Precision measurements of the total and partial widths of the charmonium meson with a new complementary-scan technique in annihilations

We present new precision measurements of the ψ ( 2 S ) total and partial widths from excitation curves obtained in antiproton–proton annihilations by Fermilab experiment E835 at the Antiproton Accumulator in the year 2000. A new technique of complementary scans was developed to study narrow resonances with stochastically cooled antiproton beams. The technique relies on precise revolution-frequency and orbit-length measurements, while making the analysis of the excitation curve almost independent of machine lattice parameters. We study the ψ ( 2 S ) meson through the processes p ¯ p → e + e − and p ¯ p → J / ψ + X → e + e − + X . We measure the width to be Γ = 290 ± 25 ( sta ) ± 4 ( sys ) keV and the combination of partial widths Γ e + e − Γ p ¯ p / Γ = 579 ± 38 ( sta ) ± 36 ( sys ) meV , which represent the most precise measurements to date.