Lino Miramonti

1
Neutrinos and (Anti)neutrinos from Supernovae
and from the Earth in the Borexino detector
Lino Miramonti
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
2
The main goal of Borexino is the direct
observation and measurement of the solar 7Be-?
flux
Unsegmented detector featuring 300 tons of
ultra-pure liquid scintillator viewed by 2200
photomultipliers
PC PPO (1,5 g/l) r 0.88 g cm-3 n 1.505
Threshold 250 keV (due to 14C) Energy
Resolution FWHM ? 12 _at_ 1 MeV Spatial
Resolution ? 10 cm _at_ 1 MeV
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
3
In 100 tons of fiducial volume we expect 30
events per day (for LMA) via the ES on e- ?e
e- ? ?e e-
Requirements for a 7Be solar ?e
detector Ultra-low radioactivity in the
detector 10-16 g/g level for U and Th.
10-14 g/g level for K Shielding from
environmental ? rays Muon veto and underground
location Low energy threshold Large fiducial
mass
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
4
antineutrino detection
By far the best method to detect antineutrino is
the classic Cowan Reines reaction of capture by
proton in a liquid scintillator
The electron antineutrino tag is made possible by
a delayed coincidence of the e and by a 2.2 MeV
?-ray emitted by capture of the neutron on a
proton after a delay of 200 µs
Threshold
The entire scintillator mass of 300 tons may be
utilized
One of the few sources of correlated background
is muon induced activities that emit ß-neutron
cascade. However, all such cases have lifetimes
t lt 1 s. Thus they can be vetoed by the muon
signal.
At LNGS µ reducing factor 106 Borexino µ veto
1/5000
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
5
Others possible goals with Borexino detector
Supernova neutrinos
Geo-neutrinos
Neutrinos from artificial sources
Long-Baseline Reactor
51Cr 90Sr
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
6
What Can We Learn from a Galactic Supernova
Neutrino Signal?
NEUTRINO PHYSICS ? absolute mass from time of
flight delay ? oscillations from spectra (flavor
conversion in SN core, in Earth) CORE COLLAPSE
PHYSICS explosion mechanism proto nstar
cooling, quark matter black hole
formation ASTRONOMY FROM EARLY ALERT some hours
of warning before visible supernova
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
7
In a liquid scintillator detector, the electron
antineutrino on proton reactions constitute the
majority of the detected Supernova neutrino
events. Nevertheless The abundance of carbon in
PC provides an additional interesting target for
neutrino interactions.
C9H12
Pseudocumene PC (1,2,4-trimethylbenzene)

• All of the reactions on 12C can be tagged in
  Borexino
• The CC events have the delayed coincidence of a
  ß decay following the interaction (t qq 10 ms).
• The NC events have a monoenergetic ? ray of 15.1
  MeV

Neutrino reactions on 12C nucleus include transition to Neutrino reactions on 12C nucleus include transition to Neutrino reactions on 12C nucleus include transition to
12Bgs Threshold 14.4 MeV
12Ngs Threshold 17.3 MeV
12C Threshold 15.1 MeV
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
8
We consider 300 tons of PC and a Type II
Supernova at 10 kpc (galactic center)

• Essentially all gravitational energy (Eb 3 1053
  ergs) is emitted in neutrinos.
• The characteristic neutrino emission time is
  about 10 s.
• The total emitted energy is equally shared by all
  6 neutrino flavors.
• Energy hierarchy rule

