The Long-Baseline Neutrino Experiment: Exploring Fundamental Symmetries of the Universe (1307.7335v3)

Abstract: The preponderance of matter over antimatter in the early Universe, the dynamics of the supernova bursts that produced the heavy elements necessary for life and whether protons eventually decay --- these mysteries at the forefront of particle physics and astrophysics are key to understanding the early evolution of our Universe, its current state and its eventual fate. The Long-Baseline Neutrino Experiment (LBNE) represents an extensively developed plan for a world-class experiment dedicated to addressing these questions. LBNE is conceived around three central components: (1) a new, high-intensity neutrino source generated from a megawatt-class proton accelerator at Fermi National Accelerator Laboratory, (2) a near neutrino detector just downstream of the source, and (3) a massive liquid argon time-projection chamber deployed as a far detector deep underground at the Sanford Underground Research Facility. This facility, located at the site of the former Homestake Mine in Lead, South Dakota, is approximately 1,300 km from the neutrino source at Fermilab -- a distance (baseline) that delivers optimal sensitivity to neutrino charge-parity symmetry violation and mass ordering effects. This ambitious yet cost-effective design incorporates scalability and flexibility and can accommodate a variety of upgrades and contributions. With its exceptional combination of experimental configuration, technical capabilities, and potential for transformative discoveries, LBNE promises to be a vital facility for the field of particle physics worldwide, providing physicists from around the globe with opportunities to collaborate in a twenty to thirty year program of exciting science. In this document we provide a comprehensive overview of LBNE's scientific objectives, its place in the landscape of neutrino physics worldwide, the technologies it will incorporate and the capabilities it will possess.

• The paper demonstrates LBNE’s capability to precisely measure neutrino oscillation parameters, including CP violation and mass hierarchy, using a 1,300 km baseline.
• It employs a wide-band neutrino beam from Fermilab and high-resolution LArTPC detectors at Sanford Underground to capture detailed neutrino interactions.
• The experiment also explores proton decay and supernova neutrino detection, potentially extending limits on Grand Unified Theories.

An Overview of The Long-Baseline Neutrino Experiment (LBNE)

The Long-Baseline Neutrino Experiment (LBNE) proposes an ambitious undertaking to probe some of the most pressing questions in particle physics and astrophysics. The primary focus of LBNE is to elucidate the unknown properties of neutrinos, offering a detailed paper of neutrino mixing, mass hierarchy, and potential charge-parity (CP) violation, which could provide clues to the preponderance of matter over antimatter in the universe. LBNE is a comprehensive experimental program that also aims to explore much broader scientific questions including Grand Unified Theories (GUTs) and supernova-neutrino physics.

Key Experimental Framework

The key components of LBNE are engineered to provide a robust scientific program leveraging advanced experimental technologies.

1. Beamline Design: At the heart of LBNE is a wide-band neutrino beam sourced from Fermilab, utilizing a megawatt-class proton accelerator. This beamline design, reminiscent of the NuMI beam configuration, is integral to capturing the first and second oscillation maxima in neutrino oscillations over a long baseline of approximately 1,300 km.
2. Detector Facilities: LBNE's experimental apparatus includes a near detector at Fermilab and a far detector located deep underground at the Sanford Underground Research Facility. The far detector employs liquid argon time-projection chamber (LArTPC) technology, renowned for its high precision in detecting neutrino interactions and delineating complex particle trajectories.
3. Research Scope:
   • CP Violation and Mass Hierarchy: Central to the paper is the investigation of CP violation in the lepton sector and determining the neutrino mass hierarchy. The sensitivity of LBNE to these parameters is designed to surpass current experimental capabilities, capitalizing on its long baseline and high-resolution detector technology.
   • GUTs and Proton Decay: LBNE seeks to uncover insights into GUTs, notably through high-sensitivity searches for proton decay, possibly extending the current experimental limits significantly.
   • Supernova Neutrinos: An unexpected supernova within our galaxy would present a rare opportunity for LBNE to record neutrino signals essential for understanding stellar collapse dynamics and nucleosynthesis.

Sensitivity and Expected Outcomes

LBNE’s innovative design and strategic choice of baseline aim to achieve unprecedented sensitivity to neutrino oscillation parameters:

• CP Violation: LBNE is expected to resolve CP-violating effects to high significance for a substantial range of the CP phase $\delta_{CP}$, leveraging complementary data from beam and atmospheric neutrinos.
• Neutrino Mass Ordering: Given the long baseline, LBNE is particularly well-equipped to discern the mass hierarchy by utilizing matter effects, offering decisive measurements that are relatively independent of the unknown mixing parameters.

Challenges and Prospective Upgrades

To maximize the scientific potential, LBNE contemplates phased upgrades to incorporate additional detector mass and beam power enhancements, potentially increasing exposure and further improving sensitivity. These developments hinge on securing extended international collaboration and funding.

Theoretical and Practical Implications

The successful realization of LBNE would address outstanding theoretical questions regarding neutrino properties and fundamental symmetries. Beyond probing the flavor structure of neutrinos, LBNE provides a testing ground for new physics scenarios including non-standard interactions and sterile neutrinos. The implications of these studies could reshape our understanding of particle physics and contribute significantly to the unification theories of fundamental forces.

Future Prospects

LBNE epitomizes the next generation of neutrino physics experiments, setting a foundation for substantial scientific advances. Through international collaboration and ongoing enhancements, LBNE could remain a pivotal facility in the quest to decode the complexities of neutrinos and uncover the underlying symmetries of the universe.

In conclusion, LBNE stands as a critical element of the global particle physics program, not only for its potential discoveries in neutrino physics but also for its broader contributions to theories of grand unification and the fundamental nature of matter and antimatter in the universe.