Physicists from the GlueX collaboration at the Thomas Jefferson National Accelerator Facility were searching for confirmation of the existence of the mysterious particle Y(2175) — a possible candidate for exotic strangonium states.
Instead of the expected signal, two other signals appeared in the photoproduction data on a proton target.
One of them, designated Y(2240), has a mass of about 2,24 GeV and reached a statistical significance of 5σ — a level corresponding to approximately 99,9994% confidence.
The second signal, X(1830) with a mass of about 1,82 GeV, showed a significance of 3σ.
Both objects may belong to the family of exotic XYZ states, which do not fit into the standard picture of quark-antiquark pairs.
The study is published in Physical Review Letters and is based on data from an experiment where a beam of high-energy photons interacted with a liquid hydrogen target.
"We were looking for a confirmed XYZ candidate with a photon beam, but we found two other structures," noted Malte Albrecht from Jefferson Lab.
Previously, Y(2175) had been observed only in electron-positron annihilation processes at the BaBar, BES, and Belle colliders.
Now, for the first time, such signals have been obtained in photoproduction, opening a new channel for studying exotic hadrons.
Exactly how quarks and gluons form these unusual configurations is a question that theorists and future experiments will have to answer.
The results also set an upper limit on the production probability of Y(2175) in photoproduction and lay the foundation for broader measurements of hadron spectroscopy at the GlueX facility.
