A new perspective on resonance suppression

What happens when particles smash into each other at nearly the speed of light? Scientists have discovered that these extreme collisions, like those at the Large Hadron Collider (LHC), can create a very special kind of matter a hot, dense soup of the building blocks of protons and neutrons. This state of matter, called a Quark-Gluon Plasma, is believed to resemble the conditions of the early universe, just microseconds after the Big Bang. To learn more about how this exotic matter behaves, researchers often look at resonances short-lived particles that form and decay almost instantly after these high-energy collisions. One curious pattern has emerged: certain resonances seem to be produced less frequently than expected. Until now, the leading explanation has been that their decay products get scrambled by bumping into other particles in the aftermath of the collision a bit like trying to spot a firework when it goes off in a storm. But this new project aims to challenge that idea. It explores whether the suppression of resonances might actually begin before particles have even finished forming during the earliest moments of the collision, when energy and color charge (a property of particles in quantum physics) are just starting to reorganize. To test this, the project will focus on two particular resonances, each of which can decay in two different ways. One decay path produces only solid particles (hadrons), and the other produces one hadron and one photon (a particle of light). If suppression is caused by later collisions, then the decay path with the photon which is less likely to get scrambled should show less suppression. But if suppression happens earlier, both decay paths should show similar results. These measurements are incredibly challenging. The decay paths involving photons are rare and have never been fully studied in this way before. However, thanks to a massive amount of new data from recent experiments, and the use of advanced machine learning techniques to better detect these elusive signals, the project now has the tools to make it possible. By comparing the new results to state-of-the-art simulations, the project will also test whether modern theoretical models especially those based on color reconnection, a quantum process that reshuffles how particles form can explain the observed behavior. No matter what the outcome, the findings will have a major impact. They will either confirm that current explanations hold true, or open the door to a whole new understanding of how particles form in high-energy environments. In either case, the project will bring us one step closer to understanding the fundamental forces that shape our universe.

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