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