Cygnus: development of a high resolution TPC for rare events

The R&D of a gas detector prototype for high precision tracking of low energy nuclear recoilsover large volume is presented in this paper. The scintillation light accompanying the electronicavalanches in a triple GEM structure is detected by a CMOS-based camera. The sensor providesvery high granularity along with a very low noise and high sensitivity. Space resolution of theorder of tens of µm were measured on the GEM plane (xy). The Negative Ion Drift methodto reconstruct the depth of track within the sensitive volume was studied. Recent tests on beamdemonstrated the feasibility of the NID method with a small amount of SF6 even at nearly ambientpressure. The use of a concurrent light readout by means of a suitable photomultiplier providesthe necessary timing informations. A time resolution of the order of 5 ns was measured.