Y. Q. Liu — Page 3 | Searcharxiv

arXiv2008

Soft X-ray spectroscopy of highly charged silicon ions in dense plasmas

Rich soft X-ray emission lines of highly charged silicon ions (Si VI--Si XII) were observed by irradiating an ultra-intense laser pulse with width of 200 fs and energy of $\sim$90 mJ on the solid silicon target. The high resolution spectra of highly charged silicon ions with full-width at half maximum (FWHM) of $\sim$0.3--0.4Åis analyzed in wavelength range of 40--90 Å. The wavelengths of 53 prominent lines are determined with statistical uncertainties being up to 0.005 Å. Collisional-radiative models were constructed for Si VI -- Si XII ions, which satisfactorily reproduces the experimental spectra, and helps the line identification. Calculations at different electron densities reveal that the spectra of dense plasmas are more complicate than the spectra of thin plasmas. A comparison with the Kelly database reveals a good agreement for most peak intensities, and differences for a few emission lines.

astro-ph↗

arXiv1995

Gluonic and leptonic decays of heavy quarkonia and the determination of $α_s(m_c)$ and $α_s(m_b)$

QCD running coupling constant $α_s(m_c)$ and $α_s(m_b)$ are determined from heavy quarkonia $c\overline{c}$ and $b\overline{b}$ decays. The decay rates of $V\rightarrow 3g$ and $V\rightarrow e^+ e^-$ for $V=J/ψ$ and $Υ$ are estimated by taking into account both relativistic and QCD radiative corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism, and the decay rates are estimated by using the meson wavefunctions which are obtained with a QCD-inspired inter-quark potential. For the $V\rightarrow 3g$ decay we find the relativistic correction to be very large and to severely suppress the decay rate. Using the experimental values of ratio $R_g\equiv \frac {Γ(V\longrightarrow 3g)}% {Γ(V\longrightarrow e^{+}e^{-})}\approx 10,~32 $ for $V=J/ψ, ~Υ$ respectively, and the calculated widths , we find $α_{s}(m_c)=0.29\pm 0.02 $ and $α_s(m_b)=0.20\pm 0.02$. These values for the QCD running coupling constant are substantially enhanced, as compared with the ones obtained without relativistic corrections, and are consistent with the QCD scale parameter $Λ_{\overline {MS}}^{(4)}% \approx 200MeV$. We also find that these results are mainly due to kinematic corrections and not sensitive to the dynamical models.

hep-ph↗