Triangle singularities waning in Heavy Ion Collisions: the case of $Y(4260)\to \pi (\pi J/\psi )$

Abstract

We have recently observed that hadron triangle singularities, that can mock new exotic hadrons, can be significanttly suppressed in relativistic heavy ion collisions, provided two conditions are met: these are, first, that the fireball lives long enough so that the triangle process has enough time to complete in the Norton-Coleman classical sense, and second, that the mass and/or width of the particles in the triangle diagram are sufficiently modified from their vacuum values. Here we add a very interesting example to the canon, which is $Y(4260)\to D_{1}D\to \pi D^{\ast }D\to \pi +J/\psi \pi$. This reaction has been proposed as a mechanism to explain the appearance of $Z_c(3900)$ in the $J/\psi \pi$ spectrum. If the two muons and two pions reconstructing the initial-state $Y$ can be isolated from the combinatorial background, then the mechanism can provide a spectroscopy test: presence of $Y(4260)$ but absence of $Z_c(3900)$ would be more indicative of such triangle mechanism, while presence of both would rather point out to $Z_c$ being an exotic hadron.

Comments: 5 pages, 4 figures. Contribution to the proceedings of the 24th High-Energy Physics International Conference in Quantum ChromoDynamics (QCD21), 5-9 Jul 2021 Montpellier-France