Search for Precursors to Chiral Transition

本研究的目的是研制一种用于寻找手征跃迁前兆现象的宽立体角γ探测器，并于1997年成功地生长出<12>了目前世界上最大的BSO晶体Bi_2Si_3O_3。然而，已经证明，仍然没有很好地确定如何生长许多大尺寸的晶体而没有问题。第2年度，由于发现在短时间内难以生长出9片大型BSO晶体，因此将研究方向改为PWO晶体。计划在8 GeV电子储存环SPring-8上，利用激光-电子光子束，进行寻找手征跃迁前兆的实验，并需要测量激光-电子光子束中的背景。气体韧致辐射被认为是光束的背景之一。在BL 11 XU光束线上用9个PWO晶体代替BSO测量了韧致辐射谱，同时获得了PWO晶体位置分辨的信息。在最大束流为70 mA时，能量大于1GeV的韧致辐射光子的强度约为600 Hz，8 GeV的韧致辐射光子的尺寸小于0.6mm。

The aim of this research was to develop a small unit of a wide solid angle gamma detector to be utilized in search for precursor phenomena of the chiral transition.We succeeded in growing a large size of a Bismuth Silicate (Bi_2Si_3O_<12>), BSO crystal, in the fiscal year 1997, which was the biggest BSO crystal in the world. It has turned out, however, that it is still not well established how to grow many crystals of a large size without problems. We changed the direction of our research to PWO crystals in the 2nd fiscal year since we found it difficult to grow 9 pieces of large BSO crystals right away.We are planning to make an experiment to search for precursors to the chiral transition by utilizing a laser-electron photon beam at SPring-8, an 8 GeV electron storage ring, And we need to measure the background in the laser-electron photon beam. Gas Bremsstrahlung is thought to be one of the backgrounds in the beam. We measured the spectrum of Bremsstrahlung with 9 PWO crystals, instead of BSO, in the BL11XU beam line and obtained information on the position resolution of the PWO crystals at the same time. We found that the intensity of Bremsstrahlung photons of the energy greater than 1 GeV was about 600Hz at the maximum beam current of 70 mA and also that the size of 8 GeV Bremsstrahlung photons was less than 0.6 mm.