Transcript During nuclear physics

Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
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% @ 1 MeV
Spatial Resolution:  10 cm @ 1 MeV
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
In 100 tons of fiducial volume we expect
~ 30 events per day (for LMA)
via the ES on e- : νe + e- → νe + e-
Requirements for a 7Be solar νe 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 γ rays
Muon veto and underground location
Low energy threshold
Large fiducial mass
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
By far the best method to detect antineutrino is the classic Cowan Reines
reaction of capture by proton in a liquid scintillator:
e  p  n  e

Threshold
The e signal energy : E(MeV)  E( ν e )  Q  2mec2 (Q  1.8 MeV)
The entire scintillator mass of 300 tons may be utilized
The electron antineutrino tag
is made possible by a delayed
coincidence of the e+ and by a
2.2 MeV γ-ray emitted by
capture of the neutron on a
proton after a delay of ~ 200 µs
One of the few sources of correlated background is muon induced activities that emit β-neutron cascade.
6
However, all such cases have lifetimes τ < 1 s. Thus they can be vetoed by the muon signal. At LNGS µ reducing factor ~ 10
Borexino µ veto ~ 1/5000
Sensitivit y : 
Lino Miramonti
1 ν e event
yr
(in 300 tons)
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
Supernova neutrinos
Geo-neutrinos
Long-Baseline Reactor
Neutrinos from
artificial sources
51Cr
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
& 90Sr
June 9-14, 2003, Nara Japan
NEUTRINO PHYSICS
ν absolute mass from time of flight delay
ν 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
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
In a liquid scintillator detector, the electron antineutrino on
proton
reactions constitute the majority of the detected
Supernova neutrino events.
C9H12
Nevertheless
The abundance of carbon in PC provides an additional
interesting target for neutrino interactions.
Pseudocumene [PC]
(1,2,4-trimethylbenzene)
Neutrino reactions on 12C nucleus include transition to:
gs
 e 12C12B  e
Threshold = 14.4 MeV
12N
gs
 e 12C 12N  e 
Threshold = 17.3 MeV
12C*
 12C12C  
Threshold = 15.1 MeV
12B
Lino Miramonti
All of the reactions on
tagged in Borexino:
12C
can be
• The CC events have the delayed
coincidence of a β decay following the
interaction (τ ~ qq 10 ms).
• The NC events have a monoenergetic
γ ray of 15.1 MeV
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
We consider 300 tons of PC and
a Type II Supernova at 10 kpc (galactic center)
1)
Essentially all gravitational energy (Eb = 3 1053 ergs) is
emitted in neutrinos.
2)
The characteristic neutrino emission time is about 10 s.
3)
The total emitted energy is equally shared by all 6
neutrino flavors.
L νe  L νe  L νμ , ν τ , νμ , ν τ
4)
Energy hierarchy rule:
E νe
 11 MeV

