The next-generation liquid-scintillator neutrino observatory LENA (1104.5620v3)

Abstract: We propose the liquid-scintillator detector LENA (Low Energy Neutrino Astronomy) as a next-generation neutrino observatory on the scale of 50 kt. The outstanding successes of the Borexino and KamLAND experiments demonstrate the large potential of liquid-scintillator detectors in low-energy neutrino physics. LENA's physics objectives comprise the observation of astrophysical and terrestrial neutrino sources as well as the investigation of neutrino oscillations. In the GeV energy range, the search for proton decay and long-baseline neutrino oscillation experiments complement the low-energy program. Based on the considerable expertise present in European and international research groups, the technical design is sufficiently mature to allow for an early start of detector realization.

• The paper introduces LENA as a next-generation observatory using enhanced liquid-scintillator technology to capture low-energy neutrino events.
• It details innovative design features such as superior energy resolution (<3% at 5 MeV) and robust background discrimination for studying supernova, solar, and geoneutrinos.
• The study highlights LENA’s potential in probing neutrino oscillation, proton decay, and astrophysical phenomena, promising breakthroughs in neutrino research.

Summary of "The Next-Generation Liquid-Scintillator Neutrino Observatory LENA"

The proposal to develop the Liquid-scintillator Electromagnetic Neutrino Astronomy (LENA) aims to advance the field of neutrino physics by deploying a next-generation, multipurpose neutrino observatory. LENA, with a planned target mass of 50 kilotons, leverages the successful liquid-scintillator techniques demonstrated in experiments such as Borexino and KamLAND to investigate low-energy neutrino phenomena. Key features of liquid scintillator detectors—such as low energy threshold, fine energy resolution, and strong background discrimination—are integral to the design of LENA. This essay provides an overview of LENA’s scientific objectives, design considerations, and the technological readiness of implementing this observatory.

Scientific Goals

LENA’s comprehensive scientific program covers several domains in neutrino physics and astrophysics:

1. Supernova Neutrinos: LENA is poised to yield high-statistics observations from galactic supernovae, enabling detailed studies on core-collapse dynamics. Its capability to distinguish multiple neutrino event channels will provide insights into flavor oscillation effects, yielding potentially unprecedented astrophysical and particle physics data.
2. Diffuse Supernova Neutrino Background (DSNB): LENA aims to detect the background flux of neutrinos from all historical core collapses, offering a glimpse into average supernova neutrino emissions, which can validate or refine theoretical models.
3. Solar Neutrinos: High-statistics measurements in LENA will enhance studies on solar neutrino fluxes and oscillation probabilities, particularly exploring the vacuum-matter transition region.
4. Geoneutrinos: Expected low background levels will allow significant measurements of geoneutrinos generated from the Earth’s radioactive decay processes, offering valuable insights into crust and mantle composition as well as the planet’s heat flow.
5. Proton Decay Searches: LENA's high efficiency in detecting proton decay channels, especially those involving kaon and antineutrino productions, could advance our understanding of nucleon decay lifetimes.
6. Neutrino Oscillation Physics: The detector could serve as a benchmark experiment in resolving questions related to neutrino mass hierarchies, CP violation, and mixing parameters like $\theta_{13}$.

Technological Features and Readiness

The proposed design capitalizes on various technical merits:

• Detection Capability: The detector offers not only enhanced light collection and radiopurity but also sophisticated signal identification (e.g., delayed neutron capture) necessary for rare decay modes and low cross-section processes.
• Energy Resolution: A planned energy resolution to achieve better than 3% at 5 MeV will be instrumental in separating closely spaced spectral features, vital for discerning the DSNB and supernova bursts.
• Scintillator Technology: Advancements in scintillator transparency and wavelength shifting will facilitate capturing detailed neutrino interaction dynamics, boosting discovery potential in areas such as solar neutrino studies.
• Adaptability for High-Energy Phenomena: Although primarily designed for low-energy neutrinos, LENA’s structural features allow it to accommodate high-energy measurements, such as multi-GeV atmospheric neutrino interactions and faint cosmic signals, as part of an extended physics agenda.

Conclusion and Future Potential

LENA represents a significant step forward in constructing an ultra-sensitive neutrino observatory with unprecedented versatility to investigate the broad spectrum of neutrino sources. Its contribution to resolving fundamental questions in cosmology and particle physics could be profound, from understanding stellar phenomena to tailoring global fits of the neutrino oscillation framework. Available data from LAGUNA feasibility studies suggest a practical path for LENA’s realization, leveraging European expertise in such large-scale underground experiments. Its successful deployment would solidify it as a cornerstone facility in the worldwide neutrino research landscape.