High-performance silicon sensors for particle tracking in 4 dimensions: achievements and future challenges

The concurrent space and time tagging of particle tracks with the same silicon detector imposes a delicate balance between two design philosophies, facing with different problems usually addressed through different technological approaches. Take into account, for instance, the case of standard pixelated silicon trackers, in which the spatial resolution is strictly dependent on the sensor granularity. On the contrary, the emerging technologies implemented for time-of-flight measurements require the highest possible weighting field uniformity across the whole sensor area, which translates into a low level of segmentation and high geometrical acceptance, with high fill factors. This divergence becomes even more significant when the requirements imposed by the physical environment are particularly demanding. As a matter of fact, in high-luminosity particle physics experiments, where the number of interactions per bunch crossing (pile-up) are expected to be orders of magnitude higher then in the current scenarios, it is crucial to preserve the quality of vertices reconstruction. This is why having high-resolutions in both space and time tracking become fundamental prerequisites for pile-up mitigation. To overcome all these challenges, physicists and particle designers are asked to reshape new frontiers of particle tracking, and take out the best performances from present technologies, or to develop new ones.