E νe
 16 MeV

E νx
 25 MeV
(ν x  ν μ , ν τ , ν μ , ν τ )
Supernova neutrino energy spectra
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
Measurements of cross-sections for
12C(ν ,e-)12N and 12C(ν,ν’)12C* have been
e
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-νe.
Cross sections for CC on p, ES, CC and NC on 12C.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
SN ν events in Borexino
from a SN at 10kpc (Eb = 3 1053 ergs)
νμ and ντ dominate the neutralcurrent reactions 12C(ν,ν’)12C with an
estimated contribution of around 90 %.
In order to exploit these aspects, a liquid
scintillator SN neutrino detector needs to be
able to cleanly detect the 15.1 MeV γ ray.
This implies that the detector require a
4.82 events
 e  p  n  e
β-inv.
Reactions on 12C
The νμ and the ντ are more energetic than νe.
 e  e  e  e
ES
CC
NC
79 events
 e 12C 12N  e 
0.65 events
 e 12C12B  e
3.8 events
 e 12C 12C   e'
0.4 events
 e 12C 12C   e'
1.5 events
 x 12C 12C   x'
20.6 events
large volume
to contain this energetic γ ray.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
Total ~ 110 events
June 9-14, 2003, Nara Japan
2.2 MeV γ rays
By studying the arrival time of neutrinos of
different flavors from a SN, mass limit on
νµ and ντ down to some 10 of eV level can
be explored
15.1 MeV γ rays
The time delay, in Borexino, is obtained by
measuring the time delay between NC
events and CC events
Continuum of e+ from inverse β decay
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
Earth emits a tiny heat flux with an average value ΦH ~ 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.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
238
U 12300
232
Th 4020
40
Bq
g
Bq
g
Bq
K
29.8
( K  0.0118 % of
40
238
232
40
40
g
nat
K)
U206 Pb  8α  6e-  6ν e  51.7 MeV
ε(U)  9.5 10-8
W
g
 (U )  7.4 104
Th 208 Pb  4α  4e-  4ν e  42.8 MeV
ε(Th)  2.7 10-8
W
g
 (Th)  1.6 104

K Ca  e  ν e  1.32 MeV (89%)
40
ε(K)  3.6 10
12
K  e  40 Ar  ν e  1.51 MeV (11%)
W
g
e
e
 ( K )  27
e
 ( K )  3.3
e
e
gs
e
g s
e
g s
e
gs
(ε is the present natural isotopic abundance)
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
The energy threshold of the reaction
 e  p  n  e
There are 4 β in the 238U and 232Th chains with energy > 1.8 MeV :
Signal energy :
is 1.8 MeV
[U]
214Bi
< 3.27 MeV
[U]
234Pa
< 2.29 MeV
[Th]
228Ac
< 2.08 MeV
[Th]
212Bi
< 2.25 MeV
E(MeV)  E( ν e ) 1.8  2mec2
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
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
Each element has a fixed ratio
Heat

H = 9.5 10-8 · M(U) + 2.7 10-8 · M(Th) + 3.6 · 10-12 M(K) [W]
LAnti-ν = 7.4·104 · M(U) + 1.6·104 · M(Th) + 27 · M(K)
Lν = 3.3 · M(K)
[ν/s]
Everything is fixed in term of 3 numbers: M(U)
Lino Miramonti
[anti-ν/s]
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
Th
U
K
U
June 9-14, 2003, Nara Japan
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
Th
 3.8
U
K
 10000
U
M Mantle= 68% M Earth
M(U) = 20 ppb · 0.68 · 6·1027g = 8.5·1019g
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.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
During the formation of the Earth’s 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
Primitive Mantle (BSE)
With these measurement, it is possible to
deduce the average U and Th concentrations
in the present depleted mantle.
232Th
20 ppb
76 ppb
Continental Crust
910 ppb
3500 ppb
Oceanic Crust
100 ppb
360 ppb
15 ppb
60 ppb
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/CrustalStructure/)
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
Borexino is homed in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E
LNGS
Data from the
International Nuclear
Safety Center
(http://www.insc.anl.gov)
Calculated anti-νe flux at the Gran Sasso Laboratory
(106 cm-2 s-1)
U
Crust
Th
Mantle
1.8
Lino Miramonti
1.4
Crust
Total (U+Th)
Reactor BKG
5.9
0.65
Mantle
1.5
1.2
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
In Borexino are expected:
7.8
events
yr
The background will be:
29
events
yr
(7.6 of them in the same
spectral region as the terrestrial
anti-ν)
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.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
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.
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan
NC reactions on 12C have no spectral information
In a low threshold detector like Borexino the ES on proton (NC reaction):
  p   ' p'
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-νe.
The νµ and ντ flavors are more energetic, increasing the total event rate.
This provide Borexino with several hundred supernova neutrino interactions
Lino Miramonti
1st Yamada Symposium
Neutrinos and Dark Matter in Nuclear Physics
June 9-14, 2003, Nara Japan