In-beam test of the RPC architecture foreseen to be used for the CBM-TOF inner wall

The Time Of Flight (TOF) subsystem is one of the main detectors of the CBM experiment. The TOF wall in conjunction with Silicon Tracking System (STS) is foreseen to identify charged hadrons, i.e. pions, kaons and protons, with a full azimuthal coverage at 2.5⁰ - 25⁰ polar angles. A system time resolution of at least 80 ps, including all contributions, such as electronics jitter and the resolution of the time reference system, is required. Such a performance should be maintained up to a counting rate larger than 30 kHz/cm² at the most inner region of TOF wall.

Our R&D activity has been focused on the development of two-dimensional position sensitive Multi-gap Resistive Plate Counter (MRPC) prototypes for the forward region of the CBM-TOF subdetector, the most demanding zone in terms of granularity and counting rate.

The in-beam tests using secondary particles produced in 30 GeV/u Pb ion collisions on a Pb target at SPS - CERN aimed to test the performance of these prototypes in conditions similar to the ones expected at SIS100 at FAIR. The performance of the prototypes is studied in conditions of exposure of the whole active area of the chamber to high multiplicity of reaction products.

The results show that this type of MRPC fulfill the challenging requirements of the CBM-TOF wall. Therefore, such an architecture is recommended as basic solution for CBM-TOF inner zone. (paper)