R&D on detector components for rare K+ decay experiment in high intensity beam environment

针对强束背景环境下稀有K ~+衰变实验，我们研制了新的探测器组件：1）在BNL-E949实验的触发系统中，采用了新型的可编程触发板和基于复杂可编程逻辑器件的数字平均定时器模块。通过在可编程触发板上引入片内预分频器，在线死区时间从4.0%降低到1.7%。通过引入平均定时器模块，在线光子否决的接收损耗从4.9%降低到1.8%。2）我们研制了一种基于钨酸铅PbWO_4（PWO）的新型Cherenkov辐射器。研究发现，在PWO中掺入三价稀土离子（La ~（3+），Gd ~（3+），Y ~（3+）等），可以提高PWO的电性能。显著提高了PWO的透光率、抗辐射性和机械性能。在研究三价离子效应的过程中，发现这些离子的重掺杂可以抑制闪烁，从而通过保持良好的透射率、优异的抗辐射性等创造出一种新的切伦科夫辐射器。3）我们开发了一种基于蓝光LED的新型监测系统。该系统被引入到E949实验中，使我们能够观察到光束溢出内的变化。利用新的监测系统的信息，Kpi ~ 2衰变中π（+）的动能分辨率从σ =3.246MeV提高到σ = 3.042MeV。4）我们研制了一个灵敏面积为92 × 92 mm**2的单面硅条探测器，作为强束本底环境下稀有K ~+衰变实验的实时、快速、中等分段速迹仪。等效噪声电荷（ENC，1 sigma）输入端为~ 1600 e（单个最小电离粒子信号的6%~ 27000 e）。

We have developed new detector components for rare K+ decay experiment to cope with high beam background environment:1)A new programmable trigger board and digital mean-timer modules using complex programmable logic device have been introduced to the trigger system of the BNL-E949 experiment. The online dead time was reduced from 4.0% to 1.7% by introducing an on-chip prescaler to the programmable trigger board. The acceptance loss of the online photon veto was reduced from 4.9% to 1.8% by introducing the mean-timer modules.2)We have developed a new heavy (XO=0.89cm) and radiation-hard (10**8 rad) Cherenkov radiators based on lead tungstate PbWO4 (PWO). We have found that doping PWO with trivalent rare-earth ions (La3+,Gd3+,Y3+,etc.) improves the characteristics of PWO dramatically including the transmittance, radiation-hardness and mechanical quality. In the course of studying the effects of trivalent ions, it has been found that heavy doping of these ions quenches the scintillation, thereby creating a new Cherenkov radiator by keeping good transmittance, excellent radiation-hardness, etc.3)We have developed a new monitoring system based on blue LED's. The system was introduced, to the E949 experiment, and enabled us to observe a variation within the beam spill. The kinetic-energy resolution of pi(+) in Kpi2 decay was improved from sigma=3.246MeV to sigma= 3.042MeV by using information of the new monitoring system.4)We have developed a single-sided silicon strip detector with a sensitive area of 92 x 92 mm**2 as a real-time, fast and medium-segmented hodoscope for rare kaon decay experiments in high beam background environment. The Equivalent Noise Charge(ENC, 1 sigma) at the preamplifier input was ~1600e (6% of the signal for single minimum ionizing particle ~27000e).