Partial wave analysis of 𝑒 + 𝑒 − → 𝜋 + 𝜋 − 𝐽/𝜓 and cross section measurement of 𝑒 + 𝑒 − → 𝜋 ± 𝑍 𝑐 (3900) ∓ from 4.1271 to 4.3583 GeV
Based on 12.0 fb −1 of 𝑒 + 𝑒 − collision data samples collected by the BESIII detector at center-of-mass energies from 4.1271 to 4.3583 GeV, a partial wave analysis is performed for the process 𝑒 + 𝑒 − → 𝜋 + 𝜋 − 𝐽/𝜓. The cross sections for the subprocesses 𝑒 + 𝑒 − → 𝜋 + 𝑍 𝑐 (3900) − + c.c. → 𝜋 + 𝜋 − 𝐽/𝜓, 𝑓 0 (980)(→ 𝜋 + 𝜋 − )𝐽/𝜓, and (𝜋 + 𝜋 − ) S−wave 𝐽/𝜓 are measured for the first time. The mass and width of the 𝑍 𝑐 (3900) ± are determined to be 3884.6 ± 0.7 ± 3.3 MeV/𝑐 2 and 37.2 ± 1.3 ± 6.6 MeV, respectively. The first errors are statistical and the second systematic. The final state (𝜋 + 𝜋 − ) S−wave 𝐽/𝜓 dominates the process 𝑒 + 𝑒 − → 𝜋 + 𝜋 − 𝐽/𝜓. By analyzing the cross sections of 𝜋 ± 𝑍 𝑐 (3900) ∓ and 𝑓 0 (980)𝐽/𝜓, 𝑌(4220) has been observed. Its mass and width are determined to be 4225.7 ± 4.1 ± 3.4 MeV/𝑐 2 and 57.5 ± 9.4 ± 12.1 MeV, respectively.