Speaker
manami fujita
(tohoku Univ)
Description
Studying hyperon-nucleon interaction is necessary for more general understanding of nuclear force. We can extend the NN interaction with the isospin SU(2) symmetry to the baryon-baryon interactions with the flavor SU(3) symmetry. For the S=-2 sector, however, experimental data are very limited. Especially there are almost no data for the ΞN interaction. To investigate the S=-2 systems, we performed the J-PARC E07 experiment for double-Λ hypernuclear search and Ξ$^-$ atom X-ray measurement.
The level energies of Ξ$^-$ atoms may shift from those with only electromagnetic interaction considered because they are affected by strong interaction between a Ξ$^-$ and nucleons. From the shift and the energy width of X-ray peaks, it is possible to extract information on the Ξ$^-$ nuclear potential. The wave function of the Ξ$^-$ particle and the Ξ$^-$ potential overlap mainly at the surface of the nucleus. Therefore, Ξ$^-$ atom X-ray spectroscopy is one of the most effective methods to investigate the shape of the potential near the nuclear surface.
In 2016 and 2017, we successfully performed the experiment using a hybrid emulsion method at the J-PARC K1.8 beam line. Ξ$^-$s were produced in a diamond target following the p(K$^-$, K$^+$)Ξ$^-$ reaction. We measured time and position of the Ξ$^-$ production using a magnetic spectrometer (KURAMA) and Silicon Strip Detectors (SSD). The former identified the reaction, while the SSD information helped to reconstruct the Ξ$^-$ track. This method, so called hybrid emulsion method, drastically reduces the time for analyzing emulsion tracks. Some of the stopped Ξ$^-$s are captured by atoms contained in emulsion such as Ag and Br. We measured the X rays with a Ge detector array, Hyperball-X. In this experiment, energy resolution of each Ge detectors was about 2 keV (FWHM) for 300-keV gamma ray. The energy shift predicted by theoretical calculations is from 0.3 to 5 keV. In Ag case, the X-ray yield is expected to be as little as ∼30 counts in total. In addition, events in which Ξ$^-$ decays inflight become background for the X-ray spectra. However, the stopped and absorbed Ξ$^-$ events can be identified by combining analysis of emulsion image, and thus we can obtain almost background free X-ray spectra. If successful, this will be the first observation of the Ξ$^-$ atom X rays.
At the present, the candidate Ξ$^-$ stop events have been selected using only the spectrometers and SSD information. At the same time, the emulsion analysis is underway. I will report on the current analysis of the Hyperball-X data. I also mention the other Ξ$^-$ atom X-ray spectroscopy (J-PARC E03).
Primary author
manami fujita
(tohoku Univ)
