Study of K^+ meson production with electromagnetic probes

人们一直认为，对K^+在核上光生的实验观测是对强子探测的补充，可以用来研究超核谱学和核奇异性。与其他可能的反应相比，（γ，K^+）反应在研究核奇异性方面的一个优势是γ和K^+在核物质中的平均自由程相对较长。这一特性使我们能够在较小的形变下研究核子和超子在核内部的行为。与（γ，K^+）反应具有相同运动学条件的（pi^+，K ^+）反应建立了LAMBDA超核的壳层结构。这些强子探测的成果必须与（gamma，K^+）和（e，e 'K ^+）反应的电磁过程结合起来，才能得到对超核和核奇异产生的统一认识。由于缺乏合适的实验设备，一直没有在核上进行K ~+的光生实验。CEBAF的项目将在 ...更多信息 对^<12>C（γ，K^+）反应的测量是利用东京大学原子核研究所1.3 GeV电子同步加速器上的标记光子装置进行的。从同步加速器中提取的1.2GeV电子束被引入光子标记系统，占空比为10%。用一套能量分辨率为10 MeV的32通道示踪示波器对能量范围为0.7- 1.1GeV的光子束进行了示踪，用基于TAGX系统的磁谱仪测量了带电粒子事例。安装了快速触发计数器和TOF墙以识别领先粒子。采用两套空间分辨率为1 mm的硅条探测器（SSD）来提高跟踪分辨率。K^+事件由质谱选择。π介子和质子事件的污染估计小于5%。获得^<12>C（γ，K^+）截面（初步）。与p（gamma，K^+）截面进行了比较。由于<gamma>K^+产额对E_的依赖性与基元过程的依赖性相似，因此准自由过程被认为是主导过程。推导<eff>出参与^<12>C（γ，K^+）反应的有效质子数N =3.5。与~（12<eff>）<12>C（pi，K^+）反应得到的N_（1.7）相比，光-K ~（12）过程是研究原子核内部的一个很好的探针。少

Experimental observations of K^+ photoproduction on nuclei to study hypernuclear spectroscopy and the nuclear strangeness have been considered complementary to that of hadronic probes. An advantage of the (gamma,K^+) reaction compared with other possible reactions in studying the nuclear strangeness is on relatively long mean-free path of gamma and K^+ in the nuclear matter. This feature makes us possible to study the behavior of nucleons and a hyperon in the nuclear interior with less deformation. The (pi^+,K^+) reactions, which are same kinematical condition as the (gamma,K^+) reaction, have established shell structure of the LAMBDA hypernuclei. These achievements done by the hadronic probes must be joined with the electromagnetic process of (gamma,K^+) and (e,e'K^+) reactions to get the unified recognition of the hypernuclei and the nuclear strangeness production. Kaon photoproduction on nuclei has not been done because of lack of the suitable facilities. The project of CEBAF will p … More ermit the detailed exploration of the nuclear strangeness in a few years.The measurement of the ^<12>C(gamma,K^+) reaction was carried out by using the tagged photon facilities at the 1.3 GeV electron synchrotron of the Institute for Nuclear Study, University of Tokyo. The 1.2 GeV electron beam extracted from the synchrotron was introduced to the photon tagging system with a duty factor of 10%. Photon beam in an energy range of 0.7-1.1 GeV were tagged by a set of 32ch tagging hodoscopes with an energy resolution of 10 MeV.The events of charged particles were measured by the magnetic spectrometer based on the TAGX system. Fast trigger counters and a TOF wall were installed to identify the leading particles. Two sets of the Silicon Strip Detectors (SSD) with lmm spatial resolution were used to improve the tracking resolution. The K^+ events were selected by the mass spectrum. Contaminations of the pion and proton events are estimated less than 5%. Obtained ^<12>C(gamma,K^+) cross section (preliminary). was compared with the p(gamma,K^+) cross sections. Since the E_<gamma> dependence of the K^+ yield behaves similar to that of the elementary process, the quasi-free process is considered to be dominant. The effective proton number N_<eff>=3.5, which is the number of the participating protons in the ^<12>C(gamma,K^+) reaction have been deduced. Comparing with the N_<eff>=1.7, which was obtained by ^<12>C(pi,K^+) reaction, the photo-Kaon process can be recognized a good probe to investigate the inside of nuclei. Less