Precision Measurement of the Mass of the hc(1P1) State of Charmonium

A precision measurement of the mass of the h(c)((1)P(1)) state of charmonium has been made using a sample of 24.5x10(6) psi(2S) events produced in e(+)e(-) annihilation at the Cornell Electron Storage Ring (CESR). The reaction used was psi(2S)->pi(0)h(c), pi(0)->gamma gamma, h(c)->gamma eta(c), and the reaction products were detected in the CLEO-c detector. Data have been analyzed both for the inclusive reaction and for the exclusive reactions in which eta(c) decays are reconstructed in 15 hadronic decay channels. Consistent results are obtained in the two analyses. The averaged results of the present measurements are M(h(c))=3525.28 +/- 0.19(stat.)+/- 0.12(syst.) MeV, and B(psi(2S)->pi(0)h(c))xB(h(c)->gamma eta(c))=(4.19 +/- 0.32 +/- 0.45)x10(-4). Using the (3)P(J) centroid mass, Delta M(hf)(1P)equivalent to < M(chi(cJ))>-M(h(c))=+0.02 +/- 0.19 +/- 0.13 MeV.