Supernova neutrino energy spectra
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
9
cross sections
Measurements of cross-sections for 12C(?e,e-)12N
and 12C(?,?)12C have been performed at KARMEN,
at LAMPF and by LSND. Since 12N and 12B are
mirror nuclei, the matrix elements and
energy-independent terms in the cross-section are
essentially identical. Only the Coulomb
correction differs when calculating the capture
rates of the anti-?e.
Cross sections for CC on p, ES, CC and NC on 12C.
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
10
SN ? events in Borexino from a SN at 10kpc (Eb
3 1053 ergs)
ES
4.82 events
The ?µ and the ?t are more energetic than ?e.
?µ and ?t dominate the neutral-current
reactions 12C(?,?)12C with an estimated
contribution of around 90 .
ß-inv.
79 events
0.65 events
CC
In order to exploit these aspects, a liquid
scintillator SN neutrino detector needs to be
able to cleanly detect the 15.1 MeV ? ray.
This implies that the detector require a
large volume to contain this energetic ? ray.
Reactions on 12C
3.8 events
0.4 events
1.5 events
NC
20.6 events
Total 110 events
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
11
Simulated spectrum from supernova neutrino in
Borexino
2.2 MeV ? rays
low energy
By studying the arrival time of neutrinos of
different flavors from a SN, mass limit on ?µ and
?t down to some 10 of eV level can be
explored The time delay, in Borexino, is
obtained by measuring the time delay between NC
events and CC events
high energy
15.1 MeV ? rays
Continuum of e from inverse ß decay
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
12
Geoneutrinos
Earth emits a tiny heat flux with an average
value FH 80 mW/m2. Integrating over the Earth
surface HE 40 TW (about 20000 nuclear plants)
It is possible to study the radiochemical
composition of the Earth by detecting
antineutrino emitted by the decay of radioactive
isotopes. Confirming the abundance of certain
radioelements gives constrain on the heat
generation within the Earth.
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
13
Radioelements
(e is the present natural isotopic abundance)
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
14
The energy threshold of the reaction is 1.8
MeV
There are 4 ß in the 238U and 232Th chains with
energy gt 1.8 MeV
U 214Bi lt 3.27 MeV
U 234Pa lt 2.29 MeV
Th 228Ac lt 2.08 MeV
Th 212Bi lt 2.25 MeV
The terrestrial antineutrino spectrum above 1.8
MeV has a 2-component shape. The high
energy component coming solely from U chain
and The low energy component coming with
contributions from U and Th chains. This
signature allows individual assay of U and Th
abundance in the Earth
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
15
Equation for Heat and neutrinos Luminosity
Each element has a fixed ratio
H 9.5 10-8 M(U) 2.7 10-8 M(Th) 3.6
10-12 M(K) W LAnti-? 7.4104 M(U)
1.6104 M(Th) 27 M(K) anti-?/s L? 3.3
M(K) ?/s
Everything is fixed in term of 3 numbers
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
16
The radiogenic contribution to the terrestrial
heat is not quantitatively understood. Models
have been considered
Primitive Mantle
The starting point for determining the
distribution of U, Th and K in the present CRUST
and MANTLE is understanding the composition of
the Bulk Silicate Earth (BSE), which is the
model representing the primordial mantle prior to
crust formation consistent with observation and
geochemistry (equivalent in composition to the
modern mantle plus crust).
BSE concentrations of U 20 ppb (20),
have been suggested
H
M Mantle 68 M Earth M(U) 20 ppb 0.68
61027g 8.51019g

• In the BSE model
• The radiogenic heat production H rate is 20 TW
• ( 8 TW from U, 8.6 TW from Th, 3 TW
  from K)
• The antineutrino production L is dominated by K.

L
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
17
During the formation of the Earths crust the
primitive mantle was depleted of U, Th and K,
while the crust was enriched.
Continental Crust average thickness 40 km
Oceanic Crust average thickness 6 km CC is
about 10 times richer in U and Th than OC
Measurements of the crust provide isotopic
abundance information
238U 232Th
Primitive Mantle (BSE) 20 ppb 76 ppb
Continental Crust 910 ppb 3500 ppb
Oceanic Crust 100 ppb 360 ppb
Present depleted Mantle 15 ppb 60 ppb
With these measurement, it is possible to deduce
the average U and Th concentrations in the
present depleted mantle.
Crust type and thickness data in the form of a
global crust map A Global Crustal Model at 5 x
5 (http//quake.wr.usgs.gov/study/CrustalStructur
e/)
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
18
Borexino is homed in the Gran Sasso underground
laboratory (LNGS) in the center of Italy 42N
14E
LNGS
Data from the International Nuclear Safety Center
(http//www.insc.anl.gov)
Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1) Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1) Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1) Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1) Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1) Calculated anti-?e flux at the Gran Sasso Laboratory (106 cm-2 s-1)
U U Th Th Total (UTh) Reactor BKG
Crust Mantle Crust Mantle
1.8 1.4 1.5 1.2 5.9 0.65
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
19
Positron energy spectrum from antineutrino events
in Borexino
In Borexino are expected The background will
be (7.6 of them in the same spectral region
as the terrestrial anti-?)
UTh
U only
European Reactors
The characteristic 2-component shape of the
terrestrial anti-neutrino energy spectrum make it
possible to identify these events above the
reactor anti-neutrino background.
The reactor anti-neutrino background has a
well-known shape it can be easily subtracted
allowing the discrimination of the U
contribution from the Th contribution.
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
20
The main characteristics that made BOREXINO
interesting for neutrino physics are
SUPERNOVAE
The very effective ability to detect the high
energy gamma peak (15.1 MeV) from NC reactions on
12C thanks to the unsegmented large volume
detector. The absence of nuclear plants in
Italy gives a very low contribution to the geo
antineutrino background.
GEONUTRINOS
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan
21
NC reactions on 12C have no spectral
information In a low threshold detector like
Borexino the ES on proton (NC reaction) can
be observed measuring the recoiling
protons. In principle, it can furnish
spectroscopic information. Furthermore the
total neutrino flux from a SN is 6 times greater
than the flux from just anti-?e. The ?µ and ?t
flavors are more energetic, increasing the total
event rate. This provide Borexino with several
hundred supernova neutrino interactions
draft
1st Yamada Symposium Neutrinos and Dark Matter in
Nuclear Physics
Lino Miramonti
June 9-14, 2003, Nara Japan