Exotic Hybrid Mesons Research Articles

Exotic hybrid mesons with light quarks

Hybrid mesons, made from a quark, an antiquark and gluons, can have quantum numbers inaccessible to conventional quark-antiquark states. Confirmation of such states would give information on the role of “dynamical” color in low energy QCD. We present preliminary results for hybrid meson masses using light Wilson valence quarks.

New limits on Primakoff production of hybrid mesons

I discuss constraints on properties of isoscalarJ PC =1−+ exotic hybrid mesons, assuming their dominant decay mode is ηπ. This work expands on a similar study by the Rochester-Minnesota-Fermilab collaboration, which excluded ϱπ as the dominant decay channel for such hybrids. The experimental limits are based on Primakoff production of such states and on a VDM argument relating their radiative widths to their ϱπ decay modes. Using data on coherent production of ηπ+ systems in π+ collisions with nuclei, I obtain few percent limits on the ϱπ branching ratios for hybrid masses ≲1.5 GeV.

Experimental constraints onJ PC=1?+,I=1, Hybrid mesons

Using data on coherent production of π+π+π- systems in π+ collisions with nuclei we exclude the existence ofJ PC=1−+,I=1, exotic hybrid mesons with masses below 1.5 GeV and widths greater than 20 MeV, provided that their primary coupling is to πρ systems. Hybrid states with just such properties have recently been predicted from arguments based on QCD sum rules. Our experimental limit is based on Primakoff production of these states, and on an argument using vector dominance to relate their radiative widths to πρ channels. There has been increasing interest of late in the existence of hybrid states, which, in the case of mesons, contain a valence gluon in addition to aq $$\bar q$$ pair in a color-octet state [1–5]. The pursuit of spectroscopic gluon degrees of freedom has been strongly motivated by the general QCD picture of hadrons, as well as by many specific calculations based on QCD sum rules, lattice simulations, and more phenomenological approaches such as QCD-bag models. Although much effort, both thoretical and experimental, has been devoted to the spectroscopy of glueballs, for which several candidates exist [6], it has also been realized that hybrid states may be as amenable to discovery, and perhaps less ambiguous to interpretation.