Precise measurement of spin-averaged chi_{cJ}(1P) mass using photon conversions in psi(2S) -> gamma chi_{cJ}

TL;DR

This paper precisely measures the masses of chi_{cJ}(1P) states using photon conversions in psi(2S) decays, achieving high energy resolution and providing accurate mass values for these charmonium states.

Contribution

The study employs photon conversion techniques to improve energy resolution in measuring chi_{cJ}(1P) masses, offering more precise results than previous measurements.

Findings

Masses of chi_{c0}, chi_{c1}, chi_{c2} determined with high precision.

Spin-averaged chi_{cJ} mass measured accurately.

Photon conversion method enhances energy resolution.

Abstract

Using photon conversions to e^+e^- pairs, the energy spectrum of inclusive photons from psi(2S) radiative decays is measured by BESII at the Beijing Electron-Positron Collider. The chi_{cJ}(1P) states (J=0,1,2) are clearly observed with energy resolution between 2.3 to 3.8 MeV, and their masses and the spin-averaged chi_{cJ} mass are determined to be M_{chi_{c0}}=3414.21\pm 0.39 \pm 0.27, M_{chi_{c1}}=3510.30\pm 0.14\pm 0.16, M_{chi_{c2}}=3555.70\pm 0.59 \pm 0.39 and M(^3P_{cog})=3524.85\pm 0.32 \pm 0.30 MeV/c^2.