A test of QCD at low energy

DIRAC experiment （PS212） aims to measure the？etime of？+？^- atoms using 24 GeV proton beam provided by the CERN PS。对生命周期可行性的精确测量，以确定一种独立的方式S-wave Pion-Pion散射长度。π散射长度被计算为指手性渗透理论的精确度为5%，在DIRAC实验的开始阶段。现在，计算的精确度比2.5%好。这项研究的结果是基于一个固有的手性对称性破坏到一个强夸克条件的假设。因此，将理论价值与一个实验提供的机会进行精确比较，以证实QCD中当前的手性对称性破坏，并检查夸克条件的强度。我们分析了收集到的数据的30%，并根据寿命计算为τ = [2.91+0.49-0.62] X10 ^<-15> s。这是对散射长度的终生对应|A0和A2| = 0.264+0.033·0.020 m_\^\-1\。在这个DIRAC实验中，日本小组开发了一个拓扑触发器设备，包括闪烁光纤覆盖（SFD）、峰值感应电路（PSC）、ADC/TDC混合读写电路（F1）和触发逻辑电路（TLC）。They can select out online a real\^+\^- pair due to a dissociation of\^+\^- atom from a huge am\of background events。作为DIRAC实验的第二阶段，我们衡量π K原子的一生。For the？K measurements more than ten time intense beam than the？^+？^- measurement is？ed。我们开发了一种新的高分辨率扫描纤维光镜（HRH），由480个280微米精细纤维和30个多阳极照片倍增器组成，配有16个通道。We found that the HRH has an excellent spatial resolution of 75μm and a time resolution of 0.56 ns in rms。

The DIRAC experiment (PS212) aims to measure the lifetime of π+π^- atoms using 24GeV proton beam provided by the CERN PS. The precise measurement of the lifetime enables to determine an s-wave pion-pion scattering length in a model independent way. The ππ scattering length has been calculated by means of Chiral perturbation theory with a precision of 5% at the starting stage of the DIRAC experiment. Now the precision of the calculation is better than 2.5%. The results are based on the assumption of a spontaneous chiral symmetry breaking due to a strong quark condensation. Therefore, a precise comparison of the theoretical value with the experimental one provides an opportunity to verify the current understanding of chiral symmetry breaking in QCD and to check the magnitude of the quark condensation.We analyzed 30% of the collected data and deduced the lifetime as τ = [2.91+0.49-0.62] X 10^<-15> s. This lifetime corresponds to the scattering length |a0・a2| = 0.264+0.033・0.020m_π^<-1>. The errors are mostly due to statistics.In this DIRAC experiment, Japan group has developed a topological trigger device consisting of scintillating-fiber hodoscopes(SFD), peak-sensing circuits(PSC), ADC/TDC hybrid read-out circuits(F1) and trigger logic circuits(TLC). They can select out online a real π^+π^- pair due to a dissociation of π^+π^- atom from a huge amount of background events. As the second stage of the DIRAC experiment we measure a lifetime of πK-atoms. For the πK measurements more than ten time intense beam than the π^+π^- measurement is required. We developed new high resolution scintillating fiber hodoscopes(HRH) consisting of 480 column made of 280μm fine fibers and 30 multi-anode photo multipliers with 16 channels. We found that the HRH has an excellent spatial resolution of 75μm and a time resolution of 0.56ns in rms.