R&D Status of Nuclear Emulsion For Directional Dark Matter Search

TL;DR

This paper reports on the development of high-resolution nuclear emulsion techniques for directional dark matter detection, including new readout methods and microscopy systems that improve angular resolution.

Contribution

Development of a novel nuclear emulsion with enhanced resolution and new optical and X-ray microscopy techniques for directional dark matter search.

Findings

Achieved 36-degree angular resolution with optical microscopy.

Improved to 17-degree resolution using X-ray microscopy.

Confirmed detection of nuclear recoil tracks induced by neutrons.

Abstract

In this study, we are doing R&D for directional dark matter search with nuclear emulsion. First of all, higher resolution nuclear emulsion with fine silver halide crystals was developed in the production facility of emulsion at Nagoya university, and we confirmed that it can detect the expected nuclear recoil tracks. The readout of submicron tracks was required the new technology. We developed the expansion technique, and could readout the signal by shape analysis with optical microscopy. The two dimensional angular resolution is 36 degrees at the original track length of range from 150nm to 200nm with optical microscopy. Finally we demonstrated by using recoiled nuclei induced by 14.8MeV neutron, and confirmed the technique.Moreover, we developed the X-ray microscope system with SPring-8 as final check with higher resolution of selected candidate tracks with optical microscopy. The angular resolution was improved from 31 degrees with optical microscopy to 17degrees with X-ray microscopy at the track length of range from 150nm to 250nm. We are developing the practical system and planning for start of the test running with prototype detector.