Comprehensive Geoneutrino Analysis with Borexino Detector Data and Earth Radiogenic Heat.
I.N. Machulin NRC «Kurchatov institute»,
(on behalf of Borexino collaboration) Comprehensive geoneutrino analysis with Borexino. PHYSICAL REVIEW D 101, 012009 (2020)
Analysis of 12-years experimental data from Borexino detector in the Gran Sasso underground laboratory (3263 days of measurements from December 2007 to April 2019). History of GeoNeutrino
G. Gamov letter to F. Reines (1953): Dear Fred, ...your background neutrinos may just be coming from high energy β decaying members of U and Th families in the crust of the Earth. G. Marx, N. Menyard Mitteilungen der Sternwarte, Budapest, 48 (1960): First estimation of neutrino fluxes from U, Th and K decays.
Only two experiments detected the predicted GeoNeutrino signal:
Borexino, Italy KamLand, Japan 2007-2019 2002-2019 Earth Structure
Crust: oceanic 7-10 km, continent 30-60 km, ρ=~2.5-3.5 g/cm3 Upper mantle: ~ 30-660 km, ρ=~3.5-4 г/cм3 Lower mantle: ~ 660-2900 km, ρ=~5 g/cm3 Outer Core (Liquid), ~ 2900-5140 km, ρ=~10-11 g/cm3 Inner Core (Solid), ~5140-6371 km, ρ=~13 g/cm3, t = 6000 ° С Metallic, Iron-Nickel alloy ~90 % Fe and ~ 5 % Ni, (without U и Th -?)
Crust (0.4% MEarth), Mantle (68% MEarth), Core (32% MEarth) Earth Structure In accordance with seismological measurements of P-type (longitudinal) and S-type (transverse) wave velocity the Earth is divided into several layers - crust, mantle and core. The seismological data allows to construct the density distribution inside the Earth.
The world's deepest Kola well 12 246 м
Preliminary Reference Earth Model (PREM) Dziewonski, Anderson (1981) Earth heat
Data of temperature gradients measurements in ~ 40000 geological wells. Total thermal capacity of the Earth: 47±2 TW (~0.09 W/m2). Heat flow from the Sun ~ 340 W/m2
Thermal power Authors of the Earth [TW] Williams and von 43 Herzen [1974] Davies [1980] 41 Sclater et al. [1980] 42 mW/m2 Pollack et al. [1993] 44 ± 1 Hofmeister et al. 31 ± 1 Sources of geothermal heat: [2005] 238 232 40 - U, Th и K decays; Jaupart et al. [2007] 46 ± 3 - Residual energy of Earth formation; Davies and Davies 47 ± 2 - Nuclear reactor inside the Earth - ? [2010] Radiogenic heat in Earth models Geo-n flux <=> Number of r/a elements<=> Energy of the Earth Three classes of models Bulk Silicate Earth (BSE) : Cosmochemical Model (CC) (Enstatitic meteorites) Geochemical Model (GCM) (Carbonaceous meteorites) Geodynamical Model (GDM) (Earth dynamics Big difference Ref. O. Šrámek et al (1) CC GCM GDM in predictions −9 AU (10 ) 12 +2 20+4 35+4 −9 ATh (10 ) 43+4 80+13 140+14 −6 AK (10 ) 146+29 280+60 350+35 Factor 3 Th/U 3.5 4.0 4.0 K/U 12000 14000 10000 Total power (TW) 11+2 20+4 33+3 Mantle power (TW) 3.3+2.0 12+4 25+3 Factor 10!! (1) O. Šrámek et al. Earth. Plan. Sci. Letters 361 (2013)356-366 Geoneutrino: neutrino from Earth
U, Th and 40K emit antineutrinos simultaneously with heat generation:
238U (99.2739% of natural U) 206Pb + 8 α + 8 e- + 6 anti-neutrinos + 51.7 MeV 232Th 208Pb + 6 α + 4 e- + 4 anti-neutrinos + 42.8 MeV 235U (0.7205% of natural U) 207Pb + 7 α + 4 e- + 4 anti-neutrinos + 46.4 MeV 40K (0.012% of natural K) 40Ca + e- + 1 anti-neutrino + 1.32 MeV (BR=89.3 %) 40K + e- 40Ar + 1 neutrino + 1.505 MeV (BR=10.7 %)
• The Earth emits mainly antineutrinos (while the Sun neutrinos).
• Geo-neutrinos from U and Th decay (but not from 40K) can be registered in the proton inverse beta decay reaction (Ethr= 1.8 MeV). • Contributions from U and Th can be separated by measuring the energy spectrum (anti-neutrinos from the decay of U have higher energy) Radiogenic heat and geoneutrino.
