lino miramontijune 9-14, 2003, nara japan 1st yamada symposium neutrinos and dark matter in nuclear...

Lino Miramonti June 9-14, 2003, Nara Japan

1st Yamada SymposiumNeutrinos and Dark Matter in Nuclear Physics

http://www.fisica.unimi.it/dipartimento/html/index.php



Threshold: 250 keV (due to 14C)Energy Resolution: FWHM 12% @ 1 MeVSpatial Resolution: 10 cm @ 1 MeV

PC + PPO (1,5 g/l) = 0.88 g cm-3 n = 1.505

Unsegmented detector featuring 300 tons of ultra-pure liquid scintillator viewed by 2200 photomultipliers



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

In 100 tons of fiducial volume we expect ~ 30 events per day (for LMA)

via the ES on e- : νe + e- → νe + e-



By far the best method to detect antineutrino is the classic Cowan Reines reaction of capture by proton in a liquid scintillator:

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.

enpeThe 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

tons)300(inyr

eventν1:ySensitivit e

MeV) 1.8(Qc2mQ)νE(E(MeV):energy signal e The 2ee

Threshold

At LNGS µ reducing factor ~ 106

Borexino µ veto ~ 1/5000



Long-Baseline Reactor

Geo-neutrinosSupernova neutrinos

Neutrinos from artificial sources

51Cr & 90Sr



NEUTRINO PHYSICSν absolute mass from time of flight delayν oscillations from spectra (flavor conversion in SN core, in Earth)

CORE COLLAPSE PHYSICSexplosion mechanismproto nstar cooling, quark matterblack hole formation

ASTRONOMY FROM EARLY ALERTsome hours of warning before visible supernova

Lino Miramonti June 9-14, 2003, Nara Japan1st Yamada Symposium

Neutrinos and Dark Matter in Nuclear Physics

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.

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.

Pseudocumene [PC] (1,2,4-trimethylbenzene)

C9H12

Neutrino reactions on 12C nucleus include transition to:

12Bgs Threshold = 14.4 MeV

12Ngs Threshold = 17.3 MeV

12C* Threshold = 15.1 MeV

All of the reactions on 12C can be

tagged in Borexino:

• 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

eBCe1212

eNCe1212

CC 1212



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.

4) Energy hierarchy rule:

Supernova neutrino energy spectra

)ν,ν,ν,ν(ν

MeV25MeV16MeV11

EEEτμτμx

ννν xee

τμτμee ν,ν,ν,ννν LLL



Measurements of cross-sections for 12C(νe,e-)12N and 12C(ν,ν’)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-νe.

Cross sections for CC on p, ES, CC and NC on 12C.


The νμ and the ντ are more energetic than νe.

νμ and ντ dominate the neutral-current reactions 12C(ν,ν’)12C with an estimated contribution of around 90 %.


eBCe1212

eNCe1212

enpe

ee ee

'1212ee CC

'1212ee CC

'1212xx CC

ES

β-inv.

Rea

ctio

ns o

n 12

C

CC

NC

4.82 events

79 events

0.65 events

3.8 events

0.4 events

20.6 events

1.5 events

SN ν events in Borexino from a SN at 10kpc (Eb = 3 1053 ergs)

Total ~ 110 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.

This implies that the detector require a

large volume to contain this energetic γ ray.



2.2 MeV γ rays

15.1 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

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



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.



MeV 51.7ν66e8αPbU e-206238

MeV 42.8ν44e4αPbTh e-208232

(89%)MeV 1.32νeCaK e4040

(11%)MeV 1.51νAreK e4040 g

W103.6ε(K) 21

g

W102.7ε(Th) 8- sg

Th e

e

4106.1)(

g

W109.5ε(U) 8- sg

U e

e

4104.7)(

sgK e

e

27)(

sgK e

e

3.3)(

K)of %0.0118K(29.8K

4020Th

12300U

nat40g

Bq40

gBq232

gBq238

K)of %0.0118K(29.8K

4020Th

12300U

nat40g

Bq40

gBq232

gBq238

(ε is the present natural isotopic abundance)

The energy threshold of the reaction is 1.8 MeV

Lino Miramonti June 9-14, 2003, Nara Japan1st Yamada Symposium

Neutrinos and Dark Matter in Nuclear Physics

enpe

There are 4 β in the 238U and 232Th chains with energy > 1.8 MeV : [U] 214Bi < 3.27 MeV

[U] 234Pa < 2.29 MeV

[Th] 228Ac < 2.08 MeV

[Th] 212Bi < 2.25 MeV

2ee c2m1.8)νE(E(MeV) :energy Signal

The terrestrial antineutrino spectrum above 1.8 MeV has a “2-component” shape.

The high energy component coming solely from U chain andThe low energy component coming with contributions from U and Th chains.

This signature allows individual assay of U and Th abundance in the Earth



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) [anti-ν/s]

Lν = 3.3 · M(K) [ν/s]

Everything is fixed in term of 3 numbers:U

K

U

ThM(U)



The radiogenic contributionradiogenic contribution to the terrestrial heat is not quantitatively understood. Models have been considered:

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).

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.

Primitive Mantle

BSE concentrations of:

U ~ 20 ppb (±20%), have been suggested

3.8U

Th 00001

U

K

M Mantle= 68% M Earth

M(U) = 20 ppb · 0.68 · 6·1027g = 8.5·1019g



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:

238U 232ThPrimitive 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 ModelGlobal Crustal Model at 5° x 5°(http://quake.wr.usgs.gov/study/CrustalStructure/)

Continental Crust: average thickness ~ 40 km Oceanic Crust: average thickness ~ 6 km CC is about 10 times richer in U and Th than OC



Borexino is homed in the Gran Sasso underground laboratory (LNGS) in the center of Italy: 42°N 14°E

Calculated anti-νe flux at the Gran Sasso Laboratory

(106 cm-2 s-1)

U Th Total (U+Th) Reactor BKG

Crust Mantle Crust Mantle

1.8 1.4 1.5 1.2 5.9 0.65

Data from the International Nuclear

Safety Center (http://www.insc.anl.gov)

LNGS



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.

In Borexino are expected:

The background will be:

(7.6 of them in the same spectral region as the terrestrial anti-ν)

yr

events7.8

yr

events92

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.



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.



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-νe.The νµ and ντ flavors are more energetic, increasing the total event rate.

This provide Borexino with several hundred supernova neutrino interactions

'' pp

lino miramontijune 9-14, 2003, nara japan 1st yamada symposium neutrinos and dark matter in nuclear...

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