- HEP Seminar
Title: Big, quiet and precise: Q-Pix, a pixel revolution for TPCs at the multi-kiloton scale.
Elena Gramellini, Fermi Lab
Noble elements Time Projection Chambers (TPC) are the detector technology of choice for the next generation of discovery at the intensity frontier. These detectors provide a number of experimental handles, such as full 3D-imaging, excellent particle identification and precise calorimetric energy reconstruction which makes them extremely flexible tools suitable for a wide range of physics measurements. Indeed, TPC applications range from dark matter, rare decays and capture, neutrino oscillations and nucleon decay, and neutrino less double beta decay.
In the context of the Deep Underground Neutrino Experiment (DUNE), the liquid argon community is showing great interest in developing a large scale pixelated charge readout for multi-kTon scale detectors. A clear benefit of pixelated readouts is the native 3D nature of the data, where the charge readout segmentation coincides with the physical spatial segmentation. Pixelated readouts lack the reconstruction ambiguities inherent to 2D projective readouts: 3D events reconstruction is straightforward. While the number of readout channels for pixelated designs is a major challenge compared to wire designs, it also makes pixelated detectors more resilient against the impact of single-element failure and potentially easier to build.
In this seminar, we present Q-Pix: the technology which could translate pixelated readout into a reality for multi-kTon scale TPCs. Q-Pix is a continuously integrating low-power charge-sensitive amplifier (CSA) viewed by a Schmitt trigger. The heart of Q-Pix resides in the elementary Charge-Integrate / Reset (CIR) circuit: when the trigger threshold is met, a comparator initiates a 'reset' transition and returns the CSA circuitry to a stable baseline. A 32-bit clock register captures the instances of reset. The time difference between one clock capture and the next sequential capture is called the Reset Time Difference (RTD): an RTD measures the time to integrate a predefined quantum of charge (Q) characteristic of the integrated circuit. An event is then characterized by the time profile and number of RTDs sequences. In quiescent mode the RTDs will be evenly spaced with time intervals of seconds. Contrary, an event appears as a sequence of varying RTDs with microsecond intervals. A dynamically established network forms the DAQ and guarantees exceptional resilience against single point failures. In such an architecture, a very detailed tracking is obtained using the collective information from arrays of few millimeters wide pixels. In Argon, 39Ar decays are a native absolute charge calibration.
To fully exploit the detection capabilities of noble elements, TPCs are traditionally equipped with light collection systems sensitive to UV scintillation light. Yet, light detection solutions used in traditional 2D wires projective readouts are not easily applicable in the case of pixelated readouts. In this seminar, we also present imaginative ideas and technologies for light detection systems compatible with the Q-Pix under development.