We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process $e^+e^-rightarrow pipi X$ based on a data set of 62 $rm{pb}^{-1}$ at the center-of-mass energy $sqrt{s}=3.65$ GeV collected with the BESIII detector.
These asymmetries can be attributed to the Collins fragmentation function. We observe a nonzero asymmetry, which increases with increasing pion momentum. As our energy scale is close to that of the existing semi-inclusive deep inelastic scattering experimental data, the measured asymmetries are important inputs for the global analysis of extracting the quark transversity distribution inside the nucleon and are valuable to explore the energy evolution of the spin-dependent fragmentation function.
We report a measurement of the parameter $y_{CP}$ in $ensuremath{D^0}xspace-ensuremath{overline{D}^{0}}xspace$ oscillations performed by taking advantage of quantum coherence between pairs of $ensuremath{D^0}xspace ensuremath{overline{D}^{0}}xspace$
mesons produced in $e^+e^-$ annihilations near threshold. In this work, doubly-tagged $ensuremath{D^0}xspace ensuremath{overline{D}^{0}}xspace$ events, where one $D$ decays to a $CP$ eigenstate and the other $D$ decays in a semileptonic mode, are reconstructed using a data sample of 2.92,fb$^{-1}$ collected with the BESIII detector at the center-of-mass energy of $sqrt{s}$ = 3.773,GeV. We obtain $y_{CP} = (-2.0pm1.3pm0.7)%$, where the first uncertainty is statistical and the second is systematic. This result is compatible with the current world average.
A method to estimate efficiency of event start time determination at BESIII is developed. This method estimates the efficiency at the event level by combining the efficiencies of various tracks ($e$, $mu$, $pi$, K, $p$, $gamma$) in a Bayesian way. Ef
ficiencies results and difference between data and MC at the track level are presented in this paper. For a given physics channel, event start time efficiency and systematic error can be estimated following this method.
We developed a least squares fitter used for extracting expected physics parameters from the correlated experimental data in high energy physics. This fitter considers the correlations among the observables and handles the nonlinearity using lineariz
ation during the $chi^2$ minimization. This method can naturally be extended to the analysis with external inputs. By incorporating with Lagrange multipliers, the fitter includes constraints among the measured observables and the parameters of interest. We applied this fitter to the study of the $D^{0}-bar{D}^{0}$ mixing parameters as the test-bed based on MC simulation. The test results show that the fitter gives unbiased estimators with correct uncertainties and the approach is credible.
