近期GasPM进展：光反馈抑制与LaB₆光电阴极研究
Recent GasPM advances: photon-feedback mitigation and LaB$_{6}$ photocathode studies
AI总结：
研究通过改进GasPM测试和引入高频数字化器，解决光反馈导致的时间分辨率退化问题，提升光电倍增器性能。
摘要：
我们报告了近期在气体光电倍增器（GasPM）上与束流和宇宙射线的开发和测试情况。GasPM是一种结合了光电阴极和电阻板室的雪崩倍增机制的光电传感器，提供出色的时间分辨率和成本效益的可扩展性。此外，当与辐射体结合时，GasPM能够提供精确且高效的切连科夫基充电粒子识别。我们的主要应用案例旨在升级Belle II探测器以抑制由束流诱导的背景光子，这些光子在非碰撞时间被检测到，会降低电磁量能器的性能。2022年，我们利用皮秒脉冲激光和LaB₆光电阴极实现了25 ps的单光子时间分辨率，3.3 x 10⁶增益。然而，2023年使用电子撞击附着在CsI光电阴极上的MgF₂窗口的束流测试显示时间分辨率恶化至70 ps。本工作旨在解决时间分辨率退化的主要原因。我们主要针对气体分子激发和去激发过程中的紫外光发射，这会导致二次信号与主信号重叠，破坏时间分辨率（光反馈）。我们设计并执行了改进的束流测试。除了几种GasPM配置更改外，我们引入了一种新的10 GSPS频率数字化器，以更好地区分主信号和二次信号，从而能够研究光反馈。我们还进行了一次使用LaB₆光电阴极的宇宙射线测试，该阴极已知具有比CsI更高的电阻，以抵抗离子向光电阴极和空气暴露的反向漂移，以探测量子效率，为即将到来的束流测试做准备。
英文摘要：
We report recent developments and tests with beams and cosmic rays of the gaseous photomultiplier (GasPM). The GasPM is a photosensor that combines a photocathode with the avalanche-multiplication mechanism of a resistive-plate chamber, offering excellent time resolution and cost-effective scalability. In addition, the GasPM provides precise and efficient Cherenkov-based charged-particle identification if combined with a radiator. Our primary use case aims at an upgrade of the Belle II detector to suppress beam-induced background photons, preferably detected off-collision time, that degrade the performance of the electromagnetic calorimeter. In 2022 we achieved a promising single-photon time-resolution of 25 ps at 3.3 x 10$^6$ gain, using a picosecond-pulse laser and a LaB$_6$ photocathode. However, a 2023 beam test with electrons impinging on a MgF$_2$ window attached to a CsI photocathode showed a worsening to 70 ps. This work aims at addressing the principal causes of the time-resolution degradation. We primarily target ultraviolet-photon emission during excitation and de-excitation of the gas molecules, which leads to a secondary signal that overlaps the primary signal, spoiling time resolution (photon feedback). We design and execute an improved beam test. Along with several GasPM configuration changes, we introduce a new 10 GSPS frequency digitizer to better discriminate primary from secondary signals thus enabling the study of photon feedback. We also conduct a cosmic-ray test using a LaB$_6$ photocathode, which is known to have higher than CsI's resistance to ions drifting backwards onto the photocathode and to air exposure, to probe quantum efficiency in view of an upcoming beam test.
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