Yoko Endo

Isotope Identification in Nuclear Emulsion Plate

We carried out the E373 experiment at KEK and detected seven double- hypernuclear events. Only the NAGARA event was uniquely identified as a   He hypernucleus among them. For some events among the other six events, unique interpretation of the nuclide would be possible if one of daughter particles from production or decay vertex was identified uniquely. In order to obtain more information about the -interaction we planned to detect about one hundred double- hypernuclei in the J-PARC E07 experiment, and obtain new knowledge for the -interaction, which is independent of the information obtained from the NAGARA event. To study the -interaction with more nuclei which are uniquely assigned, we are developing a particle identification (PID) method which identified daughter isotopes by the measurement of energy losses in the emulsion. Track width which reflects energy-losses will be measured from stopping point up to ~100m with an image processing method. Under the assumption of tracks to be made of many cylinders with length of 1 μm, track volume values given by the width are summed up and expected to distinguish light nuclear species such as H, He, Li, Be or B.

Track Following of Ξ− Hyperons in Nuclear Emulsion for the E07 Experiment

The E07 experiment is expected to provide knowledge of S=-2 systems with ten times more statistics than that of the past E373 experiment. To achieve this in a reasonable time, an automated track following system is very important. This system consists of three techniques, “emulsion surface detection”, ”alignment of plate by plate connection with K beams” and “followed track recognition in nuclear emulsion”. Ξ hyperon candidate tracks are followed from the entrance to the end point in the emulsion. If the system operates properly such that one track is processed in each plate within one minute, all Ξ candidate tracks can be followed successfully to their stopping points in a year. The development of softwares for the system is ongoing.

Mass Production of Large-sized Nuclear Emulsion Plates for J-PARC E07

In the E07 experiment at J-PARC, we systematically study double strangeness (S = -2) systems on Λ-Λ and Ξ-N interaction via S = -2 nuclei such as double Λ hypernuclei and twin Λ hypernuclei with hybrid-emulsion method. The number of S = -2 nuclei is planned to be about 10 which is 10 times or more events than that of the E373 experiment at KEK-PS. We have to prepare for large-scale emulsion plates by huge amount of emulsion gel with weight of 2.1 t, which is about 3 times’ quantity used for E373. To make it possible, we have developed methods for treatment of supporting films and for making emulsion plates. We have successfully produced 1500 plates.

Single Charged Particle Identification in Nuclear Emulsion Using Multiple Coulomb Scattering Method

In J-PARC E07 experiment, emulsion experiment for double strangeness system, particle identification is an important aspect to purify Ξ stop events. Through the experiment, we expect Ξ stop event with ten time higher statistics than that of previous experiment (KEK PS-E373). Ξ stop events which include doubleΛ hypernucleus, twinΛ hypernuclei and so on give us important information such as Λ-Λ and Ξ-N interaction. Besides, Ξ stop events are interesting itself because experimental data aboutΞ stop is very few. We are developing a PID technique for single charged particles having low momentum using by “Second difference” reflecting Multiple Coulomb Scattering. A charged particle moving in nuclear emulsion is deflected by many small-angle scatters due to Coulomb interaction, depends on the momentum of the particle. It is possible to discriminate the mass of a particle by evaluating the behavior of scattering near stopping point. We introduce “Second difference”, i.e. δ plane, defined as in Fig. (1), and intend to use its distribution as Probability Distribution Functions for likelihood method. We performed Geant4 simulation and obtained the second differences of several hundred of tracks for various single charged particles in emulsion. Fig. (2) shows their geometric mean distributions of among 0.2mm-2.0mm range. It is promising in the separation of single charged unknown particles in emulsion.

Event Analysis in Nuclear Emulsion for the E07 Experiment at J-PARC

Hammer track events in nuclear emulsion were analyzed to measure the excitation energy of 8Be* (2+) nucleus. The kinetic energies of two alpha particles of hammer track events were obtained from their ranges with use of range-energy relation. The range-energy relation was calibrated by measuring the alpha particle tracks emitted from 212Po of Thorium decay series in the emulsion. From this calibration, we obtained density and shrinkage factor of the emulsion. The excitation energy and width of 8Be* (2+) nucleus were measured to be 3.39 ± 0.24 MeV and  = 1.22 ± 0.60 MeV respectively.

Development of Automatic Alpha-Decay Track Measurement

For analysis of double- hypernucleus in nuclear emulsion, it is necessary to know shrinkage factor and density of emulsion plate by measuring the track ranges of alpha particles. The kinetic energies of nuclear fragment from double- hypernucleus are measured by their ranges in the emulsion, which is dedicated photographic emulsion for nuclear physics. Then we have to reconstruct their original ranges since the emulsion plate shrinks about half in thickness after development. Besides, we have to calibrate range-energy relation because the density depends on the emulsion content of moisture. Therefore we use alpha-rays with monochromatic energy as calibration sources which were emitted from natural RI such as Thorium series in the emulsion. Technique which performs alpha-tracks measurement by image processing is being studied. In the E07 experiment at J-PARC [1], quick analysis is required for about 10 4 alpha tracks on about 100 double- hypernuclear events within a few years. At present, we are developing automated range measurement technique instead of traditional manual measurement. Alpha tracks are seen as black, bold lines in micrographs as shown in Fig.1 and 2. Image processing program detects such lines and the positions, angles, ranges of them in micrographs.

Overall Scanning Method for the J-PARC E07 Experiment

A new scanning method named “Overall scanning” will be applied for J-PARC E07’s emulsion plates to collect alpha decays which are calibration sources for range-energy relation in emulsion, rapidly. We carried out an operation of alpha search with current Overall scanning technology by E373’s emulsion. About 100 alpha rays were selected and measured in 17 days in 30mm*110mm*0.45mm volume of the plate with less man-power than before. Development of advanced image process and scanning software is on-going for speeding up. Besides, Overall scanning method will be applied to search for more events after regular analysis with hybrid method.