MDT Noise Measurements in the X5 and H8 Test Beam

Different measurements of the MDT noise level were performed in the X5 test beam, using the Seattle/Boston EMS chamber equipped with BNL preamplifiers and shapers. This note shows the results of th ese measurements and compares them to calculations and to measurements with the Munich BOS chamber in the H8 test beam. Measurements with a charge sensitive ADC confirm the Gaussian shape of the noise distribution. Different methods agree on a sigma-noise of 3.8 ionisation electrons respectively an Equivalent Noise Charge (ENC) of ~5470 electrons. This is close to the calculated thermal n oise originating from the termination resistor (sigma-noise calculated ~3 ionisation electrons) plus the impact of parasitic capacitance in front of the preamplifier, leading to a total of 3.5 ioni sation electrons, which represents a theoretical minimum. A check of the noise level of the Munich BOS chamber shows an increased sigma-noise of ~4.8 ionisation electrons, which can partly be exp lained by the additional capacitance from signal traces.