Hypernuclear study at Φ-Factoy

利用意大利DAFNE Φ-Factory的FINUDA探测器系统，在2003年10月至2004年3月的快速数据采集期间，积累了^6Li、^7Li、^<12>C、^<27>Al和^<51> V靶的超核数据，并如期交付了250 pb^<-1>的综合亮度。由ΦK^-K^+衰变产生的几乎单色的16 MeV K束在极薄（~ 200 mg/cm^2）靶中停止。所有的数据都被带回日本，由意大利合作者独立分析。每个探测器的校准工作正在进行中。虽然定标室的位置分辨率仍未达到最佳值，但K_<μ2>和K_<π2>衰减对应的定标峰给出了正确的动量和较好的动量分辨率。我们希望在未来的分析中，分辨率可以进一步提高。对于（K^-_<stop>,π^-）反应谱，我们得到了^<12>_ΛC激发能谱，能量分辨率为1.45 MeV FWHM。这是迄今为止世界上实现的最佳能源分辨率。首次观察到一些峰状结构。即使对于较重的目标，也能在限定区域内观察到事件。我们期望在未来的分析中解决几个激发态。利用π^-中间质子的质量分布，在FINUDA探测器上成功探测到（K^-_<stop>,π^-）反应中的Λ超子。此外，我们还观察到一个Λ超子伴随着一个质子在背对背方向发射。Λ-proton对的不变质量分布表明它们来自于K_-pp束缚体系。该体系的结合能为~ 115 MeV。与正常的核结合相比，该值非常大，可能暗示系统中可能形成高密度的核环境。通过标记来自强转换过程ΣN→ΛN的Λ超子，也搜索了Σ超核的产生。

The hypernuclear data on ^6Li, ^7Li, ^<12>C, ^<27>Al, and ^<51> V targets were accumulated during the fast data taking period from October 2003 to March 2004 with the FINUDA detector system at the DAFNE Φ-Factory in Italy The integrated luminosity of 250 pb^<-1> was delivered as scheduled. Almost mono-chromatic K- beam at 16 MeV produced from the ΦK^-K^+ decay was stopped in the very thin (〜200 mg/cm^2) targets. All the data were brought back to Japan and analyzed independently from the Italian collaborators. Calibrations for each detector have been in progress. Although the position resolutions of the tiadking chambers are still not at the optimum values, the calibration peaks corresponding to the K_<μ2> and K_<π2> decays gave us the correct momenta and reasonably good momentum resolutions. We expect the resolution could be further improved in the future analysis. As for the (K^-_<stop>,π^-) reaction spectroscopy, we have obtained ^<12>_ΛC excitation energy spectrum with the energy resolution of 1.45 MeV FWHM. This is as good as so-far the best energy resolution achieved it the world. A few peak structures were observed for the first time. Even for the heavier targets, events were observed in the bound region. We expect several excited states to be resolved in the future analysis.Λ hyperons in the (K^-_<stop>,π^-) reactions were successfully detected in the FINUDA detector from the invariant mass distribution of proton mid π^-. Further we have observed a Λ hyperon accompanied by a proton emitted in the back to-back direction. The invariant mass distribution of the Λ-proton pair indicates that they are coning out from a K_-pp bound system. The binding energy of the system was found to be〜115 MeV. This value is very large as compared to the normal nuclear binding and might imply a possible formation of high density nuclear environment in the system. Production of Σ hypernuclei was also searched by tagging the Λ hyperon from a strong conversion process ΣN→ΛN.