[Paper Review] Neutrinos and (Anti)neutrinos from Supernovae and from the Earth in the Borexino detector

L. Miramonti|ArXiv.org|Jul 14, 2003

Neutrino Physics Research3 citations

TL;DR

This paper investigates the detection of supernova and geoneutrinos using the Borexino liquid scintillator detector at Gran Sasso, leveraging its ultra-low background and large fiducial volume. It demonstrates that Borexino can detect terrestrial antineutrinos from U, Th, and K decay with a signal of ~7.8 events/year, while reactor antineutrino background (~29 events/year) can be subtracted due to its distinct spectral shape, enabling separation of U and Th contributions.

ABSTRACT

The main goal of the Borexino detector, in its final phase of construction in the Gran Sasso underground laboratory, is the direct observation and measurement of the low energy component of neutrinos coming from the Sun. The unique low energy sensitivity and ultra-low background bring new capabilities to attack problems in neutrino physiscs other than solar ones. Investigation about the study of Supernoavae neutrinos and neutrino coming from the Earth (Geoneutrinos) are here resumed.

Motivation & Objective

• To assess Borexino's capability to detect high-energy neutrinos from core-collapse supernovae using inverse beta decay and carbon interactions.
• To evaluate the detection of geoneutrinos from U, Th, and K decay in the Earth's crust and mantle using antineutrino signatures.
• To quantify and subtract reactor antineutrino background in Italy to isolate terrestrial antineutrino signals.
• To determine the feasibility of measuring neutrino energy spectra from supernovae and Earth's interior using a large, unsegmented liquid scintillator detector.

Proposed method

• Utilizes the Cowan-Reines reaction ($\bar{\nu}_e + p \rightarrow n + e^+$) with delayed coincidence of positron and 2.2 MeV gamma to tag antineutrino events.
• Employs a 300-ton liquid scintillator detector with a 100-ton fiducial volume to minimize external background from photomultiplier tubes.
• Applies a graded shield and ultra-radiopure materials to achieve internal background levels of $10^{-16}$ g/g (U/Th) and $10^{-14}$ g/g (K).
• Analyzes neutrino interactions on $^{12}$C, including charged current (CC) and neutral current (NC) reactions, with characteristic 15.1 MeV gamma from $^{12}$C* de-excitation.
• Uses spectral analysis of positron energy to distinguish geoneutrino signals from reactor antineutrino backgrounds.
• Applies global crustal and reactor data to model antineutrino fluxes, with a calculated flux of $5.9 \times 10^6$ cm$^{-2}$s$^{-1}$ at Gran Sasso and background of $0.65 \times 10^6$ cm$^{-2}$s$^{-1}$.

Experimental results

Research questions

• RQ1 Can Borexino detect the 15.1 MeV gamma peak from neutral current neutrino interactions on $^{12}$C during a supernova burst?
• RQ2 What is the expected rate of antineutrino detection from terrestrial U, Th, and K decay in the Borexino detector?
• RQ3 How can reactor antineutrino background be subtracted to isolate the geoneutrino signal in a low-radioactivity environment?
• RQ4 What is the contribution of U, Th, and K to the radiogenic heat production and antineutrino flux in the Earth's bulk silicate Earth model?
• RQ5 Can the spectral shape of antineutrino events distinguish between contributions from U and Th in the Earth's interior?

Key findings

• Borexino can detect supernova antineutrinos via the Cowan-Reines reaction with a sensitivity of ~1 event per year in a 300-ton detector.
• The detector can identify the 15.1 MeV gamma peak from neutral current interactions on $^{12}$C, enabling detection of high-energy neutrino bursts.
• The expected geoneutrino signal rate is ~7.8 events per year from U, Th, and K decay in the Earth's crust and mantle.
• Reactor antineutrino background contributes ~29 events per year, with ~7.6 in the same energy range as geoneutrinos, but its spectral shape allows for effective subtraction.
• The antineutrino flux at Gran Sasso is calculated as $5.9 \times 10^6$ cm$^{-2}$s$^{-1}$, dominated by K-40 decay, with a background flux of $0.65 \times 10^6$ cm$^{-2}$s$^{-1}$ from reactors.
• The spectral shape of terrestrial antineutrinos allows for the separation of U and Th contributions, enabling constraints on the Earth's radiogenic heat production.