[Paper Review] The SuperNEMO double beta decay experiment

I. Nasteva|arXiv (Cornell University)|Oct 23, 2007

Neutrino Physics Research3 citations

TL;DR

SuperNEMO proposes a next-generation double beta decay experiment using 100 kg of enriched isotopes (82Se or 150Nd) with a tracking-plus-calorimetry technique to achieve a neutrino mass sensitivity of 50 meV. By improving energy resolution, tracker efficiency, and radiopurity, it aims to reach a half-life sensitivity of >2×10^26 years, significantly advancing the search for neutrinoless double beta decay and Majorana neutrinos.

ABSTRACT

The SuperNEMO project studies the feasibility of employing a technique of tracking plus calorimetry to search for neutrinoless double beta decay in 100 kg of enriched isotopes. It aims to reach an effective neutrino mass sensitivity of 50 meV. The current status of the SuperNEMO R&D programme is described, focusing on the main areas of improvement.

Motivation & Objective

• To develop a next-generation double beta decay experiment capable of probing the effective neutrino mass down to 50 meV.
• To extend the NEMO 3 experimental technique—combining tracking and calorimetry—over an order of magnitude in mass to 100 kg of enriched isotope.
• To reduce background levels through ultra-radiopure source foils and advanced particle identification using magnetic fields and time-of-flight.
• To achieve a half-life sensitivity of >2×10^26 years for neutrinoless double beta decay, corresponding to a reach of 50–90 meV in effective neutrino mass.
• To enable staged deployment with first modules operational by 2010, culminating in a full 20-module detector by 2013.

Proposed method

• The detector uses modular design with ~20 identical units, each containing ~5 kg of enriched isotope in a thin foil (40 mg/cm²) as the source.
• Electron tracks are reconstructed using 9-layer wire drift chambers operated in Geiger mode, with anode and cathode signals used to determine trajectory and position.
• Calorimetry is achieved via ~1000 scintillator blocks read out by low-radioactivity, high-quantum-efficiency photomultiplier tubes (PMTs), aiming for 4% FWHM energy resolution at 3 MeV.
• A magnetic field is applied to distinguish electrons from positrons and aid in particle identification, reducing background from gamma and alpha events.
• Radiopurity is ensured through ultra-low contamination levels of 208Tl (<2 μBq/kg) and 214Bi (<10 μBq/kg for 82Se), measured using a dedicated BiPo detector.
• A 100-cell prototype tracker is being developed with automated wiring via a dedicated robot to enable mass production of thousands of drift cells.

Experimental results

Research questions

• RQ1 Can the tracking-plus-calorimetry technique be scaled to 100 kg of enriched isotope while maintaining high energy resolution and background suppression?
• RQ2 What is the optimal combination of scintillator material, block geometry, and PMT characteristics to achieve 4% FWHM energy resolution at 3 MeV?
• RQ3 How can ultra-radiopure source foils be produced and characterized to minimize backgrounds from 208Tl and 214Bi decays?
• RQ4 What is the maximum achievable signal efficiency and background rejection capability using magnetic field-based particle identification and topological reconstruction?
• RQ5 Can a modular design with staged deployment enable early data-taking while achieving the full sensitivity goal by 2015?

Key findings

• The SuperNEMO R&D programme achieved a plasma propagation efficiency of nearly 100% in a 9-cell tracker prototype across the Geiger regime, validating the drift chamber design.
• Initial calorimeter samples demonstrated an energy resolution of ~6.5% FWHM at 1 MeV, approaching the target of 4% FWHM at 3 MeV.
• The BiPo detector prototype successfully measured the signature of 208Tl and 214Bi decays (electron followed by delayed alpha), enabling precise contamination assessment.
• The 4 kg 82Se sample was enriched and purified, and the collaboration is advancing large-scale enrichment of 150Nd via atomic vapour laser isotope separation.
• The tracker design study confirmed that 8–12 ground wires per cell and optimized gas mixtures yield high tracking efficiency and spatial resolution.
• The experiment is projected to reach a neutrino mass sensitivity of 50–90 meV, corresponding to a half-life sensitivity of >2×10^26 years, by 2015.