Triangle singularities waning in Heavy Ion Collisions: the case of [formula omitted

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)→D1D→πD⁎D→π+J/ψπ. This reaction has been proposed as a mechanism to explain the appearance of Zc(3900) in the J/ψπ 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 Zc(3900) would be more indicative of such triangle mechanism, while presence of both would rather point out to Zc being an exotic hadron.