Low energy astrophysical neutrino observations with megaton class detector s
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Transcript of Low energy astrophysical neutrino observations with megaton class detector s
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Low energy astrophysical neutrino observations with megaton class detector s
8B solar neutrino measurement Supernova burst neutrino observation Supernova relic neutrino observation Conclusions
NNN05, April 7, 2005
M.NakahataKamioka observatory, ICRR, Univ. of Tokyo
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Current status of solar neutrino oscillations
Solar global
KamLAND
Solar+KamLAND
95%
99.73%
P( e
e)
Vacuum osc. dominant
matter osc.
(MeV)
Expected P(e e) at best fit
SSM spectrumpp
7Bepep
8B
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Expected low energy upturn (8B)SK (e scattering)SNO CC
sin2()
0.22
0.28
0.35
m2=8.3x10-5eV2
m2 (eV2)
9.1 x 10-5
8.3 x 10-5
7.4 x 10-5
m2=8.3x10-5eV2
sin2()=0.28 sin2()=0.28
~20% in SNO and ~10% in SK upturn is expected from 4 MeV to 15 MeV.Total energy
Arb
itrar
y u
nit
Arb
itrar
y u
nit
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Measurements by SNO and SK so far
SNO pure D2O
SNO salt phase
SK spectrumNo spectrum distortion so far.Current SK and SNO measurements are limited by statistics and systematic.
Need more statistics, lower threshold and make systematic errors smaller to test spectrum distortion.
Total energy
kinetic energy
sin2=0.28, m2 =8.3×10-5 eV2
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Expected solar spectrum measurement by Mega-ton water cherenkov detector
8B spectrum distortion
Enough statistics to see distortion.
Energy scale calibration should be better than ~0.3%.
hep neutrinoSSM(BP2004) flux: hep: 7.88(1±0.16)x103 /cm2/sec = ~1/700 of 8B
Statistically possible to measure hep neutrinos.
Precise calibration of energy resolution is necessary.
Ee (MeV)
Dat
a/S
SM
5 Mton·years
Correlated sys. error of SK
(*)For the statistical error, SK background level above 5.5MeV and 70% reduction below 5.5 MeV are assumed.
5 Mton·years
Integral spectrum
sin2=0.28, m2 =8.3×10-5 eV2
1/2 of SK
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8B -- Day-Night effect• Not yet convincingly seen either in SK nor SNO
1~2% effect 2~3% effect
%0.21.2 3.12.1
%9.40.7 3.1
2.1
(Night-Day)(Night+Day)/2
AN D
=
Observations
Solar+KamLAND
SK SNOX100(%)
Solar+KamLAND
(pure D2O)
%3.54.76.5 (salt phase)
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3 level can be achieved with 0.5% systematic error for this parameter.
Day/night measurement by mega-ton detector
m2=7.1x10-5eV2, sin2()=0.28Day/night asymmetry Statistical significance
1 Mton year (0.5 Day & 0.5 Night) for no BG(2.4 Mton year (1.2 Day & 1.2 Night) for SK spallation B.G.)
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Sensitivity of Day/Night Asymmetry
Stat. only
0.5% sys. error
1.3% sys. error
1 Mton year (0.5 Day & 0.5 Night) for no BG(2.4 Mton year (1.2 Day & 1.2 Night) for SK spallation B.G.)
Solar+KamLAND(95% CL)
Expected asymmetry
3excess above this line
sin2()=0.30
Systematic error must be less than 0.5%.
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Supernova event rate in Mega-ton detector
5MeV threshold
(T.Totani et al., ApJ.496,216(1998))Livermore simulation Expected number of events
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Time profile with neutrino oscillationsSN at 10kpc, 1mega-ton
νe+p→e++n
Inverted hierarchy (PH=0)
Nomal, Inv.(PH=1)
No oscillation
PH: crossing probability at H resonance(PH=0: adiabatic)
ν + e -→ ν +e-
Total number of events in parentheses
Time variation 200 log bins from 20msec to 18sec
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Neutronization burstSN at 10kpc, 1mega-ton
Number of events from 20msec to 0.1 sec (1bin=10msec)
Neutronization burst can be observed even with neutrino oscillations.
No oscillation
Normal PH=1 orInverted hierarchy
(e-+pn+e)
ν + e -
Normal hierarchy PH=0
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e energy spectrum measurement
Time variation of average energy
SN at 10kpc, 1mega-tonVisible energy spectrum in each time range range
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Identification of e scattering events by direction to supernova
SN at 10kpc, 1 mega-ton
e scattering events can be statistically extracted using the direction to supernova.
e+pe+p
e+p e+p
+e+e
+e +e
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e+x spectrum measurement by e scattering
10kpc, 1 Mega-ton 56kpc, 1 Mega-ton
Spectrum measurement up to ~40MeV.
Spectrum measurement up to ~20MeV.
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Search for supernova relic neutrinos(SRN)
Solar 8B
Solar hep
Atmospheric
SRN predictions
Population synthesis (Totani et al., 1996)Constant SN rate (Totani et al., 1996)Cosmic gas infall (Malaney, 1997)Cosmic chemical evolution (Hartmann et al., 1997)Heavy metal abundance (Kaplinghat et al., 2000)LMA oscillation (Ando et al., 2002)
Reactor
Spallation B.G.
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SRN search in SK-I
Atmospheric → invisible → decay e
Atmospheric e
90% CL limit of SRN
Total background
1496 days (SK-I)Energy spectrum above 18 MeV
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SK limit (90% C.L.)
SK-I upper limit
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SK limit (90% C.L.)
SK-I upper limit
Ando’s talk today
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SRN event rate in Mega-ton detector
Invisible muon BG must be reduced.
1 Mega-ton, 5 years
SRN signal: 246
Background: 2518
in 15-30 MeV
Relic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003).
SRN signal: ~630 (Ando’s talk today)
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Possibilities ofe tagginge
e+
2.2MeV -ray
T = ~ 200sec
pn Possibility 1
n+Gd →~8MeV T = several 10th sec
Possibility 2
(→ M.Vagins’ talk)
e could be identified by delayed coincidence.
Positron and gamma ray vertices are within ~50cm.
n+p→d +
Nhit=~6 for 40% coverage and 20% peak QE
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Possibility of SRN detectionRelic model: S.Ando, K.Sato, and T.Totani, Astropart.Phys.18, 307(2003).
1 Mega-ton, 5 years
No B.G. reduction B.G. reduction by neutron tagging
Assuming 90% of invisible muon B.G. can be reduced by neutron tagging.
Statistically 4.6excess (Evis > 15 MeV)
Signal yield will be factor ~2.6 larger if today’s Ando’s value is used.
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ConclusionsConclusions
Precise measurements of 8B solar neutrino spectrum and day/night asymmetry by Mega-ton detectors are still important for further study of solar neutrino oscillation.
Quite high statistics of supernova events is expected for galactic supernova. It enables us to measure
• Precise nu_e_bar spectrum and time variation• nu_e and nu_x spectrum measurement by e scattering
Expected number of SRN event is ~250/5yr/Megaton. Delayed coincidence method to tag nu_e_bar is important to discover SRN neutrinos.