WP8 - TPCs as reaction and decay chambers (rare events, neutrino physics, nuclear physics)

 

WP Leaders and WP Project Leaders:

• Alan Bross
• Marco Cortesi
• Giorgio Dho
• Diego Gonzalez Diaz
• Francesc Morabal
• Esther Ferrer Ribas

 

Contact: DRD1-WP8-leaders@cern.ch

 

Participating institutes:

 

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DESCRIPTION OF THE WORK PACKAGE

TPCs employed in the field of rare event searches (historically referring to research where natural radioactivity can limit experiment performance), as well as those used (or envisaged) for neutrino physics or as active targets for nuclear reaction/decay studies, share methodological and technological characteristics. In fact, contrary to tracking TPCs (largely deployed at colliders), those used as reaction and decay chambers may not have (necessarily) external triggers, a condition stemming from the general aim of fully containing the reaction products down to the interaction vertex, with few or no ancillary detectors. The breadth of research programs often forces these TPCs to detect low and highly ionizing tracks (sometimes simultaneously), displaying reconstruction capabilities down to tens of 𝜇m sampling and keV energies, case-dependent, much below their collider counterparts. Radioactive contamination might be critical in some instances. This family of TPCs must deal with requirements (not all at the same time) such as full event containment, broad dynamic range, radiopurity, T0-tagging, diffusion close to the thermal limit, dual-phase operation, optical readout, single electron, and single ion counting, Fano-level energy resolution, tens of 𝜇m spatial sampling or keV-tracking. 

Such technological assets already provide (or are expected to provide) world-leading performance in direct dark matter searches, solar axion research, neutrino-less double-beta decay, fundamental studies of neutrino interactions and low-energy nuclear physics with radioactive beams. 

This work package contains four projects: 

• WP8 Project A - High Pressure TPCs for precision studies of neutrino interactions. 
• WP8 Project B - TPCs for low-energy nuclear physics. 
• WP8 Project C - Electroluminescence-based TPCs for Rare-Event Searches and other R&D on pure noble-gas amplification. 
• WP8 Project D - Radiopure TPCs for precise track imaging and/or calorimetry with avalanche-based readouts. 

Each project contains a detailed R&D description, list of dedicated tasks, deliverables and timelines.

 

Besides concrete action items for the next 3 years (discussed in detail in the accompanying project descriptions) the long-term plans of these projects aim to match the requirements highlighted in the 2021 ECFA detector research and development roadmap: this refers in particular to the continuous need of improvements in radiopurity techniques, detector scalability, improved sampling, higher energy resolution and lower energy threshold, pressure, mixture and gas purity stabilization and development of new gas mixtures and techniques for optical TPC readout (eco-friendly gases or gas-recuperation concepts and systems).

 

Main drivers from the facilities

The most popular technique for direct detection of WIMP Dark Matter in the 100 GeV- TeV mass range is to observe low energy nuclear recoils (e.g. MIMAC [Ch1-68], NEWAGE [Ch1-69], DRIFT [Ch1-70]). Recent experiments focus on the operation at near-atmospheric or even high pressure. In fact, electron ionization and optically based readout at 1 bar in CYGNUS [Ch1-71] will allow exploration of WIMP masses below 15 GeV using He/CF4/SF6 based TPC. Operation at 1-10 bar in Ar or Ne mixtures is considered at TREX-DM [Ch1-72] and with the NEWS-G spherical detector [Ch1-73] for low-mass WIMP (0.1-10 GeV) searches. At even lower masses, the MIGDAL experiment uses 14.1 MeV neutrons at a rate of 1010 Hz on a target gas (CF4) at low pressure (< 100 mbar) to detect visible Migdal [Ch1-74] electron tracks. In the low-mass end, solar-axion conversions into low-energy O(keV) photons can be detected in large TPC volumes operated inside strong magnetic fields (CAST [Ch1-77], IAXO [Ch1-75], [Ch1-76]). 

In the field of low energy nuclear reactions, the next-generation active-target multipurpose experiments will study very rare nuclear processes by either implantation or through inverse kinematics, induced by low-intensity exotic beams (e.g. NSCL [Ch1-78]), or selective excitation through gamma rays (e.g. ELI-NP [Ch1-79]). 

The most advanced gaseous TPC for neutrinoless double-beta decay is the one built for the NEXT experiment [Ch1-80]. It uses high-pressure enriched 136Xe gas as both the source of the decay and the detection medium, relying on the electroluminescence effect in order to approach the intrinsic energy resolution of the gas medium. Still in the field of neutrino physics, the DUNE collaboration is exploring a pressurised (10 bar) Ar-based TPC for its Near Detector to characterize precisely the beam energy and constrain nuclear effects in 𝝊-Ar interactions with much lower momentum threshold for particle detection, compared to the adjacent LAr Near Detector. 

