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Register a new userPrimary track recovery in high-definition gas time projection chambers
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We develop and validate a new algorithm called primary track recovery (ptr) that effectively deconvolves known physics and detector effects from nuclear recoil track in gas Time Projection Chambers (TPCs) with high-resolution readout. This gives access to the primary track charge, length, and vector direction (helping to resolve the head-tail ambiguity). Additionally, ptr provides a measurement of the longitudinal and transverse diffusion widths, which can be used to determine the absolute position of tracks in the drift direction for detector fiducialization. Using simulated neutron recoils we compare the performance of ptr to traditional methods for all key track variables and find that it substantially reduces a wide range of reconstruction errors, including those caused by charge integration. We show that ptr significantly improves on existing methods for head-tail disambiguation, particularly for highly inclined tracks. We demonstrate that ptr improves on existing methods for determining the absolute position of recoils on the drift axis via transverse diffusion by properly removing previously undescribed track width biases. We use experimental data to qualitatively verify these findings and discuss implications for future directional detectors at the low-energy frontier.
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Directional detection of nuclear recoils is appealing because it can confirm the cosmological origin of a dark matter signal and distinguish between different neutrino sources. Gas Time Projection Chambers (TPCs) enable directional recoil detection due to the high spatial granularity with which they can image a recoils ionization track, especially if micro-pattern gaseous detectors (MPGDs) are utilized. A key challenge in these detectors at low energies is identifying and rejecting background electron recoil events cause by gamma rays from radioactive contaminants in the detector materials and the environment. For gas TPCs with high readout segmentation, we can define observables that can distinguish electron and nuclear recoils, even at keV-scale energies, based on the measured ionizations topology. We define such observables and show that they outperform the traditionally used discriminant, dE/dx, by up to three orders of magnitude. Furthermore, these new observables work well even at ionization energies below 10 keV and remain robust even in the regime where directionality fails.
Searching for the Neutrinoless Double Beta Decay (NLDBD) is now regarded as the topmost promising technique to explore the nature of neutrinos after the discovery of neutrino masses in oscillation experiments. PandaX-III (Particle And Astrophysical Xenon Experiment III) will search for the NLDBD of $^{136}$Xe at the China Jin Ping underground Laboratory (CJPL). In the first phase of the experiment, a high pressure gas Time Projection Chamber (TPC) will contain 200 kg, 90% $^{136}$Xe enriched gas operated at 10 bar. Fine pitch micro-pattern gas detector (Microbulk Micromegas) will be used at both ends of the TPC for the charge readout with a cathode in the middle. Charge signals can be used to reconstruct tracks of NLDBD events and provide good energy and spatial resolution. The detector will be immersed in a large water tank to ensure $sim$5 m of water shielding in all directions. The second phase, a ton-scale experiment, will consist of five TPCs in the same water tank, with improved energy resolution and better control over backgrounds.
A simple but novel driver system has been developed to operate the wire gating grid of a Time Projection Chamber (TPC). This system connects the wires of the gating grid to its driver via low impedance transmission lines. When the gating grid is open, all wires have the same voltage allowing drift electrons, produced by the ionization of the detector gas molecules, to pass through to the anode wires. When the grid is closed, the wires have alternating higher and lower voltages causing the drift electrons to terminate at the more positive wires. Rapid opening of the gating grid with low pickup noise is achieved by quickly shorting the positive and negative wires to attain the average bias potential with N-type and P-type MOSFET switches. The circuit analysis and simulation software SPICE shows that the driver restores the gating grid voltage to 90% of the opening voltage in less than 0.20 $mu$s. When tested in the experimental environment of a time projection chamber larger termination resistors were chosen so that the driver opens the gating grid in 0.35 $mu$s. In each case, opening time is basically characterized by the RC constant given by the resistance of the switches and terminating resistors and the capacitance of the gating grid and its transmission line. By adding a second pair of N-type and P-type MOSFET switches, the gating grid is closed by restoring 99% of the original charges to the wires within 3 $mu$s.
Dielectric breakdown strength is one of the critical performance metrics for gases and mixtures used in large, high pressure gas time projection chambers. In this paper we experimentally study dielectric breakdown strengths of several important time projection chamber working gases and gas-phase insulators over the pressure range 100 mbar to 10 bar, and gap sizes ranging from 0.1to 10 mm. Gases characterized include argon, xenon, CO2, CF4, and mixtures 90-10 argon-CH4,90-10 argon-CO2and 99-1 argon-CF4. We develop a theoretical model for high voltage breakdown based on microphysical simulations that use PyBoltz electron swarm Monte Carlo results as input to Townsend- and Meek-like discharge criteria. This model is shown to be highly predictive at high pressure, out-performing traditional Paschen-Townsend and Meek-Raether models significantly. At lower pressure-times-distance, the Townsend-like model is an excellent description for noble gases whereas the Meek-like model provides a highly accurate prediction for insulating gases.
Radio-frequency carpets with ultra-fine pitches are examined for ion transport in gases at atmospheric pressures and above. We develop new analytic and computational methods for modeling ion behavior on phased radio-frequency (RF) carpets in gas densities where ion dynamics are strongly influenced by buffer gas collisions. The analytic theory of phased RF arrays is obtained by generalizing the conventional Dehmelt potential treatment, and the emergence of levitating and sweeping forces from a single RF wave is demonstrated. We consider the effects of finite electrode width and demonstrate the existence of a surface of no return at around 0.25 times the carpet pitch. We then apply thermodynamic and kinetic theory arguments to calculate ion loss rates from RF carpets in the presence of stochastic effects from ion-neutral collisions. Comparison to collision-by-collision simulations in SIMION validate this new and efficient approach to calculation of transport efficiencies. We establish the dependence of transport properties on array phasing, and explore a parameter space that is of special interest to neutrinoless double beta decay experiments using xenon gas: RF transport of barium ions in xenon gas at pressures from 1 to 10 bar, which could represent a promising technique for barium daughter ion tagging. We explore the allowed parameter space for efficient transport, accounting for the detailed microphysics of molecular ion formation and pressure dependent mobility, as well as finite temperature effects for both room temperature and cooled gases. The requirements of such systems lie significantly beyond those of existing devices in terms of both voltage and electrode pitch, and we discuss the challenges associated with achieving these operating conditions with presently available or near-future technologies.
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