Speaker
Mr
Hiroyuki Ekawa
(Kyoto University)
Description
Understanding of baryon-baryon interaction is one of the main topics in hadron physics.
In comparison with $S=0$ and $-1$, experimental data of $S=-2$ system is very limited.
Hyperon - hyperon interaction is especially difficult to study because of their short life-times.
Therefore, double hypernuclei, which include two $\Lambda$ hyperons in a nucleus, play an important role
to investigate $\Lambda \Lambda$ interaction.
Binding energy of double hypernuclei gives us the information of $S=-2$ state in nuclei.
Emulsion experiment is effective to study double hypernuclei because it can
detect their sequential weak decays with sub-$\mu\mathrm{m}$ resolution.
Several experiments were performed and a double hypernucleus was uniquely identified as
$^{\;\>6}_{\Lambda\Lambda}\mathrm{He}$ in KEK E373 experiment (NAGARA event).
Its binding energy ($B_{\Lambda\Lambda}$) and $\Lambda\Lambda$ interaction energy ($\Delta B_{\Lambda\Lambda}$)
were measured as $6.91 \pm 0.16$ MeV and $0.67 \pm 0.17$ MeV, respectively.
New experiment has been awaited to observe more double hypernuclei
for systematic analysis of $\Lambda\Lambda$ interaction.
J-PARC E07 experiment is a upgraded double hypernuclei search experiment with a hybrid emulsion method.
Double hypernuclei are generated by $\Xi^{-}$ captured at rest in nuclei in an emulsion layer.
$\Xi^{-}$ hyperons are produced in quasifree $p(K^{-}, K^{+})\Xi^{-}$ reaction at a diamond target
and enter an emulsion module.
Then SSDs (silicon strip detectors) placed upstream of an emulsion module record $\Xi^{-}$ tracks
with $15 \mu\mathrm{m}$ resolution to predict $\Xi^{-}$ positions and angles on the emulsion surface.
By combining spectrometer and emulsion analysis, $\Xi^{-}$ captured points are searched for effectively.
The E07 experiment aims at accumulating 10 times higher statistics of double hypernuclei
than that for the KEK-E373 experiment.
Out of $10^{4}$ $\Xi^{-}$ captures, one hundred double hypenuclei would be observed,
and ten double hypernuclear elements are clearly identified.
This experiment was carried out in 2016 and 2017.
118 modules of emulsion sheets have been exposed by $K^{-}$ beam and
photographic development have been completed.
$\Xi^{-}$ tracks are identified by KURAMA spectrometer analysis to be searched in emulsion sheets.
$10^{4}$ $\Xi^{-}$ captures are expected by considering $\Xi^{-}$ stopping ratio in simulation.
Emulsion scanning with microscope systems to follow $\Xi^{-}$ tracks is ongoing.
The current analysis result of KURAMA spectrometer and emulsion will be reported in this talk.
Primary author
Mr
Hiroyuki Ekawa
(Kyoto University)
Co-authors
E07 collaboration J-PARC
(J-PARC)
Dr
Junya Yoshida
(Advanced Science Research Center, JAEA)
Prof.
Kazuma Nakazawa
(Gifu University)
Dr
Masahiro Yoshimoto
(Gifu University)
Mr
Shuhei Hayakawa
(Osaka University)
Dr
Yudai Ichikawa
(Japan Atomic Energy Agency)
manami fujita
(tohoku Univ)
