Dr Stefania Ricciardi, RHUL, March 27th 2003

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Supernovae Neutrinos
SN 1987A
Dr Stefania Ricciardi, RHUL, March 27th 2003
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To date, the only astronomical source beside the
Sun to be observed in neutrinos is supernova
SN1987A, from which about 20 neutrinos were
detected. Order of 104 neutrinos have been
detected from the Sun over the past quarter
century. The extension of solar neutrino
astronomy to more distant sources is difficult,
but observations of SN1987A provided an historic
beginning 23 February 1987.
SN1987A is located in our neighboring dwarf
galaxy in the Southern hemisphere, the Large
Magellenic Cloud, at about 170,000 light years
away ( D 50.1 /- 3Kpc)
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In This Lecture

• Physics of SN explosion and in particular
• neutrinos as carriers of energy
• Detection of SN n in terrestrial underground
  labs
• SN1987A what have we learned about SN?
• what have we learned about
  neutrinos?

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TypeII SN Death of massive stars progenitor
Mgt8MSun becomes suddenly unstable and energy
produced cannot balance gravity bringing to core
collapse within seconds
1.5 MSUN Fe Core collapses to Neutron Star RNS
10 Km
Gravitational binding energy DEB ? G MSun2/ RNS
GMSun2/RFe-core ? 3 x 1053 ergs

? 2 x 1059 MeV
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Supernovae Explosion
Kinetic energy of explosion ? 1 x
DEB Electromagnetic radiation ? 0.01 x
DEB Neutrinos ? 99 x
DEB
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Neutrino cooling
neutronization burst
1s
10s
0.1s
Neutrino cooling p e- ? n ne prompt
from collapse Dt ms e e- ? nx
nx all flavours
Dt few s Neutrino luminosity 3 x 1053erg / 10
s 1019 Lsun The
initial proto-neutron star is dense and hot n
Trapping Cooling phase controlled by neutrino
diffusion
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Neutrinos from SN1987A
23 Feb 1987 Within 10s 12 events in
Kamiokande (2kT H2O, 7 MeV threshold) 8
events in IMB (10kT H2O, but 20 MeV
threshold) 5 events in Baksan
(scintillator) Not used in analysis SN1987 first
supernova visible by naked eye since Kepler in
1604 Discovered optically on 24 Feb1987, almost
24h later This triggered the neutrino search in
recorded data by all active detectors
Mistery 5 events in Mt. Blanc 5h earlier
11 Kamiokande events and 8 IMB events under
scrutiny were determined to come from SN. More
information extracted using other
observables energy, time distribution,angular
distribution
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SN Neutrino detection
ne p ? n e dominant process need Engt1.8
MeV Relative large x-section (10-41 cm2
_at_10 MeV) e, emitted isotropically can be
detected via Cherenkov ne 16O
? 16F e- s very small. Needs Engt13 MeV nx
e- ? nx e- sensitive to all neutrino
flavors
directionality s
10-43 cm2 _at_ 10 MeV Therefore, most probably,
ONLY ne were detected
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SN model confirmation
From number of counts n and mean energies En
measured in the Detectors infere energy emitted
ene in electron anti-neutrino and eT total
emitted energy
n ene/En ltsgt/4pL2 2 MD/18 mp
fn 0.1 fraction radiated in the neutronization
burst
eT 2Nn ene/ (1-fn)
Nn 3, measured En 10MeV , eT 3 1053 erg,
MD2.1kt (Kamioka) and averaging s above
threshold ? n10 perfectly compatible with
11-12 events observed
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SN and Neutrino n mass
Delay due to neutrino mass on a distance
L50Kpc Dt ½ L/c mn2/ En2 2.6 s
(mn/10eV)2/(En/10MeV)2 All events within 10s
? mnlt 20-25 eV
SN and Neutrino n decay
Number of observed n consistent with expectation
gt gt L/c 50 Kpc/c 0.5 1013s 1.6 105y
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Waiting for SN in our galaxy

• A supernovae within our galaxy(10Kpc) would give
  8000(!) ne events in Dtlt18 s in SuperK (22ktons).
  
• When? 1SN/(10-200)y ???
• Many other experiments are now sensitive
• (essentially all new solar n experiments)
• Aim detect other flavors via NC (KamLand and
  others)
• Flux and energy spectrum of nm, nt is
  quite uncertain
• Measure Etot and Tnx at 10
• Dual role
• Astrophysics - comparison with SN models
• Particle Physics - neutrino properties (mnx,
  oscillation)

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Lets hope for 10 bright secondsToday!
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