Physical Review D, vol.106, no.7, 2022 (SCI-Expanded)
© 2022 authors. Published by the American Physical Society.Using 448 million ψ(2S) events, the spin-singlet P-wave charmonium state hc(1P11) is studied via the ψ(2S)→π0hc decay followed by the hc→γηc transition. The branching fractions are measured to be BInc(ψ(2S)→π0hc)×BTag(hc→γηc)=(4.22-0.26+0.27±0.19)×10-4, BInc(ψ(2S)→π0hc)=(7.32±0.34±0.41)×10-4, and BTag(hc→γηc)=(57.66-3.50+3.62±0.58)%, where the uncertainties are statistical and systematic, respectively. The hc(1P11) mass and width are determined to be M=(3525.32±0.06±0.15) MeV/c2 and Γ=(0.78-0.24+0.27±0.12) MeV. Using the center of gravity mass of the three χcJ(13PJ) mesons [M(c.o.g.)], the 1P hyperfine mass splitting is estimated to be Δhyp=M(hc)-M(c.o.g.)=(0.03±0.06±0.15) MeV/c2, which is consistent with the expectation that the 1P hyperfine splitting is zero at the lowest order.