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1. Introduction
2. Method
3. Result & Discussion
4. Summary

Property of Neutrino
Neutral leptons
Weak interactions
Small mass
3 flavors and antiparticles
ne nµ nt ne nµ nt

SK collaboration, 1998

Neutrino oscillations

nµnµ
nent

nenµ → nt

nt

w/o osc.
w/ osc.

Neutrino oscillations in core-collapse supernovae
Neutrino oscillations are sensitive to coherent forward
scatterings with background medium
Collective neutrino Oscillations
2 - 103 km)(r10Proto -MSW effect(r> 103 km)

neutron starnere r 10 km
nanbe-nenbnanee-The purpose of our research
Vacuum neutrino oscillations and MSW effects are observedin neutrino experiments.
SK collaboration, 1998

Borexino collaboration, 2018

w/o osc.
w/ osc.

However, there is no evidence of collective neutrino oscillations (CNO)→ We discuss detectability of collective neutrino oscillations
in future neutrino detectors

1. Introduction
2. Method
3. Result & Discussion
4. Summary

Progenitor of Electron capture supernova (ECSN)
Janka, 2012

H envelope
He burning shell

O-Ne-Mg

ECSN

ECSN is triggered by electron capture
reactions at O-Ne-Mg core
Progenitor mass is in 8-10 Msun
The dilute envelop of ECSN-progenitor(8.8 Msun) is suitable for collectiveneutrino oscillations

Radius [km]log (density [g/cm^3])

Shock radius

Luminosity [1051 erg/s ]Hydrodynamic simulation & Neutrino radiation

Time after bounce [ms]This progenitor explodes even in the 1Dmodel because of the dilute envelope

Mean Energy [MeV]Time after bounce [ms]Neutrino oscillations are calculated
by using time snapshot of these quantities

Time after bounce [ms]

Neutrino oscillations in 3 flavor multiangle calculation
Liuville-von Neumann equationsof neutrino density matrices (Duan,2006):

qp
n sphere

MSW matter potential:

Neutrino self interactions:rqp
Multi angle (qp= 0)

Vacuum Hamiltonian:

U: PMNS matrix
Mass hierarchy is unknown
Dm232 >0: Normal hierarchy
Dm232 <0: Inverted hierarchy1. Introduction
2. Method
3. Result & Discussion
4. Summary

Survival probability of ne at 1500 km
after collective neutrino oscillations (CNO)
Inverted(Dm232 <0)Normal(Dm232 >0)

CNO appears in both mass hierarchies
CNO is suppressed in dense matter profiles

Collective neutrino oscillations (CNO) & Spectral swap
Survival Probability of neCNO

231 ms, inverted mass hierarchy
Spectralswap

CNO occurs at 250 km where GF nn  < |Dm232 |/2E >nn : Total neutrino number density

Spectral swap (green to blue) occurs after CNO,
which increases energetic neNeutrino spectra affected by oscillations
Collective neutrino Oscillations(r102 - 103 km)
Proto -MSW effect(r> 103 km)

neutron starnere r 10 km

MixingMixingFinal neutrino spectra are mixing of initial neutrino spectraNeutrino spectra on the earth
Neutrino spectra after CNO are affected by MSW effects in outer layers
NormalNormalInverted
Inverted~ 0 ne~ 0.3 ne~ 0.3 ne~ 0.7 neMSW resonances~ 0.7 neMSW resonances~ 0 nene00Fluxes of ne , ne on the earth:s213 ~ 0, s212 c213 ~ 0.3, c212 c213 ~ 0.7

nene spectrum on the earth
231 ms, inverted mass hierarchy

Softened

ne spectrum on the earth
e : Survival probability of ne after CNO

w/o CNO : e=1 → Hard spectra
w/ CNO : 0<e<1 → Soft spectraFuture neutrino detectors
HK Hyper-Kamiokande (HK)200 kton, Water Cherenkov
JUNO

ne + p → e + + n

JUNO
20 kton, Liquid scintillator
ne + p → e + + nn+p→ d+g

DUNE40 kton, Liquid Argon
ne + 40Ar → e- + 40Kr*DUNEne detection @ Hyper-Kamiokande(HK)Inverted mass hierarchy @15kpc

SoftEvent number [1/50ms]:

Ntar: Number of H2O: Flux of nes : Cross section E2Hardness ratio:

The both event number and hardness ratio
are reduced by CNO→ The softened RH/L is preferable fordetection of CNO: # of E> Ec: # of E< EcEc =20 MeV

ne detection in normal mass hierarchy
Normal mass hierarchy @15kpc

CNO make energetic neHard→ Such ne can survive
on the earth→ Event number increases
RH/L becomes hard

w/o CNO : e=1 → soft spectra
w/ CNO : 0<e<1 → Hard spectrane observation in normal mass hierarchy @ DUNE
Normal mass hierarchy @4kpc

Softw/o CNO : e=1 → Hard spectra
e : Survival probability of ne in e-x sector

w/ CNO : 0<e<1 → Soft spectrane observation in inverted mass hierarchy @ DUNE
Inverted mass hierarchy @2kpc

HardSoft0<e<1, h=1 → Hard spectra0<e<1 , 0<h<1 → Soft spectra
e : Survival probability in e-x sector, h : Survival probability in e-y sector

Summary of CNO detectability
We summarize behaviors of hardness ratio RH/LHierarchy
SpectrumNormalneSoftneDUNEHKHardInvertedHardSoftSoft

In the accretion phase, neutrino spectra naturally become hard
→ Softening neutrino spectrum is easy to distinguish
Combination of HK and DUNE gives us softening RH/L in both hierarchy

1. Introduction
2. Method
3. Result & Discussion
4. Summary

SummaryNeutrino self interactions certainly induce collective neutrino
oscillations (CNO) in core-collapse supernovae
 However, the signature of CNO has not been found in observations
We carry out numerical simulations of electron capture supernovae(8.8 M_sun) and discuss detectability of CNO
 The softening hardness ratio traces spectral swap caused by CNO
In inverted mass hierarchy, HK can distinguish softening hardness ratioof ne within 15 kpc
In normal mass hierarchy, DUNE can clarify softening hardness ratioof ne within 4 kpc