Abstract
Automatic nuclear emulsion readout systems have seen remarkable progress since the original idea was developed almost 40 years ago. After the success of its full application to a large-scale ...neutrino experiment, OPERA, a much faster readout system, the hyper-track selector (HTS), has been developed. HTS, which has an extremely wide-field objective lens, reached a scanning speed of 4700 cm$^2$/h, which is nearly 100 times faster than the previous system and therefore strongly promotes many new experimental projects. We will describe the concept, specifications, system structure, and achieved performance in this paper.
A
bstract
In the DsTau experiment at the CERN SPS (NA65), an independent and direct way to measure tau neutrino production following high energy proton interactions was proposed. As the main source ...of tau neutrinos is a decay of
D
s
mesons, produced in proton-nucleus interactions, the project aims at measuring a differential cross section of this reaction. The experimental method is based on a use of high resolution emulsion detectors for effective registration of events with short lived particle decays. Here we present the motivation of the study, details of the experimental technique, and the first results of the analysis of the data collected during test runs, which prove feasibility of the full scale study of the process in future.
Abstract
We are developing the Gamma-Ray Astro-Imager with Nuclear Emulsion project, designed for 10 MeV–100 GeV cosmic
γ
-ray observations with a high angular resolution (5′/0.°08 at 1–2 GeV) and a ...polarization-sensitive large-aperture (∼10 m
2
) emulsion telescope for repeated long-duration balloon flights. In 2018, a balloon-borne experiment was carried out in Australia with a 0.38 m
2
sensitive area and a flight duration of 17.4 hr, including 6.7 hr of Vela observations. Significant improvements compared with the 2015 balloon-borne experiment were achieved by a factor of 5, including both an increase in effective area × time and a reduction in the background contribution. We aimed to demonstrate the telescope’s overall performance based on detection and imaging of a known
γ
-ray source, the Vela pulsar. A robust detection of the Vela pulsar was achieved with a 68% containment radius of 0.°42, at a significance of 6
σ
, at energies above 80 MeV. The resulting angular profile is consistent with that of a pointlike source. We achieved the current best imaging performance of the Vela pulsar using an emulsion
γ
-ray telescope with the highest angular resolution of any
γ
-ray telescope to date.
One of the key challenges for muographic studies is to reveal the detailed
3D density structure of a volcano by increasing the number of observation
directions. 3D density imaging by ...multi-directional muography requires that
the individual differences in the performance of the installed muon
detectors are small and that the results from each detector can be derived
without any bias in the data analysis. Here we describe a pilot muographic
study of the Izu–Omuroyama scoria cone in Shizuoka Prefecture, Japan, from
11 directions, using a new nuclear emulsion detector design optimized for
quick installation in the field. We describe the details of the data
analysis and present a validation of the results. The Izu–Omuroyama scoria cone is an ideal target for the first
multi-directional muographic study, given its expected internal density
structure and the topography around the cone. We optimized the design of the
nuclear emulsion detector for rapid installation at multiple observation
sites in the field, and installed these at 11 sites around the volcano. The
images in the developed emulsion films were digitized into segmented tracks
with a high-speed automated readout system. The muon tracks in each emulsion
detector were then reconstructed. After the track selection, including
straightness filtering, the detection efficiency of the muons was estimated.
Finally, the density distributions in 2D angular space were derived for each
observation site by using a muon flux and attenuation models. The observed muon flux was compared with the expected value in the free sky,
and is 88 % ± 4 % in the forward direction and 92 % ± 2 % in the backward direction. The density values were validated by
comparison with the values obtained from gravity measurements, and are
broadly consistent, except for one site. The excess density at this one site
may indicate that the density inside the cone is non-axisymmetric, which is
consistent with a previous geological study.
Abstract
To recognize sub-micron-range low-energy tracks recorded in a super-fine-grained nuclear emulsion (Nano Imaging Tracker), an elliptical fitting method was devised to analyze anisotropic ...images taken by an optical microscope. We report on this newly developed method using a discrete Fourier transform and second-order moment analysis of the brightness distribution. We succeeded in lowering the ellipticity threshold, thereby improving the selection efficiency and angular resolution. Notably, the success of detecting carbon 30 keV tracks is the first such achievement in the world, where the incident direction of carbon 30 keV ions was determined with an accuracy of 41$^\circ$ and an efficiency of $1.7 \pm 0.1\%$.
Abstract
The Gamma-Ray Astro-Imager with Nuclear Emulsion (GRAINE) project is aimed at the precise observation of astronomical gamma-ray sources in the energy range of 10 MeV–100 GeV using a ...balloon-borne telescope utilizing a nuclear emulsion, which can help realize precise imaging with high angular resolution (1.0○ at 100 MeV), polarization sensitivity, and large aperture area (10 m2). In 2018, the third balloon experiment was carried out as a demonstration of the detection of the brightest known astronomical gamma-ray source, the Vela pulsar, with an aperture area of 0.38 m2. In these data, some gamma rays were produced by the π0 → 2γ decay, which was caused by the hadronic interactions of cosmic rays in the detector. These could be used to calibrate the reconstructed angle, energy, and so on. In this study, we establish a method of searching for hadronic interactions and concomitant gamma rays with high statistics and purity. Our analysis indicates that the performance of our detector for gamma rays is as expected in wide incidence angle and energy ranges. We plan to commence scientific observations using the proposed system with the verified high angular resolution and largest aperture area in 2022 or later.
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