Speaker
Dr
Cui Li
(Uppsala University)
Description
The Beijing Electron-Positron Collider (BEPCII) is a double ring $e^{+}e^{-}$ collider operating
within a Centre-of-Energy interval of $2.0-4.6$ GeV
with a design luminosity of $1 \times 10^{33}$ cm$^{-2}\textrm{s}^{-1}$.
The Beijing Spectrometer (BESIII) is a large detector located at the BEPCII and has
accumulated the largest sample of $J/\psi$, $\psi(2S)$, and $\psi(3770)$ events for studies of light hadron
and charmonium spectroscopy, the hadron-to-lepton ratio $R$ as a function of energy, and
high mass charmonium states including the $X$, $Y$ and $Z$ particles.
Until now, a lot of physics results have been published.
In this talk, I focus on the study of the near-threshold $\omega\phi$ mass enhancement
in doubly OZI suppressed $J/\psi\to\gamma\omega\phi$ decays. A sample of 2.25$\times$10$^8$
$J/\psi$ events was accumulated with the BESIII detector.
A strong deviation ($>$ 30$\sigma$) from three-body $J/\psi\to\gamma\omega\phi$ phase space
is observed near the $\omega\phi$ mass threshold that is consistent with a previous
observation reported by the BESII experiment.
A partial wave analysis (PWA) with a tensor covariant amplitude formalism has been performed,
assuming that the enhancement is due to the presence of a resonance, here referred to as the $X(1810)$.
PWA is an important tool in light hadron spectroscopy, used to
determine resonance properties (like mass, width, branching fraction, spin and parity).
Also PWA can deal with the interference of resonances.
The PWA confirms that the spin-parity of the $X(1810)$ is $0^{++}$.
The mass and width of the $X(1810)$ are determined to be
$M=1795\pm7$(stat)$^{+13}_{-5}$(syst)$\pm$19(mod) MeV/$c^2$ and
$\Gamma=95\pm10$(stat)$^{+21}_{-34}$(syst)$\pm$75(mod) MeV/$c^2$, respectively.
The product branching fraction is measured to be
${\cal B}(J/\psi\to\gamma X(1810))\times{\cal B}(X(1810)\to\omega\phi)=(2.00\pm0.08$(stat)$^{+0.45}_{-1.00}$(syst)$\pm$1.30(mod))$\times10^{-4}$.
These results are consistent within errors with those of the BESII experiment.
The decay $J/\psi\to\gamma\omega\phi$ is a doubly OZI suppressed process that is expected to be suppressed
relative to $J/\psi\to\gamma\omega\omega$ or $J/\psi\to\gamma\phi\phi$ by at least one order of magnitude.
The anomalous enhancement observed at the $\omega\phi$invariant-mass threshold and the large measured branching fractions
($\sim$1/2 of ${\cal B}(J/\psi\to\gamma\phi\phi)$) are surprising and interesting.
The enhancement is not compatible with being due either
to the $X(1835)$ or the $X(p\bar{p})$, due to the different mass and spin-parity.
Primary author
Dr
Cui Li
(Uppsala University)
