Measurement of the mass of the tau lepton.
Author(s): Bai, JZ; Bardon, O; Becker-Szendy, RA; Blum, I; Breakstone, A; Burnett, T; Chen, GP; Chen, HF |  A data-driven energy scan in the immediate vicinity of the τ pair production threshold has been performed using the Beijing Spectrometer at the Beijing Electron-Positron Collider. Approximately 5pb-1of data, distributed over 12 scan points, have been collected. A previous mass value for the τ lepton, obtained using only the eµ final state, has been published. In this paper, the final BES result on the mass measurement is presented. The analysis is based on the combined data from the ee, eµ, eh, µµ, µh, and hh final states, where h denotes a charged Π or K. A maximum likelihood fit to the τ pair production cross section data yields the value mT=1776.96-0.21-0.17+0.18+0.25.

title: Partial wave analysis of ψ(2S) → $p\overline{p}η$
abstract: Using a sample of 1.06 x 10(8) psi(2) events collected with the BESIII detector at BEPCII, the decay psi(2S) -> p (p) over bar eta is studied. A partial wave analysis determines that the intermediate state N(1535) with a mass of 1524 +/- 5(-4)(+10) MeV/c(2) and a width of 130(-24-10)(+27+57) MeV/c(2) is dominant in the decay; the product branching fraction is determined to be B(psi(2S) -> N(1535)(p) over bar x B(N(1535) -> p eta + c.c. = 5.2 +/- 0.3(-1.2)(+3.2)) x 10(-5). Furthermore, the branching fraction of psi(2S) -> p (p) over bar eta is measured to be (6.4 +/- 0.2 +/- 0.6) x 10(-5). Here, the first error is statistical and the second is systematic.

title: Observation of the decay $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{\pm}\pi^{\mp}+c.c.$
abstract: Using a sample of $1.06\times10^{8}$ $\psi(3686)$ events collected with the BESIII detector, we present the first observation of the decays of $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{+}\pi^{-}+c.c.$ and $\psi(3686)$ $\rightarrow$ $\Lambda\bar\Sigma^{-}\pi^{+}+c.c.$. The branching fractions are measured to be $\mathcal{B}(\psi(3686) \rightarrow \Lambda\bar\Sigma^{+}\pi^{-} + c.c.)=(1.40\pm 0.03 \pm 0.13)\times10^{-4}$ and $\mathcal{B}(\psi(3686) \rightarrow \Lambda\bar\Sigma^{-}\pi^{+}+c.c.)=(1.54\pm 0.04 \pm 0.13)\times10^{-4}$, where the first errors are statistical and the second ones systematic.

title: Observation of $\eta_{c}$ decay into $\Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$ final states
abstract: Using a data sample of $2.25\times10^{8}$ $J/\psi$ events collected with the BESIII detector, we present the first observation of the decays of $\eta_{c}$ mesons to $\Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$. The branching fractions are measured to be $(2.11\pm0.28_{\rm stat.}\pm0.18_{\rm syst.}\pm0.50_{\rm PDG})\times10^{-3}$ and $(0.89\pm0.16_{\rm stat.}\pm0.08_{\rm syst.}\pm0.21_{\rm PDG})\times10^{-3}$ for $\eta_{c} \to \Sigma^{+}\bar{\Sigma}^{-}$ and $\Xi^{-}\bar{\Xi}^{+}$, respectively. These branching fractions provide important information on the helicity selection rule in charmonium-decay processes.

title: Experimental study on the performance of a single-THGEM gas detector *
abstract: A kind of thick GEM-like gaseous electron multiplier (THGEM), which is mechanically an expansion of the GEM with its various dimensions being enlarged, is studied. The leak current of THGEM plates is measured. The effective gain and energy resolution of a single THGEM are studied with a source of 55Fe, and the effective gain of the single THGEM versus the electric field strength in the induction region is investigated. The results show that the leak current of THGEM plates is less than 200 pA. In an atmospheric-pressure standard gas mixture, 8×103 effective gain and about 32% energy resolution can be reached for the single-THGEM detector.

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: An infrared cutoff revealed by the two years of COBE observations of cosmic temperature fluctuations.
abstract: We show that a good fitting to the first two years of {\it COBE}-DMR observations of the two-point angular correlation function of CBR temperature is given by models with a non-zero infrared cutoff $k_{min}$ in the spectrum of the primordial density perturbations. If this cutoff comes from the finiteness of the universe, say, a topological T3 model, we find $k_{min} \sim (0.3 - 1.1)\pi$H$_0/c$ with confidence level 95\%. Such a non-zero $k_{min}$ universe would also give a better match to the observations both of the RMS quadrupole anisotropy of CBR and of galaxy clustering.