Dual-phase detectors, based on gaseous TPCs in equilibrium with a noble liquid, allow combined high-resolution tracking with good calorimetric response (electroluminescent signal) and a T0 signal for a trigger using primary scintillation. Large dual-phase multi-ton experiments, either based on LAr (Dune FD [Ch1-81], 

ARIADNE [Ch1-82], DarkSide-20k and an ultimate ARGO [Ch1-83]) or LXe (PandaX-4T [Ch1-84], LZ [Ch1-85] towards DARWIN [Ch1-86], [Ch1-87]) are under consideration for detection of complex neutrino and WIMP interactions.

 

Key technologies

TPCs for rare event searches represent a specific class of applications probing fundamental physics through careful optimization of the properties of the gas nuclei/atoms/molecules used for interaction, ionisation, charge transfer and amplification, wavelength-shifting and light output in general. Those applications have additional requirements like radio-purity, wide dynamic range and ultra low noise electronics. In addition, they explore core topics in detector physics, i.e. different amplifying structure designs for high/low pressure stable operation, ions as charge carriers to mitigate charge diffusion or gas electroluminescence for optical readout, with potential for many novel applications. 

 

Common challenges

· Gas handling: Reduction of the use of fluorinated gases is fundamental for future gaseous detectors. They will be banned in the new installations where alternatives are available, and emission from existing facilities needs to be minimised by checks, optimisations, and recovery systems. Possible alternatives to greenhouse gases such as CF4 should remain a strong focus of the future R&D, not-excluding concepts for recuperation and distillation. Developing purification techniques, study compatibility of the gas mixture with (and radiopurity from) getters, as well as the development of recuperation systems to deal with expensive gases will be essential. 

· Readout Electronics: Next-generation electronics for this TPC family will be focused on high granularity / integration (e.g., GEMPix, GridPix), 3D optical readout (e.g., TPX3cam), and low-noise electronics with ability to self-trigger and of course high radiopurity.

 

Relevance in context of ECFA Roadmap

• DRDT 1.1 - Improve time and spatial resolution for gaseous detectors with long-term stability. 
• DRDT 1.2 - Achieve tracking in gaseous detectors with dE/dx and dN/dx capability in large volumes with very low material budget and different read-out schemes. 
• DRDT 1.3 - Develop environmentally friendly gaseous detectors for very large areas with high-rate capability. 
• DRDT 1.4 - Achieve high sensitivity in both low and high-pressure TPCs.

 

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TASKS

 

T1: Enhanced operation of optical readout across gas densities 

Two central areas are covered by this task, that aims at tackling mostly developments in neutrino and directional-DM detection: 

· Achieve ionization-energy thresholds of at least ~1 keV in the range 10 mbar to 10 bar with scalable concepts. 

· Achieve stable operation over a broad dynamic range of ionization densities (up to ~104), to enable mm and sub-mm track reconstruction of nuclei of different charge-states, from 10's of keV to 100's of MeV. 

T2: Enhanced operation of charge readout across gas densities 

Three central areas are covered by this task, that aims at tackling mostly developments in nuclear, neutrino, axion and DM detection: 

· Achieve ionization-energy thresholds of at least ~1 keV in the range 10 mbar to 10 bar with scalable concepts. 

· Achieve stable operation over a broad dynamic range of ionization densities (up to ~104), to enable mm and sub-mm track reconstruction of nuclei of different charge-states, from 10's of keV to 100's of MeV. 

· Suppression of ion backflow down to G*IBF=10 or better. 

T3: Enhanced operation of pure or trace-amount doped noble gases 

This task is mainly concerned with the operation of m2-scale and 100 kg to ton-scale detectors with single-electron sensitivity and near-Fano level energy resolution. Small R&D on dual-phase concepts is covered too. 

T4: Ultra-low-energy reconstruction of highly ionizing tracks (including R\&D on negative-ion readout) 

A reasonable target for the technology is to be able to track 10-100keV nuclear tracks with a concept that is scalable to m2 and beyond. 

T5: Determination of the interaction time (T0) 

Achieving a viable timing signal while keeping electron diffusion low and high amplification of the ionization signal represents an important enabling asset for fiducialization in the field of Rare Event Searches, as well as spill-assignment, time-of-flight determination, vertex reconstruction and PID in neutrino interactions. 

T6: Microscopic gas properties and gas handling 

The aim of this task is to investigate, introduce, and thoroughly characterize new gas mixtures, operated in conditions of high purity. 

T7: Radiopurity 

Improve manufacturing processes and purification as well as material-selection standards are covered by this task.

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