Development of a Reconfigurable Monolithic Active Pixel Sensor in Radiation-hard Technology for Outer Tracking and Digital Electromagnetic Calorimetry

随着粒子物理学的进步，对探测器技术的需求总是朝着需要精细分割、更快的读出和更强的辐射耐受性的方向发展；所有这些都是以更低的成本进行的。为了发现质量太大而尚未被观测到的粒子，粒子对撞机必须不断地向更高的能量推进。然而，随着碰撞能量的增加，包含这种新物理的潜在证据的事件的几率作为总数的一小部分下降，这使得在高能量时也具有非常高的相互作用率是很重要的。此外，随着能量的增加，每次碰撞产生的粒子数量增加，产生的感兴趣粒子的平均能量增加。后者意味着带电粒子在探测器磁场中更难弯曲，因此需要更好的空间精度(因此更小的传感元件)，从而需要更大的粒度(单位面积的像素数)。在更高的能量下，粒子簇射也往往更加准直，使得在单位面积上没有更多读出单元的情况下，轨迹分离也变得更加困难。最后，在强子对撞机上，高对撞率需要每束交叉多次碰撞，所以有趣的相互作用通常被同时产生的200个无趣的相互作用所掩盖。从有趣的碰撞中分离出轨迹也需要非常精确的测量。最后，每秒数十亿次的碰撞会导致运行多年的辐射水平远远超出正常电子设备的能力，需要专业设计在预期剂量之后工作。粒子物理传感器无法利用许多商业设备中超廉价百万像素相机的开发，因为这些相机没有所需的速度或辐射硬度，但它们很容易满足粒度方面的要求。因此，如果能够设计出快速、防辐射的版本，就传感器的可负担性而言，这将改变游戏规则。最近的工作表明，现有的商业cmos技术可以支持抗辐射设计，这项提议试图利用这些技术来展示可以让非常大的实验区域以负担得起的价格配备这样的探测器的设备。使传感器难以辐射的设计方面也使它们更快，这对这些应用来说是一个额外的优势。然而，证明具有所需特性的小型传感器是迈向最终阵列的第一步，需要数千平方米的传感器，而且在设想非常大的阵列之前需要大量的开发时间。因此，尽管可能的应用还有相当长的路要走，但开发新技术到所需的成熟度以在如此大的阵列中使用的时间意味着这一研发非常及时。在这方面，英国在许多技术方面处于领先地位，但在国际上也有许多其他组织在追求同样的目标，因此，如果不想失去目前的领导地位，这项提议也很重要。目前的领导地位很大程度上是通过ATLAS和CMS升级以及国际线性收集器的工作发展起来的。

As particle physics progresses, the demands in terms of detector technologies always push toward needing fine segmentation, faster read-out and greater radiation tolerance; all at lower cost. To find particles too massive to have been seen already, particle colliders have to continuously push towards higher energies. However, as collision energies increase, the rates for events containing potential evidence for such new physics decreases as a fraction of the total, making it important at high energies to also have very high interaction rates. Also, as energies increase, the numbers of particles produced per collision increase and the mean energies of the produced particles of interest increase. The latter means that charged particles become harder to bend in the detector magnetic field and so better spatial precision (hence smaller sense elements) is needed leading to the need for much greater granularity (number of pixels per unit area). At higher energies, particle showers tend to also be much more collimated, making track separation also harder without many more read-out cells per unit area. Finally, at hadron colliders, high rates require many collisions per beam crossing so the interesting interactions are typically buried in 200 uninteresting ones produced at the same time. Unpicking the tracks from the interesting collision also requires very precise measurements. Finally, billions of collisions per second lead to radiation levels over years of operation that go way beyond the capabilities of normal electronics requiring specialist designs to work after the expected doses.Particle physics sensors are not able to exploit the development of ultra-cheap mega-pixel cameras in many commercial devices because these neither have the speed or radiation hardness needed but they easily meet the requirements in terms of granularity. Therefore, if fast, radiation-hard versions could be designed, these would be a game-changer in terms of sensor affordability. Recent work has shown that there are commercial CMOS technologies available that can support radiation-hard designs and this proposal seeks to exploit these to demonstrate devices that could allow very large areas of experiments to be equipped with such detectors affordably. Aspects of the design that makes the sensors radiation hard also make them faster which is an added advantage for these applications. Nevertheless, proving small sensors with the required properties is a first step towards final arrays requiring thousands of square metres of sensors and much development time is needed before a very large array could be envisaged. Therefore, even though the possible applications are quite a long way off, the amount of time to develop new technologies to the required maturity to be exploited in such large arrays means that this R&D is very timely. The UK has a lead in a number of the technology aspects for this but there are many other groups internationally pursuing the same goals and so this proposal is also important if current leadership, much of it developed through work for ATLAS and CMS upgrades and for the International Linear Colldier, is not to be lost.