We present a measurement of the azimuthal asymmetries of two charged pions in the inclusive process e+ e- arrow right pipiX, based on a data set of 62 pb super(-1) at the center-of-mass energy of ...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.
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A search for a massless dark photon gamma' is conducted using 4.5 fb(-1) of e(+)e(-) collision data collected at center-of-mass energies between 4.600 and 4.699 GeV with the BESIII detector at ...BEPCII. No significant signal is observed, and the upper limit on the branching fraction B(Lambda(+)(c) -> p gamma') is determined to be 8.0 x 10(-5) at 90% confidence level.
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