Speaker
Dr
Takeshi Yamamoto
(KEK IPNS)
Description
The charge symmetry breaking (CSB) effect reported in the A=4 mirror hypernuclei
is one of the hot topics in strangeness nuclear physics.
Precise gamma-ray spectroscopy with an energy resolution of a few keV
is a powerful tool to investigate such an effect.
Recently, a gamma-ray spectroscopy study of $^4_{\Lambda}$He was performed
at the J-PARC K1.8 beam line (J-PARC E13) for this purpose.
$^4_{\Lambda}$He hypernuclei were produced by the $(K^-,\pi^-)$ reaction
with a 1.5 GeV/$c$ kaon beam.
The excitation energy of first excited state of $^4_{\Lambda}$He(1$^+$)
was successfully determined to be 1.406$\pm $0.004 MeV.
On the other hand, that of the mirror hypernucleus ($^4_{\Lambda}$H)
was reported as 1.09$\pm $0.02 MeV in average from old studies.
By comparing these results,
we conformed the existence of CSB effect in the excitation energy.
Reported values of the excitation energy ($E_x [^4_{\Lambda}$H(1$^+$)])
in old studies show rather large deviation.
In these measurements,
the energy accuracy was limited by statistics and
the gamma-ray response function including the resolution as well as the Doppler broadening effect.
Therefore, our next step is a more precise measurement
of the excitation energy of $^{4}_{\Lambda}$H($1^{+}$)
to experimentally establish the A=4 mirror hypernuclei system.
We are planing a gamma-ray spectroscopy of $^4_{\Lambda}$H
at the J-PARC K1.1 beam line (J-PARC E63) via the $^7$Li$(K^-,\pi^-)$ reaction.
We selected the SKS spectrometer system for tagging the reaction,
which is common with the previous J-PARC E13.
The gamma-ray energy will be measured with a Ge detector array, Hyperball-J,
of which performance was already established.
An outline of the J-PARC E63 experiment will be given in this contribution.
Primary author
Dr
Takeshi Yamamoto
(KEK IPNS)
