RN-QCD-2016-002

Although being the first of the new charmonium-like states discovered since 2003 \cite{BelleX3872}, the $X(3872)$ is still one of the most puzzling ones concerning the properties. Since the mass is indistinguishably close to the sum $m(D^0) + m(\bar{D}^{\ast 0})$, it is unclear whether it lays above or beneath the $DD^{\ast}$ threshold. Furthermore, the natural width is very small and basically unknown up to a rather rough upper limit of $\Gamma_X < 1.2$ MeV \cite{PDG15}. Due to these extra-ordinary properties, this state is frequently suggested to be an exotic hadron, possibly featuring a different and more complex internal structure than a simple conventional mesonic $q\bar{q}$ state. In particular, several theoretical models (e.g. \cite{BraatenLS,HanhartLS,KalashLS}) relate not only the mass $m_X$ and the Breit-Wigner-like width $\Gamma_X$ to the internal structure, but explicitly also the line-shape of the resonance. This offers another experimental handle to identify the nature of the $X(3872)$.

In this work, we study the expected sensitivity of energy scans of narrow resonances performed with the HESR in combination with the PANDA detector at FAIR. The goal is to access experimentally the aforementioned properties for different hypothetical experimental and physical scenarios of the $X(3872)$. It represents an update and extension of an earlier simulation study of that state carried out in 2011 based on a different software revision \cite{Galuska2012}. Furthermore, this exemplary study serves as a proof of principle for high precision spectroscopy using the energy scan method with the PANDA experiment in general.