From the line shape of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>X</mml:mi><mml:mo stretchy="false">(</mml:mo><mml:mn>3872</mml:mn><mml:mo stretchy="false">)</mml:mo></mml:math> to its structure

Abstract

From a study of the line shape of the $X(3872)$, the LHCb collaboration measures a sizeable negative effective range. This cannot be reconciled with a shallow $D{\overline{D}}^{*}$ bound state hypothesis. Based on Weinberg's compositeness criterion, together with a theorem by Smorodinsky, it follows that the $X$ has to have a compact hidden charm structure interacting with unbound $D{\overline{D}}^{*}$ pairs via short-distance color forces. This conclusion is strengthened by the general pattern recently emerging from exotic mesons.

Topics & Concepts