Speaker
Description
There remains a significant discrepancy between the effective ionization rate measured at low pressure on a Pulsed Townsend (PT) setup and that obtained at ambient pressure with Resistive Plate Chambers (RPC). This mismatch becomes particularly pronounced at high reduced electric field strengths, i.e. equivalently in small-gap RPCs . In these fields, RPC measurements systematically yield lower ionization rates than PT measurements, with differences reaching several standard deviations.
To investigate this discrepancy, we analyze signal waveforms from RPC measurements of cosmic muons conducted at LIP Coimbra , using pure R-134a in a chamber with a variable gap distance. The experimental setup is simulated in detail, employing state-of-the-art detector physics tools to reproduce the measured waveforms and the ionization rate to be extracted using the two-threshold method as in the experimental procedure. The simulations use ionization rates calculated with Magboltz, based on pulsed Townsend measurements at low pressure.
We demonstrate how the ionization rate fed into the simulation is effectively modified when applying the two-threshold method, due to space-charge effects, electron diffusion, boundary conditions, and finite readout bandwidth. With this approach, we show that the observed discrepancy can be partially resolved.