Bound and resonant impurity states in a narrow gaped armchair graphene nanoribbon

An analytical study of discrete and resonant impurity quasi-Coulomb states in a narrow gaped armchair graphene nanoribbon (GNR) is performed. We employ the adiabatic approximation assuming that the motions parallel ("slow") and perpendicular ("fast") to the boundaries of the ribbon are separated adiabatically. The energy spectrum comprises a sequence of series of quasi-Rydberg levels relevant to the "slow" motion adjacent from the low energies to the size-quantized levels associated with the "fast" motion. Only the series attributed to the ground size-quantized sub-band is really discrete, while others corresponding to the excited sub-bands consist of quasi-discrete (Fano resonant) levels of non-zero energetic widths, caused by the coupling with the states of the continuous spectrum branching from the low lying sub-bands. In the two- and three-subband approximation the spectrum of the complex energies of the impurity electron is derived in an explicit form. Narrowing the GNR leads to an increase of the binding energy and the resonant width both induced by the finite width of the ribbon. Displacing the impurity centre from the mid-point of the GNR causes the binding energy to decrease while the resonant width of the first excited Rydberg series increases. As for the second excited series their widths become narrower with the shift of the impurity. A successful comparison of our analytical results with those obtained by other theoretical and experimental methods is presented. Estimates of the binding energies and the resonant widths taken for the parameters of typical GNRs show that not only the strictly discrete but also the some resonant states are quite stable and could be studied experimentally in doped GNRs

Measurement of B(J/psi->eta_c gamma) at KEDR

We present a study of the inclusive photon spectrum from 6.3 million J/psi decays collected with the KEDR detector at the VEPP-4M e+e- collider. We measure the branching fraction of the radiative decay J/psi -> eta_c gamma, eta_c width and mass. Taking into account an asymmetric photon line shape we obtain: M(eta_c) = (2978.1 +- 1.4 +- 2.0) MeV/c^2, Gamma(eta_c) = (43.5 +- 5.4 +- 15.8) MeV, B(J/psi->eta_c gamma) = (2.59 +- 0.16 +- 0.31)%$.Comment: 6 pages, 1 figure. To be published in the proceedings of the 4th International Workshop on Charm Physics (Charm2010), October 21-24, 2010, IHEP, Beijin

Precise measurement of RudsR_{\text{uds}} and RR between 1.84 and 3.72 GeV at the KEDR detector

The present work continues a series of the KEDR measurements of the $R$ value that started in 2010 at the VEPP-4M $e^+e^-$ collider. By combining new data with our previous results in this energy range we measured the values of $R_{\text{uds}}$ and $R$ at nine center-of-mass energies between 3.08 and 3.72 GeV. The total accuracy is about or better than $2.6\%$ at most of energy points with a systematic uncertainty of about $1.9\%$. Together with the previous precise $R$ measurement at KEDR in the energy range 1.84-3.05 GeV, it constitutes the most detailed high-precision $R$ measurement near the charmonium production threshold.Comment: arXiv admin note: text overlap with arXiv:1610.02827 and substantial text overlap with arXiv:1510.0266

Observation of D0→ρ0γD^0\to \rho^0\gamma and search for CPCP violation in radiative charm decays

We report the first observation of the radiative charm decay $D^0 \to \rho^0 \gamma$ and the first search for $CP$ violation in decays $D^0 \to \rho^0 \gamma$, $\phi\gamma$, and $\overline{K}{}^{*0} \gamma$, using a data sample of 943 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(D^0 \to \rho^0 \gamma)=(1.77 \pm 0.30 \pm 0.07) \times 10^{-5}$, where the first uncertainty is statistical and the second is systematic. The obtained $CP$ asymmetries, $\mathcal{A}_{CP}(D^0 \to \rho^0 \gamma)=+0.056 \pm 0.152 \pm 0.006$, $\mathcal{A}_{CP}(D^0 \to \phi \gamma)=-0.094 \pm 0.066 \pm 0.001$, and $\mathcal{A}_{CP}(D^0 \to \overline{K}{}^{*0} \gamma)=-0.003 \pm 0.020 \pm 0.000$, are consistent with no $CP$ violation. We also present an improved measurement of the branching fractions $\mathcal{B}(D^0 \to \phi \gamma)=(2.76 \pm 0.19 \pm 0.10) \times 10^{-5}$ and $\mathcal{B}(D^0 \to \overline{K}{}^{*0} \gamma)=(4.66 \pm 0.21 \pm 0.21) \times 10^{-4}$