Seminar on Theoretical Nuclear Physics

9.04.18 16:15

Stable Exotic Heavy Mesons?

Mikhail Voloshin (University of Minnesota)


Mesonic states consisting of two heavy quarks and two lighter antiquarks are considered. A bound state in such system below the threshold for dissociation into two heavy mesons would decay only due to weak interaction. At a small ratio of the lighter to heavier quark masses an expansion parameter arises for treatment of the binding in such systems. In the limit where all the quarks and antiquarks are so heavy that a Coulomb-like limit can be applied to the gluon exchange between all of them, such bound states arise when this parameter is below a certain critical value. The parametric dependence of the critical mass ratio on the number of colors N is found and confirmed by numerical calculations. In particular there is no stable bound states if all constituents have the same mass. An application is discussed of a similar expansion in the large N limit to realistic systems where the antiquarks are light and their interactions are nonperturbative. In this case the findings are in agreement with the recent claims from a phenomenological analysis that a stable 'double bottom' state is likely to exist, unlike those where one or both bottom quarks are replaced by the charmed quark.