Charmonium decay and Charmoniumlike spectroscopy study in experiment

title: Search for the Lepton Flavor Violation Process J/ψ→eμ at BESIII
abstract: We search for the lepton-flavor-violating decay of the J/psi into an electron and a muon using (225.3 +/- 2.8) x 10(6) J/psi events collected with the BESIII detector at the BEPCII. Four candidate events are found in the signal region, consistent with background expectations. An upper limit on the branching fraction of B(J/psi -> e mu) <1.6 x 10(-7) (90% C.L.) is obtained.

title: Partial wave analysis of $J/\psi \to \gamma \eta \eta$
abstract: Based on a sample of $2.25\times 10^{8}$ $J/\psi$ events collected with the BESIII detector at BEPCII, a full partial wave analysis on $J/\psi\to\gamma\eta\eta$ was performed using the relativistic covariant tensor amplitude method. The results show that the dominant $0^{++}$ and $2^{++}$ components are from the $f_0(1710)$, $f_0(2100)$, $f_0(1500)$, $f_2'(1525)$, $f_2(1810)$ and $f_2(2340)$. The resonance parameters and branching fractions are also presented.

title: Measurement of the Lepton Forward-Backward Asymmetry in Inclusive $B \rightarrow X_s \ell^+ \ell^-$ Decays

title: Observation of $Z_c(3900)$ both by BESIII and Belle
abstract: Using $525$ pb$^{-1}$ data collected with the BESIII detector at $e^+e^-$ central-of-mass energy 4.26 GeV, the BESIII Collaboration observed a charged charmoniumlike state $Z_c(3900)\to\pi^{\pm}J/\psi$ with mass $M[Z_c(3900)]=3899.0\pm 3.6 \pm 4.9$ MeV/c$^2$, and width $\Gamma[Z_c(3900)]=46\pm 10 \pm 20$ MeV. The significance of this state was estimated to be $>8\sigma$ in all kinds of systematic tests. Using $967$ fb$^{-1}$ data recorded by the Belle detector on or near $\Upsilon(nS)$, n=1, 2, $\cdots$, 5 resonances, the $e^+e^- \to \pi^+\pi^-J/\psi$ process has been studied through initial-state-radiation (ISR) method. Except for the $Y(4260)$ resonance, an intermediate state $Z(3900)^{\pm}$ has been observed in the $\pi^{\pm}J/\psi$ mass spectrum, with significance $>5.2\sigma$. The measured mass $M[Z(3900)^{\pm}]=3894.5\pm6.6\pm4.5$ MeV/c$^2$ and width $\Gamma[Z(3900)^{\pm}]=63\pm24\pm26$ MeV, shows good agreement with the BESIII measurement within errors, which means $Z_c(3900)$ and $Z(3900)^{\pm}$ is the same state.

title: A Measure for Isotropy-Equilibrium Degree of a Multi-Particle System
abstract: Aiming at using sphericity as a tool to study the isotropy-equilibrium property of a multi-particle system, in particular the hadronic final state IFS produced in instanton-induced DIS events, we discuss in detail the dependence of sphericity on multiplicity and the multiplicity distribution, as well as on the isotropy degree of the system. A rotational symmetric model with a fluctuating isotropy-degree is constructed, which can fit the mean and width of sphericity of the Monte Carlo IFS-results simultaneously The IFS from the Monte Carlo simulation is found to be not ideally isotropic but has a probability of 4.7% to be isotropic within error of 5%. The results provide us a description of how far the IFS departs from equilibrium. The method developed is applicable to any Monte Carlo generated multi-particle system, for which the isotropy-equilibrium property is significant.

