This movie shows the signal given by a noble liquid time-projection chamber (TPC). A cylindrical volume filled with a noble liquid has photodetectors (each individual circle) at the top and bottom caps. In the case of LUX, there are 61 photomultiplier tubes (PMTs) in each cap array. Generally, the walls of the cylindrical container are made with a reflective material (PTFE aka Teflon® for LUX).
A particle interaction in the noble liquid volume produces primary scintillation photons, which are instantaneously captured (speed of light) by the PMTs. Electrons are also produced by the particle interaction. An electric field in the TPC “pulls” these electrons upwards and out of the liquid. In the gas phase above the liquid, a much stronger electric field makes the electrons give off light (much like a neon sign), which we call the S2.
Because of the proximity of the S2 generation point to the top PMT array, the “hit pattern” in the top array can be used to reconstruct the x-y position of the event. Because the electrons move at a constant speed, the depth of the event (the z-coordinate) can be measured from the time between the S1 and S2 pulses. In LUX, this is a few microseconds.
Post time: Oct-21-2017