KIPAC Tea Talk: Uncovering the Ultrahigh Energy Universe with PUEO / No Cluster Left Behind: Multiwavelength Cluster Analysis with All the Data

Scrandis Abstract: The ultrahigh energy (UHE) neutrino flux has yet to be measured above ~100PeV, yet can contain otherwise inaccessible information about the highest energy events in space. The Payload for Ultrahigh Energy Observations (PUEO) is a NASA Pioneers long duration balloon that flew over Antarctica between December 2025 and January 2026 in search of this elusive flux. As the most sensitive instrument ever built for UHE neutrino detection, PUEO aims to either constrain or present first measurements of neutrinos near 1 EeV energies. In this talk, I will discuss the PUEO instrument, our recent Antarctic campaign, and the science searches currently underway.

Zhou Abstract: Cluster abundance is among the most powerful cosmological probes, but its constraining power is currently limited by systematic uncertainties in mass calibration. Optically selected samples in particular suffer from line-of-sight projection effects that bias both richness and lensing measurements. Jointly modeling clusters observed across multiple wavelengths offers a path to self-calibrating these systematics ― yet previous multiwavelength analyses have typically discarded clusters lacking tSZ or X-ray counterparts, sacrificing much of the sample's statistical power. In this talk, I will present an analysis framework that retains every cluster detected in at least one survey: no cluster left behind. Applying it to Dark Energy Survey and South Pole Telescope data, I will show joint constraints on cluster mass calibration and optical projection effects. I will conclude by looking forward to multiwavelength cluster cosmology in the era of Rubin, Roman, SPT-3G, and eROSITA.