Post on 30-Dec-2015
description
L/E analysis of the atmospheric neutrino data from Super-
Kamiokande
Itaru Higuchi
ICRR
for Super-Kamiokande collaboration
ICRC2005 Aug, 2005
Motivation
• Other models can explain zenith angle dependent muon deficit. How can we distinguish oscillation from other hypotheses ?
• Muon neutrino disappearance probability as a function of neutrino flight length L over neutrino energy E was studied to distinguish neutrino oscillation from other hypotheses.
• A dip in the L/E distribution was observed in the data from Super-Kamiokande-I during 1489 live-days exposure.
• We report preliminary result from SK-II during 627 days live-days exposure.
P = (cos2sin2x exp(– ))2m2
Survive probability
Neutrino oscillation :
P = 1 – sin22sin2(1.27 )
m2LE
Neutrino decoherence :
P = 1 – sin22 x (1 – exp(–))
21
Use events with high resolution in L/E
Neutrino decay :
The first dip can be observed
Direct evidence for oscillations Strong constraint to oscillation parameters, especially m2 value
LELE
Event samples in L/E analysis
Classify PC events using OD charge
I. OD stoppingII. OD through going
FC (tracks are contained inside the ID)
PC (deposits visible energy in the OD)
observed charge / expectation from through-going
OD stopping
OD through-going
OD through-going MC
OD stopping MC
I. Single-ring , μ-likeII. Multi-ring , μ-like
Reconstruction of E and L
E
Eobserve
d
Eobserved E
Neutrino energy is reconstructed from observed energy using relations based on MC simulation
Zenith angle Flight length
Neutrino flight length is estimated from zenith angle of particle direction
Neutrino energy Neutrino flight length
L/E resolution cut
horizontally going events due to large dL/dcos
low energy events due to large scattering angle
Bad L/E resolution for
Select events with high resolution in L/E
Full oscillation
1/2 oscillation
(L/E)=70%
Event summary of L/E analysis
1619 2105.6 (98.3%)
502 813.0 (94.2%)
114 137.0 (95.4%)
491 670.1 (99.2%)
single-ring
multi-ring
stopping
through-going
FC
PC
Data MC CC
2726 3725.7Total
686 876.6 (98.6%)
222 329.4 (93.6%)
51 48.5 (94.4%)
162 269.7 (99.2%)
Data MC CC
1121 1524.2
SK-I 1489 days SK-II 627 days
L/E in atmospheric neutrino data
Preliminary
Null oscillation MC
Best-fit expectation
Mostly downward
Mostly upward
Null oscillation MC
Best-fit expectation
Mostly downward
Mostly upward
SK-I FC+PC SK-II FC+PC
L/E in atmospheric neutrino dataSK-I FC+PC
First dip is observed as expected from neutrino oscillation
Best fit expectation w/ systematic errors
Preliminary
SK-II FC+PC
Best fit expectation w/ systematic errors
Constraint to neutrino oscillation parameters
m2=2.4x10-3,sin22=1.00
2min=37.8/40 d.o.f
(sin22=1.02, 2min=37.7/40 d.o.f)
1.9x10-3 < m2 < 3.0x10-3 eV2
0.90 < sin22 at 90% C.L.
Preliminary
m2=2.6x10-3,sin22=1.00
2min=54.8/40 d.o.f
(sin22=1.02, 2min=54.7/40 d.o.f)
1.8x10-3 < m2 < 4.0x10-3 eV2
0.83 < sin22 at 90% C.L.
SK-I SK-II
Best fit results
Constraint to neutrino oscillation parameters
m2=2.4x10-3,sin22=1.00
2min=37.8/40 d.o.f
(sin22=1.02, 2min=37.7/40 d.o.f)
1.9x10-3 < m2 < 3.0x10-3 eV2
0.90 < sin22 at 90% C.L.
Preliminary
m2=2.6x10-3,sin22=1.00
2min=54.8/40 d.o.f
(sin22=1.02, 2min=54.7/40 d.o.f)
1.8x10-3 < m2 < 4.0x10-3 eV2
0.83 < sin22 at 90% C.L.
SK-I SK-II
Best fit results
Constraint to neutrino oscillation parameters
m2=2.4x10-3,sin22=1.00
2min=37.8/40 d.o.f
(sin22=1.02, 2min=37.7/40 d.o.f)
1.9x10-3 < m2 < 3.0x10-3 eV2
0.90 < sin22 at 90% C.L.
Preliminary
m2=2.6x10-3,sin22=1.00
2min=54.8/40 d.o.f
(sin22=1.02, 2min=54.7/40 d.o.f)
1.8x10-3 < m2 < 4.0x10-3 eV2
0.83 < sin22 at 90% C.L.
SK-I SK-II
Best fit results
Tests for neutrino decay & decoherence
Oscillation
Decay
Decoherence
2 = 2decay - 2
osc
=11.4(3.4σ)
2 = 2decoherence - 2
osc
=14.6(3.8 σ)
SK-I SK-II
Preliminary
cannot be explained by alternative hypotheses
2 = 2decay - 2
osc
=7.9(2.8σ)
2 = 2decoherence - 2
osc
=8.7(2.9 σ)
Conclusions
Measurement of L/E dependence of flavor transition probability
First dip was observed as expected from neutrino oscillation
The results from SK-I and SK-II agree well.
cannot be explained by alternative hypotheses
gives strong constraint to neutrino oscillation parameters
Next step : combine SK-I and SK-II