Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of...

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Results on geoneutrinos at Borexino experiment Heavy Quarks and Leptons 2018 - Yamagata Davide Basilico

Transcript of Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of...

Page 1: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Results on geoneutrinos atBorexino experiment

Heavy Quarks and Leptons 2018 - Yamagata

Davide Basilico

Page 2: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

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Outline

1. Geoneutrinos

2. Borexino

3. Analysis and results

Page 3: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

What are geoneutrinos?

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Distribution of long-lived nuclides in the

Earth (238U and 232Th chains)

β- decay

Page 4: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

What are geoneutrinos?

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Distribution of long-lived nuclides in the

Earth (238U and 232Th chains)

β- decay

Anti-neutrinos: geoneutrinos

Energy net release: heat

Page 5: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

What are geoneutrinos?

• Direct messengers of theabundances of radioactive elements

• Measuring their flux and spectrum→ understand the radiogeniccontribution to the total heatbalance of the Earth.

• Discriminate Earth models(cosmochemical, geochemical,geodynamical etc…)

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Distribution of long-lived nuclides in the

Earth (238U and 232Th chains)

β- decay

Anti-neutrinos: geoneutrinos

Energy net release: heat

Page 6: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

How to measure geoneutrinos?

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What do we need to measure geoneutrinos?Anti-neutrinos have low interaction rates: σ ~ 10-44 cm2 @ MeV

→ experiments with extremely low background

• Large volume detectors• Construction materials → high radiopurity

Page 7: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

How to measure geoneutrinos?

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What do we need to measure geoneutrinos?Anti-neutrinos have low interaction rates: σ ~ 10-44 cm2 @ MeV

→ experiments with extremely low background

• Large volume detectors• Construction materials → high radiopurity

KamLAND in Japan• Main goal: reactor anti-neutrinos measurements

Borexino experiment in Gran Sasso, Italy• Extreme radiopurity achieved to perform solar neutrinos spectroscopy (main goal) • But also able to measure anti-neutrinos!• No nuclear power plant in Italy → smaller background wrt Kamland• Underground lab → shielding cosmic rays radiation and related background

Page 8: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Gran Sasso National Laboratory (Italy)

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Abruzzo

Page 9: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Gran Sasso National Laboratory (Italy)

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Abruzzo

Gran Sasso

LNGS

Page 10: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Gran Sasso National Laboratory (Italy)

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Abruzzo

Gran Sasso

LNGS

Hall C(Borexino)

Page 11: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Borexino detector

• DAQ started in 2007

• Main analysis: solar neutrinos spectroscopy (see David Bravo’s talk)

• 300 ton of ultra-pure liquid scintillator

• Extremely low radioactive background

• 2000 PMTs to measure: • positions → photons time arrival• energy → number of photons

detected

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Page 12: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

How to detect geo-ν in Borexino? (→ 𝝂)

Prompt signal: • e+ scintillation + annihilation (2γ)• Eprompt ≈ Egeoneutrino - 0.782 MeV

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𝜈𝑒 + 𝑝 → 𝑒+ + 𝑛

Delayed signal (neutron):• n capture on H• Edelayed ≈ 2.2 MeV• <Δt> = 254.5 ± 1.8 μs

Inverse Beta Decay

Energy 𝜈𝑒 threshold: 1.8 MeV

Page 13: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

How to detect geo-ν in Borexino? (→ 𝝂)

Prompt signal: • e+ scintillation + annihilation (2γ)• Eprompt ≈ Egeoneutrino - 0.782 MeV

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𝜈𝑒 + 𝑝 → 𝑒+ + 𝑛

Coincidence in time / space / energy between prompt and delayed guarantees a very high signal/background ratio (100:1 in Borexino)

Delayed signal (neutron):• n capture on H• Edelayed ≈ 2.2 MeV• <Δt> = 254.5 ± 1.8 μs

Inverse Beta Decay

Energy 𝜈𝑒 threshold: 1.8 MeV

Page 14: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Reactor 𝝂 background• MeV anti-ν background: nuclear power plants (E < 8 MeV)• 98% European ones• Estimation of the exp. events from the spectral components of 235U, 238U, 239Pu

and 241Pu

Sum over reactors

Sum over months

Power(r,m)

distance

Component fraction

Page 15: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Reactor 𝝂 background• MeV anti-ν background: nuclear power plants (E < 8 MeV)• 98% European ones• Estimation of the exp. events from the spectral components of 235U, 238U, 239Pu

and 241Pu

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Expected: 5.7 ± 0.3 events / (100 ton yr)

