Since a large area (~150 square meters) has to be covered, a gaseous detector is the only choice.
In the framework of the LAA project at CERN an intensive R&D programme has proved that the best solution for the Time of Flight detector is the Multigap Resistive Plate Chamber (see the following figure).
The key aspect of this technology is that the electric field is high and uniform over the whole sensitive gaseous volume of the detector. Any ionisation produced by a through-going charged particle will immediately start a gas avalanche process which will eventually generate the observed signals on the pick-up electrodes. There is no time jitter associated with the drift of the electrons to a region of high electric field.


The main advantages of the MRPC technology are:
  • it operates at atmospheric pressure;
  • the construction requires commercially available glass;
  • the signal is the analogue sum of signals from many gaps, so there is no late tail and the charge spectrum is not of an exponential shape, it has a peak well separated from zero;
  • the resistive plates quench the streamers so there are no sparks, thus high gain operation becomes possible;
  • both an array of single cells and a multicell strip design produce good uniformity: for the second option, the geometric arrangement is far simpler and it explains the choice of this design.
The results obtained with a 10-gap double-stack strip design (see previous and following figures)


show that this new detector has an intrinsic time resolution smaller than 50 ps and an efficiency of 99.9% (see following figure).

Experimental results