Multi-ring event analysis
1289 days (79.3 kt . yrs)
Zenith angle distributions
preliminary
No oscillation
Best fit (Dm22.0x10-3eV2, sin22q1.00)
Sub-GeV muti-ring m-like sample
0.6 GeV lt E lt 1.33 GeV
cosq
Multi-GeV muti-ring m-like sample
E gt 1.33 GeV
cosq
The zenith angle distortion is consistent with
single-ring analysis.
15
Zenith angle distributions of upward-going muons
Upward through-going muons
1416 events / 1268 days
No oscillation c2(shape)18.7 / 10 d.o.f.
(prob.0.044)
Osc. best fit (Dm25.2x10-3eV2,sin22q0.86)
horizontal
vertical
Upward stopping muons
)
(
stopping m
345 events / 1247 days
through m
Data
)
(
stopping m
through m
MC
No oscillation (Bartol, GRV94)
0.013
0.241 ? 0.016
- 0.011

0.368
0.049
- 0.044
0.65 ? 0.04 ? 0.09

ltlt 1
Oscillation (Dm23.2x10-3eV2,sin22q1.00)
16
Allowed region (FC PC UP-thru UP-stop)
nm?nt
79.3 kt . yrs
Best fit Dm22.5x10-3eV2, sin22q1.00
(c2142.1 / 152 d.o.f.)
68 C.L.
90 C.L.
99 C.L.
SK combined result Dm2 (1.74)x10-3eV2 sin22q gt
0.89 (90 C.L.)
17
Allowed region - II(FC PC UP-thru UP-stop)
nm?nt
79.3 kt . yrs
Best fit Dm22.5x10-3eV2, sin22q1.00
(c2142.1 / 152 d.o.f.)
unphysical region
Dm2 (eV2)
68 C.L.
90 C.L.
99 C.L.
sin22q
SK combined result Dm2 (1.74)x10-3eV2 sin22q gt
0.89 (90 C.L.)
18
Zenith angle distributions for the best fit
19
Allowed region (grand global fit)(FC PC
UP-thru UP-stop multi-rings)
79.3 kt . yrs
Within physical region x2min 157.5/170
dof at sin22q 1.0, Dm2 2.5?10-3 eV2 With
unphysical region x2min 157.4/170 dof at
sin22q 1.01, Dm2 2.5?10-3 eV2
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Zenith angle distributions for the best
fit(grand global fit)
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Zenith angle distributions for the best fit
(cont)(grand global fit)
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Systematics in the 1D fit
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nm?nsterile (p0 method)
(p0/m)Data

gt 1 for nm?nt ? 1 for nm?ns
(p0/m)MC
Data 355.2 events (BG subt.)
MC 323.2 events
(p0/m)Data
1.49 ?0.08(stat.) ?0.11(sys.)
(p0/m)MC
Experimental only
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p0 info from K2K-1kt
0.99 ? 0.03 ? 0.1
PRELIMINARY
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(p0/m)data vs (p0/m)MC-no-osc
PRELIMINARY
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nm?nsterile (matter in earth)
Using matter effect and enriched NC sample
nm?nt No matter effect nm?ns With matter
effect
Neutrino oscillation in matter
(
)
(
)
(
)
cosqm
nm
sinqm
n1

ns
- sinqm
cosqm
n2
sin22q
sin22qm

(z-cos2q)2sin22q
z - 2 GFnnEn / Dm2
?
1
sin22qm

For sin22q 1
z2 1
And for En 30100 GeV
z gtgt1 and sin22qm ltlt1
Suppression !
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.
27
Allowed region using only FC events
28
Zenith angle of high energy PC events
gt 45000 p.e. (Egt 5 GeV) ltEgt25 GeV
nm?ns
nm?nt
Dm2 3 x10-3eV2 sin22q 1
Zenith angle of upward-going muon
nm?ns
Dm2 3 x10-3eV2 sin22q 1
nm?nt
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Zenith angle of NC enriched events
Criteria gt 400 MeV visible energy Multi-ring
event e-like ring is the most energetic ring
Contents NC 29 ne CC 46 nm CC 25

Dm2 3 x10-3eV2 sin22q 1
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Ratios vs. Dm2
sin22q 1
nm?nt
lt-0.4
Up/Down ( cosQ ) ratio of NC
enriched multi-ring
gt 0.4
Data
nm?ns
nm?ns
nm?ns
Data
Data
nm?nt
nm?nt
10-3
10-2 eV2
10-3
10-2 eV2
lt-0.4
Up/Down (cosQ ) ratio of High Energy PC
gt 0.4
Vertical/Horizontal ratio (cosQ -0.4) of up
muons
gt
lt
31
Allowed vs. excluded regions
combine NC enriched, high E PC and up muons
excluded
excluded
excluded
nm?ns is excluded with 99 C.L.
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Search for t leptons
Neutrino CC cross sections
Expected t events
sin22q 1
20ev./yr for 3x10-3 eV2
nm CC
All
nt CC
cosqlt-0.2
En(GeV)
Signature of t appearance nt N ? t N p
p .....
Dm2(eV2)
cosqgt0.2
mnn, enn, nhadrons(p,p,....)

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

Search for t appearance (3 methods)
(1) Energy flow and event shape analysis (2)
Likelihood method using of rings, m?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.)
33
Multi-ring samples
atm nm ne w/o nt
nt CC
34
Zenith-angle distribution
MC without t
Dm23x10-3eV2, sin22q1.00 (expected of t 74
events)
MC with t
Energy flow method
14
Observed of t 25.5
-13
Efficiency for t 32
44
of t production 79
-40
Likelihood method
9
17
Observed of t 27
-8
-16
Efficiency for t 43.5
39
21
of t production 62
-18
-27
Neural network method
13
Observed of t 42 ?19
-13
Efficiency for t 45
14
of t production 92 ?35.3
-0
cosq
All methods show 2s excess of t-like events. The
result is consistent with nm?nt oscillations.
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Probability of exotic oscillation models
Test nm?nt oscillation with P(nm?nt)sin22q
sin2(bL?En)
(q, b, n parameters)
n-1 is the standard neutrino oscillation
Use FC, PC, Up-through, and Up-stop data
c2
-2
-1
0
1
Magnified view
index n
n -1.06 ? 0.14
36
Neutrino decay
Let neutrinos oscillate and decay n3
X(invis) P(nm nm) sin4q cos4q exp(
) sin2q exp( ) cos(
) Consider two cases ldcygtgtlosc, and
ldcyltltlosc, where ldcy , losc

t3E m3
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ldcy gtgt?osc
For Dm2 ?, c2min 221.2/153 dof
Bad fit !
38
ldcy ltlt losc
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Up/down of NC enriched events (short ldcy)
FC, Nringgt1, Evisgt400MeV, Brightest ring
e-like
Allowed from FCPCUpmu
Excluded from NC
The case of ldcyltltlosc is disfavored
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Conclusions on atmospheric neutrinos

• Oscillation parameters for nm ? nt Dm2 1.7
  4 x 10-3 eV2, sin22q gt 0.89(90CL)
• 3D flux does not change the conclusion but more
  precise 3D calculations are needed
• nm ? ns is strongly disfavored
• p0/m ratio is consistent with nm ? nt
• Excess from t leptons 2s
• Decay senario is disfavored with gt 2sfor
  ldcygtgtlosc and ldcyltltlosc