→ Information on fuel power composition (in time!) is required

Sum over reactors

Sum over months

Power(r,m)

distance

Component fraction

Page 16: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Other background (not 𝝂 related)

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1) Cosmogenic-muon related:• 9Li and 8He decaying β- + neutron;• High-energy neutrons: neutronscattering + neutron capture = prompt + delayed

2) Accidental coincidences

3) Internal radioactivity:(α,n) and (γ,n) reactions

Almost negligible (if compared to reactors)

Source Rate [events/100ton yr]

Page 17: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Selection cuts

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Prompt signal:• Qprompt > 408 p.e.• Fiducial Volume Cut

Delayed signal:• 860 < Qdelayed < 1300 p.e.

Coincidence:• Time: 20 < Δt < 1280 μs• Space: ΔR < 100 cm

Muon correlated cutsPulse shape discrimination cuts

1 MeV ≈ 500 p.e.

Page 18: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Selection cuts

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Prompt signal:• Qprompt > 408 p.e.• Fiducial Volume Cut

Delayed signal:• 860 < Qdelayed < 1300 p.e.

Coincidence:• Time: 20 < Δt < 1280 μs• Space: ΔR < 100 cm

Muon correlated cutsPulse shape discrimination cuts

1 MeV ≈ 500 p.e.

Total efficiency = (84.2 ± 1.5)% (MC). 77 candidates selected

Page 19: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Spectrum from 2056 days data-taking

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• Un-binned likelihood fit of prompt events energy spectrum• Reactor spectrum is obtained by MC simulations and left free in the fit• Non- 𝝂𝒆 background considered in the fit but constrained to

independent estimations → completely negligible

Two fits: U/Th ratio

1. Fixed to chondritic value model

2. Free

Energy [photoelectrons]

Page 20: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Evidence and implications

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Fixing mass ratio U/Th=3.9

N𝑔𝑒𝑜 = 23.7−5.7+6.5 𝑠𝑡𝑎𝑡 −0.6

+0.9(𝑠𝑦𝑠𝑡)

geoneutrino events: 5.9σ evidence

Sgeo = 43.5−10.4+11.8 stat −2.4

+2.7 syst TNU

1 TNU = 1 event detected over 1 year exposure of 1032 target protons at 100 % efficiency

Page 21: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Evidence and implications

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Fixing mass ratio U/Th=3.9

N𝑔𝑒𝑜 = 23.7−5.7+6.5 𝑠𝑡𝑎𝑡 −0.6

+0.9(𝑠𝑦𝑠𝑡)

geoneutrino events: 5.9σ evidence

Sgeo = 43.5−10.4+11.8 stat −2.4

+2.7 syst TNU

1 TNU = 1 event detected over 1 year exposure of 1032 target protons at 100 % efficiency

Mass ratio U/Th free parameterBest fit value compatible with U/Th=3.9

Page 22: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Implications: heat

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11 5223 36

Vertical band between red and blue line due to U+Thdistribution in the mantle

U+Th: radiogenic heat is 23-36 TW (best fit) and 11-52 TW for 1σ intervalComplete – U+Th+K: mass ratio U/Th=3.9 and K/U = 104, radiogenic heat 33+28

-20TW

Independently measured total Earth surface power: 47 + 2 TW→ large contribution from radioactive decays!

Page 23: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Conclusions

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1) The background level in Borexino allows to perform areal-time spectroscopy of geoneutrinos, limited only by thesize of the detector;

2) Borexino-only data: geoneutrinos exist, with 5.9 significance;

3) The radiogenic heat gives an important contribution to theEarth power balance;

4) Interdisciplinary field between physics and geoscience.

Page 24: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Thank you!

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Page 25: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

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Page 26: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Geoneutrinos energy spectra

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Energy spectra of geo-neutrinos released in the reactions: 238U chain in black, 232Th chain in red, 40K in blue. Vertical line: IBD threshold (1.806 MeV)

Page 27: Results on geoneutrinos at Borexino experiment · •Direct messengers of the abundances of radioactive elements •Measuring their flux and spectrum → understand the radiogenic

Chondrites

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• Chondrites are primitive, undifferentiated meteorites, a collection of the earliest formed material in the solar system.

• Studies of meteorites add much to our understanding of the age of the solar system and the nature of the building blocks that makes up the planets.

• Mixture of silicate and metal materials in proportions similar to that found in the terrestrial planet