Proof of Principle for CMS High-Granularity Calorimeter

粒子物理学是研究自然界的基本组成部分以及支配它们相互作用的力的学科。在过去的40年里，我们发展了所谓的粒子物理学的“标准模型”，概括了我们对这个亚原子世界的理解。虽然取得了惊人的成功，而且确实是20世纪基础物理学的至高无上的荣耀，但我们知道这不是最终的答案。例如，它没有包含重力，也没有解释暗物质。更直接的是，它预测了一种与质量产生有关的粒子--希格斯玻色子的存在。在2012年欧洲核子研究中心大型强子对撞机(LHC)的ATLAS和CMS合作发现之前，没有实验证据证明这一标准模型的基石。希格斯粒子的发现为了解超越标准模型的新物理学打开了一扇窗。通过对新粒子的详细研究和寻找其他希格斯玻色子来理解这一发现的意义，是世界粒子物理学中最重要的任务之一。为了足够详细地研究希格斯玻色子，实际上对于许多其他重要的物理课题，我们需要比我们迄今拥有的更大的数据集。大型强子对撞机将经历广泛的升级，通过以更高的速度碰撞在大型强子对撞机中加速的质子来产生这些更大的数据集；这种升级被称为“高亮度大型强子对撞机”(HL-LHC)。同时，CMS等记录这些碰撞的实验也必须升级，以应对辐射水平的增加，以及与LHC升级相关的增加的速率。CMS将需要在前沿区域更换其所谓的“热量计”，因为这是辐射剂量最高的区域。为量热计的升级提出了一个新的概念，这里提出的工作将构成这一工作的关键部分。传统上，量热仪只测量碰撞中产生的粒子的能量，但技术的进步及其在粒子物理中的应用(部分由英国首创)现在使人们有可能考虑使用高粒度量热计。这样的设备还可以有效地测量粒子在量热仪内遵循的路径或轨迹。这在区分近距离粒子方面带来了巨大的优势，这将被视为传统量热仪中的一个沉积物。高粒度量热计将由致密的吸收材料组成，这些材料会导致入射粒子失去能量，中间散布着能够跟踪单个粒子通过的硅探测器。这些额外的信息在克服hl-lhc具有挑战性的环境方面可能非常强大。这项提案将实现该项目的两个关键方面。首先，我们将清楚地证明，在大型强子对撞机这样的环境中，这种探测器提供的单个粒子跟踪的潜在收益可以完全实现。作为这项工作的一部分，我们将提供优化的探测器布局，即确定吸收体和硅传感器的最佳比例，以及优化硅传感器本身的尺寸。第二个目标是证明，即使在恶劣的大型强子对撞机环境中，也可以使用从这种设备获得的附加信息来有效地触发，即实时选择感兴趣的可能事件。作为这项工作的一部分，可以预见将这些触发算法编码到最先进的‘FPGA’中，这将提供一种原则证明，即这种方法在当前技术下是可能的。

Particle physics is the study of the fundamental building blocks of nature and the forces that govern their interactions. Over the last 40 years we have developed the so-called 'standard model' of particle physics, encapsulating our understanding of this sub-atomic world. Whilst amazingly successful, and indeed a crowning-glory of 20th century fundamental physics, we know it cannot be the final answer. For example it doesn't incorporate gravity or explain dark matter. More immediately it predicts the existence of a particle, the Higgs boson, associated with mass generation. Until the discovery by the ATLAS and CMS Collaborations at the Large Hadron Collider (LHC) at CERN in 2012 there was no experimental evidence for this corner-stone of the standard model. The discovery of a Higgs particle has opened a window onto the new physics beyond the standard model. Understanding the implications of this discovery through detailed study of the new particle and searches for other Higgs bosons is one of the highest priorities within particle physics worldwide.To study the Higgs boson in sufficient detail, and indeed for many other important physics topics, we need much larger datasets than we have so far. The LHC will undergo extensive upgrades to generate these larger data sets by colliding the protons accelerated in the LHC at even greater rates; this upgrade is referred to as the 'High-Luminosity LHC' (HL-LHC). In parallel, the experiments, such as CMS that record these collisions, must also be upgraded to cope with the increased radiation levels, and increased rates associated with the LHC upgrades.CMS will need to replace its so-called 'calorimeters' in the forward regions as this is where the radiation doses are highest. A novel concept is proposed for the calorimeter upgrade, and the work proposed here would form a key part of this. Traditionally calorimeters have only measured the energy of the particles produced in the collisions, but advances in technology and their application to particle physics, in part pioneered by the UK, now make it possible to consider high granularity calorimeters. Such devices can effectively also measure the path, or track, that a particle follows within the calorimeter. This brings large advantages in distinguishing close-by particles, which would be seen as one deposit in a traditional calorimeter. A high granularity calorimeter would consist of dense absorbing material that causes incident particles to lose energy, interspersed with silicon detectors able to track the passage of individual particles. This additional information can be very powerful in overcoming the challenging environment of the Hl-LHC. This proposal will deliver on two key aspects of this project. First we will clearly demonstrate that the potential gains of individual particle tracking that such a detector offers can be fully realised in an environment such as the LHC. As part of this we will deliver an optimised detector layout i.e. determine the optimum ratio of absorber and silicon sensors, along with optimising the size of the silicon sensors themselves. The second goal is demonstrate that the additional information available from such a device can be used, even in the harsh LHC environment, to effectively trigger, i.e. select in real time, possible events of interest. As part of this, coding these trigger algorithms into a state-of-the art 'FPGA' is foreseen and this will provide a proof-of-principle that such an approach is possible with current technology.