Development of the TORCH Time-of-Flight Detector

该提案描述了一项为期两年的研究和开发计划，旨在开发一种名为TORCH的飞行时间（ToF）探测器，用于未来的粒子物理实验。TORCH使用一种新颖的技术来测量通过它的带电粒子的到达时间。由于ToF与粒子的速度成正比，粒子的类型（介子、质子或介子）可以通过粒子的动量来确定，动量是通过粒子在实验磁场中的弯曲来测量的。TORCH使用10毫米厚的石英作为切伦科夫光的光源。当带电粒子穿过介质时，当粒子的速度超过介质中的光的速度时，光子就会发射出来。在石英板中辐射的光子通过全内反射传播到石英板的上边缘，然后聚焦到微通道板（MCP）光子探测器阵列上。每个轨道的ToF分辨率将超过15 ps，这将导致pi/K/p粒子分离的动量高达10 GeV/c甚至更高。TORCH模块将由石英散热器条和聚焦块构成，MCP探测器将安装在其上。然后，该模块将在欧洲核子研究中心的带电粒子束中进行测试。将编写软件来重建探测到的光子，评估它们到达的时间，然后计算辐射它们的入射粒子的飞行时间。然后，TORCH将被转移到LHCb实验中，执行一个完整的系统测试，以验证带电轨道和光子的定时能力。这项研究将带来几个重要的好处。TORCH探测器将具有独特的能力，为粒子识别（PID）至关重要的实验提供ToF。举个例子，LHCb升级是一个所谓的风味物理实验，它在很大程度上依赖于区分碰撞中所有粒子的能力。此外，未来在FCC-ee机器上进行的实验，被提议作为大型强子对撞机之后可能的欧洲加速器，也将高度受益于TORCH在紧凑空间体积中进行的PID测量。TORCH也可以用于ToF探测器，它将带电粒子和高能伽玛与它们起源的主要碰撞点（顶点）联系起来，将它们的来源与LHC光束束交叉时出现的几个顶点区分开来。未来风味物理实验的一个关键物理目标是了解CP违背的起源，这仍然是实验粒子物理的一个谜题，也是宇宙中物质-反物质不对称之谜的关键部分。新一代的实验将利用大量的b强子（含有b夸克的粒子）来研究稀有b强子衰变的物质-反物质不对称性。因此，TORCH将使研究新的和意想不到的物理学成为可能，这可以代表我们对自然的理解向前迈出了一大步。最后，TORCH提案在很大程度上依赖于新型MCP光子探测器的研发，这是TORCH与工业界合作开发的。mcp因其良好的使用寿命、优异的时序分辨率（~20-30皮秒）和空间精度而被量化。mcp是很有前途的探测器，可用于粒子物理、天体粒子物理实验，以及空间和地面天文学项目。它们在医学成像方面也有应用。正电子发射断层扫描（PET），以及许多其他需要检测具有良好空间精度和时间的低水平光的应用。

This proposal describes a two-year research and development programme towards developing a time-of-flight (ToF) detector, named TORCH, for future particle physics experiments. TORCH uses a novel technique to measure the arrival time of a charged particle which passes through it. Because the ToF is proportional to the particle's velocity, the particle type (pion, proton or kaon) can be determined from knowledge of the particle's momentum, measured from the particle's bend in the experiment's magnetic field. TORCH uses a plane of 10 mm thick quartz as a source of Cherenkov light. The photons are emitted when a charged particle traverses a medium in which the particle's velocity exceeds that of light in the medium. The photons radiated in the quartz plate propagate by total internal reflection to the top edge of the plate and are then focused onto an array of Micro-Channel Plate (MCP) photon detectors. A ToF resolution of better than 15 ps per track is to be achieved, which will result in a pi/K/p particle separation up to a momentum of 10 GeV/c and beyond.A TORCH module will be constructed from a quartz radiator bar and focussing block, to which the MCP detectors will be mounted. The module will then be tested in a charged particle beam at CERN. Software will be written to reconstruct the detected photons, to evaluate their arrival times, and then to calculate the time of flight of the incident particle which radiated them. TORCH will then be moved to the LHCb experiment, to perform a full system test to verify the timing capabilities for charged tracks and photons.There are several important benefits that this research will bring. The TORCH detector will have a unique capability to provide ToF to experiments where particle identification (PID) is paramount. As an example, the LHCb Upgrade is a so-called flavour-physics experiment which relies heavily on the ability to distinguish all particles in the collision. Also, future experiments at the FCC-ee machine, proposed as a possible European accelerator after the LHC, would also highly benefit from PID measurements made in a compact spatial volume that TORCH facilitates. TORCH can also be used for a ToF detector which will associate charged particles and high-energy gammas with the primary collision point (vertex) from which they originate, differentiating their source from the several vertices present in the crossing of LHC beam bunches. A key physics aim of future flavour-physics experiments is to understand the origin of CP violation, which remains one of the mysteries of experimental particle physics and is a key piece in the puzzle of the matter-antimatter asymmetry in the universe. New generations of experiments will exploit the large number of B-hadrons (particles containing a b-quark), produced in order to investigate matter-antimatter asymmetries of rare B-hadron decays. Hence TORCH will enable the study of new and unexpected physics, and which can represent a huge step forward in our understanding of nature. Finally, the TORCH proposal relies heavily on the R&D of novel MCP photon detectors, which are developed by TORCH in collaboration with industry. The MCPs have been quantified for their good lifetime, excellent timing resolution (~20-30 picoseconds) and spatial accuracy. The MCPs are promising detectors for use in particle physics, astro-particle physics experiments, and also space and ground-based astronomy projects. They also have applications in medical imaging, eg. positron emission tomography (PET), and many other applications that require detection of low levels of light with good spatial accuracy and timing.