A cold low noise preamplifier for use in Liquid Xenon

In this paper a low-noise preamplifier for liquid- xenon ionization detectors is presented. The preamplifier has a cold front-end to be operated in liquid xenon at ~160 K and a warm part installed 15-cm apart and working at room temperature. It features an unusually high sensitivity of ~70 mV/fC. This specification is required because the net charge delivered in liquid xenon per unit energy is one order of magnitude lower than in silicon or germanium detectors. The preamplifier consists of a JFET-input charge-sensing stage with a feedback capacitance as low as 0.2 pF and a low-noise gain stage with differential output stage, able to drive 50Omega terminated cables. With a detector capacitance of 33 pF the preamplifier features an Equivalent Noise Charge of ~110 electrons r.m.s. at a shaping time of 6 mus, and a risetime of ~75 ns.