Precise measurement of the χ c0 resonance parameters and branching fractions of χ c0,c2 → π + π −/K + K − *

By analyzing a ψ(3686) data sample containing (107.7±0.6)×106 events taken with the BESIII detect- or at the BEPCII storage ring in 2009, the χc0 resonance parameters are precisely measured using χc0,c2 → π+π−/K+K− events. The mass of χc0 is determined to be M(χc0) = (3415.63±0.07±0.07±0.07) MeV/c2, and its full width is Γ(χc0) = (12.52±0.12±0.13) MeV, where the first uncertainty is statistical, the second systematic, and the third for mass comes from χc2 mass uncertainty. These measurements improve the precision of χc0 mass by a factor of four and width by one order of magnitude over the previous individual measurements, and significantly boost our knowledge about the charmonium spectrum. Together with additional (345.4±2.6)×106 ψ(3686) data events taken in 2012, the decay branching fractions of χc0,c2 → π+π−/K+K− are measured as well, with precision improved by a factor of three compared to previous measurements. These χc0 decay branching fractions provide important inputs for the study of glueballs.