Precision Measurement of the Mass of the hc(1P1) State of Charmonium
Abstract
A precision measurement of the mass of the hc(1P1) state of charmonium has been made using a sample of 24.5 million psi(2S) events produced in e+e- annihilation at CESR. The reaction used was psi(2S) -> pi0 hc, pi0 -> gamma gamma, hc -> gamma etac, 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 etac decays are reconstructed in fifteen hadronic decay channels. Consistent results are obtained in the two analyses. The averaged results of the present measurements are M(hc)=3525.28+-0.19 (stat)+-0.12(syst) MeV, and B(psi(2S) -> pi0 hc)xB(hc -> gamma etac)= (4.19+-0.32+-0.45)x10-4. Using the 3PJ centroid mass, Delta Mhf(1P)=<M(chicJ)> - M(hc) = +0.02+-0.19+-0.13 MeV.
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