[Paper Review] High-$\gamma$ Beta Beams within the LAGUNA design study

Christopher Orme|arXiv (Cornell University)|Apr 6, 2010

Neutrino Physics Research65 references3 citations

TL;DR

This paper proposes a high-$\gamma$ Beta Beam configuration using 18 Ne and 6 He ions boosted to $\gamma=570$ and $\gamma=350$ at CERN, directed toward a 50 kton Liquid Argon detector at Slanic (1570 km) and Pyhäsalmi (2300 km), combined with a concurrent run to a Water Čerenkov detector at Canfranc (650 km). The synergy of these baselines enables determination of the neutrino mass ordering for $\sin^2 2\theta_{13} > 4 \times 10^{-3}$ and achieves physics reach comparable to conservative Magic Baseline proposals.

ABSTRACT

Within the LAGUNA design study, seven candidate sites are being assessed for their feasibility to host a next-generation, very large neutrino observatory. Such a detector will be expected to feature within a future European accelerator neutrino programme (Superbeam or Beta Beam), and hence the distance from CERN is of critical importance. In this article, the focus is a $^{18}$Ne and $^{6}$He Beta Beam sourced at CERN and directed towards a 50 kton Liquid Argon detector located at the LAGUNA sites: Slanic (L=1570 km) and Pyh\\"{a}salmi (L=2300 km). To improve sensitivity to the neutrino mass ordering, these baselines are then combined with a concurrent run with the same flux directed towards a large Water \\v{C}erenkov detector located at Canfranc (L=650 km). This degeneracy breaking combination is shown to provide comparable physics reach to the conservative Magic Baseline Beta Beam proposals. For $^{18}$Ne ions boosted to $\\gamma=570$ and $^{6}$He ions boosted to $\\gamma=350$, the correct mass ordering can be determined at Slanic for all $\\delta$ when $\\sin^{2}2\ heta_{13}>4\\cdot 10^{-3}$ in this combination.

Motivation & Objective

• To evaluate the physics reach of high-boost Beta Beams using 18 Ne and 6 He ions for determining the neutrino mass ordering and CP-violation in the context of the LAGUNA design study.
• To assess the feasibility of using 50 kton Liquid Argon detectors at Slanic and Pyhäsalmi as far detectors for long-baseline neutrino oscillation experiments.
• To investigate whether a combination of short- and long-baseline detectors can break degeneracies in neutrino parameter determination, particularly for the mass ordering and CP phase.
• To demonstrate that a non-Magic Baseline configuration can achieve physics reach comparable to conservative Magic Baseline proposals, reducing reliance on a single optimal baseline.

Proposed method

• Simulating neutrino oscillation signals from 18 Ne and 6 He Beta Beams accelerated to $\gamma=570$ and $\gamma=350$ at CERN, respectively, using a 1 TeV machine as the accelerator infrastructure.
• Modeling neutrino flux and detector response for a 50 kton Liquid Argon detector at Slanic (1570 km) and Pyhäsalmi (2300 km), with conservative assumptions on energy resolution and detection efficiency.
• Combining data from the long-baseline Liquid Argon detectors with a concurrent run to a large Water Čerenkov detector at Canfranc (650 km) to break degeneracies in $\theta_{13}$ and $\delta$.
• Using binned event reconstruction to extract oscillatory structure in the signal, enabling sensitivity to $\theta_{13}$, $\delta$, and $\Delta m_{31}^2$ sign.
• Assessing physics reach via Monte Carlo simulations of neutrino appearance channels ($ν_\mu \to \nu_e$ and $\bar{\nu}_\mu \to \bar{\nu}_e$) in the presence of background and systematic uncertainties.
• Evaluating the impact of varying ion boost and baseline length on sensitivity to mass ordering, CP-violation, and $\theta_{13}$, particularly in degenerate solution regimes.

Experimental results

Research questions

• RQ1 Can a combination of long-baseline Liquid Argon detectors and a short-baseline Water Čerenkov detector provide competitive sensitivity to the neutrino mass ordering compared to conservative Magic Baseline configurations?
• RQ2 What is the minimum value of $\sin^2 2\theta_{13}$ for which the correct neutrino mass ordering can be determined using this multi-baseline setup?
• RQ3 How does the boost of 18 Ne ions ($\gamma=570$) affect sensitivity to CP-violation and mass ordering at the Slanic baseline?
• RQ4 To what extent does the reduced flux at the Pyhäsalmi baseline ($L=2300$ km) compromise sensitivity to $\theta_{13}$ and $\delta$ despite larger matter effects?
• RQ5 Can the synergy between a short baseline (Canfranc) and two long baselines (Slanic and Pyhäsalmi) resolve degeneracies in $\theta_{13}$ and $\delta$ more effectively than single-baseline configurations?

Key findings

• The correct neutrino mass ordering can be determined at the Slanic site (1570 km) for all values of the CP-violating phase $\delta$ when $\sin^2 2\theta_{13} > 4 \times 10^{-3}$, using the combined data from the Slanic, Pyhäsalmi, and Canfranc detectors.
• The combination of baselines provides physics reach comparable to conservative Magic Baseline Beta Beam proposals, particularly in resolving degeneracies in $\theta_{13}$ and $\delta$.
• The short baseline at Canfranc provides a clean measurement of $\theta_{13}$ and $\delta$ down to $\sin^2 2\theta_{13} \sim 10^{-4}$, enabling degeneracy breaking for the long-baseline data.
• For the Slanic baseline with $\gamma=570$ for 18 Ne and $\gamma=350$ for 6 He, non-zero $\theta_{13}$ can be established down to $\sin^2 2\theta_{13} \sim 10^{-3}$, with significant sensitivity to CP-violation.
• The Pyhäsalmi baseline ($L=2300$ km) shows much weaker sensitivity for $\sin^2 2\theta_{13} < 10^{-2}$ due to reduced flux, despite larger matter effects, and degenerate solutions remain statistically significant for small $\theta_{13}$.
• The synergy between the short baseline (Canfranc) and long baselines (Slanic and Pyhäsalmi) demonstrates that the Magic Baseline is not mandatory for determining the sign of $\Delta m_{31}^2$, offering a viable alternative configuration.