title: Low Mass Gluino within the Sparticle Landscape, Implications for Dark Matter, and Early Discovery Prospects at LHC-7
abstract: We analyze supergravity models that predict a low mass gluino within the landscape of sparticle mass hierarchies. The analysis includes a broad class of models that arise in minimal and in nonminimal supergravity unified frameworks and in extended models with additional U(1) n hidden sector gauge symmetries. Gluino masses in the range (350 − 700) GeV are investigated. Masses in this range are promising for early discovery at the LHC at √ s = 7 TeV (LHC-7). The models exhibit a wide dispersion in the gaugino-Higgsino eigencontent of their LSPs and in their associated sparticle mass spectra. A signature analysis is carried out and the prominent discovery channels for the models are identified with most models needing only ∼ 1 fb 1 for discovery at LHC-7. In addition, significant variations in the discovery capability of the low mass gluino models are observed for models in which the gluino masses are of comparable size due to the mass splittings in different models and the relative position of the light gluino within the various sparticle mass hierarchies. The models are consistent with the current stringent bounds from the Fermi-LAT, CDMS-II, XENON100, and EDELWEISS-2 experiments. A subclass of these models, which include a mixed-wino LSP and a Higgsino LSP, are also shown to accommodate the positron excess seen in the PAMELA satellite experiment.

title: Lattice study on $\eta_{c2}$ and X(3872)
abstract: Properties of 2(-+) charmonium eta(c2) are investigated in quenched lattice QCD. The mass of eta(c2) is determined to be 3.80(3) GeV, which is close to the mass of D-wave charmonium psi(3770) and in agreement with quark model predictions. The transition width of eta(c2) -> gamma J/psi is also obtained with a value of Gamma = 3.8(9) keV. Since the possible 2(-+) assignment to X(3872) has not been ruled out by experiments, our results help to clarify the nature of X(3872). DOI: 10.1103/PhysRevD.87.014501

title: Precision measurement of the mass of the tau lepton
abstract: An energy scan near the tau pair production threshold has been performed using the BESIII detector. About 24 pb(-1) of data, distributed over four scan points, were collected. This analysis is based on t pair decays to ee, e mu, eh, h, hh, e.,. and p. final states, where h denotes a charged p or K. The mass of the t lepton is measured from a maximum likelihood fit to the t pair production cross- section data to be m(tau) = 1776.91 +/- 0.12_0.10 - 0.13 _ MeV/c(2), which is currently the most precise value in a single measurement.

title: Lattice study on exotic vector charmonium relevant to X(4260)
abstract: In the quenched approximation and with very high statistics, a heavy vector charmonium state, with a mass of 4.33(2)GeV, is disentangled from the conventional charmonium states by using spatially extended hybrid-like interpolating field operators. Through a simultaneous fit of correlation functions built from different operators, the leptonic decay constant this state is estimated to be 31(15)MeV, which gives a much smaller leptonic decay width of 23(20)eV in comparison with that of conventional vector charmonia. The connection of this state with X(4260) is also discussed.

title: Formation of the $\eta_c$ in Two-Photon Collisions at LEP
abstract: The two-photon width $\Gamma_{\gamma\gamma}$ of the $\eta_{\mathrm{c}}$ meson has been measured with the L3 detector at LEP. The $\eta_{\mathrm{c}}$ is studied in the decay modes $\pi^+\pi^-\pi^+\pi^-$, $\pi^+\pi^-$K$^+$K$^-$, K$_s^0$K$^\pm\pi^\mp$, K$^+$K$^-\pi^{0}$, $\pi^+\pi^-\eta$, $\pi^+\pi^-\eta'$, and $\rho^+\rho^-$ using an integrated luminosity of 140 pb$^{-1}$ at $\sqrt{s} \simeq 91$ GeV and of 52 pb$^{-1}$ at $\sqrt{s} \simeq 183$ GeV. The result is $\Gamma_{\gamma\gamma}(\eta_{\mathrm{c}}) = 6.9 \pm 1.7 \mbox{(stat.)} \pm 0.8 \mbox{(sys.)} \pm 2.0$(BR) keV. The $Q^2$ dependence of the $\eta_{\mathrm{c}}$ cross section is studied for $Q^2 < 9$ GeV$^{2}$. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a $\rho$-pole. In addition, a signal of $29 \pm 11$ events is observed at the $\chi_{\mathrm{c}0}$ mass. Upper limits for the two-photon widths of the $\chi_{\mathrm{c}0}$, $\chi_{\mathrm{c}2}$, and $\eta_{\mathrm{c}}'$ are also given.