Transcript Document
Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan
Unsegmented detector featuring of ultra-pure
liquid scintillator 300 tons
viewed by 2200 photomultipliers r
PC + PPO (1,5 g/l) = 0.88 g cm -3 n = 1.505
Threshold: 250 keV
(due to 14 C)
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
Lino Miramonti
In
100 tons
of fiducial volume we expect ~
30 events
via the ES on e
-
: per day (for LMA)
ν e + e → ν e + e -
Requirements for a
7
Be solar ν
e
detector:
Ultra-low radioactivity in the detector :
10 -16 10 -14 g/g level for U and Th. g/g level for K
Shielding from environmental γ rays Muon veto and underground location Low energy threshold Large fiducial mass 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 2m e c 2 (Q 1.8
MeV) The electron antineutrino
tag
is made possible by a
coincidence
of the e +
delayed
and by a
2.2 MeV γ-ray
emitted by capture of the neutron on a proton after a delay of ~ 200 µs
The entire scintillator mass of 300 tons may be utilized
One of the few sources of correlated
background
is muon induced activities that emit β-neutron cascade. However, all such cases have lifetimes τ < 1 s. Thus they can be vetoed by the muon signal.
At LNGS µ reducing factor ~ 10 6 Borexino µ veto ~ 1/5000 Sensitivit y : 1 ν e event yr
Lino Miramonti
(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
Lino Miramonti
Neutrinos from artificial sources
51 Cr & 90 Sr
1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics 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.
Nevertheless
The abundance of
carbon
in PC provides an additional interesting target for neutrino interactions.
C 9 H 12 Pseudocumene [PC] (1,2,4-trimethylbenzene)
All of the reactions on tagged in Borexino: 12 C can be Neutrino reactions on 12 C nucleus include transition to:
12 B gs 12 N gs
e
12
C
12
B
e
e
12
C
12
N
e
Threshold = 14.4 MeV Threshold = 17.3 MeV • The
CC
events have the delayed coincidence of a β decay following the interaction (τ ~ qq 10 ms).
12 C*
Lino Miramonti
12
C
12
C
Threshold = 15.1 MeV • 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 ( E b emitted in neutrinos.
= 3 10 53 ergs ) is 2) The characteristic neutrino emission time is about 10 s .
3) The total emitted energy is neutrino flavors.
L ν e L ν e equally shared L ν μ , ν τ , ν μ , ν τ by all 6 4) Energy hierarchy rule : 11 E ν e MeV 16 E ν e MeV 25 E ν x MeV (ν x ν μ , ν τ , ν μ , ν τ )
Lino Miramonti
Supernova neutrino energy spectra
1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan
Measurements 12 C(ν e ,e ) 12 N and of
cross-sections
12 C(ν,ν’) 12 C* for have been performed at KARMEN , at LAMPF and by LSND .
Since 12 N and 12 B 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-ν e .
Lino Miramonti
Cross sections for CC on p, ES, CC and NC on 12 C.
1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan
The ν μ and the ν τ are more energetic than ν e .
current
ν μ
and reactions
ν τ dominate
12 C(ν,ν’) 12 C the neutral with estimated contribution of around 90 %.
an
SN ν events in
Borexino
from a SN at 10kpc (E
b
= 3 10
53
ergs)
ES
e
e
e
e
4.82 events β-inv .
e
p
n
e
79 events 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
.
CC
e
12
C
12
N
e
e
12
C
12
B
e
0.65 events 3.8 events NC
e
12
C
12
C
e
'
e
12
C
12
C
e
'
x
12
C
12
C
'
x
This implies that the detector require a
large volume
to contain this energetic γ ray.
Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics
0.4 events 1.5 events 20.6 events Total ~ 110 events
June 9-14, 2003, Nara Japan
2.2 MeV γ rays 15.1 MeV γ rays Continuum of e + from inverse β decay By studying the arrival time of neutrinos of different flavors from a SN, mass limit on ν µ and ν τ 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 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 Φ H ~ 80 mW/m 2 .
Integrating over the Earth surface:
H E ~ 40 TW
(about 20000 nuclear plants) It is possible to study the Earth by detecting
radiochemical composition antineutrino
of the emitted by the decay of radioactive isotopes.
Confirming the abundance of certain
radioelements
constrain on the
heat generation within the Earth
.
gives
Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics June 9-14, 2003, Nara Japan
238 U 12300 Bq g 232 Th 4020 Bq g ( 40 K 40 K 29.8
0.0118
% of Bq g nat K) 238 U 206 Pb 8α 6e 6 ν e 51.7
MeV 232 Th 208 Pb 4α 4e 4 ν e 42.8
MeV ε(U) 9.5
10 8 W g ε(Th) 2.7
10 8 W g 40 K 40 Ca e ν e 1.32
MeV (89%) 40 K e 40 Ar ν e 1.51
MeV (11%) ε(K) 3.6
10 1 2 W g
(ε is the present natural isotopic abundance)
Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics
e
(
U
) 7 .
4 10 4
g
e s
e
(
Th
) 1 .
6 10 4
g
e s
e
(
K
) 27
g
e s
e
(
K
) 3 .
3
g
e
s
June 9-14, 2003, Nara Japan
The energy
threshold
of the reaction
e
p
n
e
is
1.8 MeV
There are 4 β in the 238 U and 232 Th chains with
energy > 1.8 MeV
: [U] [U] [Th] [Th] 214 Bi 234 Pa 228 Ac 212 Bi < 3.27 MeV < 2.29 MeV < 2.08 MeV < 2.25 MeV Signal energy : E(MeV) E( ν e ) 1.8
2m e c 2 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] L Anti-ν = 7.4·10 4 · M(U) + 1.6·10 4 · M(Th) + 27 · M(K) [anti-ν/s] L ν = 3.3 · M(K) [ν/s]
Everything is fixed in term of 3 numbers:
M(U) Th U
Lino Miramonti 1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics
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 U 1 0000 M Mantle = 68% M Earth M(U) = 20 ppb · 0.68 · 6·10 27 g = 8.5·10 19 g 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. Measurements of the crust provide isotopic abundance information:
Continental Crust:
average thickness ~ 40 km
Oceanic Crust:
average thickness ~ 6 km CC is about 10 times richer in U and Th than OC With these measurement, it is possible to deduce the average U and Th concentrations in the present depleted mantle .
Primitive Mantle (BSE) Continental Crust Oceanic Crust Present depleted Mantle
238 U
20 ppb 910 ppb 100 ppb 15 ppb
232 Th
76 ppb 3500 ppb 360 ppb 60 ppb Crust type and
thickness
data in the form of a global crust map: A
Global Crustal Model
(http://quake.wr.usgs.gov/study/CrustalStructure/)
at 5° x 5°
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
U Calculated anti-ν e flux at the Gran Sasso Laboratory (10 6 cm -2 s -1 ) Th Total (U+Th) Reactor BKG
Crust
1.8
Lino Miramonti
Mantle
1.4
Crust
1.5
Mantle
1.2
5.9
1st Yamada Symposium Neutrinos and Dark Matter in Nuclear Physics
0.65
Data from the
International Nuclear Safety Center
(http://www.insc.anl.gov)
June 9-14, 2003, Nara Japan
In Borexino are expected: 7.8
events yr The background will be: 2 9 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
Lino Miramonti
the discrimination of the U contribution from the Th contribution.
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
12
C 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 12 C 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-ν e .
The ν µ and ν τ 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