[Paper Review] A CERN-based high-intensity high-energy proton source for long baseline neutrino oscillation experiments with next-generation large underground detectors for proton decay searches and neutrino physics and astrophysics

A. Rubbia|arXiv (Cornell University)|Mar 9, 2010

Neutrino Physics Research36 references19 citations

TL;DR

This paper proposes a CERN-based high-intensity, high-energy proton source (30–50 GeV) to produce a neutrino superbeam for long-baseline oscillation experiments in Europe. By leveraging multi-MW proton beams and next-generation underground detectors at baselines of 130–2300 km, it enables precise measurement of the neutrino mixing angle θ₁₃, determination of the neutrino mass hierarchy, and discovery potential for CP violation in the leptonic sector, with Pyhäsalmi (Finland) emerging as a particularly favorable site due to its long baseline and low matter effects.

ABSTRACT

The feasibility of a European next-generation very massive neutrino observatory in seven potential candidate sites located at distances from CERN ranging from 130 km to 2300 km, is being considered within the LAGUNA design study. The study is providing a coordinated technical design and assessment of the underground research infrastructure in the various sites, and its coherent cost estimation. It aims at a prioritization of the sites within summer 2010 and a start of operation around 2020. In addition to a rich non-accelerator based physics programme including the GUT-scale with proton decay searches, the detection of a next-generation neutrino superbeam tuned to measure the flavor-conversion oscillatory pattern (i.e. 1st and 2nd oscillation maxima) would allow to complete our understanding of the leptonic mixing matrix, in particular by determining the neutrino mass hierarchy and by studying CP-violation in the leptonic sector, thereby addressing the outstanding puzzle of the origin of the excess of matter over antimatter created in the very early stages of evolution of the Universe. We focus on a multi-MW-power neutrino superbeam (="hyperbeam") produced by high-intensity primary protons of energy 30$÷$50 GeV. We argue that this option is an effective way to establish long baseline neutrino physics in Europe with the high-stake prospects of measuring $θ_{13}$ and addressing CP-violation in the leptonic sector.

Motivation & Objective

• To establish a European next-generation very massive neutrino observatory (100,000–1,000,000 tons) for probing fundamental physics beyond the Standard Model.
• To address the outstanding puzzle of matter-antimatter asymmetry by searching for CP violation in the leptonic sector via high-precision neutrino oscillation measurements.
• To improve sensitivity to proton decay by extending lifetime limits to 10³⁵ years, testing GUT-scale physics.
• To enable precision studies of astrophysical neutrinos from supernovae, the early universe, and dark matter annihilation.
• To provide a technically feasible, cost-effective path to frontier long-baseline neutrino physics using a high-power proton source and optimized beamline design.

Proposed method

• Utilizes a high-intensity proton beam (30–50 GeV) from the CERN High-Power Proton Synchrotron (HP-PS2) to generate a wide-band neutrino superbeam.
• Employs off-axis beam focusing to optimize the neutrino energy spectrum for resonance at the first and second oscillation maxima.
• Designs a new beamline with advanced target and magnetic horn systems (modeled after NUMI-ME) to achieve multi-MW beam power.
• Evaluates performance across seven candidate sites (e.g., Pyhäsalmi, Boulby, Slanic) with varying baselines (130–2300 km) and rock overburden (600–4800 m.w.e.).
• Performs GLOBES-based simulations to compute discovery potential for θ₁₃, mass hierarchy, and CP violation using 5 years of neutrino and antineutrino runs.
• Optimizes beam parameters (e.g., 3×10²¹ pot/year) and baseline selection to maximize sensitivity to CP violation and mass hierarchy.

Experimental results

Research questions

• RQ1 Can a CERN-based high-intensity proton source produce a neutrino superbeam capable of measuring the last unknown mixing angle θ₁₃ with high precision?
• RQ2 What is the optimal baseline and beam energy configuration to maximize sensitivity to CP violation in the leptonic sector?
• RQ3 Can the neutrino mass hierarchy be determined with high confidence using a long-baseline superbeam from CERN?
• RQ4 How does the performance of the superbeam vary across different candidate sites with distinct depths and distances from CERN?
• RQ5 Can a multi-MW proton source enable a significant improvement in proton decay sensitivity, reaching 10³⁵ years?

Key findings

• The CERN-based hyperbeam with 50 GeV protons and 3×10²¹ pot/year achieves 3σ discovery potential for θ₁₃ down to sin²2θ₁₃ ≈ 0.01, even with a 5-year neutrino run.
• The Pyhäsalmi site (2300 km baseline) offers the highest sensitivity to CP violation due to optimal matter effects and reduced ambiguity from π-transit effects.
• Mass hierarchy discrimination is significantly enhanced at longer baselines, with the 2300 km baseline providing the best performance for excluding the wrong hierarchy.
• The 1300 km baseline (e.g., Fréjus) is near the 'magical' distance where matter effects are maximized for CP violation detection.
• The combination of 5 years of neutrino and 5 years of antineutrino runs improves sensitivity to CP violation and mass hierarchy compared to neutrino-only runs.
• The study confirms that a multi-MW proton source is a technically viable, cost-effective, and timely solution to advance long-baseline neutrino physics in Europe before the realization of neutrino factories or beta-beams.