  Non-adiabatic production of massive particles is a generic feature of many
inflationary mechanisms. If sufficiently massive, these particles can leave
features in the cosmic microwave background (CMB) that are not well-captured by
traditional correlation function analyses. We consider a scenario in which
particle production occurs only in a narrow time-interval during inflation,
eventually leading to CMB hot- or coldspots with characteristic shapes and
sizes. Searching for such features in CMB data is analogous to searching for
late-Universe hot- or coldspots, such as those due to the thermal
Sunyaev-Zel'dovich (tSZ) effect. Exploiting this data-analysis parallel, we
perform a search for particle-production hotspots in the Planck PR4 temperature
dataset, which we implement via a matched-filter analysis. Our pipeline is
validated on synthetic observations and found to yield unbiased constraints on
sufficiently large hotspots across $\approx 60\%$ of the sky. After removing
point sources and tSZ clusters, we find no evidence for new physics and place
novel bounds on the coupling between the inflaton and massive particles. These
bounds are strongest for larger hotspots, produced early in inflation, whilst
sensitivity to smaller hotspots is limited by noise and beam effects. Through
such methods we can constrain particles with masses $\mathcal{O}(100)$ times
larger than the inflationary Hubble scale, which represents possibly the
highest energies ever directly probed with observational data.
