Speaker
Description
The possibility of performing 2D vertex reconstruction in the sLHC by resorting to accurate 10-20ps time resolution (per minimum ionizing particle) has triggered a new wave of R&D in the timing frontier. Such detectors will be operating close to the beam, and the anticipated rates exceed those typical of RPCs in many orders of magnitude. We will introduce in this presentation a detector based on a late idea of Charpak, together with Giomataris. It consists on coupling a micro-pattern amplification stage to a 50-200um micro-drift region, the latter receiving the photo-electrons from the Cherenkov emission produced in a highly VUV-transparent crystal (e.g., MgF, CaF). The concept relies on the approximate simultaneity of the Cherenkov photons and thus on the absence of any limiting jitter in the production of the initial photo-electrons that trigger the signal generation process. Diffusion before the amplification stage can be kept small through the minimization of the drift region and a proper gas choice. We will show with the help of simulations that the experimental results obtained with this type of detector are indeed purely diffusion-limited, a concept that sets the natural scale for single-photon time resolution to around or below 100ps. Without an optimal timing gas (Ne+C2H6, 90/10 was used) a time resolution around 200ps(sigma) per photo-electron has been measured on a laser facility, which allows ultra-fast pulses and a good control on the number of photo-electrons. Similar to RPCs, the measured time resolution scales well with the square root of the number of initial electrons, and this should be sufficient for a 40ps time resolution on a~0.5cm spot, already with this early prototype. Besides providing a detailed description of the experimental results, we will examine critically possible improvements on “diffusion-limited” timing related to this new development, and will also discuss them in the context of “avalanche statistics – limited” timing RPCs.