The heat generated by the decays of r/a elements, the antineutrino flux and the total mass of U, Th and K are directly related. Neutrine Luminosity L [1024 с-1] = 7.64 M(U) + 1.62 M(Th) + 27.10·10-4 M(K) , M[1017 kg]
Radiogenic heat H [TW] = 9.85· M(U) + 2.67· M(Th) + 3.33· ·10-4 M(K), M[1017 kg] Radiogenic Heat in Modern Geological Models: 1) Crust: ~ 7-9 TВт 2) Mantle: (1-27) TВт 3) Core: 0 TW
6 2 Фn 4 10 n/(cм с) Laboratori Nazionali del Gran Sasso (LNGS, Italy) Depth ~ 3800 m w.e.
Abruzzo Gran Sasso Hall C (Borexino)
LNGS
10 Borexino detector
278 tons of liquid scintillator
(C9H12 + 1.5 g/l PPO) 6 1028 protons 2212 8-inch PMT Active Cherenkov muon veto Charge Yield = 500 ph.el./MeV DE/E ~ 6% at 1 MeV
Spatial resolution sx,y,z~11cm at 1 MeV
a(238U) < 9.4 10-20 g/g
a(232Th) < 5.7 10-19 g/g Antineutrino detection
+ + Eν ≅ Ee + En + (Mn-Mp) + me
Evis = Eν - 0.784 MeV Delayed coincedences: τ = 254.5 ± 1.8 мкс
• Geoneutrino signal unit: Terrestrial Neutrino Unit (TNU)
1 TNU = 1 event/1032 protons/year 1032 protons ~ 1 kton of liquid organic scintillator egeo = 0.87 ± 0.015 (Psevdocumen С Н , LAB С H etc/) 32 9 12 18 30 ep = (1.29 ± 0.05) 10 proton·year Antineutrinos in Borexino.
antineutrino Reactor antineutrino Atmospheric from the Earth antineutrino interior
Ngeo = ? Nreactor = 18.7 ± 0.5 Natm = 2.2 ± 1.1 (for geoneutrino energy (for geoneutrino energy window) window) Expected geoneutrino signal in the Borexino detector
Regional and global geological data Energy spectrum of geoneutrino
1 TNU = 1 event / 1032 target protons (~1kton LS) / year with 100% Geoneutrino signal in Borexino detection efficiency (withν oscillations effect
Local Crust (~500 km 9.2 ± 1.2 0.24 - around LNGS) Bulk Lithosphere +4.9 0.29 +1.9 25.9 -4.1 8.1 -1.4 (observed) Mantle = Bulk Silicate 2.5 – 19.6 0.26 3.2 – 25.4 Earth model (assuming for BSE – lithosphere chondritic value of 0.27) Total 28.5 – 45.5 0.27 11.3 – 33.5 (chondritic) Reactor antineutrinos 2007-2019 data on operation of 443 Contribution from reactors at reactors (~1.2 TW of total thermal different distances to power) geoneutrino signal in Borexino IAEA PRIS (Power Reactor Information System) Database: The main contribution to the detector signal from ~193 European nuclear power plants. 250 NPPs outside Europe contribute 2.5%. Spent fuel 1%. Fuel composition accounts for different reactor types: pressurized water, boiled water, light water graphite, gas cooled, heavy water reactors; also as for MOX fuel in 30 PWR.
Sреакт=79.6 + 1.4 TNU (En 1.8-8 MeV) Optimized event selection criteria
Energy selection . 1) First (positron) event Q1 > 408 ph.el. . 2) Second time-delayed event Am-Be neutron calibration source. First and second 700 < Q2 < 3000 ph.el. (delayed) events. (neutronы capture on hydrogen or in 1% cases on carbon)
Charge output 500 ph.el. / 1 MeV Energy resolution : 5% at 1 MeV energy Efficiency = 0.87 ± 0.015 Optimized event selection criteria
Time correlation Space correlation dt = (2.5-12.5) ms + dR < 1.3 м (20-1280) ms
Events multiplicity Optimized event selection criteria
Dynamic Fiducial Volume Distance to the edge of a nylon vessel, containing scintillator:
Distribution of 210Bi events near the nylon vessel surface Reconstructed nylon vessel form Optimized event selection criteria
Improved muon veto New effective α/β Muons in external detector - 2 signal discrimination msec cuts in the detector using a Muons in internal detector - neural network cuts for 2 s, 1.6 s and 2 ms, depending on the location of the approach (MLP) muon track Dead volume along the muon track 154 candidates for antineutrino events in the Borexino detector Prompt charge spectrum Delayed charge spectrum • Time: 9.12.2007 – 28.4.2019 3262.74 days of data taking
• Average target mass= (245.8 ± 8.7) ton n+1H n+12C • Exposure = (1.29 ± 0.05)·1032 proton·year Including systematics on position reconstruction and muon veto loss, for 100% detection eff.
