HEP@VUB Colloquium: "Holding Galaxies Together: The Challenge of Observing Elusive Dark Matter as Manifest in the TPC Wire-grid"

External Speaker: Rijeesh Keloth (Virginia Tech)

The seminar will be done in person and it will be accompanied by sandwiches provided by the VUB.

Abstract:

Every galaxy in the universe is held together by an invisible gravitational force. Observational evidence is overwhelming: dark matter comprises 27% of the universe's mass-energy density. From galaxy rotation curves to gravitational lensing to the cosmic microwave background, the presence of dark matter is manifest at cosmic scales.

Yet this observational certainty masks an extraordinary experimental challenge: observing the elusive particles that constitute dark matter. While we can confidently map dark matter's gravitational influence across billions of light-years, detecting individual dark matter particles in the laboratory requires precision engineering of the highest order.

This colloquium explores how this cosmic challenge manifests in concrete experimental requirements. I will discuss DarkSide-20k, a dual-phase liquid argon time projection chamber currently under construction at Laboratori Nazionali del Gran Sasso in Italy. DarkSide-20k features a 20-tonne fiducial mass of ultra-radiopure underground argon as its dark matter detection target, contained within a ~50-tonne active liquid argon volume. It is designed to directly detect Weakly Interacting Massive Particles (WIMPs)—leading candidates for the dark matter.

The focus will be on a critical component that exemplifies precision engineering at its finest: the TPC wire-grid electrode. This 200-micrometer-thick stainless steel wire grid, spaced with millimeter-level precision, must maintain micrometer-scale accuracy under extreme cryogenic conditions (87 K) for extended operational lifetimes. Why is this small component so crucial? Because its performance directly determines whether we can reconstruct dark matter interactions with sufficient fidelity to claim discovery. It embodies a universal principle in experimental physics: small technical challenges can become fundamental barriers to major discoveries.

Through this lens, we will examine how the challenge of observing the elusive translates into unforgiving engineering specifications, and how innovations in the TPC wire-grid design help to unlock order-of-magnitude sensitivity improvements. This talk reveals what lies beneath experimental breakthroughs: the marriage of bold scientific vision with meticulous precision engineering.