Speaker
Dr
Takeshi Koike
(Tohoku University)
Description
In 2015, the first hypernuclear gamma-ray spectroscopy experiment at J-PARC has been completed. In this experiment (J-PARC E13), K- beams of 1.5 GeV/c and 1.8 GeV/c are transported through the K1.8 beam line and delivered to a liquid hydrogen target and liquid CF4 target, respectively, to populate $^4_{\Lambda}$H and $^{19}_{\Lambda}$F. In the first half of this contribution, some of the results from the E13 experiment will be highlighted. From the precise determination of the spin-flip gamma transition from the first excited 1$^+$ state to the 0$^+$ ground state, a sizable charge symmetry breaking effect in ${\Lambda}$N interaction in comparison to NN interaction has been experimentally confirmed, which awaits full theoretical explanation to this day. On the other hand, low-lying energy levels of sd-shell $^{19}_{\Lambda}$F are identified. In particular, the energy splitting of the ground state spin doublet is determined providing the first look into the strength of spin-spin ${\Lambda}$N interaction in the sd-shell sector.
The second half of the presentation pertains the future gamma-ray spectroscopy experiments at J-PARC, namely the last phase of the E13 experiments with some twist. The planned experiment (J-PARC E63) will take place at the K1.1 beam line with a setup almost identical to that for E13. $^7_{\Lambda}$Li will be populated for lifetime measurement of the gorund state spin-doublet transition, from which a B(M1) value should be extracted and eventually leads to g-factor of ${\Lambda}$ in nuclear medium. Another objective of E63 is to determine the energy spacing of the ground state spin doublet in $^4_{\Lambda}$H, mirror hypernucleus to $^4_{\Lambda}$He. The new measurement will establish the A=4 hypernuclear system on more experimentally solid ground for the investigation into the origin of the large charge symmetry breaking in ${\Lambda}$N interaction. An overview of the current preparation status of the E63 experiment will be discussed.
Primary author
Dr
Takeshi Koike
(Tohoku University)
