Letter of Intent for KM3NeT 2.0 (1601.07459v2)

Abstract: The main objectives of the KM3NeT Collaboration are i) the discovery and subsequent observation of high-energy neutrino sources in the Universe and ii) the determination of the mass hierarchy of neutrinos. These objectives are strongly motivated by two recent important discoveries, namely: 1) The high-energy astrophysical neutrino signal reported by IceCube and 2) the sizable contribution of electron neutrinos to the third neutrino mass eigenstate as reported by Daya Bay, Reno and others. To meet these objectives, the KM3NeT Collaboration plans to build a new Research Infrastructure consisting of a network of deep-sea neutrino telescopes in the Mediterranean Sea. A phased and distributed implementation is pursued which maximises the access to regional funds, the availability of human resources and the synergetic opportunities for the earth and sea sciences community. Three suitable deep-sea sites are identified, namely off-shore Toulon (France), Capo Passero (Italy) and Pylos (Greece). The infrastructure will consist of three so-called building blocks. A building block comprises 115 strings, each string comprises 18 optical modules and each optical module comprises 31 photo-multiplier tubes. Each building block thus constitutes a 3-dimensional array of photo sensors that can be used to detect the Cherenkov light produced by relativistic particles emerging from neutrino interactions. Two building blocks will be configured to fully explore the IceCube signal with different methodology, improved resolution and complementary field of view, including the Galactic plane. One building block will be configured to precisely measure atmospheric neutrino oscillations.

• The paper outlines strategic plans for ARCA and ORCA to enhance neutrino astrophysics and determine the neutrino mass hierarchy.
• It details a scalable detector design integrating thousands of digital optical modules with multi-PMT technology for superior photon detection.
• Simulations and advanced reconstruction algorithms demonstrate the detector’s potential to improve measurement precision and accelerate neutrino research.

Overview of KM3NeT 2.0: Letter of Intent for ARCA and ORCA

The KM3NeT Collaboration outlines its strategic plan for the ARCA and ORCA initiatives in its detailed Letter of Intent, focusing on advancing astroparticle and neutrino oscillation research. These endeavors aim to discover high-energy neutrino sources in the universe and determine the neutrino mass hierarchy, leveraging the capabilities of deep-sea neutrino detection infrastructure distributed across selected Mediterranean locations.

Detector Design and Technology

The proposed detector system comprises thousands of digital optical modules (DOMs) integrated into detection units, a scalable structure optimized for neutrino interactions. The use of multi-PMTs within each DOM significantly enhances angular coverage and photon detection efficiency while maintaining cost-effectiveness. This modularity facilitates phased and distributed implementation, crucial for expanding the instrumented sea volume.

Scientific Objectives

1. High-energy Neutrino Sources with ARCA: ARCA (Astroparticle Research with Cosmics in the Abyss) targets the paper of high-energy cosmic neutrinos. With IceCube's recent detection of a cosmic neutrino signal, ARCA aims to provide complementary insights and refine measurements through its unique geographic perspective.

2. Neutrino Mass Hierarchy with ORCA: ORCA (Oscillation Research with Cosmics in the Abyss) focuses on resolving the neutrino mass hierarchy using atmospheric neutrinos. ORCA's sensitivity benefits from enhanced matter effects in water, promising notable contributions to understanding neutrino oscillations and associated parameters.

Simulation and Reconstruction Performance

Sophisticated simulation frameworks assess the detector's response to neutrino interactions, optimizing solutions for photon detection, data acquisition, and noise rejection. The simulations inform design choices such as optimal DOM spacing, critical for achieving desired energy thresholds and effective volumes. Advanced reconstruction algorithms reconstruct neutrino interaction vertices and directions, refining measurement precision.

Sensitivity to Neutrino Mass Hierarchy

ORCA's reported sensitivity to the neutrino mass hierarchy shows potential for definitive determination within a few years of operation. The sensitivity varies with true mixing parameters, notably _θ_23, underscoring the need for precise parameter control. Implementation of the most effective inelasticity reconstruction methods and identification algorithms can significantly improve discriminator metrics between normal and inverted hierarchy models.

Organizational and Scientific Cooperation

KM3NeT iterates its commitment to an open data policy while maintaining a phased approach towards full-scale deployment via collaborative efforts with national and international partners. The planned European Research Infrastructure Consortium (ERIC) aims to streamline resource allocation and infrastructural management. Engagements with the Global Neutrino Network will facilitate integrated analyses and resource sharing across complementary instruments like ANTARES and IceCube.

Future Prospects

With continued refinements in computational analyses and demonstration of its prototypes' efficacy, KM3NeT is positioned to enhance our understanding of neutrino physics significantly. Its multidisciplinary approach also seeks to contribute to areas like geophysics and marine science, capitalizing on observational synergies. Advanced proposals for a neutrino beam experiment further exemplify KM3NeT's ambition for expanding neutrino research frontiers.

In summary, the KM3NeT Letter of Intent articulates a detailed and strategic framework for tackling fundamental scientific questions through large-volume neutrino detection. The orchestrated deployment of ARCA and ORCA represents a landmark effort in astroparticle physics, promising to yield transformative insights into neutrino properties and astrophysical processes.