The Large Hadron Collider (LHC) at CERN smashes particles together at record-breaking energies and intensities, unlocking the secrets of our universe. But lurking beneath the excitement of groundbreaking discoveries lies a constant battle against the inevitable - detector ageing. These colossal detectors, instrumental in capturing the fleeting interactions within the collider, are not invincible. Their continuous exposure to a harsh environment takes a toll, causing them to degrade over time. Understanding and mitigating these ageing phenomena is crucial for ensuring the detectors' longevity and the success of LHC experiments.

The "3rd International Conference on Detector Stability and Aging Phenomena in Gaseous Detectors", held at CERN in November 2023, served as a key platform for researchers to share their latest findings and explore innovative solutions to mitigate detector aging issues. The conference follows the initiative started in 1986 with the first workshop held at LBL (Berkeley) and the second one in 2001 at DESY (Hamburg). Extending the scope of the first two workshops, the 3rd edition incorporated detector stability in addition to ageing phenomena as highlighted in the title to account for the challenges of long-term gas detector operation in high-rate environments. 

The Invisible Threats
What are key ageing processes affecting the performance of gaseous detectors? Chemical reactions and processes including etching and polymerization, as a result of the disintegration of polyatomic molecules under intense irradiation, may damage the active elements in detectors ranging from wire-based detectors to MicroPattern Gaseous Detectors (MPGDs) and Resistive Plate Chambers (RPCs). Additionally, materials used in the detectors can release gas molecules over time, contaminating the environment and potentially impacting electrical properties. The intense radiation environment within the high-energy physics experiments continuously exposes detectors to high currents and particle rates, altering the materials' properties and eventually impacting their ability to measure particle interactions accurately. High interaction rates in combination with impurities or certain compounds used in the construction of detectors or employed gas mixtures may also produce harmful compounds that degrade detector components. A prominent example for this destruction process is the production of the formation of hydrofluoric acid (HF) from fluor originating from the breakup of gases such as CF4 commonly used in gaseous detectors and residual humidity in the gas.

Combating the Challenges
Ongoing efforts to minimize and suppress ageing processes in gaseous detectors address the selection and development of robust materials, the design of novel detector geometries with inherent resistance against known ageing phenomena and the evaluation of suitable gas mixtures. Clean detectors and non-polymerizing gases are crucial and in addition to the selection of materials with low outgassing rates and the implementation of rigorous cleaning procedures, methods for recovering of partially aged detectors in operating conditions are studied and employed. Optimized detector design minimizes electrical fields and potential breakdown pathways, while exploration of alternative gas mixtures helps extend detector lifetime by minimizing unwanted chemical reactions studies of the influence of gases on detector longevity are also especially important for identifying and validating novel gases with low greenhouse warming potential (GWP) to replace fluorinated gases in gaseous detectors while maintaining the required performance.  

Lessons Learned from Experience
Despite challenges, various detector systems have been successfully operated for decades. The conference highlighted the importance of rigorous material selection and thorough supplier qualification, as well as suitable methods for sharing and retaining experiences. The MEG experiment's drift chamber system initially faced challenges due to "helium pocket" formation, which were resolved through a design revamp. However, long-term operation revealed classical anode wire and cathode ageing phenomena, highlighting the need for ongoing monitoring and maintenance. This emphasizes the importance of stringent quality assurance (QA) and control methods.

Robust materials and gases
A comprehensive understanding of ageing mechanisms allows for better predictions and mitigation strategies. The conference showcased successful examples of extending detector lifetimes through material selection and design improvements, as documented by the work presented. Modern imaging and surface characterisation techniques offer unprecedented insight into microscopic ageing mechanisms and may allow the identification of novel ways to mitigate them. As colliders like the LHC reach higher luminosities, detector systems will need continuous improvement to maintain optimal efficiency. The ever-increasing performance of novel detector systems also calls for careful control of any parameters that may lead to ageing and performance degradation.

In addition to detector construction materials, novel materials are also crucial for applications of gaseous detectors for photon detection and as timing detectors. Photocathode ageing and possible robust photocathode materials are being studied and hold great potential for high performance gaseous detectors.

Infrastructure and Expertise
The conference underscored the importance of robust infrastructure and a skilled workforce for detector development and maintenance. Dedicated facilities for gas analysis and development of gas recirculation systems with purification modules are crucial for maintaining optimal gas quality and detector performance and minimise the use of deprecated cases in current and future experiments.  A team of highly skilled professionals with expertise in QA and control procedures as well as a community-wide exchange of experiences and best practices is vital for ensuring the quality and longevity of detector components. The newly formed DRD1 collaboration (https://drd1.web.cern.ch/) addresses this need with dedicated working groups on materials and gases as well as common facilities and aims at facilitating the exploitation of synergies and expertise in the gaseous detector development community.

The Takeaway
The battle against detector ageing is an ongoing process. As the LHC continues to push the boundaries of discovery, researchers will need to constantly refine their strategies and develop ever-more resilient gaseous detector technologies. This relentless pursuit ensures that these marvels of engineering continue to provide us with invaluable data, shedding light on the fundamental nature of our universe. Collaborative efforts on the development of new materials and the identification of alternative gas mixture are crucial for the next generation of gaseous detectors are being addressed by the newly formed DRD1 collaboration.

The 3rd International Conference on Detector Stability and Aging Phenomena brought together experts and researchers from various fields and communities. The organising committee (Florian Brunbauer, Anna Colaleo, Roberto Guida, Beatrice Mandelli, Eraldo Oliveri, Leszek Ropelewski, Maksym Titov) would like to thank all speakers and attendees for valuable discussions of the state-of-the-art understanding of ageing mechanisms and mitigation strategies. A special thank you to Veronique Wedlake for her dedicated support in the organization of a successful conference.