T-1065: Secondary Emitters Study
One possibility to make a fast and radiation resistant shower maximum (SM) detector or preshower detector is to use a secondary emitter (SE) as an active element. This method was proposed in 1990. Micro channel plates (MCP) were used as SE in the SM. The attractive properties of such SM are: 1) a two-dimensional map of energy at the SE location; 2) timing information at few tens of picosecond level, also as transverse shower size and 3) possible separation of electromagnetic and hadronic energy based on the differences of the shower size and timing. An electron-multiplier-based sampling calorimeter requires thin planar detectors at an affordable cost. Large-area photo detectors based on ALD-functionalized 20-cm-square borosilicate glass capillary micro-channel plates (MCPs), currently being developed by the LAPPD Collaboration, are candidates for the active elements. The first results of the new shower maximum detector with the micro channel plate photomultiplier (MCP-PMT) as active elements are described. The current proposal is the next natural step in this direction. The experimenters propose using large-area MCPs assembled without the usual bialkali photocathodes as the active element in sampling calorimeters. LAPPD modules without photocathodes can be economically assembled in a glove box and then pumped and sealed using the process to construct photomultipliers, bypassing the slow and expensive vacuum-transfer process required by bialkali photocathodes. The first use of electron multipliers, in this case MCPs (Fig. 1, left) as an active element in multi-layer sampling calorimeters is described. A chevron of two MCPs in vacuum, was located behind a tungsten plate on which 5 GeV and 26 GeV electrons were incident (Fig. 1, right). The amplitude of the MCP signal (Fig. 2) as a function of the tungsten thickness was measured. The primary electrons produce a shower of secondary particles, including positron-electron pairs and gammas; the response of the MCPs (Fig. 2, left) is proportional to the number of particles in the shower, which is dependent on the initial particle energy. The MCP signal shape is presented in the Fig. 2, right). The FWHM of the signal is 1 ns.