Speaker
Dr
Masahiro Yoshimoto
(Gifu University)
Description
Nuclear emulsion is a tracking detector with sub-micron spatial resolution.
The nuclear emulsion has a potential to measure binding energies of mirror hypernuclei such as $_{\Lambda}^{4}$H and $_{\Lambda}^{4}$He directly.
The binding energies provide valuable information for charge symmetry braking (CSB) in $\Lambda$-N interaction.
In the nuclear emulsion experiment in the 1960s and 1970s, the binding energies of light hypernuclei were measured.
For example, the difference of binding energy of mirror hypernuclei ($_{\Lambda}^{4}$He$-_{\Lambda}^{4}$H) was measured as +0.35$\pm$0.04 MeV.
Analysis of the nuclear emulsion plate for hypernuclei experiment is performed by the following method.
We search for hypernuclei events and measure the range and angle of these tracks with high positional and angular accuracy.
In the past experiments, the range and angle were measured manually.
From the 1970s, microscopic images were read out from the image sensor and displayed on the CRT.
An automated stage was developed to move the nuclear emulsion plate to a specific coordinate.
These developments greatly shortened the analysis time.
In the 2010s, with the development of computer graphics technology, the selection of events with a vertex, which is a characteristic of hypernuclei events, has been automated.
This read-out system, called Vertex-Picker, achieved a read-out speed (volume per hour) of 100 times compared to the previous manual search.
In addition, an automated track following method have been developed instead of following manually.
These developments increased the number of hypernuclei events dramatically.
KEK-PS E373 experiment, that is a hypernuclei experiment with nuclear emulsion, was conducted in 1999.
The few double hypernuclear events identified so far showed that the $\Lambda$-$\Lambda$ interaction is a weak attractive interaction.
The J-PARC E07 experiment, which is the latest hybrid emulsion experiment, is expected to increase the number of double hypernuclei by a factor of 10 as compared to the E373 experiment.
The exposure with a 1.8 GeV/c K$^-$ beam was completed in July 2017, the photographic development was completed in February 2018, and the analysis of the nuclear emulsion is currently carried out.
We also search the whole volume of this nuclear emulsion for hypernuclei event candidates (with two vertexes) using the Vertex-Picker.
In this talk, I will report the summary of past experiments, the development of recent emulsion technology, and the expected outcome on CSB from E07 experiment.
Primary author
Dr
Masahiro Yoshimoto
(Gifu University)
Co-authors
J-PARC E07 collaboration
(J-PARC)
Dr
Junya Yoshida
(Advanced Science Research Center, JAEA)
Kazuma Nakazawa
(Gifu University)
