Jun 2 – 7, 2019
Carnegie Mellon University
America/New_York timezone

The $X(1835)$ and $X(p\bar{p})$ puzzle at BESIII

Jun 6, 2019, 2:00 PM
Rangos 1

Rangos 1

Contributed Hadron Spectroscopy Hadron Spectroscopy


Mr Johannes Bloms (Westfälische Wilhelms-Universität Münster)


The BESIII experiment at the Beijing Electron Positron Collider (BEPCII) has collected the world's largest data sample at the $J/\psi$ resonance including 10 billion events, which offers an unique opportunity to study hadron spectroscopy and search for light exotic states. In 2003, BESII reported the first observation of a $p\bar{p}$ mass threshold enhancement $X(p\bar{p})$ in $J/\psi \rightarrow \gamma p \bar{p}$. In addition, a structure was observed in $J/\psi \rightarrow \gamma \eta^\prime \pi^+ \pi^-$ and $J/\psi \rightarrow \gamma K_s K_s \eta$ in 2005 and 2015 called $X(1835)$. Both were determined to have spin-parity $J^P = 0^-$. While the masses of the $X(p\bar{p})$ and $X(1835)$ are in agreement with each other, their widths are significantly different, in fact $\Gamma_{X(p\bar{p})} < 76$ MeV (90% C.L.) and $\Gamma_{X(1835)} = 245$ MeV. Additionally, detailed studies of $J/\psi \rightarrow \gamma \eta^\prime \pi^+ \pi^-$ show a significant abrupt change in slope of the $X(1835)\rightarrow \eta^\prime \pi^+ \pi^-$ line shape at the $p\bar{p}$ mass threshold. An overview of recent developments of the mentioned observations as well as approaches to understand the line shape will be presented in this talk.

Graduate Student Yes

Primary author

Mr Johannes Bloms (Westfälische Wilhelms-Universität Münster)

Presentation materials