Distribution in time Radial distribution Distance to the Inner Vessel Non-antineutrino backgrounds
(b-n) decays of 9Li within 2 s 13C(210Po(α), n) 16O Accidentals after muons
210Po rate = (12.75 ±0.08) cpd/ton Expected (Monte-Carlo) spectra of the first (positron) events of reactor and geo antineutrinos Spectral Fit with chondritic Th/U ratio Reactor signal expectations
1σ 3σ • Unbinned likelihood fit of charge spectrum of 154 prompts 5σ 8σ • S(Th)/S(U) = 2.7 (corresponds to chondritic Th/U mass ratio of 3.9) Observed number of geoneutrino • Reactor signal unconstrained and result compatible with events in the Borexino detector: expectations • 9Li, accidentals, and (α, n) brgs constrained according to 52.6+9.4 (stat) +2.7 (sys) 68 % C.L. expectations −8.6 −2.1 • Systematics includes atmospheric neutrinos, shape of reactor spectrum, vessel shape and position reconstructions, detection efficiency Geoneutrino in the Gran Sasso laboratory, comparison with Earth models predictions Manntle (U + Th) FFL (far-field lithosphere) BSE model – +4.8 LOC (local crust) (16.3 -.3.7) TNU LITHOSPHERE (9.2 ± 1.2) TNU
Earth models
+8,4 +2,4 S (U+Th) = 47. 0 −7.7(стат.) −1.9 (сист.) TNU
+0,6 6 -2 -1 +0,5 6 -2 -1 Фn(U) = 2.8 −0.4 10 см с Фn(Th) = 2.6 −0.4 10 см с Spectral Fit with independent Th and U signals
Th/U mass chondrite ratio is a free parameter for fitting.
3σ 2σ Resulting number of geoneutrinos1σ
1σ 3σ 5σ 8σ
Resulting number of geoneutrinos : no sensitivity to measure Th/U ratio 50.4+47 соб. Large error −44 : Geoneutrino from the Earth mantle
# Mantle events
• Fit performed with signal from lithosphere constrained to (28.8 ± 5,6) events with S(Th)/S(U) = 0.29 Mantle signal • Mantle PDF constructed with S(Th)/S(U) = 0.26, 23.7+10.7 events maintaining the global Th/U ratio as in CI −10.1 chondrites +9.6 • Sensitivity study using log-likelihood ratio 21.2−9.0 TNU method: null hypothesis rejected with 99.0% C.L. Earth radiogenic heat
Htot = (47 ± 2) TВт
Mantle radiogenic heat from U+Th Earth radiogenic heat from U+Th+K +11.1 TW +13.6 24.6−10.4 38.2−12.7 TW Compatible with predictions, but least (2.4σ) o Assuming 18% 40K mantle compatible with the CosmoChemical model contribution (CC), predicting lowest U+Th mantle o Lithospheric radiogenic heat from +1.9 abundances U+Th+K 8.1 -1.4ТВт Search for Geo-Reactor Herndon et al, J. Geomagn. Geoelectr. 45, 423 (1993), Proc. Natl. Acad. Sci. U.S. A. 93, 646 (1996). Hypothetical georeactor with thermal power < 30 TW in the central part (core) of the Earth Fuel composition 235U:238U=0.76:0.23
Geo-Reactor Power < 0.5 TW (95% C.L.) D=2900 km < 2.4 TW (95% C.L.) Earth’s center < 5.7 TW (95% C.L.) D=9840 km Summary 1) Borexino detector achieved record accuracy of ~18% in the measurement of geoneutrino signal from the decays of U, Th:
2) Borexino observes geoneutrino mantle signal with a null observation excluded at a 99.0% CL:
3) Borexino estimates a radiogenic power from (U+Th) in the mantle: +11.1 Hrad (U+Th) = 24.6−10.4 TW
Geoneutrinos is the proved tool to study our Earth and new generation of neutrino experiments are needed to check the Earth geology models Thank you for attention. Borexino Collaboration
Milano
Genova Petersburg APC Paris Nucl. Phys. Institute
Perugia
Princeton University
Dubna JINR Kurchatov Virginia Tech. University (Russia) Institute (Russia)
Munich (Germany) Heidelberg Jagiellonian U. Cracow (Germany) (Poland)