[Paper Review] Experiments For CP-Violation: A Giant Liquid Argon Scintillation, Cerenkov And Charge Imaging Experiment ?

A. Rubbia|ArXiv.org|Feb 10, 2004

Dark Matter and Cosmic PhenomenaPhysics and Astronomy7 references69 citations

TL;DR

This paper proposes a 100-kiloton liquid argon time projection chamber (LAr TPC) with scintillation and Cherenkov light readout as a technically feasible, multi-purpose detector for measuring CP violation in neutrino oscillations. It argues that such a detector—capable of observing superbeams, beta-beams, atmospheric and solar neutrinos, supernova bursts, and proton decay—would offer superior energy resolution and background suppression, making it ideal for future high-precision CP-violation experiments.

ABSTRACT

In this paper we address a class of ``ultimate'' generation experiments for the search of CP-violation in neutrino oscillations. Neutrino factories require large magnetized detectors. New generation superbeams or beta-beams need giant detectors. The liquid Argon TPC technology has great potentials for both applications. Although the ICARUS program has demonstrated that this technology is mature, the possibility to built a giant liquid argon TPC is viewed by many as a technically impossible and unsafe task. We argue that a giant liquid argon Cerenkov and charge Imaging experiment would be an ideal match for a superbeam or a betabeam. Such a detector would in addition cover a broad physics program, including the observation of atmospheric neutrinos, solar neutrinos, supernova neutrinos, and search for proton decays, in addition to the accelerator physics program. We show a potential implementation of such a giant LAr detector and argue that it could be technically feasible. The possibility to host such a detector in an underground cavern is under study.

Motivation & Objective

• To demonstrate the technical feasibility of a giant liquid argon TPC for next-generation neutrino experiments.
• To establish that such a detector can simultaneously address CP violation in neutrino oscillations and a broad range of non-accelerator physics.
• To argue that liquid argon technology, already proven in ICARUS, can be scaled up for megaton-scale physics programs.
• To compare the physics potential of a 100-kton LAr TPC with a 1-Mton water Cherenkov detector, showing competitive sensitivity.
• To advocate for underground deployment in a dedicated cavern to minimize cosmic-ray-induced backgrounds.

Proposed method

• Utilizes liquid argon time projection chamber (LAr TPC) technology with dual readout of scintillation and Cherenkov light for improved particle identification and energy resolution.
• Applies charge imaging and Cherenkov light detection to enhance reconstruction of neutrino interactions and distinguish signal from background.
• Proposes a bi-phase operation mode with charge amplification to enable long drift distances, critical for large-scale detectors.
• Models the detector as a 100-kiloton target with a cryostat system using LNG technology, assuming 5% efficiency for argon liquefaction and separation.
• Evaluates performance using oscillation probability equations (Eq. 2) to calculate CP-violation discriminants: Δδ, ΔCP, and ΔT.
• Assesses background suppression by estimating cosmic muon-induced neutron rates and proposes underground caverns in mines or mountains to reduce them.

Experimental results

Research questions

• RQ1 Can a giant liquid argon TPC with scintillation and Cherenkov readout achieve the necessary energy resolution and background suppression for CP violation measurements?
• RQ2 Is a 100-kiloton liquid argon detector technically feasible and economically viable for long-baseline neutrino experiments?
• RQ3 How does the physics reach of a 100-kiloton LAr TPC compare to a 1-megaton water Cherenkov detector in terms of sensitivity to rare processes?
• RQ4 Can such a detector simultaneously measure CP violation, atmospheric neutrinos, solar neutrinos, supernova neutrinos, and proton decay with high precision?
• RQ5 What are the cryogenic power requirements and operational challenges for maintaining a 100-kiloton liquid argon detector?

Key findings

• A 100-kiloton liquid argon TPC with scintillation and Cherenkov readout is technically feasible, with estimated cryogenic power requirements of 6.2 MW assuming 5% efficiency.
• The detector would observe approximately 324,000 solar neutrino events per year with recoil energy above 5 MeV, enabling high-precision studies of the solar neutrino spectrum.
• It would detect about 20,000 supernova neutrino events from a Type-II supernova at 10 kpc, providing early warning and detailed signal reconstruction.
• The detector would achieve a proton lifetime sensitivity of τp/Br > 10^34 years × T(yr) × ε at 90% C.L., reaching 10^35 years within 10 years of operation.
• For a 130 km baseline, the detector would record 460 νμ charged-current events per 10^21 protons at 2.2 GeV, and 15,000 νe events per 10^19 18Ne decays with γ=75.
• The ΔT discriminant method is theoretically cleanest for CP violation detection, as it is insensitive to matter effects and directly probes the δ-phase through νe→νμ vs νμ→νe asymmetry.