The cross section of the process e+e-→η′J/ψ is measured at center-of-mass (c.m.) energies from s=4.178 to 4.600 GeV using data samples corresponding to a total integrated luminosity of 11 fb-1 collected with the BESIII detector operating at the BEPCII storage ring. The dependence of the cross section on s shows an enhancement around 4.2 GeV. While the shape of the cross section cannot be fully explained with a single ψ(4160) or ψ(4260) state, a coherent sum of the two states does provide a reasonable description of the data.
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The BESIII detector is a magnetic spectrometer located at the Beijing Electron-Positron Collider (BEPCII) . The cylindrical core of the BESIII detector consists of a helium-based multilayer drift chamber (MDC), a plastic scintillator time-of-flight system (TOF), and a CsI(Tl) electromagnetic calorimeter (EMC), which are all enclosed in a superconducting solenoidal magnet providing a 1.0 T magnetic field. The solenoid is supported by an octagonal flux-return yoke with resistive plate counter muon identifier modules interleaved with steel. The acceptance of charged particles and photons is 93% over the solid angle. The charged-particle momentum resolution at is 0.5%, and the resolution is 6% for the electrons from Bhabha scattering. The EMC measures photon energies with a resolution of 2.5% (5%) at 1 GeV in the barrel (end cap) region. The time resolution of the TOF barrel part is 68 ps. The end cap TOF system was upgraded in 2015 with multigap resistive plate chamber technology, providing a time resolution of 60 ps .
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